D O C T O R A L D I S S E R T A T I O N SERIES

TheDereloymeni Of tieatlblighlk Of
W hfflj Caused Bu Gfibbetella. Zene
CSchte) Telch upd Helin l'ntli asporiu m
T IT L E

__________ SaHYutnT.lI.
AUTHOR
U N IV E R S I

%Xfl Lanqnrad Andersen
naanSMe Colleaeb 1947
ATE

*•

^ U T t

DEGREE

and$.

4 U* *LA

P U B L IC A T IO N NO.

O y Q
/

JL 7_____

^

UNIVERSITY MICROFILMS

H

ANN

ARBOR

-

MICHIGAN

A ndersen,

Axel L.

lQl+7 •

The d e v e lo p m e n t o f h e a d b l i g h t

ca u se d by G ib b e r e l l a

zeae

of wheat

( Schw.) k e t c h and H elm intho so o r lu n

sativum k . K . and 3 .

AS ST3ACT

The e f f e c t s
snore

g e rm in a tio n o f G ibber a l i a

the b e h a v io r of th e
fects

of tery ern tu re

of the

and the
o f the

reactio n of

host to

the

s h o w e d some g r o w t h a t

g r o w t h o f G.
H.

w h e r e a s G.
C.

stage

the

ef­

of iiost m a t u r i t y ;

i n o c u l a t i o n w i t h mixed s u s p e n s i o n s

m y c e l ia and e l o n g a t i o n o f t h e i r

3f°

inoculum ,

shoved a v e r y wide t e m p e r a t u r e

grow th and spore g e rm in a tio n ;

the

and

c o iiid ia o f b o t h p a th o g e n s were s t u d i e d .
B oth o n th eg en s

sativum

when c o m b i n e d i n c u l t u r e ;

of co n id ial

the

sro ru latio n ,

z e a e a n d He 1 r i n t ho s u e r iurn s a t i v u m ;

two n a t h o g e n s

q u an tity

on g r o w t h ,

most r e p i d r a d i a l

?2°

for
th eir
C.

H.

C ., a te m p e ra tu re 'u n fa v o ra b le f o r

zeae .

s a t ivum p r o d u c e d no

co u id ia

below 1-°

-m.-d a b o v e

2 'c °

C.

z e a e n r o o u c e d a f e w b e l o w l c " ' C. a n d a maximum n u m b e r a t

C onidia were produced on in f e c te d

f r o ,, l !o - J O °

0.,

p ath o g en s.

G.

v;i ';h t h e
zeae

n u m b e r s t h a n H.

in o cu lu m up to
tire c o n i d i a

largest

-'roiuceci

hears

of wheat p l a n t s

number p r o d u c e d a t

conic ia

ore

up, i d l y

?^°

C.

by b o t h

a n d 1:. l a r g e r

sativ u m .

D isease

sev erity

l.O -f.C

Host

no

in c re a s e d w ith an in c re a s e

m illio n

were a p p l i e d

G en erally ,
flo w erin g .

grow th o f

germ tuber, t o o k n i e c e a t

3c°

rw qe

coniuia

in aqueous
in fectio n

su sco o tib ility

to

per pot of

in

the

10 w h e a t

jimount o f

p l a n t s wh en

suspension.

o c c u rr e d on w heat heads p r i o r
i n f e c t i o n end d is e a s e

to

developm ent

u n d e r s e a , A x e l L.

13•-»7 *

i n c r e a s e d f r o x the f l o w e r i n g s t a g e to the; p ? s t - f lov'erixig s t a g e of
development.
T.ifc most favorr-bl*- te.vr-o ratnrc r. f o r i n f e c t i o n were 2p~30°
0.

H. s a t i v um v»s

l o o t e-Ty.rlIy p n tn o g e n ic i n t h i s ran.-e where?s

G. zeae was i e f i ' x i t e l y more p a t h o g e n i c a t ?5° C.
The

ic ri ou o f c o n t i n u e d w e t n e s s ( t h e

m o i s t u r e on the p l a n t s )

rese u c e of f r e e

r e q u i r e d f o r maximum i n f e c t i o n and d i s e a s e

development v a r i e d wi tii tuo s t a g e o f c l o u t development and the a i r
temper? ture at the time o f e x p o s u r e .

I t v;ns the s ; u r t e s t a t the op­

timum tox.oeratui'a ruin cn p l a n t s in the l a t e r s t a n c e o f d e ve lo pm e nt ,
i n c h patho gen e x h i b i t e d " c r i t i c a l e xpo su re o e r i o d s " f o r i n f e c t i o n
and h e n d b l i g h t d e v e l o p m e n t .

These p e r i o d s were g e n e r a l l y t h e some

f o r G. geac bat d i f f e r e n t f o r H. s a t i yam.
The l e n g t h o f t h e i n c u b a t i o n o e r i o c s v a r i e d w i t h the s i r
te mc era to rn and mo i s t a r e c o n n i t i c u o .

Those

i»:..t v e r o o s e j t h e l o n g ­

e s t to con t i no.ef. we trie rr at t h e o o t i n u n te m n e r a tn r e s f o r i n f e c t i o n
vxd d i s e a s e d e v e lo p .vent mac the shor t e s t i n c u b a t i o n uf r i o c ? .
A s h or t o e r i o d o f ex.oo s ere to c o n t i n u e d wc tne e s r f t r r i n ocv.la t i.,.. To Ll.u;ed by ;■ dry ;-r.d : r; u . d >, t I u:r i.m, r cmv.cc’ the
;1..ount ex.o. : ovo r r .*, c ^ inr ec * ron c L ot:. ■.a t : . 0 - , -ir .
In g e n e r a l ,

the

resor.ee o f mycelium or f a i r l y heavy con­

c e n t r a t i o n s o f c o n i d i a o f G. zene r e t a r d e d t he » rov;th o f t h e
iu... end the g e r m i n a t i o n o f t h e c u n i din o f H. s a t Ivum.

y.-ecl-

The ore sen ce

on p l r n t s o f h i g h co ncc ntr -.t i o r s o f c o n i d i a o f cue pathogen w i t h a
low c o n c e n t r a t i o n o f t h e o t h e r pa th ogen r e s u l t e d in a s u o n r o s s i o u o f

A n d e r s e n , A x e l L.

the l e t t e r .

lyU7 .

V,"hon '■ . . . i x t r r e u f h i . -h C o n c e n t r - t i o n s o f c o n i d i a o f

"both s p e c i e s w e r e n;>i/li*-d t o u l n r t s ,
crease

in the p e r c e n t a . e of seeds

t h e r e was a. s i g n i f i c a n t

de­

i n f e c t e d by e i t h e r p a t h o g e n a s

c o r e n a r e d t c t h e c e r c o n t n ^ e i n f e c t e d ’•■hen t h e sr.tic c o n c e n t r a t i o n
o f c o n i d i a o f e i t h e r p a t h o y e n was a . p l i e d ? l o n e . ----- A. L. A n d e r s e n .

A nnroved:

TH3 DEVELOFi'ISvT 03 HEADBLIGHT OF WHEAT CAU SED BY GIBBERELLA
ZEAE (SCHiV.) FETCH Ai-'ID HELMIKTHQSFQRIUM SATIVUM F . K. ADD B.

sy
AXEL LAHGVAD Ai-iDER SVLJ

A THESIS
Submitted to the School o f Graduate S t u d i e s o f Michigan
S t a te C o l l e g e o f A g r i c u l t u r e and A p p li ed Sc ie nc e
in p a r t i a l f u l f i l l m e n t o f the requirements
f o r the degree of

DOCTOR OF FH1LOSOFHY

Department o f Botany

ACKMOi&aiXkSaT

The w r i t e r w is h e s to e x p r e s s h i s a p p r e c i a t i o n to Dr. J . H.
Muncie and Dr. hay i.'elsoii f o r a d v i c e i n c o n d u c t i n g t h i s s t u d y , to Dr
F. L. Wynd and Dr. J . H. ..un cie f o r c r i t i c i s m and c o r r e c t i o n o f the
m a n u s cr ip t , and to Cajnp D e t r i c k , F r e d e r i c k , Maryland, f o r the us e o f
t h e i r f a c i l i t i e s v/hich made t n e s e s t u d i e s o o s s i o l e .

Ta BIR of CG1T7J21TTS

I n t r o d u c t i o n ..................................................................................................................

1

R eview o f L i t e r a t u r e ..............................................................................................

?.

C ilf b e r e l l a s e r e ..............................................................................................

2

H e l x i i i t h o s ' p c r i u c i s a t i v x u 1.

M a t e r i a l s and M e t h o d s ....................................................................................
Laboratory s t u d i e s

12

...............................................................................

12

Greenhouse s t u d i e s ...............................................................................

14

C u lt u r a l S t u d i e s ..................................................................................................

1?

The r e l a t i o n o f t e n y e r a t u r e to yrcv/th,

snorulation,

and j t e r o i i i i e t i o n .........................................................................................

13

Gricberelia z e a e ...........................................................................

13

Helmintho s oor im/i s a t i v u m ........................................................

CP

i f f e c t s of a s s o c i a t i o n o f G-ibberrlfr

z e a e ?rul

Heuuint i .o sue r i uxa s:-t i v u ' n .................................................................

?H

p a t h o g e n e s i s ...........................................................................................................

3i

i f f e e t o f inoculur. oosa^e on d i s e a s e s e v e r i t y ...................

31

G-ibberella z e a e ...........................................................................

31

H e l m i n t ho snor i u m s a t i v u m ........................................................

33

R e l a t i o n o f head m a t u r it y to d i s e a s e development

. . .

33

G i b b e r e l f a z e a e ...........................................................................

33

Helmintho s'oorium s a t i v u m ...........................................................

4l

I n f l u e n c e o f a i r teinpersture and mois tu re on
...........................................................................

46

G-lbberelia z e a e ...........................................................................

46

Helminthosnoriurr. s a t i v u m ........................................................

6.2

d i s e a s e development

I n f l u e n c e o f a i r t e mjerat^rt. andm o is tu r e

ons u o m l a t i o n

Jo

Gid o e r e l l a z e a e ................................................................................

76

H elm intho sporrirn s a t i v u m ............................................................

82

E f f e c t ox mixed inoculum on d i s e a s e i n c i d e n c e ......................

?,S

D i s c u s s i o n .................................................................................................................

59

Summary

......................................................................................................................

93

G-i’b 'berella z e a e ..........................................................................................

93

Kelmiuthosporium s a t i v u m .......................................................................

99

A sso cia tio n

9 <j

Literature c ited

...................................................................................................

100

TA3LS OF FLATS a

PLAT'S I .

Humidity t e n t without t h e o u t e r t e n t end temperature
control sjsteu .

PLATS I I .

The r e l a t i o n o f the s t a g e o f h os t m a t u r it y to the de­
velopment o f G i t ' c e r e i l a he a d h li g h t on Nev/thatch w h e a t .

PLATE I I I .

The r e l a t i o n o f the s t a g e o f h o s t m at ur it y to the de­
velopment o f Helminthosporium h e a d c l i g h t or. New-thatch
whe a t .

PLATE IV.

The r e l a t i o n o f temperature and p e r i o d o f c o n ti n u e d
we tne ss to the development of G-iVoerr 11a h e a d e l i g h t
on lev th a t c h wheat i n o c u l a t e d i n the r n s t - f l o w e r i n g
stage.

PLATE

V.

G-ic'oerella zeae aye e l ium proving over the s u r f a c e of
the glumes of i'.ewthatch wheat from i n f e c t e d extruded
anthers.

1

-

-

THE DEVELOPMENT OF HEADSLIGHT OF WHEAT CAUSED BY GIBBERELLA
ZEAE (SCHW.) FETCH AI'ID HELMINTHOSPO-RIUM SATIVUM P . K. AND B.

INTRODUCTION

The c e r e a l d i s e a s e complex commonly c a l l e d h e a d b l i g h t i s -oreva l e n t th roughout t h e o r i n c i p a l c e r e a l p r o d u c in g s e c t i o n s of th e w o r ld .
In t h e U n i t e d S t a t e s , G-ibberella zeae (S chw.) F e t c h and Helmin thoso o rlam
sativum Famael, King, and Bakke a r e commonly a s s o c i a t e d ,

and t h e y are

c h i e f l y r e s p o n sib le f o r the head b lig h t d is e a s e o f c e r e a l s .

Much o f the

i n f o r m a t i o n p e r t a i n i n g to t h e s e p a t h o g e n s d e a l s w i t h the s e e d l i n g b l i g h t ,
and t h e r o o t - and f o o t - r o t d i s e a s e o f c e r e a l s w i t h which t h e y a r e a l s o
associated.

L ittle

i n f o r m a t i o n i s a v a i l a b l e o e r t a i n i n g to t h e e f f e c t o f

th e a e r i a l environment upon th e development o f wheat h e a d b l i g h t .

A thor­

ough knowledge o f t h e e n v ir o n m e n t a l f a c t o r s as w e l l a s t h o s e f a c t o r s a s s o c ­
i a t e d w i t h t h e p a t h o g e n and th e h o s t ,

i s r e l e v a n t to the development o f

c o n t r o l methods.
The importance o f th e environment to t h e development o f p l a n t
d i s e a s e s was s t r e s s e d by Jon es ( 3 9 ) •

Much p r o g r e s s has be e n made in t h i s

d i r e c t i o n in th e c a s e of r oot and v a s c u l a r d i s e a s e s i n which t h e pa t h o g e n s
g a i n e n t r a n c e throu gh t h e r o o t s y s t e m s o f p l a n t s and are t h u s l a r g e l y i n ­
f l u e n c e d by the s o i l e nv ir on m e nt .

T h i s i s o r o b a b i y be c au s e o f the r e l a ­

t i v e e s s e w i t h which the s o i l f a c t o r s i . e . m o i s t u r e , te m p e r a t u r e , f e r t i l ­
ity, e tc .,

can be e x p e r i m e n t a l l y c o n t r o l l e d .

The c o n t r o l o f c e r t a i n en­

v ir o n m e n t a l f a c t o r s o f the atmosphere i s more d i f f i c u l t .

As a r e s u l t ,

t h i s i n f o r m a t i o n i s l a c k i n g f o r many o f th e p a t h o g e n s which a t t a c k the
a e r ia l portions of p la n ts .
The pu rpose o f t h i s s t u d y was t o s u p p ly a d d i t i o n a l in f o r m a t i o n
r e g a r d i n g t h e development o f h e a d b l i g h t o f wheat c a u s e d by G i b b e r e l l a

zea£ ana Helmi n t h o s p o r I uju sativura.
o f temperature on growth,

I t i n c l u d e s s t u d i e s on the e f f e c t s

s p o r u l a t i o n , end spore geimiiiuition o f b o t h

o nt ho g e ns ; end the e f f e c t s o f t h e c o n c e n t r a t i o n c f c o n i d i a l inoculum,
s t a g e o f h o s t m a t u r i t y , fmci t h e f a c t o r s a i r temperature and m o i s t - r e
on d i s e a s e d e v e lo p m e n t.

The a s s o c i a t i v e e f f e c t s o f the two pathogens

was deter mine d "by o b s e r v i n g t h e i r beh avi or when combined in c u l t u r e and
o b s e r v i n g the h o s t r e a c t i o n when the p l a n t s were i n o c u l a t e d ■i t u mixed
suspensions of t h e i r conidia.

REVIEW OF LITZRATurx
G -i b b e r e ll a zeae
The d i s e a s e

A tan& soff

(p;

presented

an

Tier G a i n i n g

to fnc; r i e l h e a d b li g h v of

sp ecies

f f u s o r i tur,

ed

by

to

tbs

of

.-ipclnnc?
d isea se

pad

cn

.-able

j?’os £lman

caused

of

ex ten siv e
cerea ls

cau sin g

(V O

a .n c

tht-

fid e

up

review

t o Ipf-3 •

d isea .se.
( Po)

of

the

T
r*e

litera tu r e
li s t s

elev en

Tne r e v i e w s c r e s e n t -

r.erta in

m ore

s p e c if leal ly

c-y Gibc-erel3.a z e a e .

During the p e r i o d from IdyG to io$;3* r e p o r t s and d e s c r i p t i o n s
o f f u s a r i a l h o ■-d e l i g h t or wheat sca b were made by Chester (1 0) i n Dela­
ware; by Detimers ( 1 8 ) i n Ohio; by Arthur ( 3 ) i n Indiana;
j: ? )

r.v ra.nmel (51 ,

i n Iowa; ana by .Buckhout ( 5 ) i u r e n n s y l v n n i n .
Among th e more r e c e n t d e s c r i p t i o n s o f h e a d b l i g h t or scab on

wheat are t h o s e o f k a d n n o s and Fogci.-an ( V i ) , A t a n a s o f f ( 5 ) , k e l s o n (U3 )
and D ic ks on and Hain es ( ?3) •

A c co r di n g to Maclnree run. Fogdiaan ( V-!},

"The d i s e a s e may become e v i d e n t soon a f t e r the heads have emerged from the
s h e a t n , alt hough i t mey not become; a Torrent u n t i l Much l a t e r .

Affected

s p i k e l e t s o f t e n appear to have r i p e n e d p r e m a tu r e ly , w h i l e h e a l t h y s p i k e l e t s ar e s t i l l Or o e n .

The glumes o f the d i s e a s e d s p i k e l e t s ,

however, are

-

u s u a l l y p a l e and s i c k l y ,

3

-

e s p e c i a l l y when t h e y a r e a t t a c k e d w h i l e s t i l l

young; and t h e y may he p a r t l y c o v e r e d w i t h a v a r y i n g amount o f w h i t e or
s l i g h t l y p i n k i s h mycelium.

They a r e o f t e n cemented t o g e t h e r b y a smooth

p i n k i s h , or ang e, or r e d d i s h i n c r u s t a t i o n .

The number o f a f f e c t e d s p i k e -

l e t s i n a head v a r i e s g r e a t l y ; o n l y a s i n g l e one may be a f f e c t e d or n e a r ­
l y a l l may be d i s e a s e d .

In f a c t , when th e organism a t t a c k s any p a r t o f

t h e r a c h i s , t h e e n t i r e hea.d above t h e n o i n t of a t t a c k may be k i l l e d .
T hi s o c c u r s q u i t e f r e q u e n t l y i n a bad scab y e a r .

The a f f e c t e d p o r t i o n

o f t h e r a c h i s at f i r s t appears w a t e r - s o a k e d , and l a t e r becomes dark in
color.

S t ill later,

somewhat b l e a c h e d .
season

t h e dark c o l o r may d is a p p e a r and t h e r a c h i s appears
The s m a ll dark p e r i t h e c i a u s u a l l y d e v e l o p l a t e r i n the

. 11
T hi s organism has a worldwide d i s t r i b u t i o n .

A t a n a s o f f (p) r e ­

p o r t e d t h a t i t i s common thro ug hou t t h e wheat growing s e c t i o n s o f the
U n it e d S t a t e s , H o ll a n d , B u l g a r i a , and Southern R u s s i a .
p o r t e d i n England by B e n n e tt ( 6 ) ,
Japan by N is ik a d o et_ a l .

I t has b e e n re­

i n A u s t r a l i a by Hynes ( 3 S ) ,

(50).

The economic importance o f t h i s d i s e a s e i s i n d i c a t e d by Dick­
son and Maines (? 3) who s t a t e t h a t the l o s s o f s p r i n g and w i n t e r wheat
a l o n e during th e e p id e m i c i n 1919 was 80 m i l l i o n b u s h e l s .
were a g a i n s u s t a i n e d in 19BS ( D i c k s o n and Maines,
V e s t a l and C u r t i s , U5 ) .

Heavy l o s s e s

23; N e l s o n , l+9» Mains,

In 19^6 t h e aut hor o b s e r v e d some f i e l d s i n Min­

n e s o t a i n which n e a r l y 100 ;oer c e n t o f the heads were i n f e c t e d .

Prom 5

to 10 p e r c e n t head i n f e c t i o n was common.

Taxonomy

A t a n a s o f f (5 ) g i v e s a good a cco u nt o f the v a r i o u s Fusarium s p o .
a s s o c i a t e d w i t h h e a d b l i g h t o f wheat and r e c o r d s t h e synonyms f o r t h e s e

-

species.

H

-

Tanja ( b o ) p r e s e n t s a. b r i e f review o f th e taxonomy o f Gibber­

ella zeae.

Up u n t i l 193^»

name u n i v e r s a l l y ac c e p t e d was G. saubin-

e t i i (i-iont.) Sacc. w i t h Fusarium graminearum Schv/abe as i t s im p e r fe c t
stage.

In 123°» F e t c h (35) e s t a b l i s h e d the name G. zeae and i n c l u d e d G.

seubl n e t i i as a synonym.

According to P a t c h , S c h w e in it z d e s c r i b e d a fun­

gus from dead corn s t a l k s about 100 y e a r s ago which he named Sphaeria
zeae.

A f t e r the genus G l b b e r e l l a was d i s t i n g u i s h e d and. the type s p e c i e s

G. cyanogens (Desm.) Sacc. d e s c r i b e d , i t was r e c o g n i z e d t h a t S. zeae be­
lo ng e d i n the newer genus .

G. cyanogena o c c u r r e d on herbaceous d i c t y l e -

Gonous stems, as d i d the l a t e r d e s c r i b e d s p e c i e s , G. s a u b i n e t i l (i-iont.)
Sacc.

Saccarao i n c l u d e d under the l a t t e r name, the s p e c i e s growing on

n a i z e and small g r a i n s .
c i e s were co ncerned.

P e t c h (55) no te d t h a t two e n t i r e l y d i s t i n c t spe­

The one on the d i c o t y l e d o n o u s stems pr oved to be a

synonym o f th e e a r l i e r G. c y an og e n s , whereas the one on corn was the e a r l i e r Sphaeria zeae o f S c h w e i n i t z , which Saccardo thought was i d e n t i c a l w it h
G. s a u b i n e t i i .

P e t c h (55) t r a n s f e r r e d S c h w e i n i t z ' s s p e c i e s to the genus

G i b b e r e l l a . thus th e name G. zeae (Schw.) P e t c h .

In I 5U5 , Snyder and Han­

sen ( u5) s u g g e st e d t h a t a l l B p e c i e s , v a r i e t i e s and forms o f the s e c t i o n s
Hoseum, A r t h r o s p o r i e l l a , Gibbosum, and D i s c o l o r o f the Fusarium c l a s s i ­
f i c a t i o n e s t a b l i s h e d by Wollenweber et_ a l . ( 73) be i n c l u d e d i n one spe­
c i e s which i s Fusarium roseum (LK.) Snyder e t Hansen.

They f u r t h e r sug­

g e s t t h a t a l l th o s e members of t h e s e s e c t i o n s which a t t a c k c e r e a l s be
f u r t h e r d i s t i n g u i s h e d by the form name C e r e a l i s (Cke.) to i n d i c a t e patho­
genesis.

They a l s o s u g g e s t e d tha t the p e r f e c t s t a g e f o r t h i s s p e c i e s be

G i b b e r e l l a roseum (LK.) f_. c e r e a l i s (Cke.) Snyder e t Hansen.

The termin­

o l o g y in t ro d u c ed by Snyder and Hansen was r e c e n t l y d is p u te d by Sherbakoff
(b3).

-

5

-

Host range

G-itiberella zeae has a v e r y wide h o s t r a n g e .

Johnson and Dick­

son (3 7) mention wheat, r y e , s p e l t , "barley, corn and v a r i o u s g r a s s e s ,
ka d u n e s and Foglernan (^U) found s c a t on the heads of v a r i o u s t y r e s o f
wheat, r y e , b a r l e y , o a t s ,

s p e l t , e inner, ei nk orn , and s e v e r a l g r a s s e s .

They r e p o r t e d l o c a l eui dem ics on w e s t e r n wheat g r a s s ( Agropyron s m i t h i i ) .
A t a n a s o f f (5) l i s t s
has been fo u nd .

genera in 19 d i f f e r e n t f a m i l i e s upon v/hich G. zeae

Se lby and Kanns (62) found G. zeae a t t a c k i n g c l o v e r and

a lfalfa.

In fectio n studies

In 18Q8, Selby ( 6 l ) t r i e d t o produce h e a d b l i g h t o f wheat by
a r t i f i c i a l i n o c u l a t i o n w i t h c o n i d i a o f Fusarium.

L ate r,

in I 9 0 9 , Selby

and Manns ( o?) r e p o r t e d an e x t e n s i v e study of th e h e a d b li g h t d i s e a s e of
vrheat.

They were s u c c e s s f u l i n e s t a b l i s h i n g heavy i n f e c t i o n by so r a y in g

t h e wheat p l a n t s w i t h c o n i d i a l s u s p e n s i o n s b e f o r e ,
ing.

during or a f t e r f l o w e r ­

They r e p o r t e d t h a t the same organism was r e s p o n s i b l e f o r he a d b li g h t

o f wheat, o a t s , b a r l e y , r y e , eraser, and s p e l t .
out t h a t " . . .

In a d d i t i o n ,

they pointed

scab i n f e c t i o n doe s not take p l a c e by r e a c h in g the head

through permeation o f the stem."

By d e n t i n g i n f e c t e d s e e d t h e y demon­

s t r a t e d that the fungus over w i n t e r s as an i n t e r n a l i n f e c t i o n i n wheat
kernels.
Se e d li n g b l i g h t , r o o t - ,

s t a l k - , and e a r - r o t of corn ca us ed by

G ib b e r e ll a zeae was f i r s t demonstrated to be a s s o c i a t e d w i t h h e a d b li g h t
o f wheat i n 1918 by H of fe r and H o ib er t (32) and H o f f e r , Johnson and Atano s o f f ( 33 ) -

They ob se rv e d a g r e a t e r abundance o f h e a d b li g h t i n f i e l d s

where wheat was grown immediately f o l l o w i n g corn t h a t had been i n f e c t e d

w i t h Fusarium r o t of t h e r o o t and s t a l k .

In the ne xt y e a r , H o l b e r t ,

Trost and H o f f e r (3 5 ) r e p o r t e d t n a t where i t f o l l o w e d ?. y e a r s of corn
wheat showed a v e r y h ig h pe r ce n t a g e of scah i n p r a c t i c a l l y e v e r y c a s e .
In 1920, Holb ert and H o f f e r (3*0 c o n c lu d e d t h a t th e wheat scab organism
i s pr o b a b ly t h e most common p a t h o g e n r e s p o n s i b l e f o r most o f the ro ot
and s t a l k r o t t i n g o f corn p l a n t s i n the c e n t r a l s t a t e s .

L a te r Manns

and P h i l l i p s (*4-6) r e p o r t e d t h a t Cr. zeae was t h e most a c t i v e s e e d l i n g
b l i g h t o f corn and may be an important f a c t o r i n r e d u c in g s t a n d s .
That f u s a r i a l h e a d b l i g h t of wheat i s f a v o r e d by p e r i o d s o f
wet, humid weather and h i g h te m p er a tu r e d u ri n g t h e h e ad in g p e r i o d has
been mentioned b y s e v e r a l wor kers.

Schmitz (5 5) o b s e r v e d t h a t the d i s ­

e ase was worse when the weather

wet, hot and muggy.

w p .s

Mortensen (**-7)

o b s e r v e d t h a t i n f e c t i o n was s e v e r e i n wet y e a r s between the ti m e o f
f l o w e r i n g and m a t u r a t io n o f t h e c e r e a l s .

Johnson, Dickson and Johann

(38) s t a t e d t h a t "The abundant p r e s e n c e o f t h e p a r a s i t e s and t h e m o i s t ,
warm w ea the r f o l l o w i n g t h e b lo s s o m in g n e r i o d o f th e g r a i n f a v o r e d d e v e l ­
opment o f the d i s e a s e . "

Haclnnes and Fogleman (^L) o b s e r v e d t h a t h ig h

h u m id it y and temperature f a v o r e d i n f e c t i o n .

A t a n a s o f f (^O p o i n t e d out

t h a t r a i n s and c l o u d y weather fa v o r t h e development o f f u s a . r i a l head­
b l i g h t and are a l s o important f a c t o r s in sn or e p r o d u c t i o n .

K o e h le r ,

D ic ks on and Holb ert (U?) co nc lu de d t h a t m o is tu r e was the c h i e f f a c t o r
i n pro du cin g t h e s e a s o n a l d i f f e r e n c e s in i n f e c t i o n be tween the ye a r s
I 919 and 1920, b e c a u s e t h e weather du rin g and f o l l o w i n g f l o w e r i n g i n
I 919 was v e r y m o i s t , whereas i n 1920 the e n t i r e p e r i o d was dr y .
( 60) s t a t e d t h a t "There seems t o be but l i t t l e

Scott

doubt t h a t m od er ate ly

h i g h temper atur es and heavy r a i n f a l l , accompanied by c o n s i d e r a b l e cl oud y
weather a t the time o f i n f e c t i o n , r e s u l t in e p id e m i c s of s c a b . "

Mains,

V e s t e l end Cur tis (*+5)» *n r e f e r r i n g to the e o i p h y t o t i c o f wheat b l i g h t
i n 1928, s t a t e d t h a t " . . . p r o lo n g e d wet weather i n f e y and June, during
and f o l l o w i n g t h e bl o s s o m in g o f sm el l g r a i n s , was v e r y f a v o r a b l e f o r the
development o f scab and as a r e s u l t reached eoide mic p r o n o r t i o n s such as
had not been a t t a i n e d s i n c e 101S*"

N e ls on (hg) i n d i c a t e d t h a t because o f

the abundance and d i s t r i b u t i o n o f r a i n f a l l i n Michigan during the season
o f 1 9 2 8 , c o n d i t i o n s were v e r y f a v o r a b l e f o r the development o f h e ad b lig h t
o f wheat and oth e r c e r e a l s .

I t was observed by C h r is t e n s e n , Stskmen and

Immer ( l o ) th at abundant moi st ure from blo ss om ing time u n t i l t h e dough
s t a g e was conducive t o the development o f f u s a r i a l h e a d b li g h t and t h a t the
patho gen spreads r a p i d l y on wheat when a few h o t , r a i n y days f o l l o w the
flowering neriod.

Warm, r a in y weather durin g t h e f l o w e r i n g p e r i o d of th e

g r a in crop g r e a t l y f a v o r s the spread and development o f h e a d b li g h t o f
wheat ac cor din g t o Dickson and Mains ( 23) .
found,

Pugh, Johann and Dickson ( 5 8 )

in t h e i r s t u d i e s on the r e l a t i o n o f temperature t o i n f e c t i o n , th at

the g r e a t e s t o e r c e n t a g e o f wheat heads became i n f e c t e d when in the f l o w e r ­
ing s t a g e a t h ig h er temperatures (2 8 - 3 2 ° C.) and th e i n c u b a t i o n n e r i o d was
a l s o sh or te n e d .
Se ve ral f a c t o r s o t h e r than m e t e o r o l o g i c a l ar e known to p r e d i s ­
pose p l a n t s to i n f e c t i o n .

Thus Arthur ( 3) observ ed t h a t h e a d b l i g h t in­

f e c t i o n was worse in th ose f i e l d s in which the l a t e s t sowing o f wheat were
made.

Selby and Manns (u2) n o t e d F u s a r i a l h e a d b l i g h t o f wheat was s e v e r e

on p l o t s on which c o n ti n u o u s cropping was p r a c t i c e d .
Dickson, Johann and V'ineland ( 22) and Pugh, Johann and Dickson
( 8 8 ) concluded t h a t i n i t i a l i n f e c t i o n u s u a l l y oc cu rs through caught and
extruded a n t h e r s .

Adams ( l ) thought i t probable t h a t i n f e c t i o n f i r s t

became e s t a b l i s h e d i n the d e ve lo p in g embryo.

He found hyphae p e n e t r a t i n g

-

s

-

t h e glumes ns w e l l a s d i s o r g a n i z e d c e l l s .

Adams found no i n d i c a t i o n

t h a t i n f e c t i o n p r o g r e s s e d i n th e r a c h i s from s p i k e l e t to s p i k e l e t .

He

s t a t e d t h a t "The development o f t h e fu ngus in t h e glumes and c e l l s ex­
t e r n a l to t h e n u c e l l u s would seem t o be subsequent to 7)rima.ry i n f e c t i o n
of the kernel."

Tu ( 08) n o t i c e d t h a t the i n i t i a l p o i n t o f i n f e c t i o n on

Minsturdi b a r l e y and Marquis wheat was alw ay s marked by a brownish, c h l o r o t i c snot on the glume.
Pugh, Johann and Dickson ( 5 8 ) s t u d i e d some o f the f a c t o r s in ­
f l u e n c i n g th e development o f G i b b e r e l l a zeae h e a d b l i g h t o f w he at .

They

determined the l e n g t h o f the i n c u b a t i o n p e r i o d a t v a r i o u s s t a g e s o f head
development and at v a r i o u s te m p e r a tu r e s o f i n c u b a t i o n as w e l l as t h e
p r o g r e s s of i n f e c t i o n as r e l a t e d t o a n t h e s i s .

V arietal resistan ce

V a r i e t a l d i f f e r e n c e s to f u s a r i a l heao.bli ght a r e a l s o known to
e x i s t i n w hea t.

T h i s was r e p o r t e d by Arthur ( 3 ) *

Schmitz ( 5 9 ) , Atana-

s o f f ( 4 , 5 ) , Maclnnes and Fogleman ( 4 4 ) , C h r i s t e n s e n and Stakman ( 1 4 ) ,
S c o t t (GO), C h r i s t e n s e n , Stakman and Immer ( l o ) , Tu ( 6 7 , 08) ,

and Pugh,

Johann and Dickson (5 8 ) f u r t h e r demonstrated t h a t v a r i e t i e s d i f f e r in
their s u s c e p tib ilit y .

Ph ysiologic sp ecia liza tio n
P h y s i o l o g i c s p e c i a l i z a t i o n has been n o t e d i n G i b b e r e l l a zeae
by s e v e r a l i n v e s t i g a t o r s .
g e n i c i t y of i s o l a t e s .

Henry (3 1 ) ob s e rv e d d i f f e r e n c e s i n t h e patho­

C h r i s t e n s e n and Stakman (1 4) and C h r i s t e n s e n ,

Stakman and Immer ( l o ) found marked d i f f e r e n c e s i n the de gr ee o f i n f e c ­
t i o n i n the same v a r i e t i e s grown a t d i f f e r e n t l o c a l i t i e s i n t h e same
yea r or a t t h e same p l a c e in d i f f e r e n t y e a r s , and s u g g e s t e d t h a t t h i s

-

9

-

was p r ob ab ly due to the nre se nc e o f p h y s i o l o g i c forms o f the ont hog en.
Tu (6 7 , 68 ), Greaney and B a i l e y ( 2 8 ) , Tanja. ( b o ) , a n d H i s i k a d o , Mat su­
mo to and Yamauti (5 0) n o t e d p h y s i o l o g i c a l d i f f e r e n c e s among i s o l a t e s .
U l l s t r u p (b9) shoved th at c o n s i d e r a b l e v a r i a t i o n e x i s t e d among s i n g l e a s co s p o r e and h y p h a l - t i p c u l t u r e s o f G. s a u b l n e t i i w h i l e growing under
an a r t i f i c i a l environment, and t h a t t h i s v a r i a b i l i t y was e x p r e s s e d a l s o
in p a t h o g e n i c i t y .
An e x t e n s i v e i n v e s t i g a t i o n on the p a t h o g e n i c i t y and g e n e t i c s
G i b b e r e l l a s a u b i n e t i l was p r e s e n t e d by Eide ( 2 c ) .

He found t h a t a l l

but 31 o f 325 i s o l a t i o n s made from n a t u r a l l y o c c u r r i n g a s c o s p o r e s o f G.
s a u b i n e t i i were o f t h e same c u l t u r a l t y p e , v a r y i n g o n l y in de gr ee o f
color in t e n s it y .

Of the 31* 2U were l i k e t h e m a j o r i t y on p o t a t o dex­

t r o s e agar , but d i f f e r e d on Coons' ag ar.

The remaining seven comprised

t h r e e t y p e s , two r e p r e s e n t e d by one c u l t u r e ea ch , and the t h i r d t y r e by
fiv e cultures.

These a eco sn ore i s o l a t e s from f i e l d m a t e r i a l were not

found t o d i f f e r g r e a t l y i n o a t h o g e n i c i t y e x c e n t f o r c u l t u r a l v a r i a n t s
which d i f f e r e d to the e x t e n t t h a t some were l e s s v i r u l e n t than the nareut c u l t u r e .

Helmintho suoriuT, sat ivum

As compared to G i b b e r e l l a z e a e , Hel-mint ho snor iurn s a t ivum i s a
r e l a t i v e l y new c e r e a l pa th og e n.

I t was f i r s t d e s c r i b e d by Pammel, King

and Bakke (93) as the c aus e of a new d i s e a s e o f b a r l e y .

I t s importance

became e v i d e n t i n th e e a r l y 2 0 ' s when C h r i s t e n s e n (11 , 1 3 ) and D o sd a ll
( 2U) p u b l i s h e d t h e i r s t u d i e s on t h e h o s t r ang e, p a t h o g e n i c i t y ,
p h y s i o l o g y o f the organism.

and th e

D r e c h s l e r ( 25) p r e s e n t e d a good d i s c u s s i o n

on H. sativum about the same ti m e, c o v e r i n g b o t h the m y c o l o g i c a l and
p a t h o l o g i c a l a s p e c t s o f th e problem.

R e c e n t l y , Mschacek and Greaney (U3 )

-

10

-

r e v ie w e d t h e l i t e r a t u r e which d e a l s s p e c i f i c a l l y w i t h t h e h e a d b l i g h t
phase o f th e d i s e a s e .
H e a d b l ig h t o f c e r e a l s c aus ed by He lminthosuorium s a t ivum has
been r e f e r r e d t o by s e v e r a l names.

H o l l e y ( 7 ) , Evans ( ? 7 ) . Weniger (7<?) ,

D r e c h s l e r ( 2 5 ) , Henry ( 3 1 ) , D ss tu r ( 1 7 ) , and Waldron ( 7 0 , 71) u s e d t h e
term " b l a c k - p o i n t " to d e s c r i b e a b l a c k e n i n g r e s u l t i n g from i n f e c t i o n o f
t h e wheat k e r n e l by H. sativum and sometimes by s u e d e s o f A l t erne r i ft.
1-iachacek and Greaney (U3 ) p r e f e r the u s e o f the term "k er ne l smudge" to
describe th is tyre of in fe c tio n .

C h r i s t e n s e n (1 1 )

used t h e term "head

b l i g h t " to d e s c r i b e i n f e c t i o n o f t h e heads b y H. s a t i v u m , and C h r is te n ­
sen and Stakman (1 5) r e f e r r e d t o t h e d i s e a s e complex r e s u l t i n g in the
d i s c o l o r a t i o n o f b a r l e y k e r n e l s by K. sa tivum and s p e c i e s of Fusarium
as ,rb l i g h t ."
C h r i s t e n s e n ( l l ) was t h e f i r s t t o g i v e a thorough d e s c r i p t i o n
o f th e symptoms r e s u l t i n g from Helff li nth oso or ium sativum i n f e c t i o n during
th e v a r i o u s s t a g e s o f p l a n t d e ve lo p m e n t .

With r e s p e c t t o h e a d b l i g h t he

n o t ed t h a t not o n l y th e s eed s me.y become d i s c o l o r e d but the e n t i r e head
or p o r t i o n s of t h e head may be b l i g h t e d . .

Ke s t a t e d t h a t "The o var y o f

t h e f l o r e t may be a t t a c k e d a t any s t a g e i n i t s development, and the k e r ­
n e l may f a i l to form o r , when formed,

i t raay be b a d ly shrunken."

Dastur

( 1 7 ) d e s c r i b e d s i m i l a r symptoms r e s u l t i n g from i n f e c t i o n of the wheat
heads du rin g f l o w e r i n g .
Helminthosnorium sa tiv um i s found i n a l l s e c t i o n s o f the world.
Christensen ( l l )

mnd.e i n o c u l a t i o n s w i t h c u l t u r e s o b t a i n e d from d i f f e r e n t

s e c t i o n s of the United S t a te s,

Canada, A r g e n t i n a , A u s t r a l i s , and Mexico

and o b t a i n e d t y p i c a l symptoms on wheat and o t h e r c e r e a l s .

Machacek and

Greaney (U3 ) s t a t e d t h a t t h e " B la c k -p o in t" d i s e a s e o f c e r e a l s probab ly
o c c u r s wherever c e r e a l s are grown.

They l i s t ,

i n a d d i t i o n to t h o s e

-

11

-

c o u n t r i e s mentioned, above, A r g e n t i n a , Germany, Morocco, South A f r i c a ,
I n d i a , and J a v a .

In l d ? 5 , C h r i s t e n s e n (12) r e n o r t e d i t s p r e s e n c e i n

Serbia.
A t t e n t i o n was drawn t o th e d e s t r u c t i v e n e s s o f t h e H e lm in th o s norimn d i s e a s e by StaJcnan ( bU), H o l l e y ( 8 ) ,
(2U ), and Henry ( 3 1 ) •

Christensen ( l l ) ,

Dosdall

C h r i s t e n s e n (1 1 ) and Kenry ( 3 1) showed t h a t the

pa th ogen i s abundant i n many s e e d l o t s o f wheat, b a r l e y , and r y e .

Mach-

acek and Greaney (U3) s t r e s s th e importance o f th e " b l a c k - p o i n t 11 d i s e a s e
o f c e r e a l s and me nt io n t h a t "As y e t ,

few i n v e s t i g a t o r s have a t t e m p t e d to

e s t i m a t e th e l o s s r e s u l t i n g from t h i s p a t h o l o g i c a l c o n d i t i o n o f t h e s e e d ."
The h o s t range f o r t h i s organism i s v e r y w i d e .
(ll)

Christensen

found t h a t w he at , b a r l e y , and r y e were t h e most s u s c e p t i b l e c e r e a l s ,

and t h a t some s p e c i e s o f o a t s and c o m ar e o r a c t i c a l l y immune.
c e s s f u lly infected

Ke suc­

out o f 13^- s p e c i e s o f c e r e a l s and g r a s s e s i n the

gre e nh ous e w i t h Helminthosporium s at iv um by s p r a y i n g them w i t h spore s u s ­
pensions.

In f i e l d t e s t s , 57 out of no s n e c i e s were i n f e c t e d as a r e s u l t

of sim ilar treatments.
High te m p e r a t u r e s combined w i t h abundant r a i n f a l l f a v o r s s e e d
i n f e c t i o n a c c o r d i n g to C h r i s t e n s e n ( 1 3 ) .

Dastur (1 7 ) p o i n t e d out t h a t

" b l a c k - p o i n t " i s a s s o c i a t e d w i t h h i g h a t m o s p h e r ic h u m i d i t y .

Greaney and

t'achacek (?9) n o t e d t h a t most s e v e r e Helminthosnorium sa tivum s e e d i n f e c ­
t i o n s o c c u r r e d i n l o c a l i t i e s h a v i n g th e h i g h e s t r a i n f a l l d u r i n g t h e grow­
ing season.
Tne i n i t i a l p e n e t r a t i o n and the t i s s u e s a t t a c k e d by Helm in tho 3porium sativum have bee n i n v e s t i g a t e d by s e v e r a l w o r k e r s .

B o l l e y (J)

n o t e d t h a t th e s c u t e l l u m o f t e n became d i s e a s e d , c a u s i n g t h e f o o d surroly
i n t h e endosperm t o be u n a v a i l a b l e to the g e r m i n a t i n g embryo.

Weniger

-

12

-

( 7 ?) found the mycelium i n the p e r i c a r p and t e s t a ,
and th e embryo, and a l s o i n t h e embryo i t s e l f .

between t h e s e l a y e r s

P e y r o n e l (Ho) showed

t h a t t h e f i r s t symptom o f d i s e a s e i n a k e r n e l was a d i s c o l o r a t i o n of the
l o d i c n l e s , which are organs i n c l o s e p r o x i m i t y to the s c u t e l l u m .

A

t i s s u e o f t h i n w a l l e d c e l l s r i c h i n n u t r i e n t s was found at the bas e o f
these l o d i c n l e s .

The t i s s u e w i t h e r e d a f t e r f e r t i l i z a t i o n o f the f l o w e r

and became a v e r y s u i t a b l e substratum f o r the growth o f the f u n g i , the
my ce lin o f which o f t e n p e n e t r a t e d the dead c e l l s and th en inv aded the
in tegu me nts over the embryo.

He b e l i e v e d t h a t t h e r a p i d i t y o f d i s i n t e ­

g r a t i o n o f the l o d i c u l a r t i s s u e was a d e te r m in in g f a c t o r in the d e v e lo p ­
ment o f seed d i s c o l o r a t i o n ,

Destur ( 1 7 ) foun d t h a t the fungus hynhoe

invaded the k e r n e l in teg um ents but d id not r e a c h the embryo.

This f r e e ­

dom o f the embryo from i n f e c t i o n e x p l a i n e d why many d i s c o l o r e d k e r n e l s
ge rmi n a t ed nor m o l l y .
The p r e s e n c e o f a i r borne inoculum,

the s t a g e of h o s t m a t u r it y ,

and v a r i e t a l r e s i s t a n c e w i t h r e s p e c t t o the g e n e r a l p r e v a l e n c e o f k e r n e l
smudge caused by Helmintho s p o r iuin s a t ivum and A l t e r n a r in s p p . were st ud ­
i e d by Kachacek and G-reaney (*+3 ) .

They found t h a t the l a r g e s t number o f

sp or es were p r e s e n t i n t h e a i r over Manitoba du ring the p e r i o d of wheat
growth from headi ng to m a t u r i t y ; t h a t i n f e c t i o n o f the k e r n e l took p l a c e
during th e mature s t a g e s o f p l a n t growth; and t h a t t h e r e were d i f f e r e n c e s
in v a r ie t a l reaction ,

t h e durum type b e in g more s u s c e p t i b l e to the d i s ­

e a s e than v a r i e t i e s o f th e Vulgare t y r e .

MATERIALS A'dD M5TKQSS
La bo r ato r y S t u d i e s
S e v e r a l i s o l a t e s o f G-ibberolla zeae and Helm in tho snor ium s a t i 7X1111 were o b t a i n e d from Dr. J . J . C h r i s t e n s e n , U n iv e r si t y ' o f Minnesota.

-

X3 -

Konosporous c u l t u r e s o f t h e s e i s o l a t e s were o b t a i n e d by p o u r i n g d i l u t e
c o n i d i a l s u s p e n s i o n s o v e r th e s u r f a c e o f 3 Pe r cen t w ate r agar i n a Pe­
t r i p l a t e and a l l o w i n g th e c o n i d i a t o g e r m i n a t e .

S in g le g e r m i n a t i n g

c o n i d i a were s e l e c t e d u s i n g t h e l o mm. o b j e c t i v e o f the m ic ro sco pe and
t r a n s f e r r e d , by means o f a g l a s s n e e d l e p r e p a r ed b y drawing out a 1 mm.
g l a s s rod, to agar s l a n t s in t e s t t u b e s .

The monosporous c u l t u r e s were

th e n t e s t e d f o r s e e d l i n g p a t h o g e n i c i t y on o v a r i e t i e s of wheat and the
most p a t h o g e n i c s t r a i n of each pa th ogen was s e l e c t e d f o r u s e .
The c o n i d i a l s t a g e o f G-ibberella zeae was produced on Coons'
agar i n i t i a l l y a d j u s t e d to pH J . 2 .

Helmlnthosporium sa tivum c o n i d i a

were produced on commercial l i f c o bean-pod a g a r .

These media were us ed

i n t h e temperature s t u d i e s on growth and s p o r u l a t i o n and a l s o f o r pro­
ducing t h e c o n i d i a u s e d f o r p l a n t i n o c u l a t i o n s .
The s t u d i e s on e f f e c t s o f temp erature on growth, s p o r u l a t i o n ,
and g e r m i n a t i o n were c on du ct ed i n i n c u b a t o r s m a in t a in e d w i t h i n i 0 . 5 ° C.
o f t h e d e s i r e d t e m p e r a tu r e .

The growth s t u d i e s were made on agar i n Pe­

t r i p l a t e s which had been i n o c u l a t e d b y th e agar p l u g method ( G-ibberella
zea e) or w i t h a fe w c o n i d i a on t h e end o f a t r a n s f e r n e e d l e ( He lminthosporium s a t ivum) .

Records o f t h e di am et er growth o f t h e m y c e l i a were

ta h en a t d e f i n i t e ti m e i n t e r v a l s or at the time the f i r s t c o l o n y neared
the edge o f the p l a t e .

E i g h t e e n by 150 ran. t e s t tu be s c o n t a i n i n g 8 ml.

o f agar medium s l a n t e d u n i f o r m l y and se e de d w i t h a 5 2Un* w ir e l o o p f u l o f
a s u s p e n s i o n o f c o n i d i a \<rere u s e d i n the s p o r u l a t i o n s t u d i e s .

They were

p l a c e d i n the v a r i o u s i n c u b a t o r s a f t e r s e e d i n g and a t d e f i n i t e i n t e r v a l s ,
t u b e s from each s e t were removed, wa te r added, and the agar s u r f a c e
s cr ape d w it h a wir e lo o p to g e t the c o n i d i a i n t o a s u s p e n s i o n .

A "Howard

c o u n t i n g chamber, m o d i f i e d f o r molds" was u s e d f o r d e t e r m in in g the con­
c e n t r a t i o n o f c o n i d i a i n th e s u s p e n s i o n .

A l l the c oun ts r ec or d e d are the

-

lU

-

a ve ra ge number o f c o n i d i a in 10 f i e l d s u s i n g t h e 10X low-power o b j e c t i v e
o f th e m ic r o s c o p e .

For t h e g e r m i n a t i o n s t u d i e s , a c o n i d i a l s u s p e n s i o n

was -orepared u s in g a s t e r i l e wheat nerd d e c o c t i o n .

Two to H drops o f

t h i s s u s p e n s i o n were p l a c e d on a g l a s s s l i d e and then i n c u b a t e d in P e t r i
olates.

The p e r c e n t a g e g e r m in a t io n was based on co un ts o f more than 200

c o n i d i a from each sample.

S i m i l a r t e c h n i q u e s were employed i n l a b o r a t o r y

s t u d i e s on the a s s o c i a t i v e e f f e c t s o f the two o r g a n is m s .

Greenhouse S t u d i e s

Newthatch s p r in g wheat was the p r i n c i p a l v e r i e t y u s e d i n the
green ho us e e x p e r i m e n t s .

The wheat was sown in s o i l in o n e - g a l l o n g l a z e d

p o t s and t h i n n e d to 10 p l a n t s pe r p o t s h o r t l y a f t e r emergence.

I t was

grown a t r e l a t i v e l y c o o l te m p er atu r e s (1 0 - 1 5 ° C.) f o r the f i r s t two
months, and t h e r e a f t e r in a warm gr ee nh ous e ( 2 0 - 2 5 ° C.) w i t h supplemen­
tary l i g h t i n g .

Uniform heads were o b t a i n e d n e a r l y i d e n t i c a l to t h o s e

produced on wheat grown in t h e f i e l d .
F i v e s t a g e s o f development were used i n t h e s e e x p e r i m e n t s .
They i n c l u d e (1) the boot s t a g e , i n which t h e head was s t i l l e n c l o s e d
in the l e a f sh eath;

( 2 ) the b e f o r e - f l o w e r i n g s t a g e i n which t h e heads

v?ere out o f the boot but none o f t h e f l o w e r s d i s p l a y e d a n t h e r s ;

( 2) the

f l o w e r i n g s t a g e i n which most o f t h e f l o w e r s were in the p r o c e s s o f ant h e s i s or had a l r e a d y d i s p l a y e d a n t h e r s ; (U) the a f t e r - f l o w e r i n g stn.-.e
in which small immature s e e d s were in t h e p r o c e s s of develonment ; and
(5) t h e p a s t - f l o w e r i n g , s t a g e i n which t h e k e r n e l s were n e a r l y f i l l e d out
and i n the m il k t o s o f t dough s t a g e .
The t e c h n iq u e u s e d f o r p l a n t i n o c u l a t i o n was t h e same as t h a t
r e p o r t e d by Andersen e t a l . ( 2 ) .

This c o n s i s t e d of a s u s p e n s i o n of con­

i d i a a p t . l i e d w it h a hand-made a t o m i z e r .

U n l e s s mentioned o t h e r w i s e , the

standard, a p p l i c a t i o n of inoculum in a l l expe rim ents v/as ap p r o x im a te ly
one m i l l i o n Helmintho3porlum s a t ivum or two m i l l i o n G i b b e r e l l a zeae
c o n i d i a per r o t o f p l a n t s .

C o n i d i a l g e rm in at io n was chocked p r i o r to

the use o f the inoculum.
I n f e c t i o n was o'otained by p l a c i n g t h e i n o c u l a t e d p l a n t s i n
s p e c i a l l y d e s ig n e d hu mi di ty t e n t s .

Four o f t h e s e t e n t s ,

each w it h a

s e p a r a t e temperature c o n t r o l , were u s e d s i m u l t a n e o u s l y in some o f the
e x p e r im e n t s .

These t e n t s were t h e same as th o s e d e s c r i b e d by Andersen

e t a l . ( 2) , ex cept t h a t th e o r i g i n a l t e n t v/as e n c l o s e d i n an o u t e r t e n t
to a s s u r e b e t t e r c o n t r o l o f th e i n s i d e t e m oe ra t u r e ( F l e t e I ) .

Constant

te mp era tu re s were ma intained by c o n t r o l l i n g the temperature of the water
b ei ng aivplied to th e e x t e r i o r o f the t e n t and t h a t e n t e r i n g th e t e n t
through the Standard H u m i d i f i e r .

Thus, temper atu re s from 15° to JO0 C.

were ma in tai ne d f o r i n d e f i n i t e p e r i o d s w it h v a r i a t i o n s o f ^ 1° C.
In a l l th e s t u d i e s on p a t h o g e n e s i s , th e p l a n t s were e xpo sed
to c o n ti n u e d w e tn e ss f o r d i f f e r e n t p e r i o d s i n the humidity t e n t s b e f o r e
they were removed to the gr eenh ouse bench t o complete t h e i r i n c u b a t i o n
period.

Greenhouse temp era tur es were m ai n ta in e d a t ap p r o x im a te ly 25° C.
The r e s u l t s from t h e s e e xne rim ents are bas ed on r e p e a t e d ex­

p e r im e n ts i n v o l v i n g the u s e o f more than 2000 o n e - g a l l o n n o t s .

CULTURAL STUDIES
The R e l a t i o n o f Temperature t o Growth,
S n o r u l a t i o n and Germination
G i b b e r e l l a zeae

The r a t e o f grov/th o f G i b b e r e l l a zeae 011 Coons* agar was conpared a f t e r H days at d i f f e r e n t te mp era tu re s ( F ig u r e 1 ) .

There v/as a

v e ry r a p i d i n c r e a s e in the r a t e of growth from 8 ° to 28° C. w i t h an

Average r a d ia l growth of mycelia in mm. in 5 days

jy
o

o

8
3- *S

W
o

*t

*
oa
a*

0

13

IO
a

K
>
0>

u>
o

-F
o-

\ji
o

s

-J
o

- 17 -

e s p e c i a l l y s i g n i f i c a n t in c r e a s e betw een 20
.o
c u rred a t 4 C.,
4° C.

0

\

and 24

0

C.

Slow growth o c -

so th e minimum te m p er a tu r e i s p r o b a b ly s l i g h t l y below

ho grow th o c c u r r e d a t 3 b° C.

These r e s u l t s ag ree w ith th o se o f

D ick son ( 1 9 ) , Maclnnes and Fogleman ( 4 4 ) , Tu ( 08 ) , and Tanja ( 66) .
le c tiv e ly ,

Col­

the c a r d i n a l te m p er a tu r e s r e o o r t e d by th e s e workers f o r G.

zeae w ere 3°» 2 4 - 2 8 ° , and 3 2 -3 6 ° C. r e s p e c t i v e l y .
S t u d ie s on th e e f f e c t o f te m o era tu re on spore p r o d u c t io n v;ere
c o n d u cted a t th e same te m p er a tu r e s as in the grow th r a t e s t u d i e s .

The

most r a p id spore p r o d u c t io n o c c u r r e d i n i t i a l l y a t 28° and 32° C ., but
on lo n g e r i n c u b a t io n ( a f t e r 7
produced at 32° C.

(F ig u r e 2 ) .

12 days) c o n s i d e r a b l y more c o n i d i a were
The s t r a i n used i n t h e s e s t u d i e s -produced

v e r y few c o n i d i a a t tem p era tu res b e lo w 20

o

-0

C. and none a t 34

C.

Thus th e

b e s t tem p era tu re f o r s p o r u l a t i o n i n c u l t u r e was not th e same a s th a t fo r
g r o w th .
The tim e r e q u ir e d f o r s p o r u l a t i o n v a r ie d a c c o r d in g to th e t e c h ­
n iq u e i n v o l v e d and th e te m p e r a tu r e s a t which th e s t u d i e s were condu cted .
The most r o o id p r o d u c t io n o f c o n i d i a o b s e r v e d d u rin g t h e s e s t u d i e s took
p l a c e in l e s s than 20 hours at te m p e r a tu r e s from 2b° t o 28° C. in wheat
head d e c o c t i o n s on g l a s s s l i d e s .
o c c u r r e d a t 12° and lb ° C.

S e v e r a l days e la p s e d b e fo r e s p o r u l a t i o n

D ic k so n and Johann (2 1 ) and D ic k so n (2 0) a l s o

found t h a t h ig h e r tenroeratures s t i m u l a t e e a r ly c o n i d i a p r o d u c tio n by t h i s
fu n g u s .
M acro sco p ic o b s e r v a t i o n s made w h ile making snore c o u n ts i n d i ­
c a t e d t h a t sp o r e s from c u l t u r e s in c u b a te d a t d i f f e r e n t ten roera tu res d i f ­
f e r e d m o r p h o lo g ic a lly .

In ord er to d eterm in e w hether the in c u b a t io n tem­

p e r a t u r e s e x e r t e d an i n f l u e n c e on th e l e n g t h o f the c o n i d i a , measurements

Average number of oonldia per tube - m illio n s

Key
20

Temperature - d eg rees C entigrade
Pig u re 2 .
Coons' a g a r.

E ff e c t o f tem perature on s p o ru la tio n by

as a s on

-

19

_

find reco rd s o f 50 to 23 c o n id ia from one c u ltu r e incub ated a t each o f
the tem perntures showing abundant s p o r u la t io n (2 0 -3 5 ° C.) were taken at
random.

At 20

0

\0
and 24 C ., o0-70 per cent of the c o n id ia were ^ - s e n t a t e
.

end the remainder 3“ ahd 4 - s e p t a t e .

At 28

o

C., o n ly 27 per cen t were

5- s e p t a t e w h ile o ver 40 per cen t were 3 ~ serJ^s 't e
tate.

At 32

o

the remainder 4—seo-

C., over ^ 0 per c e n t were 2 - s e p t a t e , more than 30 Pe r cent

were 3 - seP t a t e , and a few 1 - and U - s e p t a t e .

In g e n e r a l, c o n id ia w ith the

same number of s e p ts .t io n s were a p p roxim ately equal in l e n g t h .

The aver­

age le n g t h of the c o n i d i a , however, in c r e a s e d w ith an in c r e a s e in the
number o f s e r t a t i o n s .

Thus tem perature in f lu e n c e d the le n g t h o f the

c o n id ia produced on a r t i f i c i a l media through a r e d u c t io n i n th e number
o f s e p ta in each conidium .
The c o n i d i a o f G-ibberelln zeae germ inate v e r y r a p i d l y ,
were observed to have germ inated in 3 hours a t 28° or 32° C.

’-’any

In o hours

n e a r ly a l l the c o n id ia exposed at 20 , 24 , 28°, and 32° C. had germin­
a te d (T able 1 ) .

At lower tem peratures the r a te o f germ in atio n was con­

s i d e r a b l y slow er, a lth o u g h the p e r c e n ta g e g e rm in a tio n a t the lower tem­
p e r a tu r e s a f t e r 48 and J 2 hours o f in c u b a tio n was as hig h as t h a t recorded
a t 28° C. in o h o u rs.
Records on th e p e r c e n ta g e germ in a tion o f the c o n id ia (Table 1)
supplemented by measurements o f th e germ tu b es (Table 2) gave more re­
l i a b l e in fo rm a tio n on the e f f e c t o f tem perature on g e rm in a tio n a s w e ll
as growth.

Measurements on germ tube le n g th made at the end o f b hours

showed a very d e f i n i t e peak a t 28° C. which f e l l o f f r a p id l y a t 24° and
32

C.

The germ tube measurements from c o n id ia germ inated a t the d i f f e r ­

ent tem peratures c o in c id e c l o s e l y w ith the data on m ycelia growth pre­
sen te d in Figure 1.

- 20 -

Table 1. — E f f e c t o f tem perature on the germ in a tion o f G-ibtere l l a zeae c o n id i a

Time in hours
Temperature
d eg rees C

r

2U

Ug

7?

P e r ce n ta g e g e r m in a tio n 0.
1+
8
12
16
20
24
28
3?37

0.0
0.0
0.0
50.3
85.2
3 9 .7
93-5
91.0
0.0

0.0
1 7 -U
8 5 .9
8 8 .5
——
—-------0.0

88 . G
95 • c
9 b .8
___
--------------0.0

.aased upon counts o f 200-U-00 c o n id ia f o r each sasrale.

93-7
--------

__

0.0

- 21 -

Table 2 . — E f f e c t o f tem perature on th e le n g t h o f th e germ
ta b e s o f G ib b e r e lla zeae

Time i n hours
Temperature
degrees C

2U

6

Ug

72

Average le n g t h o f germ tu b es i n m icrons6
U

s
12
lo
20
28

0 .0
0.0
0.0
10 . G
31.6
05.2
111.1
03.2

e
s
51. b
131.8

38.9
1U6 .3

137-3
-------- ■

. . . .

---------

---

____—

—

—— _
—_ _

---------

— ——

— —_

______

__ _

---------

---------

---------

g = s h o r t knobby germ tu b es j u s t b e g in n in g to protrud e from the
c o n id ia .

H elminthosporlum gat ivum
A growth curve s i m i l a r in many r e s p e c t s to t h a t p r e s e n t e d fo r
G ib b e r e lla zeae in r e s p o n s e to tem p erature (F ig u r e l ) was o b t a in e d w ith
Kelminthosnoriurn sativum (F ig u r e 3 ) •

The most r a p id r a d i a l grow th occu r­

red a t 28° C. w ith h u t s l i g h t l y l e s s r a p id grow th a t ?U° C. and a sharp
d e c l i n e in th e grow th r a t e a t 3^° C.

Some growth occu rred a t 3^° C ., a

tem perature which was u n fa v o r a b le f o r the growth o f G. z e a e .

T his d e c l i n e

in th e growth curve was not as sharp a s th a t e x h i b i t e d f o r G. zeae and a s
a r e s u l t i t may be e x p e c t e d t h a t K. sativum would be more e f f e c t i v e a t
h ig h e r tem p eratures than G. z e a e .

P axton ( ^ )

o b t a in e d b e s t growth at

30° C ., w h ile J o n e s , Johnson and D ickson (Uo) r e p o r t e d t h a t 25° C. was
the optimum tem perature f o r g row th .

The r e s u l t s o b t a in e d in t h e s e stud­

i e s a g r e e more c l o s e l y w it h t h o s e o b ta in e d by D o sd a l1 (2*+', who con clu d ed
th a t the minimum tem p erature f o r grow th l i e s near 0 -2 ° C ., w ith a maximum
betw een 35°

39° aJaa an optimum betw een 2U° and 28° C.

The p r o d u c t io n o f c o n i d i a on bean nod agar was compared a t hday i n t e r v a l s f o r a 20-d ay p e r io d at tem p eratu res from U° to 36° G.
(T a o le 3) •

c o n i d i a were produced i n 20 days a t tem p era tu res below

1 6 °, and above 28° C.

The most r a p id s p o r u l a t i o n o c cu rr e d a t 28° C.

A fte r 12 days in c u b a tio n the h i g h e s t spore y i e l d s were o b ta in e d from the
2U hour s e r i e s , and a f t e r 20 days in c u b a tio n the c u l t u r e s h e ld a t 20° C.
gave th e h ig h e s t snore y i e l d s .

The tem perature l i m i t s f o r good s o o r u la -

t i o n by Kelminthosporium sativum were r e s t r i c t e d to th e 20° to 28° C.
range.
e lle

In t h i s r e s p e c t i t was s l i g h t l y narrower than th a t f o r Gibber-

zeae.

pn Baoto baan-pod

Avwrage r a d ia l growth of mycella in ran.

g

agar*

CO

o

n

*
3

I

ft

?

ct
9(fc

16

8

*

$

'S

Table 3*— The e f f e c t o f tem perature on s p o r u la t io n by Kelminthosnorlum sativum on Bacto Bean-pod agar

Day 8 o f In c u b a tio n
Temperature
degrees C

8

k

12

16

20

M i l l i o n s o f sp o r e s per tubea
12
16
20
23
32

0.0
0.0
0.0
1 .5
3-1
few

a Average f o r U t e s t tu b e s

0.0
0.0
i.h

3 -2
0.0

0.0
0.3
2 .5
3 -3
2 .S
0.0

0.0
0.2
2-5
3.0
3 -1
0.0

0.0
C.U
U.O
3.0
3.0
0.0

Helminthosporium sativum never produced c o n id ia a s abundantly
a s G ib b e r e lla z e a e .

In g e n e r a l, c o n i d i a l p r o d u c tio n o c cu rr e d more slow­

l y w ith t h i s p a th o g en a lth o u g h i t was observed w ith in 24 hours i n wheat
head d e c o c t io n s on g l a s s s l i d e s .

At l e a s t two days were r e q u ir e d f o r

s p o r e 8 to be produced on a r t i f i c i a l media and th en the number ob serv ed
was r e l a t i v e l y few .
C h r is te n s e n ( 1 3 ) n o ted t h a t a much h ig h e r p e r c e n ta g e germina­
t i o n o f Helminthosuorlum sativum r e s u l t e d when h o st t i s s u e was added to
t h e w ater i n which th e c o n id ia were g erm in ated .
many t im e s .

This was s u b s t a n t ia t e d

On s e v e r a l o c c a s io n s o n ly 1 to 2 per cent g e r m in a tio n oc­

cu rred in w a ter, but upon the a d d i t i o n o f a sm all amount o f s t e r i l i z e d
w heat-head d e c o c t io n , a l l the c o n i d i a germ inated.
The e f f e c t o f tem perature on g e r m in a tio n was s t u d ie d f o r a 72hour p e r io d (T ab le 4 ) .

The most r a p id g e r m in a tio n occu rred a t 32° C.

At t h i s tem perature 36 p e r cen t o f th e c o n id ia germ inated i n 3 h o u r s.
A fte r 5 h ou rs, a l l t h e c o n id i a in c u b a te d at 28° and 32° and n e a r ly a l l
a t 24° and 36° C ., had germ inated.

A fte r 72 hours o f in c u b a t io n a l l the

c o n id ia at a l l th e tem p eratures had g erm in a ted .
The im n ed ia te e f f e c t o f tem perature on th e g e r m in a tio n o f th e
sp o r es

(Table 4) was e s p e c i a l l y r e f l e c t e d i n the l e n g t h o f th e

germ tube

A f t e r th re e hours e x p o su r e , short and knobby germ tu b es were e v id e n t on
the c o n id i a in c u b a te d at 24° and 3^° C.

At 28

C ., th e y were app roxi­

m ately o n e - h a lf th e le n g t h o f th e o o n id ia , and at 32° C ., th e germ tubes
were a s lo n g as the c o n id i a .
l a t e r (T able 5 ) •
a t 28

A d i f f e r e n t resp o n se was noted 2 hours

At t h i s time th e germ tu b e s on th e c o n id i a in c u b a te d

C. were more than th ree tim e s a s lo n g as th o s e produced

C. and c o n s id e r a b ly lo n g e r than th o se at 24° C. Thus the r a t e

a t 32°
o f growth

T able
— The e f f e c t o f teranerature on th e g e r m in a tio n o f
H elm inthosporium s a t ivum

Time i n hours
Temperature
degrees C

3

5

2U

U8

P e r c e n ta g e g e r m in a tio n
k

8
12
16
20
2k

28
32
36

0.0
0.0
0.0
0.0
0.0
31.8
09.9
9 6 .9
5 U. 1+

0.0
0.0
o.u

3 5 -2
7 0 .5
96.3
100.0
100.0
95.7

0.0
91.1
100.0
100.0
100.0
100.0
100.0
100.0
100.0

72

a

91.0
100.0

100.0

a Based upon c o u n ts o f 200-400 c o n i d i a from each sample.

----_ _ _

———

----—

----—

—

Table 5*— E f f e c t of tem perature on the le n g t h o f th e germ
tubes o f Helminthospor ium sativum

Temperature
d e g r ee s C

Time in hours
'
2U
k8

5

I'd

Average le n g t h o f germ tu bes in microns
u
g
12
lo
20
dk

22
32
36

0.0
0.0
6

0.0
21.2
123.0

S

18 .5
U2.1
6S .7
10 .7
lo .b

22 .0
167.6
---------

_ _ _

-------------

Si

1 2 5 .2
--- —
----— --_

— — —
_ _ _

-----

---------

a g = short knobby germ tu b es j u s t begin n in g to orotrude from c o n id i

- 28 -

"based upon th e l e n g t h o f th e germ tu b e s a f t e r 5 hours in c u b a t i o n ap­
p e a r e d to f o l l o w v e r y much th e same curve a s t h a t f o r c o lo n y grow th
( F ig u r e 3)» w it h t h e optimum tem p era tu re a t 28° C. and some grow th oc­
c u r r in g a t 3^° C.
E f f e c t s o f A s s o c i a t i o n o f G i b b e r e lla zeae and
Helminthosrporium sativu m

The e f f e c t s o f a s s o c i a t i o n were d eterm ined in t h r e e g e n e r a l
ty p e s o f e x p e r im e n ts -

In the f i r s t t y p e , m y c e l i a l t r a n s f e r s o f bo th

p a th o g e n s were p la c e d in c l o s e p r o x im ity to each o t h e r on beanpod agar
in P e t r i p la t e s .

O b s e r v a tio n s o f th e r e a c t i o n s o f th e raycelia o f both

were made a t th e tim e th e y met and f o r s e v e r a l days t h e r e a f t e r .

The

second ty p e c o n s i s t e d o f s e e d in g th e agar in P e t r i e l a t e s w it h mixed
c o n i d i a l s u s p e n s io n s .

U n iform ly s l a n t e d t e s t tu b e s c o n t a i n i n g bean

pod agar were a l s o see d e d w ith a 5 *nl. l o o p f u l o f mixed s u s p e n s io n and
c o n i d i a l c o u n ts made to d eterm in e whether or not t h e r e was any in h ib ­
i t i o n in s p o r u l a t i o n o f e i t h e r p a th o g e n .

F i n a lly , a s e r i e s of e x p e ri­

ments was conducted in which mixed c o n i d i a l s u s p e n s io n s o f v a r i o u s
c o n c e n t r a t io n s were p la c e d on g l a s s s l i d e s and t h e g e r m in a tio n o f th e
c o n i d i a o b se rv e d a f t e r 6 and 2U hours o f i n c u b a t io n a t 26- 28° C.
A s l i g h t i n h i b i t i o n o f th e r a d i a l growth o f th e mycelium o f
Helm inthosporium sativum was n o te d when i t came i n c o n ta c t w ith th e
mycelium o f G i b b e r e l l a z e a e .

T his was e v id e n t by th e f l a t t e n i n g o f th e

s id e o f th e c o lo n y w hich was n e a r e s t t o th e G. zeae m ycelium .
away from the G. z ea e c o lo n y c o n tin u e d t o grow.

The s id e

G. zeae so on overgrew

th e H. sativum c o lo n y so t h a t t h e o r i g i n a l c o lo n y was v i s i b l e o n l y from
th e bottom o f th e p l a t e .

-

29

_

Two ty p e s o f r e a c tio n , were ob serv ed when s e v e r a l m y c e lia l
p l a n t i n g s o f each n a th og en were made i n se p a r a te P e t r i o l a t e s .

Hel­

mintho s-porium sativum c o l o n i e s showed d e f i n i t e a v e r s io n w ith a d i s t i n c t
l i n e o f dem arcation between each c o lo n y .
hand, showed no a v e r s i o n .

G ib b e r e lla z e a e , on the o th er

The r e a c t i o n s o f both pathogens were r e f l e c t ­

ed i n th e ty p e of m y c e l i a l growth and i n th e degree o f s p o r u la t io n when
c o n id i a o f each p athogen were mixed in s u sp e n sio n and seeded i n agar
p l a t e s and s l a n t s .

When p l a t e d s e p a r a t e l y both organism s produced a

sm all amount o f a e r i a l mycelium and s n o r u la te d h e a v i l y .

When mixed, no

a e r i a l mycelium was produced and G ib b e r e lla zeae s p o r u la te d h e a v i l y
o ver th e e n t i r e s u r fa c e o f th e medium w it h in

hours; whereas Hel­

mintho s-porium sativum s n o r u le te d s p a r s e l y , the c o n id ia b e in g formed
a e r i a l l y over the l a y e r o f G. zeae c o n i d i a .

Snore counts i n d i c a t e d

tliat th er e were t w ic e as many G. zeae c o n id ia produced i n th o se t e s t
tu b es seeded w it h G. zeae alon e a s th e r e were i n th o se seed ed w ith a
m ixture o f the two p a th o g e n s .
The r e s u l t s from th e l a s t o f a s e r i e s of g e rm in a tio n t e s t s on
combined spore s u s p e n s io n s should s u f f i c e to o o i n t out the g e n e r a l o b ser­
v a t io n s f o r th e th r e e t e s t s v’h ic h were condu cted .

In t h i s exp erim en t,

c o n i d i a l su s p e n s io n s c o n t a in in g 0 . 1 , 0 . 5 , end 1 . 0 m i l l i o n c o n id i a per
ml. were prepared f o r each organism .

The p e r c e n ta g e g e r m in a tio n o f

the sp o r es in each s u s p e n s io n and i n m ix tu r es o f the p o s s i b l e combin­
a t i o n s o f the above su s p e n s io n s was determ ined a f t e r 6 and 2*4 hours
on g l a s s m icroscope s l i d e s .

Two drops o f an in d iv id u a l su sp e n sio n

o f a s i n g l e fungus or a m ixture of 1 drop each o f th e two organism s
were u se d per s l i d e .

From 90 to 97 per c en t o f the G ib b e r e lla zeae

c o n id ia germ inated i n 6 hours whether th ey were in mixed s u sp e n sio n or

- 30 not.

The G. zeae c o n i d i a i n hea vy c o n c e n t r a t i o n s (2 drops o f th e 1 . 0

c o n c e n t r a t io n ) g e r m in a te d 9 6 .0 Per c e n t hut th e germ tu b e s were sh o rt
and unbranched i n d i c a t i n g th a t v e r y h ig h c o n c e n t r a t io n o f G. z ea e a lo n e
would p r e v en t normal grow th o f th e germ t u b e s .

A ll c o n c en tr a tio n s o f

s u s p e n s io n s o f th e Helminthosporiuru sativum s e r i e s showed normal germin­
a t i o n ( 9 6 p er c e n t ) and growth o f th e germ t u b e s .

The germ t u b e s p ro­

duced by H. sativu m were v e r y s h o r t and knobby i f th e c o n i d i a were mixed
w ith c o n c e n t r a t io n s o f 0 . 9 and 1 . 0 m i l l i o n / m l . G. zeae c o n i d i a .

The

p e r c e n t a g e g e r m in a tio n o f H. sa tiv u m was red u ced s i g n i f i c a n t l y i n th a t
s e r i e s mixed w ith th e 1 . 0 m i l l i o n c o n c e n t r a t i o n o f G. z e a e ; but mixed
w ith lo w er c o n c e n t r a t i o n s o f G. z ea e c o n i d i a , no r e d u c t io n i n p e r c e n t a g e
g e r m in a tio n o c c u r r e d .

Kormal germ tu b e s o f H. sa tiv u m were produced in

th a t s e r i e s mixed w it h G. zeae a t 0 . 1 m i l l i o n / m l .
The p r e s e n c e o f h ig h c o n c e n t r a t i o n s o f G i b b e r e lla z ea e c o n i d i a
or low c o n c e n t r a t i o n s o f G. zeae mixed w it h Helm inthosporium sa tivu m con­
i d i a , appeared t o s t i m u l a t e t h e p r o d u c t io n o f c o n i d i a on th e p a r t o f G.
zeae.

I t was o b se r v e d t h a t a l l th e s l i d e s c o n t a in in g mixed s u s p e n s io n s

o f G. z ea e and H. sativum and t h o s e w ith th e 0 .5 and 1 . 0 c o n c e n t r a t io n s
o f G. zeae a lo n e , p rodu ced, w i t h i n 2^ h ou rs, an abnorm ally l a r g e q u a n tit y
o f secondary G. z ea e c o n i d i a .

Low c o n c e n t r a t i o n s o f G. zeae ( 0 . 1 m i l l i o n /

m l.) on the o th e r hand, produced no seco n d a ry c o n i d i a .
i d i a germ in a ted and d e v e lo p e d v e g e t a t i v e l y .

I n s t e a d , th e conr-

I t was c o n c lu d e d from t h e s e

s t u d i e s th a t (1 ) G. z e a e was not i n h i b i t e d i n development by th e p r e se n c e
o f H. sativu m , e i t h e r i n th e m y c e l i a l or c o n i d i a l form, (2 ) t h a t the
p r e s e n c e o f abn orm ally l a r g e numbers o f G. zeae c o n i d i a te n d s to r e t a r d
v e g e t a t i v e growth but not th e p r o d u c t io n o f o o n id ia by G. z e a e . (3 ) t h a t
th e p r e s e n c e o f mycelium o r f a i r l y heavy c o n i d i a l c o n c e n t r a t i o n s o f G.
zeae r e t a r d e d the growth o f th e mycelium o f H. sativu m and th e g e r m in a tio n
o f th e c o n i d i a o f th e organ ism .

- 31 PATH0GMSSI3
E f f e c t o f Inoculum Dosage on D is e a s e S e v e r it y
G ib b e r e lla zeae
The s t u d i e s on the e f f e c t o f th e amount o f inoculum on d is e a s e
s e v e r i t y were made to determ ine th e approxim ate c o n c e n t r a t io n s o f inocu­
lum to he u se d in the remainder o f the e x p e rim en ts on d i s e a s e developm ent.
I n i t i a l experim ents i n d i c a t e d t h e o ccu rr e n c e o f c o n s id e r a b le v a r i a t i o n
i n the amount o f i n f e c t i o n e s t a b l i s h e d and i n the number o f heads and
s p i k e l e t s k i l l e d when v a r io u s q u a n t i t i e s o f G ib b e r e lla zeae c o n id i a were
a p p lie d to the p l a n t s .

In order t o sta n d a r d iz e th e p r o c e d u r e s , s e v e r a l

experim en ts were co n d u cted on t h e e f f e c t b o f a p p l i c a t i o n o f v a r io u s quan­
t i t i e s of c o n id ia .
in Table 6 .

The r e s u l t s of two o f th e s e experim en ts are p r e se n te d

The amount o f d i s e a s e development from a g iv e n q u a n t it y o f

c o n id i a was not th e same i n the two e x p erim en ts e x c e p t a t the h ig h er con­
c e n tr a tio n s.

This was pro b a b ly becau se th e p l a n t s t r e a t e d i n th e f i r s t

experim ent were exp osed f o r ^8 hours a t 25° C. i n the hu m idity t e n t ,
whereas th e o th e r s e r i e s r e c e iv e d 60 hours exposure at the same temper­
atu re.

With an a p p l i c a t i o n o f 2 m i l l i o n c o n id i a p er p o t o f p l a n t s and

a h8-h o u r exposure p e r io d , 90 per cen t o f th e s p i k e l e t s became i n f e c t e d
and 82 per cen t were k i l l e d a s a r e s u l t o f i n f e c t i o n .

There was o n ly a

s l i g h t in c r e a s e i n d is e a s e s e v e r i t y when the q u a n t it y o f c o n id i a was in­
c r e a s e d to 5 m i l l i o n p e r p o t .

Comparable r e s u l t s were o b t a in e d w ith 0 . 5

m i l l i o n sp ores when the p l a n t s were ex p o sed f o r bO h o u rs.

S in ce the ap­

p l i c a t i o n o f 2 m i l l i o n c o n id ia p e r p o t r e s u l t e d in a h ig h er p e r ce n ta g e
o f i n f e c t i o n in Us hours a t 25° C. and i n 100 p er c en t o f th e heads and
s p i k e l e t s becoming i n f e c t e d and k i l l e d w ith bO hours exposure, t h i s
q u a n t it y of c o n id ia was s e l e c t e d a s the standard amount f o r u s e i n the
rem aining e x p erim en ts w ith G. z e a e .

Table 6
G ib b e re lla h e a d b lig h t r e s u l t in g from th e a p p lic a t io n o f d if f e r e n t amounts o f
c o n id ia l inoculum to p la n ts in th e flo w e r in g s ta g e o f developm ent.

T r ia l

Aa

B^

C on id ia l
C oncentration
per
1 g a llo n pot

Heads

S p ik e le t s

T otal

In f e c te d

K ille d

T ota l

I n fe c te d

K ille d

M illio n s

Number

Per cen t

Per cent

Number

Per cent

Per cent

0 .1
0.5
1.0
2.0
5 -0

22
21
2o
23
20

8 1 .S
9 0 .5
9 2 .U
100 .0
10C.0

9-5
23.1
52.2
5 0 .0

220
200
258
216
197

0.1
0 .5
1.0
2.0
5 -0

24
22
IS
2U

S7 .o
10 0.0
10 0.0
10 0.0
100.0

s.7

5 S .2
S 2.0
100.0

90.0

a Exposed to co n tin u e d w etness f o r M-S hours a t 25° C.
^ Exposed to c o n tin u ed w etn ess f o r 60 hours a t 25° C.

236
273
297
220
293

Uo.U
U6.5
o5-5
92.6
9 2 .u

20.k
1+2.0
5 2 .7
8 2 .4
87-3

b l .9
88 .3
9 3 .6
1 0 0 .0
9 8 .3

1+7.0
S1 .0
9 1 .2
100.0
9 7-0

Helminthosporlum sativum

F ive s t r a i n s o f Helminthosporium sativum were used i n the
f i r s t experiment on th e e f f e c t o f the amount o f inoculum on d is e a s e
se v e r ity .

The p l a n t s were in o c u la t e d in the e f t e r - f l o w e r i n g s ta g e

w ith c o n c e n tr a tio n s o f 0 . 1 , 0 . 2 5 , G.5 , PJa“-

m i l l i o n c o n id ia per

p o t o f p la n t s and exposed to c o n tin u ed w e tn e ss i n the hum idity t e n t s
f o r J>6 hours a t 25° C.

Sin ce th e s t r a i n s r e a c te d s i m i l a r l y , o n ly th e

r e s u l t s from the s t r a i n o f H. sa tivum used in th e s e experim en ts are
p r e s e n te d (Table 7)*

The a p p l i c a t i o n o f 0 .5 and 1 .0 m i l l i o n c o n id ia

per p o t r e s u l t e d in the i n f e c t i o n of a l l th e s p i k e l e t s w ith th e l a t t e r
c o n c e n tr a tio n r e s u l t i n g i n the k i l l i n g o f 75 per cent o f th e s p i k e l e t s .
The amount o f i n f e c t i o n and the s e v e r i t y o f the d i s e a s e was
app roxim ately the same i n another experim ent in which c o n c e n tr a tio n s
o f c o n id ia up t o 5 . 0 m i l l i o n were a p p lie d to p l a n t s in the f lo w e r in g
sta g e and s u b jec te d to contin ued w e tn e ss f o r hg hours a t 30° C.

D is­

e a se s e v e r i t y in c r e a s e d approxim ately 25 Per cen t w ith an a p p l i c a t i o n
o f 2 .0 m i l l i o n c o n id ia per p o t .

On the b a s i s o f the r e s u l t s p r e se n ted

in Table 7* i t seemed d e s ir a b le to u s e approxim ately 2 .0 m i l l i o n con­
i d i a per pot o f wheat which would be the same amount as used w ith Gibb e r e lla zeae.

However, from v i s u a l o’: s e r r a t io n s i t anpeared th at an

a p p l i c a t i o n o f 1 .0 m i l l i o n co n id ia per pot should s u f f i c e t o g iv e
heavy i n f e c t i o n and cause s e v e r e h e a d b lig h t .

For t h i s res.son and

because i t was d i f f i c u l t to produce la r g e q u a n t i t i e s of Helm inthosporlum sativum c o n id ia on agar media, an a p p l i c a t i o n o f 1 . 0 m i l l i o n
c o n id ia per pot was s e l e c t e d as the standard amount- f o r u se in the
r e s t o f the Helminthosporium h e a d b lig h t s t u d i e s .

Table 7 - —Helm inthosporium h ea d b lig h t r e s u lt in g from th e a p p lic a tio n o f d if f e r e n t amounts
o f c o n id ia l inoculum to p la n ts in th e a f t e r - f lo w e r in g and flo w e r in g s ta g e s o f developm ent.

Stage cf
Development
at inoculation

a
After
flowering

Conidial
Concen.
per 1
gal. pot

Total

Infected

Killed

Millions

Number

Per cent

Per cent

0.00
0.10

0.25
0 .5 0
1.00

Flowering13

0.00

0.50
1.00
2.00
5.00

Heads

Spikelets

0.0
21.S
30.4
29 •c
62 .S

0.0

45
46
46
27
35

5^-3
100.0
100.0
100.0

27
27
2o
2o
27

0.0
100.0
100.0
100.0
100.0

0.0
40.8
57-s

a Exposed to continued wetness for 3c hours at ?5° C.
v

,
o
Exposed to continued wetness for 48 hours at 30

C.

Total

Infected

Killed

Number

Per cent

Per cent

273

0.0
25-7
58.2

300
340
21b
264

317
357

92.4

296
300

100.0

342

8 9.8

0.0
21.0
33.5
43.9

53.8

73-9

0.0
So.S
100.0
100.0
100.0

5 9.1
71.3
96.0

0.0

100.0

- 35 R e la t io n o f Head. M aturity to D is e a s e Development
G ib b e r e lla zeae

The s t u d i e s on the r e l a t i o n

of

q u a n t it y o f c o n i d i a l inoculum

to d i s e a s e development in d ic a te d th a t th er e was a d i f f e r e n c e i n suscep­
t i b i l i t y o f wheat heads to G ib b erella . zeae i n f e c t i o n during th e v a r io u s
s t a g e s o f head m a t u r ity .

S e v e r a l experim en ts were oonducted to d e te r ­

mine th e r e l a t i v e s u s c e p t i b i l i t y o f th e heads and s p i k e l e t s to i n f e c t i o n
from th e boot to th e p a s t - f l o w e r i n g s ta g e o f developm ent.
In order t o determ ine th e s u s c e p t i b i l i t y i n th e v a r io u s s t a g e s
o f developm ent, s e v e r a l wheat heads were ta gg ed and a r ec o r d o b ta in e d o f
each o f the s p i k e l e t s on each nead p r io r to i n o c u l a t i o n w ith G ib b e r e lla
zeae.

A fte r i n o c u l a t i o n the p l a n t s were s u b j e c te d to co n tin u e d w etness

for

hours a t 25° C.

Records on i n f e c t i o n were taken 3 days a f t e r in­

o c u l a t i o n and on k i l l e d s p i k e l e t s 5 days l a t e r .
experim ent are summarized in Table 8 .

The r e s u l t s from t h i s

In a nother experim ent heads in

th e b e f o r e - f lo w e r in g s t a g e of development were ta gg ed and observed be­
f o r e and a f t e r i n o c u l a t i o n .

The r e s u l t s were th e same a s t h o s e o b ta in e d

i n th e p r e v io u s ex p erim en t.

Ho i n f e c t i o n was ob serv ed on s p i k e l e t s

which had not blossom ed p r io r to th e tim e when th e p l a n t s were removed
from th e hum idity t e n t , e xcen t i n th e c a se o f two s p i k e l e t s which were
i n f e c t e d a t the b a s e .

The i n f e c t i o n o f one o f t h e s e appeared to have

r e s u l t e d from c o n t a c t w ith an i n f e c t e d extruded anther from th e s p i k e l e t
j u s t below i t .
and th e r a c h i s .

The an th er i n t h i s c a s e , was lo d g e d betw een th e s p i k e l e t
On th e heads showing p a r t i a l a n t h e s i s , o n ly th o s e spike­

l e t s which had blossom ed were i n f e c t e d .

In t h i s r e s p e c t the r e s u l t s ap­

pear to support th e t h e o r ie s o f Pugh, Johann and Dickson (58) who con­
clu d ed t h a t the p r o g r e s s o f i n f e c t i o n o f the s p i k e l e t s was dependent upon
a n th e sis.

A pparently wheat heads are v e r y r e s i s t a n t to i n f e c t i o n u r io r

to f lo w e r in g .

Table 8
ella headblight.a

Comparative susceptibility of plants in different stages of heading to Gibber­

Stage of Development
at inoculation

Heads

Snikelets

Inoculated

Infected

Inoculated

Infected

Killed

Humber

Per cent

Humber

Per cent

Per cent

131 *

0

53

37S

6

20

100

188

19

zb

6

100

U6

98

87

60

100

5 U9

ICO

100

Boot

23

0

Before flovirering

36

Flowering
After flowering
Past flowering

0

£
Records on infection made 3 days efter inoculation, and on spikelets killed 5 days later.
were exposed U 8 hours to continued wetness at 25° C. after inoculation.
"k Does not include those spikelets on 8 heads which were still in the boot stages.

Plants

-

- 37 -

A ta n a s o ff (5 ) and Pugh, Johann and D ic k so n (5 8 ) found t h a t
p l a n t s in o c u l a t e d i n th e f lo w e r in g s t a g e were more s u s c e p t i b l e to i n ­
f e c t i o n than th o s e t r e a t e d s i m i l a r l y in the l a t e r s t a g e s o f d e v e lo p ­
ment.

The s t u d i e s m entioned in th e p r e v io u s paragraph d id not appear

to support t h e i r c o n c l u s i o n s .

In o r d e r to o b t a in f u r t h e r in fo r m a tio n

r e g a r d in g the com parative s u s c e p t i b i l i t y o f p l a n t s i n the f l o w e r i n g ,
a f t e r - f l o w e r i n g , and p a s t - f l o w e r i n g s t a g e s o f developm ent, 18 p o t s o f
wheat were in o c u l a t e d in

each o f th e above s t a g e s .

S ix p o t s from each

s e t o f 18 were p la c e d in each o f th e 20° , 25° 0-n.d 30° C* h u m id ity t e n t s .
Two p o t s were removed from each t e n t a f t e r 3&, ^8 , and 60 h o u r s .
r e s u l t s are p r e s e n t e d in

Table 9 and i l l u s t r a t e d i n F ig u r e U.

The

The

p l a n t s in o c u l a t e d in th e p a s t - f l o w e r i n g s t a g e were more s u s c e p t i b l e
to i n f e c t i o n and h e a d b lig h t developm ent than t h o s e g iv e n a s i m i l a r
tr e a tm e n t in th e f l o w e r i n g s t a g e .
3b hou rs o f c o n tin u e d w etn ess a t 25

For exam ple, th e s e r i e s ex p osed to
°

\
/C. had 5^. oS, and 98 p e r c en t o f

th e s p i k e l e t s i n f e c t e d and lH, 7^i aad 9U p e r c e n t o f th e s p i k e l e t s
k i l l e d in the f l o w e r i n g , a f t e r - f l o w e r i n g and p a s t - f l o w e r i n g s t a g e s re­
s p e c tiv e ly (P la te I I ) .
T his d is c r e p a n c y w ith p r e v io u s work may have r e s u l t e d from
d i f f e r e n c e s in the method o f e v a l u a t i n g i n f e c t i o n .

Pugh, Johann and

D ick son (58) b ased t h e i r c o n c lu s io n on the g r e a t e r r e d u c t io n i n k e r n e l
w eig h t and on th e l a r g e r number o f i n f e c t e d s e e d s which th e y o b ta in e d
from p l a n t s i n o c u l a t e d in the f l o w e r i n g s t a g e , w hereas th e r e s u l t s p re­
s e n te d i n t h i s paper were b a se d on th e number o f i n f e c t e d and k i l l e d
sp ik e le ts.

I f th e s e e d s from th e 3o-k our s e r i e s a t 25° C. had been

w eigh ed , no doubt t h o s e from th e f l o w e r i n g s t a g e would have w eighed
m ost.

However, had th e 60-hour s e r i e s a t 25° C. been u s e d a s a b a s i s

Table 9 - — G-ibberella h ea d b lig h t r e s u l t i n g from th e exposure o f p l a n t s , in o c u la t e d
in th r e e d i f f e r e n t s ta g e s o f development, to 3 6 , 1+8 and 60 hours o f c o n tin u ed w etness a t 20°,
25w, and 30°

Stage at
in o c u l a t io n

Flowering

Temp
0 C.

Hours
exposure

20

25

48
6o
36
1+8
cO

A fte r
Flowering

Infected

K ille d

Humber

Humber

Per cent

Per cen t

13
1*+
13
17
IS
13

1U0
15l+
157
189
1SS
l l +6
201+
138
15 c
181
199
2ll+
172
181
23?
198
21C
2l+2
185
208
230
158
215
21U
I 89
205
239

0 .7
2 2 .1
6 0 .5
5U.0
9 7 -0
97-9
3 9 -7
8 2. b
9S-7
2.8
3^-7
3 5 .0
68 .0
1 0 0 .0
1 0 0 .0
70.2
1 00 .0
1 0 0 .0
10.8
1+2.3
8 0 .U
98.0
1 0 0 .0
1 0 0 .0
95.g
1 0 0 .0
1 0 0 .0

0
1+.6
8 .9
1U.3
87-8
8 8 .3
« *J7
w

12
13
17

1+8

IS

oO

19
lc
16
19
16
18
20
15
17
18
17
19
18
15
16
20

20

25

36
1+8

30

36
Us
cC

20

36
48

25

3o
1+8

bO

oO

30

In o c u la t ed

43
60

oO

Fast
Flowering

I n o c u la te d

lc

30

36
1+8
60

£ Recorded J days a f t e r i n o c u l s t i o n .

S p ik e le ts

Heads

Experiment conducted in d u p l i c a t e .

cS. 0

0
IS .0

76. c
7U.3
10 0.0
1 0 0 .0
27-3
1 00 .0
1 0 0 .0
11.9
27.U
57.u
93-9
100.0
100.0
93.6
1 0 0 .0
100.0

100

Key
F - F lo w e rin g s ta g e
AF - A f t e r - f l o w e r i n g s t a g s
FF - F a s t - f l o w e r i n g s ta g e

APT

60

s p ik e le ts

killed

- per

cent

80

40

AF

20

0
20
T em perature - d e g r e e s C e n tig ra d e
F l a i r s 4*

c o m p a ra tiv e s u s o s p t l b d l l t y o f N ew thatch w heat i n

d i f f e r e n t s t a g e s o f developm ent t o i n f e o t l o n b y O lb b e r e lla s e a s .
P l a n t s w ere exposed 36 h o u rs t o c o n tin u e d w e tn e ss a f t e r in o c u la tio n *
( D a ta In T hbla 9 )•

-

Uo

-

f o r com parison, th en h ig h e r y i e l d s would d o u b t l e s s have been o b t a in e d
from t h o s e p l a n t s in o c u l a t e d in th e p a s t - f l o w e r i n g s ta g e s i n c e th e r e
were few or no k e r n e l s produced on t h o s e p l a n t s i n o c u l a t e d in the flo w ­
e r in g s t a g e .

T his would i n d i c a t e th a t the r e l a t i v e s u s c e p t i b i l i t y o f

th e p l a n t s in the d i f f e r e n t s t a g e s o f development was dependent upon
th e l e n g t h o f ex p osu re to c o n tin u e d w e tn e s s , a f a c t o r t o be c o n sid e re d
la te r .

However, in a l l t h e ex p erim en ts on G ib b e r e lla h e a d b lig h t r e ­

p o r te d upon in t h i s p ap er, i t was c o n s i s t e n t l y n o ted t h a t the p l a n t s
in o c u l a t e d in the v a s t - f l o w e r i n g s t a g e were more s u s c e p t i b l e than th o se
g iv e n a s i m i l a r tr e a tm e n t in the f lo w e r in g s t a g e .
A d i f f e r e n c e was n o ted in th e s i z e o f the k e r n e ls produced
on p l a n t s in o c u la t e d in the v a r io u s s t a g e s and s u b j e c te d to optimum
c o n d it io n s f o r i n f e c t i o n and b l i g h t d evelopm ent.

Few or no k e r n e ls

were produced on t h o s e p l a n t s i n o c u l a t e d in the f lo w e r in g s t a g e .

The

k e r n e l s from p l a n t s in o c u l a t e d in the a f t e r - f l o w e r i n g and p a s t - f l o w e r ­
in g s t a g e s became p r o g r e s s i v e l y l a r g e r .

The k e r n e l s from p l a n t s inocu­

l a t e d du rin g or a f t e r th e f lo w e r in g s t a g e and up to th e dough s ta g e
were alw ays sm all and s h r i v e l l e d .
The d eg ree o f symptom e x p r e s s io n a l s o v a r ie d w ith th e s ta g e
o f development a t th e time i n f e c t i o n o c cu rr e d .

Heads o f wheat i n f e c t e d

in the f lo w e r in g or a f t e r - f l o w e r i n g s t a g e s were marked by deep brown to
s l i g h t l y r e d d is h or c r e o s o t e - c o l o r e d l e s i o n s .

These symptoms f i r s t ap­

p eared on the lemma, then on th e b a se o f th e s p i k e l e t , th e r a c h is and
the culm.

H e a v ily i n f e c t e d s p i k e l e t s , k i l l e d as a r e s u l t o f i n f e c t i o n ,

g r a d u a lly l o s t t h e i r deep brown d i s c o l o r a t i o n and became s t r a w - c o lo r e d .
G e n e r a lly , th e dark brown d i s c o l o r a t i o n was r e t a i n e d on the culm and

-

r a ch is.

Ul

-

Those p l a n t s in o c u l a t e d i n th e -p a s t - f lo w e r in g s t a g e o f d e v e l­

opment showed no d i s t i n c t c o l o r a t i o n .

In stead ,

th e i n f e c t e d heads and

s p i k e l e t s became b le a c h e d and s t r a w - c o lo r e d .
Helmintho s-porium sativum

The s u s c e p t i b i l i t y o f N evtnatch wheat to i n f e c t i o n by Helmin­
tho sooriam sativum v a r i e d a c c o r d in g to the s t a g e o f head m a t u r ity at
th e tim e o f i n o c u l a t i o n .

The h ig h d egree o f r e s i s t a n c e in the bo ot and

the b e f o r e - f l o w e r i n g s t a g e s o f developm ent were e s p e c i a l l y n o t i c e a b l e
in an experim ent i n which S3 ta g g e d heads o f wheat i n th e v a r i o u s s t a g e s
o f developm ent were s t u d ie d i n t e n s e l y b e f o r e i n o c u l a t i o n and s h o r t l y
a f t e r th e y were removed from th e h u m id ity t e n t .
experim ent are b r i e f l y summarized i n Table 1 0 .

The r e s u l t s from t h i s
In t h i s e x p e rim en t,

o n ly two s p i k e l e t s on one head became i n f e c t e d b e f o r e the f l o w e r s had
b lo sso m e d .

The f a c t th a t l 6 p e r c e n t o f the s p i k e l e t s became i n f e c t e d

when i n the b e f o r e - f l o w e r i n g s t a g e does not i n d i c a t e t h a t i n f e c t i o n
took p l a c e b e fo r e th e f lo w e r s had b lo ssom ed .

On the c o n tr a r y ,

some o f

t h e s p i k e l e t s blossom ed w h ile t h e p l a n t s were i n th e t e n t s , but i t was
e a sy t o d i s t i n g u i s h t h o s e s p i k e l e t s which had blossom ed b e f o r e and
th o s e which b lo sso m ed a f t e r th e p l a n t s were removed from th e hu m id ity
ten ts.

U n f o r t u n a t e ly ,

th er e were no p l a n t s a v a i l a b l e i n the a f t e r -

f lo w e r in g s t a g e o f development a t the time t h i s experim ent was c a r r ie d
ou t.
There was an i n c r e a s e in s u s c e p t i b i l i t y t o i n f e c t i o n as the
p l a n t s p a s s e d from th e f lo w e r in g t o th e p a s t - f l o w e r i n g s t a g e o f d e v e l­
opment.

(T able 1 0 ) .

T h is was dem on strated i n a n o th e r experim en t i n

Table 1 0 — Comparative s u s c e p t i b i l i t y o f p la n t s in d i f f e r e n t s t a g e s o f heading to
Helininthosporium h e a d b lig h t , a

Stage o f
development
at in o c u l a t io n

Heads

S p ik e le t s

I n o c u la te d

In fected

I n o c u la te d

In fected

K ille d

Humber

Per cen t

Humber

Per cen t

Per cen t

Boot

21

0

1 S1

0

B efo re Flow ering

29

1+5

30 ?

15

r\
W

U

100

50

_lO*
cy

0

23

100

27 1

Flow ering
P a s t Flowering

100

0

72

a Records on i n f e c t i o n made 3 days a f t e r i n o c u l a t io n , and on k i l l e d s p i k e l e t s 5 days l a t e r .
P l a n t s were exposed Ug hours to continued w etn ess at 30° G- a f t e r i n o c u l a t i o n .

- ^3 which wheat wap in o c u la t e d and exposed for d i f f e r e n t p e r io d s to con­
tin u e d w etness a t 20°, 25°. and 30° C. in the hum idity t e n t s .

The re­

s u l t s from t h i s experiment are p r e se n ted i n Table 11 and i l l u s t r a t e d in
F igure 5-

^k® o e r c e n ta g e of k i l l e d s p i k e l e t s gave th e b e s t in d ic a t io n

as to the r e l a t i v e r e s i s t a n c e o f th e heads to i n f e c t i o n at v a r io u s
s t a g e s o f development.

In most in s t a n c e s , the order of in c r e a s in g sus­

c e p t i b i l i t y was from th e flo w e r in g to the p a s t - f l o w e r i n g s ta g e o f de­
velopment (P la t e I I I ) .

This was fu r t h e r demonstrated i n o th e r e x p e r i­

ments which w i l l be d is c u s s e d in a l a t e r s e c t i o n .
I t was c o n s i s t e n t l y observed throughout th e s e and o th er ex­
perim en ts on Helminthosoorium h e a d b lig h t th at d i f f e r e n c e s r e s u l t e d in
the degree of symptom e x p r e s s io n when the p l a n t s were in o c u la te d in
the v a r io u s stageB o f development.

The p l a n t s in o c u la te d during the

flo w e r in g s ta g e produced v ery dark brown to c r e o s o t e - c o lo r e d l e s i o n s
on th e glumes, lemma, p a le a , and r a c h i s .

The symptoms on th o se heads

in o c u la te d in the a f t e r - f l o w e r i n g s ta g e were ve ry s im ila r to th o se o f
th e flo w e r in g s t a g e .

The s p i k e l e t s on heads which were in o c u la te d

•while the p l a n t s were i n th ese s t a g e s anc which were su b seq u en tly
k i l l e d by the fungus, always had a tendency to r e t a i n the dark c o lo r
r e s u l t i n g from i n f e c t i o n and, as a r e s u l t ,
brown to str a w -c o lo r e d appearance.

they a t t a in e d a m o ttle d

On the o th er hand, the heads in o c­

u la t e d i n th e p a s t-flo v r e r in g s ta g e of development v e r y r a r e l y showed
any dark c o l o r a t i o n .

In t h i s c o se th e s p i k e l e t s r a p id ly l o s t th e ir

green c o lo r , becoming bleached and s tr a w -c o lo r e d a s soon as th ey were
k ille d .
The k e r n e ls produced on the p l a n t s in o c u l a t e d i n the v a r io u s
s t a g e s o f development d i f f e r e d i n s i z e .

They were shrunken and dark in

f a b l e 1 1 .— H e lB in th o e p o riu a h e a d b lig h t r e s u l t i n g fro m t h e e x p o su re o f p l a n t s , in o c u la te d
i n th ree d i f f e r e n t s ta g e s o f development, to 3 6 , Ug, and oO hours of contin ued w etness at 20°, 25° ,
and 3^° C.a
Stage o f
development
a t in o c u l a t io n

Flowering

Temu.
0 C.

Hours;
exposure

20

25

30
A fter
Flow ering

20

25
30

P ast
Flowering

20

25
30

Recorded 7 days a f t e r i n o c u l a t i o n .

36
Ug
6o
36
Ug
So
36
Hg
So
36
4g
60
36
48
SO
36
Ug
So
36
Ug
So
36

Us
60
36
Us
So

Reads
I n o c u la te d

I n o c u la te d

Number

Humber

Per cen t

Per cent

lo

159

89-3
78.8
96. 0
9 S.U
100.0
100.0
70.2
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
98.8
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0

0.0
0.0
0.0
0.0
33.7
82.3
0.0
3 .U
3 0 .8
0 .0
2.1
33.1
7.7
70.7
100.0

16
IS
15
1b
is
12
18
13
18
19
lS
18
lS
15
13
15
17
lS
lS

15
15
15
19
20
1?
17

isu
169
1 S9
16 S
158
1U1

179
1U3
189
193
160
181
IRQ
iu s

125
lUs
17U
170
176
177
152
171
212
198

172
185

Experiment conducted i n d u p l i c a t e .

S p ik e le t s
In fected

K illed

2U.S
75-0
100.0
0.0
0.0
o.S
21.7
100.0
100.0
90.9
100.0
100.0

100

Key
7 — flo w e rin g s ta g e
A7 — A f t e r - f l o w e r i n g s t a g e
F ? — F a s t-flo w e rin g s ta g e

iFF

Spikeleta killed - per cent

80

6o

20

0
20
T e m p e ra tu re - d e g r e e s C e n tig r a d e

? l 0 i r e 5*

c c m p a r a t l r e s u s o e p t l b l l l t y o f N ew thatoh w h e at i n

d i f f e r e n t s t a g e s o f d e v e lo p m e n t t o l n f e o t l o n b y H e lm ln th o sp o rlu m
sativ u m *

F l a n t s w ere e x p o se d t o c o n tin u e d w e tn e s s f o r 3 6 h o u rs a f t e r

I n o c u l a t i o n . (D a ta i n T a b le 11 )•

- U6 c o lo r.

There was a p r o g r e s s iv e in c r e a s e i n th e s i z e of the k e r n e ls

produced on p la n t s i n o c u l a t e d i n th e flo w e r in g t o the p a s t - f lo w e r in g
stages.

Many p o s s e s s e d small b la ck or brown l e s i o n s .

There i s no

doubt th a t a heavy i n f e c t i o n o f H. sat ivum during any of th e s e s ta g e s
would r e s u l t i n lo w e r in g th e q u a l i t y and y i e l d o f the g r a in c o n s id e r ­
a b ly .

I n flu e n c e o f A ir Temperature and Moisture on D isea se Development
G fb b e r e lla zeae

Several i n v e s t i g a t o r s , in c lu d in g Schmitz ( 5 9 ) . Mortensen
(U 7), Johnson, Dickson and Johann ( 3 2 ) , A ta n a s o ff ( 5 ) . Maclnnes and
Fogelman (Uh), S c o tt (uO), C h r is te n se n , Stakman and Immer ( 1 o ) , Pugh,
Johann and Dickson (58 ) and o t h e r s , have p o in te d out th a t h ig h temper­
a tu r e s to g e th e r w ith abundant m o istu re were major f a c t o r s in the i n i t i ­
a t i o n and development o f G-ibberella h e a d b lig h t .

L i t t l e i s known, how­

e v e r , about th e i n t e r r e l a t i o n s h i p o f tem perature, m o istu re , and s ta g e
o f p la n t development w ith r e s p e c t to i n f e c t i o n and h e a d b lig h t develop­
ment .
S evera l experim ents were conducted in which a i r temperature
and m oistu re were stu d ied in r e l a t i o n to i n f e c t i o n of wheat heads in ­
o c u la te d with G ib b e re lla z e a e .

Only th ree o f th e s e w i l l be mentioned

s p e c i f i c a l l y s in c e the r e s u l t s o b ta in e d c o in c id e ve ry c l o s e l y to those
in the o th er e x p e rim en ts.

The experiment on the e f f e c t of th e s e f a c ­

t o r s on the development o f h e a d b lig h t of wheat in the flo w e r in g , a f t e r flo w e r in g , and p a s t - f l o w e r i n g s t a g e s o f development was mentioned in
the p reced in g s e c t i o n (Table 9. F ig u re H ).

In another experim en t, 72

p o t s o f wheat in the p a s t - f l o w e r i n g s ta g e o f development were in o c u la te d

- 47 in l o t s o f S a t r e g u la r i n t e r v a l s over a bO-hour p e r io d .

Two p o t s from

each l o t were im m ediately p la c e d i n each o f the fou r hum idity t e n t s
m aintained at 15°> 2 0 ° , 2 5°, and 30° C. r e s p e c t i v e l y .

A l l th e p o ts

were removed to th e greenhouse bench a t the end o f the bO-hour p e r io d .
Thus i t was p o s s i b l e to make comparisons o f in o c u la t e d p la n t s exposed
fo r b, 12, 18, pH, Ji O, y b , U2, h g f pud bO hours to continued w etness
a t the U tem p eratures.

The r e s u l t s are summarized in Table IP and i l ­

l u s t r a t e d in F igure b and P l a t e IV.

A s im ila r experim ent was conducted

u s in g 9 ° p o ts o f wewthatch wheat in the flo w e r in g s t a g e .

In t h i s ex­

perim ent the p l a n t s were a l l in o c u l a t e d a t one time and. d i s t r i b u t e d
e q u a lly among the b hum idity t e n t s m aintained a t the same tem peratures
as in the experiment Just mentioned.

Three p o t s were removed from each

te n t a f t e r 6, 12, IS , ?H, 3^» ^S, oO and 72 h o u rs.

The r e s u l t s o f t h i s

experiment e re p r e se n te d i n Table 13 and i l l u s t r a t e d in F igure 7The p e r io d o f c o n tin u ed w etn ess appeared to be an important
fa c t o r in the d e te r m in a tio n o f the b e s t tem perature f o r i n f e c t i o n and
h e a d b lig h t development.

Long p e r io d s o f exposure at 25° ^ d 30° C. r e ­

s u l t e d in complete k i l l i n g o f a l l in o c u la t e d wheat heads.

When the

p e r io d o f exposure was reduced, the p la n t s exposed to c o n tin u e d w etness
at 25° C. always developed the most sev ere h e a d b lig h t ( P l a t e IV ).

The

d i s e a s e was g e n e r a l l y more s e v e r e a t 30° than a t 20° C. and. o n ly a tr a c e
o f i n f e c t i o n o ccu rred a t 15

C.

Pugh, Johann and Dickson (58) concluded

th a t tem peratures from 28-32 ° C. were the most fa v o r a b le f o r i n f e c t i o n o f
wheat h ead s.

T his was above the optimum tem peratures recorded in the

present in v e s tig a tio n s .
There appeared to be a d e f i n i t e p e r io d during the exposure o f
in o c u la t e d p la n t s to contin ued w e tn e ss a t tem peratures from 20° to 30° C.,

fa b le 1 2 .—(H bberella headblight r e e o ltin g fro * exposure o f p le a ts , in ocu lated in th e past->
flow erin g stage, to d iffe r e n t periods of continued w etn ess a t d i f f e r e n t tem p eratures.®

Temo.
o
C.

exposure
p e r io d 0

Heads

S o ik elets
T otal
Humber

r.our s
15

20

25

ig
?U
3o
Us
6o

35
30
2c

2U
3o
Us
6o

30
aS2
*
31
27

IS
pU

2U
33
33

US
IS

21S
283
239

35

20U
290
25c
197
312

2S

211

22

2U
3c
Us
a

32S
250
2oQ
271
2U7
20S

IS

3o

30

Infected

20 c

33
33

305

cent
0.0
0.0
3-5
0 .7
-•5
0.0
0.0
c. 1
2S.3

50.7
0.5
S.o

Per cent
c .o
0. 0
0.0
r> ^
.u
0.0
0.0
0.Q
13.1
7^.9
Om'J
^ r\

75 - U
9 2 .U

ox L
7c. c

2.U
3.6
4 3 .2
7 8 .2
ci U

0 .0

D u p lic a te p o ts were used for each trea tm en t.

c Recorded S days a f t e r in o c u l a t io n .
c Ho i n f e c t i o n a t c and IP hours.

K illed

Data fo r 3^ mil U? hours s e r i e s o m itte d .

r\

/—

kj .<J

3-U
52.7
c l.c

■P"
oa

100

r

60-hour

60

Spikelets

killed

- per cent

80

40

20

0

20

Temperature - degrees Centigrade
Figure 6 .

The r e la tio n of tongerature and period of continued

wetness to G lbbsrella headblight.
flow ering stags*

P lan ts inoculated in the p a st-

( Data in Table 12 )•

Tstble 13*- -G-iVberella h e a d h lig h t r e s u l t i n g from exposure of p l a n t s , in o c u la te d in the flo w e r ­
in g s ta g e , to d i f f e r e n t p e r io d s o f contin ued w etness at d i f f e r e n t te m p e r a tu r e s.3

Teiao.
0 cl

Exposure
p eriod

S p ik e le t s

Heads
T o ta l

I n f e c t e d *3

Sunder

Her cent

K ille d 0

Hours

ihrnber

15

IS
24
30
4s
cO
72

22
29
2c
27
29
2S

253
216
217
24g
2UU
241

0.0
0.0
0.0
1.0
0.0
0.0

»vj
0.0
0.0
2 .0
0.0
1.2

20

IS
24
4g
60
72

29
28
27
27
28
27

P3U
273
239
214
239
253

1.3
2.9
4 .2
5 .2
30.0
80. c

1 -3
5*9
0.3
s .o
1 2 .6
cS.S

IS
24
3o
'48
60
72

29
27
2c
29
27
23

212
237
232
2o7
2^3
223

2 .4
5 .5
I S .5
77-1
8 3 .0
9 5 -0

2.5
19.0
6 4.0
76.2
8 4 .9

IS

2o
28
27
25
23
2d

I 89
232
221
232
196
213

0 .0
0 .0
c .0
2 7.1
61 .2
8 6 .4

0 .0
0 .0
8 .2
2 7.1
2°. 6
___d

}o

LP\
OJ

30

2k
5b

48
60
72
a
0
c
a

There were 3 r e p l i c a t i o n s f o r each treatm ent
Recorded o days a f t e r in o c u l a t i o n .
Recorded 12 days a f t e r in o c u l a t i o n .
Some o f p l a n t s v?ere k i l l e d hy f o o t - r o t .

p er cent

C . 0

.00

Tem perature - d eg rees C entigrade
F igu re 7*

®ie r e la t io n o f tam pereture and p e r io d o f oontlm ied

w etn ess t o G U bberella h ea d b lig h t*
e r in g stag e*

( D ata in Cable 13 )•

P la n ts In o cu la ted In th e flow­

i n w h ic h t h e r e was a c o n s i d e r a b l e
sev erity .

F or exam ple,

and in c u b a te d a t
cent w ith
disease

25

° C.

ho u rs to

30

sev erity

those p la n ts

A t 2 0 ° C.

hours

t o 80 p e r c e n t w i t h

increase

lated

13)-

to

13

stage

as the

13

developm ent

and F ig u re

6U

n e r cent during the

cent to

rer

56

7-

(T able

12).

at

tio n and

23 ° C. t h e
20

"critical
was n o t

exoosure p erio d "
as n o tic e a b le

from t h e s e

At t h e

as g r e a t . This

W i t h 3& h o u r s
wore k i l l e d

flow ering

stag e,

in

is

sp ik elets

27-3

for

o

at

J>0

6

infecC.

w ith those

stages of

further

p e r c e n t m or e i n f e c ­

13

in the n a s t- flo w e r in g than

illu strated

o f e x p o s u r e a t 25° C .,
the f l o w e r i n g s t a g e ,

a n d 9^ P e r c e n t

9^-0 P e r c e n t;

7

in

T a b l e 9 nn<^

^ per cent

exposed

d iffer­

1^-3 Pe r cent of th e

in the p a s t-flo w e rin g
series

in

developm ent.

s h o r te r exposure w eriods the

C om parative f i g u r e s f o r th e

were 3 . 3 ,

inocu­

experim ents re p re s e n t

s e r i e s e x p o s e d oO h o u r s h a d

sp ik elets

m ent.

c e n t d u r i n g t h e seme

i n T a b l e 12 m d F i g u r e

^he r e s u l t s

in the flo w erin g s ta g e .

F i g u r e U.

sev erity

t o i n f e c t i o n a n d h e a d b l i g h t m ay r e a d i l y b e

p e r c e n t more k i l l e d

e n c es were not

same p e r ­

This d e f i n i t e w erio d ,

a com parison o f th e p a n t- f lo w e r in g and flo w e rin g
Thus,

and th e

of th e i n t e r a c t i o n of m o istu re , tem p eratu re,

seen by com paring th e r e s u l t s
'Table

° to

per

developm ent,

The i m p o r t a n c e
and s t a g e o f

1

stage

i n i n f e c t i o n f r o m 18 -per

h o u rs of exposure and d is e a s e

J2

in the n a s t- f l o w e r in g

and h e a d b lig h t

in the flo w e rin g

S i m i l a r r e s u l t s were o b t a i n e d w i t h p l a n t s

w h i c h may b e r e f e r r e d
tio n

inoculated

i n i n f e c t i o n was f r o m 3 0 p e r c e n t w i t h bO

i n c r e a s e d from a p p ro x im a te ly
(Table

i n f e c t i o n and d is e a s e

p e r c e n t w ith h8 h o u rs of e x p o su re ,

77

iod.

period

in

showed an i n c r e a s e

i n c r e a s e d from
the

increase

36

a n d a t 2 0 ° C. 0 . 0 ,

in

the a f t e r ­

s ta g e of develop­

hour3 at
0.0,

J>0°

C.

and 1 2 .0 p e r

- 53 cen t,

resp ectiv ely .

h eadblight
m oisture,
of

Fr om t h e s e r e s u l t s

developm ent i s
the

air

tem perature,

and t h e

the

stu d ies

and

1

t

the e f f e c t

hum idity.

and m o istu re

series

which w ere e x p o s e d f o r

JO

o days f o r
decrease
lated

the f i f t t
C. h a d a n

It

in the le n g th

the

whereas

S im ilarly ,

Jo

of the

hours

J

the

length of
of

the

in itial

same

of in ­

th o se p l a n t s inocu­

C. F o r e x a m p l e ,

days f o r

2*4— a n d
the

incubation u erio d is

the fungus i n

e sta b lish m e n t of th is

20°

J

te m p e ra tu re and m o is tu re

the

e x p o s e d f o r US

for

oG-, and

bench,

hours at

days a s com paredto

^ days fo r

w ere removed from t h e

the

series

the 18-,

tim e th e p l a n t s

Jo

show any' s i g n s

incubation p erio d

days f o r

(T able lU ) .

e x p o s u r e . T h e r e was a g r a d u a l

stage and exposed a t

by th e e s ta b lis h m e n t

and t h a t

the

various

the p la n ts

chose p l a n t s from

hours did not

ph

day.

t h e *4-8-, U d a y s f o r

apnears th a t

tirely

days,

those r e c e iv in g o n ly

i n c u b a t i o n p e r i o d was

from th e tim e

i n c u b a t i o n p e r i o d o f 2 Pi

in the flo w erin g

day's f o r

P.

the in ­

on trie i n c u b a t i o n p e r i o d

stag e and exposed fo r

showed symptoms i n

tim e

In th e p ro se n t

the flo w e rin g

?5° 0 .

hours a t

m aintained • t

sy m pt om s b e c a m e v i s i b l e

in o cu lated in

the

the le n g th of

ten ts u n til

P lan ts

to

t e m p e r a t u r e wh en i n o c u l a t e d

w.-s d e t e r m i n e d by m a k i n g d a i l y o b s e r v a t i o n s

fectio n u n til

the degree of

developm ent a t

) noted th a t

relativ e

of tem perature

were rem oved from t h e

that

in fectio n .

in incubators

per cent

JO

8

in cu b atio n

were e x p o s e d c o n t i n u o u s l y

tem peratures

stage of

co n d itio n s fo r

Johann and D ickson ( 5

c u b a tio n p e rio d v a r i e d w ith
p lan ts

appears

d e p e n d e n t upon th e - .e r io a of e x p o s u re

i n o c u la tio n and exposure to
Pugh,

it

tents
are

in fectio n .

Jo

- ,

the
5

72-hour s e r ie s .

d e t e r m i n e d en­

the h o s t t i s s u e s

at

the

an d p l a c e d on t h e g r e e n h o u s e
the

co n tro llin g

facto rs

in

Tattle lH . — I n c u b a t io n p e r i o d s f o r p l a n t s i n o c u l a t e d i n t h e
f l o w e r i n g s t a g e w i t h G i b b e r e l l a z ea e and e x p o s e d to d i f f e r e n t o e r i o d s
o f c o n t in u e d w e t n e s s a t 15^ , 2 0 ° , 2.5° and 3 0 ° C .a

Hours o f e x p o s u r e
T em perature
d e g r e e s C.

IS

2*+

36

^

°0

72

I n c u b a t i o n p e r i o d - d ay s

20

7

6

6

5

^

3

25

6

5

2

2

2

2

30

—

—

6

2 .5

2 .5

2 .5

a P l a n t s were in c u b a t e d on t h e g r e e n h o u s e bench a t 25° C. a f t e r r e ­
moval from th e h u m id i t y t e n t .

The p r e s e n c e o f a e r i n l mycelium was c o n s i s t e n t l y o b se r v e d on
th e s u r f a c e o f t h e glum es a t th e tim e th e p l a n t s were removed from th e
h u m id ity t e n t s .

In ord er to d e te r m in e i f t h e r e was any r e l a t i o n s h i p

b etw een i t s p r e s e n c e and th e l e n g t h o f e x p osu re to c o n tin u e d w e tn e ss
a t v a r i o u s te m p e r a tu r e s , r e c o r d s were ta k en on th e p r e s e n c e or absence
o f mycelium on i n o c u l a t e d wheat h eads a t th e tim e th e y were removed from
th e t e n t s .

In g e n e r a l , th e amount o f a e r i a l mycelium i n c r e a s e d w ith the

l e n g t h o f exposure a t any one te m p e r a tu r e .

There was c o n s id e r a b ly more

a t 30° than a t 25° C ., w it h s t i l l l e s s a t 20° C.

The p r e s e n c e o f a e r i a l

m ycelium on a s p i k e l e t was not a s i g n o f i n f e c t i o n o f t h a t p a r t i c u l a r
s p ik e le t.

I t was c o n s i s t e n t l y n o t e d th a t mycelium growth o c c u r r e d most

f r e q u e n t l y i n d e g e n e r a t in g a n th e r t i s s u e ( P l a t e V ).

T h is i s

in com olete

agreem ent w i t h th e o b s e r v a t i o n s o f Pugh, Johann and D ic k so n ( 5 8 ) .

The

p r e s e n c e or a b s e n c e ox v i s i b l e a e r i a l mycelium on p l a n t s i n o c u l a t e d i n
th e f l o w e r i n g and a f t e r - f l o w e r i n g s t a g e s and e x p o se d to d i f f e r e n t p e r io d s
o f c o n tin u e d w e t n e s s ; t v a r io u s te m p e r a tu r e s i s

shown i n T able 1 5 .

These

o b s e r v a t i o n s show t h a t tem p erature and m o i s t u r e , a s w e l l a s s t a g e o f de­
v e lo p m e n t, i n f l u e n c e th e grow th o f a e r i a l mycelium on th e s u r f a c e o f th e
s p ik e le ts.
R ecords a l s o were ta k e n on the r e l a t i o n o f tem p erature and
m o is tu r e to the e x p r e s s i o n o f symptoms.
produced th e l e a s t d i s c o l o r a t i o n .

Those p l a n t s ex p o sed a t 30° C.

The d e e n e s t browning o c c u r r e d on

th o s e p l a n t s exroosed to te m p er a tu r e s o f 20° and 2 5 ° C.

For t h o s e i n the

l a t t e r group, the symptoms ap p eared to b e more pronounced i n th o s e p l a n t s
ex p o sed th e l o n g e s t to c o n tin u e d w e t n e s s .

However, when th e exposure

p e r io d became so l o n g t h a t r a p id i n f e c t i o n and k i l l i n g o f the s p i k e l e t s
r esu lted , l i t t l e

c o l o r d e v e lo p e d .

T a b le 1 5 . — I n f e c t i o n o f e x tr u d e d and ca u g h t a n t h e r s on
p l a n t s i n o c u l a t e d i n t h e f l o w e r i n g and p a s t - f l o i t e r i n g s t a g e s o f de­
v e lo p m e n t v i t h G -ih b e r e lla zeae and in c u b a te d f o r d i f f e r e n t p e r i o d s
a t 15° , 2 0 ° , 25° and 30u cT®

Stage o f p la n t
developm ent

Tem perature - 0 c .

Exposure
p e r io d

20

25

30

0*
0
0
0
0
0

0
0
0
X
X
X

0
0
X
X
X
X

0
0
X
X
X
X

0
0
0
0
X

0
0
0
X
X

0
0
X
X
X

X
X
X
X
X

15?
Hours
F lo w e r in g

18
2U
36

bs
60
72
p a st-flo w e r in g

18
2k

36
bs

60

R e co r d e d a t th e tim e th e p l a n t s were removed from th e h u m id ity t e n t s .
*h

_

0 = no v i s i b l e mycelium; X - v i s i b l e m ycelium .

- 57 To what e x t e n t a s h o r t , wet p e r i o d im m e d ia te ly a f t e r in o c u ­
l a t i o n f o l l o w e d by a dry o e r i o d w ould have upon h e a d b l i g h t developm ent
was d e te r m in e d i n a s e r i e s o f g r e e n h o u s e e x p e r i m e n t s .

In c o n ju n c tio n

w it h t h e s e e x p e r im e n t s , th e e f f e c t upon h e a d b l i g h t d e velop m en t o f a dry
p e r i o d im m e d ia te ly a f t e r i n o c u l a t i o n was a l s o d e te r m in e d .

In o t h e r

w o r d s, what e f f e c t w ou ld d i s c o n t i n u o u s o r i n t e r m i t t e n t w e t n e s s have
upon d i s e a s e developm ent?
Three e x p e r im e n ts on d i s c o n t i n u o u s w e t n e s s were c o n d u c t e d .
The r e s u l t s w h ic h w ere o b t a i n e d i n an i n i t i a l e x p e rim en t i n v o l v i n g 9 S
p o t s o f L eep la n d w i n t e r wheat i n o c u l a t e d i n th e p a s t - f l o w e r i n g s t a g e
and s u b j e c t e d t o d i f f e r e n t w e t n e s s p e r i o d s up t o 24 hours a t 2h° C .,
in d ic a te d th a t very l i t t l e
occurred a ft e r a (sh o rt)

or no r e d u c t i o n i n t h e amount o f i n f e c t i o n

d r y in g p e r i o d o f 1 2 h o u r s .

An e x p e r im e n t s im i­

l a r to th e one j u s t m e n tio n e d was c o n d u c te d l a t e r i n t r i p l i c a t e u s i n g

96 p o t s o f N ew th atch wheat in th e f l o w e r i n g s t a g e .

The p l a n t s were i n ­

o c u l a t e d i n g r o u p s o f IS a t v a r i o u s i n t e r v a l s and 6 p o t s were p l a c e d i n
e a c h o f t h e t h r e e h u m id ity t e n t s m a in t a in e d a t 2 0 ° , 2 5 ° , and J>0° C.

A ll

th e p l a n t s were rem oved from th e t e n t s a t th e end o f 36 h o u r s .
At the t i n e o f rem oval from th e t e n t 9 , 3 p o t s from e a c h i n i t i a l
t r e a t m e n t were p l a c e d on the g r e e n h o u s e bench to s e r v e as c o n t r o l s .

The

o t h e r 3 were d r i e d a t 25° 0 . and 40 p e r c e n t r e l a t i v e h u m id ity f o r 24’lo u r s b e f o r e t h e y w ere r e - s u b j e c t e d f o r 54 a d d i t i o n a l h o u rs o f c o n t in u e d
w e t n e s s a t 25 ° C.

R e co r d s were ta k e n 8 d a y s a f t e r i n o c u l a t i o n .

3 -d a y r e c o r d s had b e e n o b t a in e d on th e c o n t r o l s c r i e s ,

t h e s e p l a n t s were

a l s o r e - s u b j e c t e d t o 5*+ h ou rs o f c o n t in u e d w e t n e s s a t 23° C.
from t h i s e x p e r im e n t a r e j j r e s e n t e d i n T able l o .
th e s p i k e l e t s '-ere k i l l e d

A f t e r th e

The r e s u l t s

N in e ty - tw o p e r c e n t o f

in th e c o n t r o l s e r i e s w hich was s u b j e c t e d

Table l c
The e f f e c t on r e s u l t i n g h e a d b lig h t , on p l a n t s in o c u la t e d in th e flo w e r in g stag e
w ith G-ibberella z e a e , o f an i n i t i a l exposure to contin ued w etness at d i f f e r e n t tem peratures fo llo w e d
by a dry and a second wet p e r io d a t 25° C.

Length o f drying
a fte r i n i t i a l exposure to c o n tin ­
ued w etness

Temp,
0 C.

Days
b

1

20

25

I n itia l
exposure
p e r io d

S p ik e le ts
T o ta l

In fected a

K ille d

Hours

Number

Number

Per cent

Per cent

0
0
12
18
2U
3c

20
IT
20
2h
15

209
195
20U
2lU
229
132

9c .c
b s .7
75-5
3 5 .5
9 7 .S
100.0

60.3
2 3 .I
37-3
79.9
9 1 .7
1 00 .0

0
12
18

217
181
217
201
187

U.b

3b

2*4
IS
23
21
is

85.1
92.6
9 5 -0
9 7 -9

b s .b
5 8 .0
92.6
37 .0
100 .0

6
12
18
2-4
3c

18
21
?u
23
20

ish
203
2c l
211
196

78.8
9 0 .6
9 3 .1
3 8 .1
1 0 0 .0

38.0
b s .s
7^.7
9 7 .6
10 0.0

2b

30

Heads

2b

la id * l 6 . — Ooatizmsd.

le n g t h o f drying
a ft e r i n i t i a l exposure to c o n tin ued w etness

Teiap.
u 0.

Days
9C

2C

In itia l
exposure
n e r io d

30

0

25

S n ik elets
T otal

In fected 6

R ille d

P er cent

Per cent

Hours

Humber

Humber

6
■
<
id0
is

00
O
'.Cl
22
?3
23
23

31k
21p
210
nnn
. hi c
213

0.0
0.0
0.0
1 .3
n £*
A n

2k

C'J

Heads

w
12
13
2a
3-

2h
20
0p
f.-L
lU

2c3
10 2
23S
207
12$

0
12
13

AAA
lc~J
^ C
ny:
:- G
y

0.0
c .o
7X 0~H
r

2k

20
on
u-C.
A
A
c. c_
on

3o

is

21k
IfcC

O.o
3 ,S

;ck

°2

223

? - •r

O.C
\
j) . “
3*3
lc .3

i n o c u l a t io n .
a A l l record s on i n f e c t i o n taken 6 days a:
C^
O
j j n e a in pn in c u b a tio n chamber at 2p C. and UG per cent r e l a t i v e hum idity f o r 2^ h ou rs.
on k i l l e d s p i k e l e t s fo r t h i s s p r i e s o b ta in ed 11 days a f t e r i n o c u l a t i o n .

J*n . j
a-_
So .0
7U.3
7( ^.
- ]j.
I 0.3

rp
l-y• tj^
100.0
y l-3
I rr a
32. g
t^c
5:/
^^ . U
apO.
a 0
•—
10C.0
00
^- •h■

Records

c D ried and incubated on -greenhouse tench; temperature m aintained at 25° C. The records on i n f e c t i o n
in t h i s s e r i e s are th e c o n t r o ls fo r th e 1-day dried s e r i e s and were taken p r io r to the second wet­
n e s s p e r io d . Records on s p i k e l e t s k i l l e d were taken 7 days a f t e r r e - e x p o s u r e .

im m ediately a f t e r

C.

The p l a n t s

in o cu latio n

in th e

series

k illed ,

[■ iia 3

o-hour s e r ie s

and th e
of

2 U-

and

the

6

the
-

and

12

-hour

-hour
the

the d ise a se

it

hours at
and

1+

in

25°

C.

30°

to

3

at

^°

2 0 °.,

C.

series.

(T able l

6-H

the

6-h

our

nroducea

less

S im ilar r e s u l t s
dry f o r

after

9

as

9

2 pots

su b jected f o r

A c o m p a rab le amount

o b tain e d in the

first

10

in stances

in

i n amount

at

severe

25° C .,

and

headblight

I n some i n s t a n c e s

the

the

2

b-hour

b- and 12-hour

sev erity

increased

w ith

p o t s o f ITewthatch w heat were

6

hours a t

1+8 h o u r s t o

the p r e c e d in g e x p e rim e n t.

o-hour

continued w etness at

of re d u c tio n in

disease

25 ° C.

d i s e a s e developm ent to

occurred a f t e r

series.

2 5 ° C.

in o cu latio n .

th e u n e x p o s e d and 2 from th e

increase in

s e rie s over th e h-day d rie d

25° C .,

Ttvo o f t h e n o t e w e r e e x o o s e d f o r 1+8

experim ent

T h e re was a s l i g h t

at

?k-

On t h e o t h e r

- hay th a n i n

Four u o ts were exposed

of

The

) .

in o cu latio n ,

co n tro ls.

spike­

days on th e g ree n h o u se

severe in

the

°

were o b t a i n e d w ith

2 5 ° C.

the flo w e rin g s ta g e .
0.

series

to w e tn e ss a t

6

series

hours d ry in g .

2b

determ ine w hether d ise a s e

days l a t e r ,

8

17)-

exposure.
d ried

series

sev erity .

C . f shov red no r e d u c t i o n

T h i s wa s e s p e c i a l l y n o t i c e a b l e f o r

exposed s e r i e s were

that

°

cent of t h e i r

were p l a c e d on t h e g r e e n h o u s e b e n c h i m m e d i a te l y a f t e r

Four and

(T able

30

23

e x p o s u re to wet­

U- a n d 3 b - h o u r

2

w h i c h was a l l o w e d t o

drying p e rio d s

in o cu lated

18-,

at

was r e - s u b j e c t e d

20° a n d

w etness a t

in d ise a s e

developm ent a f t e r

con tro l

In o rd er
lo n g er

the

d e v e lo p m e n t was m ore

series.
at

oer cent

series

series at

series

bench before

series

20° C .,

c- and 1 2 -h o u r

con tro l

d ried

at

and d i s e a s e

than e ith e r of
the

36

^ hours o f continued

w h i c h r e c e i v e d no i n i t i a l

or a red u ctio n of

in fectio n

hand,

5

d r i e d f o r 2*+ h o u r s h a d CO p e r

n e s s "before th e y w ere
lets

to

0

and

sev erity

6

hours of

in

T h is was n o t i c e d i n

C o llectiv ely ,

the

8

-day

certain

t h e r e s u l t s from

Table 1 7 . — E f f e c t on r e s u l t i n g h e a d b lig h t on p l a n t s in o c u la te d in the f lo w e r in g s ta g e
w ith G ib b e r e lla z e a e . o f no exposure and a 6-hour i n i t i a l exposure to c o n tin u e d w etness at 25 C.
f o llo w e d by U and 8 days o f drying and a second w etn ess p e r io d o f *+8 hours at 25° C.

Exposure
p e r io d

Drying
p e r io d

S p ik e le ts

Heads
T otal

In fected 0

K ille d 0

Hours

Days

Humber

ITumber

Per cent

Per cent

0

U

13

111

15-3

1 0 .0

s

1?

130

3 6 .7

15-3

k

17

191

2 1 .5

9.U

s

13

191

3 3 .0

I 9.9

0

13

lUU

0 3 .O

5 2 .1

c

&

Recorded 10 days a f t e r i n o c u l a t io n

t h e s e e x p e r im e n ts show t h a t i n the g r e e n h o u s e , a dry p e r io d im m ed ia tely
f o l l o w i n g p la n t i n o c u l a t i o n or a s h o r t w e t n e s s p e r io d o f 6 - 1 2 hours f o l ­
low ed b y a d r y p e r i o d , r ed u c ed th e d i s e a s e developm ent c o n s i d e r a b l y .
However, th e r e d u c t i o n i n d i s e a s e development was a lw a y s l e s s on th o se
p l a n t s \tfhicli v;ere d r i e d the l o n g e s t ; th e d i s e a s e b e in g more s e v e r e on
t h o s e p l a n t s r e c e i v i n g 8 days o f d r y in g than t h o s e which r e c e i v e d o n ly
hours o f d r y in g .

T h is i n c r e a s e i n d i s e a s e s e v e r i t y a f t e r lo n g e r dry­

in g p e r i o d s can p o s s i b l y be e x p l a i n e d on th e b a s i s o f th e in c r e a s e d su s­
c e p t i b i l i t y o f tn e n l a n t s in th e l a t e r s t a g e s o f head m a t u r i t y .

H elm in th osooriu m sativu m

The s t u d i e s on th e e f f e c t o f a i r tem p eratu re and m o is tu r e
upon i n f e c t i o n o f N ew thatch wheat heads by H elm inthosnorium sativum
f o l l o w v e r y c l o s e l y t h o s e d e s c r ib e d f o r G ib b e r e lla zeae i n th e p r e c e d ­
in g s e c t i o n .
p e r im e n ts.
p la n ts,

The same methods and t e c h n iq u e s were a p p lie d in t h e s e ex­
The r e s u l t s from an experim en t on the e f f e c t o f e x p o s u r e o f

in o c u l a t e d in th e f l o w e r i n g ,

a f t e r - f l o w e r i n g and p a s t - f l o w e r i n g

s t a g e s of d ev elop m en t, to d i f f e r e n t p e r io d s o f c o n tin u e d w e t n e s s a t 20° ,
25° and 30° C ., a r e p r e s e n t e d i n T able I I .
s e r i e s a r e i l l u s t r a t e d in F ig u r e q .

The data from th e 3 6-hour

The d a ta p r e s e n t e d i n Table 18

and i l l u s t r a t e d i n F ig u r e 8 , a r e f o r p l a n t s in o c u l a t e d in th e p a s t f l o w e r i n g s t a g e o f developm ent and e x p o sed f o r d i f f e r e n t p e r i o d s t o
c o n t in u e d w e tn e s s a t 15° . 20° ,

25° and 30° C* i n th e h u m id ity t e n t s .

The r e s u l t s from a s i m i l a r e x p e r im e n t, in w hich th e p l a n t s were in o c u ­
l a t e d in th e f l o w e r i n g s t a g e , a r e j>r e s e n t e d in T able 19 and i l l u s t r a t e d
in F ig u re 9 .

Table I S . — K elninthosporium h e a d b lig h t r e s u l t i n g from exposure o f p l a n t s , in o c u la te d in
the past—flo w e r in g s t a g e , to d i f f e r e n t p e r io d s o f con tin u ed w etness at d i f f e r e n t te m p e r a tu r e s.a

Terno.
0 C*.

Expo sure
p e r io d

S r ik e le ts

Heads
T otal

In fected
Her cen t

w

K ille d 0

Hours

Humber

Humber

15

12
24
V,
Us

25
28
23
2c

233
230
212
22o

0 .0
0 .0
0 .0
2 .2

0 .0
0 .0
0 .0
0 .0

20

1?
2d

25
27
12
27

157
201
93
2?S

0 .0
9.5
1 8 .3
11.0

0 .0
0 .0
0 .0
3 1 .1

12
24
3c
4s

28
?4

213
210
197
18$

O.d
1 2 .4
73-1
0 7 .h

0.0
'4 .3
7 .S
4 0 .2

12
24
35
4s

32
27
30
2$

284

3 -2
1 5 .7
8 3 .9
99-3

0.0
24.1
27.4

?C

4s
25

30

22
24

D u p lic a te p o t s were used f o r each tr e a tm e n t.
^ Recorded 6 days a f t e r in o c u l a t i o n .
Q

Recorded 13 days a f t e r i n o c u l a t io n .

216
254

272

Her cent

25.6

Spikeleta

killed

- per cen t

100

•hour
•hour

20

30

25

Tem perature - d eg rees C en tigrad e
F ig u re 8*

R e la tio n o f tem perature and p e r io d o f con tin u ed

w e tn e ss to H elm ln th ogp orlu a h e a d b lig h t.
in th e p a s t-flo w e r in g sta g e*

P la n ts w ere in o c u la te d

( Data in lfa b le 18

)•

Table 1 9 -— Helminthosporium h ea d b lig h t r e s u l t i n g from exposure o f p l a n t s , i n o c u l a t e d i n
th e f l o w e r i n g s t a g e , to d i f f e r e n t p e r i o d s of co nti nu ed v/etness at d i f f e r e n t te m p e r a tu r e s. a

Temu.
0

c".

Ip

Exposure
p e rio d

30

Total

In fected

P er cent

Pum'cer

Humber

12
■24
3o
4g

25
27
28
27
23

29:6
235
323
294
307
252

2?
31
27
25
7 5-.,

230
o34?
f

•V")

25

S p ik e le ts

Hours

7/ 7
20

Heads

12
oh
3o
43
00
72
12
24
3o
4s
oO
72
12
?4
3^
4a
oO
72

OR

30
30
23
24

27
26
25
26
24
21
30
28

a Experiment conducted in t r i p l i c a t e .

^ Recorded 7 days a f t e r i n o c u l a t io n .

230
277
290
32 ?
328
295
2U1
23S
?4i
297
296
271
267
227
294
? i4

0 .0
0 .0
0 .0
11.4
17.4

0a
7 .3
7 7.2
100.0
10c . 0
100.0
21.6
100.0
100.0
100.0
100.0
100.0

38.6
82.2
100.0
100.0
100.0
100.0

b

K illed^
P er cent
0 .0
0 .0
0 .0
0 .0
0 .0
0.0

0 .0
c .o
0.0
0 .0
0 .0
16.4
0 .0
0 .0
27.8
3S .1
79-3
100.0
0 .0
0.0
14.2
37.0
88.5
96.8

15

20

25

3°

Temperature - d eg rees C entigrade

F igu re 9«

R e la tio n o f teaoperature and p erio d o f oontlnned

w etn ess to H eln ln th o sp o rlu a h ea d b lig frtl
th e flo w er in g sta ge*

P la n ts In ocu la ted In

( Rata In liab le 19 )•

- 67 I n f e c t i o n app eared t o be n e a r ly e q u a l l y s e v e r e a t 25° and 30°
C.

In some o f t h e e x p e r im e n ts 3 ° ° c * was th e most f a v o r a b l e w h ile in

o t h e r s 25° C. was t h e most f a v o r a b l e tem perature f o r h e a d b lig h t d e v e lo p ­
ment.

In s t i l l o t h e r e x p e r im e n ts , th e t o t a l number o f s p i k e l e t s k i l l e d

was a p p r o x im a te ly th e same a t b o th te m p e r a tu r e s .

An a ttem p t was made to

d e te r m in e more e x a c t l y th e optimum te m p e r a tu r e s f o r i n f e c t i o n and b l i g h t
development by i n o c u l a t i n g wheat heads p r e v i o u s l y removed from the p l a n t s
and in c u b a t i n g them i n m o ist chambers a t 2 0 ° , 2^ °, 26° ,
C.

2 8 °, 30° and 3 2 °

The i n c u b a t io n n e r i o d was 40 h ou rs in th e f i r s t and hg hou rs i n t h e

sec o n d e x p e r im e n t.
same.

In b o th o f t h e s e e x p e rim en ts the r e s u l t s were the

Maximum i n f e c t i o n o c c u r r e d on th o s e heads in c u b a te d a t 26° ,

and 30° C.

28°

S l i g h t l y l e s s i n f e c t i o n o c c u r r e d a t ?k° and 3?° C ., w h ile

o n l y a t r a c e of i n f e c t i o n was v i s i b l e at 20

o

C.

Two o t h e r e x p e rim en ts

were made i n which th e te m p e r a tu r e s were compared.

In the f i r s t the

lo w e r tem p era tu re v a r i e d from 2^ - 26° C. and th e h ig h e r from 2 9 -3 0 ° 0.
S t a t i s t i c a l a n a l y s i s o f th e y i e l d s i n d i c a t e d t h a t th e r e were no s i g n i f i ­
ca n t d i f f e r e n c e s b e tw e en t h e s e two tem p erature r a n g e s a s f a r as h e a d b lig h t
developm ent o f H. s a tiv u m was con c er n e d a lt h o u g h s l i g h t l y more s p i k e l e t s
were k i l l e d a t th e lo w e r t e m p e r a t u r e s .

I n th e o t h e r e x p e rim en t, the low er

\^
O
tem p eratu re was m a in ta in e d b e tw e en 24 and 25 C. and th e upper between
27° flnd 29° C.

In t h i s c a s e t h e r e was a s i g n i f i c a n t l y h ig h e r r e d u c t io n

in y i e l d from p l a n t s e x p o sed a t t h e h ig h e r te m p e r a tu r e s .

I t was apparent

from a l l t h e s e r e s u l t s t h a t H. sativum has a w ide tem p eratu re range fa v o r ­
a b le f o r i n f e c t i o n and h e a d b lig h t development w it h th e optimum tempera­
t u r e s p r o b a b ly around 2 8 -29 ° C.

These c o n c l u s i o n s a g r e e w it h th e o b se r ­

v a t i o n s made by C h r is t e n s e n ( 1 3 ) who n oted t h a t h ig h a i r tem p eratu res
fa v o r e d i n f e c t i o n .

- 68 There i s th e p o s s i b i l i t y t h a t th e s t a g e o f p la n t d e v e lo p ­
ment may h e r e s p o n s i b l e f o r d i f f e r e n c e s i n d i s e a s e s e v e r i t y a t 25°
and 30

o

C.

Those p l a n t s i n o c u l a t e d i n th e p a s t - f l o w e r i n g s t a g e o f

developm ent n e a r ly alvrays d e v e lo p e d more h e a d b lig h t at 30° C. than at
?5° C.

(T a b le 1 1 , 18) .

Those p l a n t s i n o c u l a t e d in th e f l o w e r i n g and

a f t e r - f l o w e r i n g s t a g e s appeared to d e v e lo p e q u a l l y s e v e r e h e a d b lig h t
a t ?5° C. and 30° C. (T a b le 1 1 , 1 9 ) .
H e a d b lig h t developm ent was much l e s s

s e v e r e on t h o s e p l a n t s

e x p o sed to c o n tin u e d w e tn e ss a t the low er te m p e r a tu r e s .

Heavy i n f e c ­

t i o n was r e c o r d e d a t 20° C. y e t th e p l a n t s n e v e r d e v e lo p e d v e r y s e v e r e
h e a d b lig h t.

F i f t e e n d e g r ee tem p era tu n es were d e c i d e d l y u n fa v o r a b le

f o r e i t h e r i n f e c t i o n or b l i g h t developm ent.
C h r i s t e n s e n ( 1 3 )* D astur ( 1 7 ) , and G-reaney and Kachacek ( 29)
n o t e d t h a t abundant m o is tu r e v a s a major f a c t o r to i n f e c t i o n and head­
b l i g h t d e v e lo p m e n t.

The s i g n i f i c a n c e o f t h e i r o b s e r v a t i o n s was borne

out i n the p r e s e n t s t u d i e s .

There u s u a l l y was a c e r t a i n p e r io d o f ex­

p o s u r e to c o n tin u e d w e tn e s s a t e a ch tem p erature during which th e r e was
a g r e a t i n c r e a s e in i n f e c t i o n and one a t w hich th e r e was a. g r e a t i n ­
c r e a s e in d i s e a s e s e v e r i t y .

Thus, w ith p l a n t s in o c u l a t e d in the f lo w e r ­

in g s t a g e and e x p o s e d to c o n tin u e d w e tn e ss a t 25° C ., i n f e c t i o n in c r e a s e d
from 21 n er c e n t w i t h 12 hours to ICO per cen t w it h ?b hours e x p o su r e.
Under t h e s e c o n d i t i o n s no s p i k e l e t s were k i l l e d .

D is e a s e s e v e r i t y ,

how ever, in c r e a s e d from 38 p e r c e n t w ith U8 hou rs t o 79 Pe r cen t w ith
oO h o u rs o f e x p o s u r e a t the same tem oeratu re (T a b le 19 ) •

A sim ila r

i n c r e a s e in i n f e c t i o n and h e a d b lig h t development was n o te d on p l a n t s
i n o a u l a t e d in the flo w e r i:^ ; s t a g e and e xp o sed a t JiQ° C.

Those p l a n t s

i n o c u l a t e d i n th e p a s t - f l o w e r i n g s t a g e a l s o e x h i b i t e d c e r t a i n p e r io d s
when t h e r e was a s i g n i f i c a n t i n c r e a s e in i n f e c t i o n and d i s e a s e s e v e r i t y
For exam ple, i n f e c t i o n in c r e a s e d from 1 2 p e r c e n t w ith

2b

hours to 73

p er c e n t w ith 3b h ou rs o f ex p o su r e to c o n tin u e d w e tn e ss a t 25° C. and
d i s e a s e s e v e r i t y i n c r e a s e d front 7 ~ e r cen t w ith 36 hours to UO u e r cent
w ith Ud hours e x p o su r e (T ab le l g ) .

I t i s e v id e n t th a t E. sativum has

two c r i t i c a l e x p o su r e p e r i o d s , one f o r i n f e c t i o n and one f o r d i s e a s e de
v e lo p m e n t.

T hese p e r i o d s g e n e r a l l y d e c r e a s e d w ith an i n c r e a s e in tem­

peratu re .
Coiaprrisons were rra.oe to d eterm in e w hether t h e i n c u b a t io n
p e r i o c was i i i f l u e n c e u by d i f f e r e n t p e r io d s o f exp osu re to c o n tin u e d
w e tn e ss at d i f f e r e n t te m p e r a tu r e s (T a b le 2 0 ) .

The s h o r t e s t in c u b a tio n

p e r i o d ( l h days) occurred, on t h o s e p l a n t s e x p o sed f o r
t in u e d w e tn e s s a t 25° and 30° C.

hou rs to con­

E xposures o f l e s s than J>6 hours a t

t h e s e te m p er a tu r e s r e s u l t e d i n c o r r e s p o n d in g ly lo n g e r in c u b a t io n p e r ­
io d s.

The i n c u b a t i o n p e r io d s were lo n g e r f o r th o s e p l a n t s e x p o sed a t

th e l o v e r te m p e r a tu r e s .

For exam ple, p l a n t s in o c u l a t e d i n th e f lo w e r ­

in g s t a g e and e x p o s e d f o r oO hours to c o n tin u e d w e tn e s s a t 20° C. had
an in c u b a t io n p e r i o d o f 2)- days a s compared to 7 days a t 15° C.

Thus,

i t i s e v id e n t th a t the le n g t h o f ex p o su re to c o n tin u e d w e tn e ss and the
tem p erature a t the tim e o f e x p o s u r e were b o th im portant in d eterm in in g
the l e n g t h o f th e i n c u b a t io n p e r i o d .
An nttenrpt was made to d eterm in e w hether d i f f e r e n t p e r io d s
o f e x p o su r e to .moisture a t v a r io u s tem p era tu res in f lu e n c e d th e e x p r e s s ­
io n o f symuto ms.

By making d a i l y o b s e r v a t i o n s ,

i t was n o ted th a t the

Table 20 . — I n c u b a tio n p e r io d s f o r p l a n t s in o c u l a t e d in the
f lo w e r in g s t a g e w ith H elm inthosoorium sativum and exposed to d i f f e r ­
ent p e r io d s o f c o n tin u e d w e tn e ss a t d i f f e r e n t te m p e r a tu r e s ,a

Hours o f ex p o su re to c o n tin u e d w etn ess
Temu.
0 c.

12

24

3o

Ug

to

7?

7

7

o

I n c u b a t io n o e r i o d - days
15

—

—

20

—

5

2d-

2i.

2b

2f

25

h

2-;

1'

l£

1b

1?>

30

k

2-;

Id.

I 1-

li

If

FV

—

P l a n t s were in c u b a te d on g r ee n h o u se bench a t 25
from th e h u m id ity t e n t s .

O

C. a f t e r removal

- 71 c o l o r a t i o n v;n s more pronounced, on th o s e p l a n t s which r e c e i v e d enough
f a v o r a b le ex n o su r e f o r i n l ' e c t i o n to hecome s u f f i c i e n t l y e s t a b l i s h e d i n
th e h o s t t i s s u e t o the e x t e n t t h a t i t r e s u l t e d i n a slo w and gradual
k i l l i n g o f th e s p i k e l e t s .

This o c c u r r e d w ith th o s e n l a n t s e x p o sed to

c o n t in u e d w e tn e s s f o r 60 and 7? hours a t 20° C.

The i n f e c t e d n o r tio n s

became dark to r e d d ish -b r o w n and when th e heads were f i n a l l y k i l l e d ,
tu e dark d i s c o l o r a t i o n was r e t a i n e d to a c e r t a i n d e g r e e , g i v i n g the
heads a dark m o t t le d t o b le a c h e d .appearance.

E xposures a t more fa v o r ­

a b le temperat a r e s ( 2h° and 30° C.) f o r kg hours or more r e s u l t e d in
r a p id k i l l i n g of the wheat heads and, as a r e s u l t , th e i n f e c t e d -carts
d id n o t d e v e lo p much c o l o r .

I t app eared t h a t tem perature and m oistu re

were more im p ortan t f a c t o r s to symptom e x p r e s s i o n fo r t h i s pa th o gen
tnnn f o r G. z e a e .
S e v e r a l e x p e r im e n ts on the e f f e c t o f d is c o n t in u o u s w e tn e ss
on th e developm ent o f Helm inthosporium h e a d b lig h t were c o n d u cted a t the
same tim e and in a l i k e manner to s i m i l a r e x p e r im e n ts w ith G ib b e r e lla
zeae d i s c u s s e d i n an e a r l i e r s e c t i o n .

N i n e t y - s i x p o t s o f L eapland w in ter

wheat were e x p o se d to c o n tin u e d w e tn e s s f o r s h o r t p e r io d s up to 2k hours,
f o l l o w e d by a 1 2 -h o u r

d ryin g

d r y in g p e r io d was not

s u f f i c i e n t to r ed u ce i n f e c t i o n and h e a d b lig h t de­

velopm ent .

n e r io d

anda secon d w e tn e ss p e r i o d .

This experim en t was l a t e r r eu e r te c u s in g j o p o t s o f Hewthntch

wheat i n o c u l a t e d i n th e f l o w e r i n g s t a g e .

The p l a n t s were exposed to con­

tin u e d w e tn e s s f o r 0 ,

o, 12, I S ,

?k and Jo hours a t 3 ° ° 0.

d r ie d f o r 2k hours a t

23° C.and

kO p er c e n t r e l a t i v e h u m id ity and the

o t h e r vaas k ep t d ry on the g r ee n h o u se bench a t PS

0. for j

One s e t was

days b e fo r e

a l l th e p o t s were r e - e x p o s e d to c o n tin u e d w e tn e s s f o r ^k hours a t 30° C.
(T a b le 2 1 ) .

The

Table 21 . — The e f f e c t on r e s u l t i n g n e e u t l i g h t , on p la n t s in o c u la te d in the flo w e r in g s ta g e
w ith Kelminthosporium sativum, of an i n i t i a l exposure to contin ued w etness a t d i f f e r e n t tem peratures
f o llo w e d by a dry and s second w etn ess p e r io d .

Drying p e r io d
a fter i n i t i a l
expo sure

Temp.
0 C.

Days
d

20

25

In itia l
exposure
p e r io d

T o ta l

S p ik elets
«
In fected

K ille d

Hours

Number

Number

Per c en t

Per cent

0
6
12
18

21

9S*1
7c .8

2k

2k

212
21o
220
171
208

36

21

17k

76.0
93-5
100.0

9 9 .1
2 2 .7
03.2
08.k
1 0 0 .0
1 00 .0

6
1?
18

18
17
21
22
25

18k

62 .0

2c . 6

174
200

I2 .k

o k .k

235

9 0 .5
96.1
99.6

9 6 .5
100.0
9 9 .1

228
138
20U
163
177

93*9
7 7 .2
97.0
51.1
99.k

35 .1
71 .5
97.6
1 0 0 .0
99 .1

2k

36
30

Heads

0
12
IS
2k

36

2k

25
21

2U
17
21
20
20

20k

6 8 .2

*

r

y

*

-

■■■■■;!’v ';- "

Table 2 1 .— Continued.

Drying p e r io d
a fter in i t ia l
exposure

Temc.
0 C.

Days
9C

In itia l
expo sure
p e r io d
Hours
r

a

T otal

In fected

K ille d

Number

Number

Per c en t

P er cent

20

D
12
18
2*+
3d

20
2^
17
21
20

153
197
138
163
157

0 .0
0 .0
0 .0
0 ?
15 .5

o^.U
58.*+
1 0 0 .0
1 0 0 .0
100.0

25

0
12
18

2b

22

220
201

0.0
1.0

2b

19b

2k

22
22

193
159

b .i
13.2
b & .h

34.1
7 2 .6
100.0
1 0 0 .0
1 0 0 .0

17 b

3b

18
22
22
20
19

205
l$*+
186
173

1+0.5

78.2
73-2
Sb. 5
100.0
100.0

51+

17

188

9 k .7

1 00 .0

3d
30

6
12
18
2b

o

S p ik elets

Heads

25

0.0
0.0
0.0

a A ll r eco rd s on i n f e c t i o n taken 8 days a f t e r in o c u l a t i o n .
13 D ried in an in c u b a tio n chanter a t 25° C.
and *+0 p er cen t r e l a t i v e hum idity fo r 2 b hou rs.
on k i l l e d s p i k e l e t s f o r t h i s s e r i e s made 8 days a f t e r i n o c u l a t io n .

Eecords

c Dried and incubated on greenhouse te n c h . Temperature m aintained a t
25° C-The record s
on in f e c ­
t i o n in t h i s s e r i e s are the c o n t r o l s fo r
th e 1-d a y d r ie d s e r i e s andwere tak en p r io r to th e second
w etness p e r io d . The records on s p i k e l e t s k i l l e d were made 7 days a f t e r th e p l s n t s were r e-ex p o se d
to w e tn e ss .

74

-

-

A 24-h our d r y in g p e r io d im m ed iately a f t e r i n o c u l a t i o n r e s u l t e d
in no r e d u c t io n in d i s e a s e s e v e r i t y .

However, th o se p l a n t s s u b j e c te d to

h ou rs or l e s s exposure to c o n tin u e d w e tn e ss a t 2 0°, 25° and 30° C.,
0
and l o r 18 hours a t 20 C. f o l l o w e d b y 24 hours o f d r y in g , a l l showed a
12

r e d a c t i o n in d i s e a s e s e v e r i t y .

There was a g e n e r a l ten d en cy f o r th o se

p l a n t s kept dry f o r 9 days on the g reen h ou se bench to be more s e v e r e l y
b l i g h t e d than t h o s e kept dry f o r o n ly 24 h o u rs.
In o r d e r t o c o r r o b o r a te the o b s e r v a t io n made i n the p r e ce d in g
e x p e rim en t, a n o th e r was con d u cted i n which 20 p o t s o f wheat were inocu­
l a t e d i n the f lo w e r in g s t a g e .

O n e -h a lf o f t h e s e were p la c e d on the g r ee n ­

house bench and the remainder v/ere exp osed to b hours o f c o n tin u e d w e tn e ss
a t 30° C. and th en p l a c e d on th e g reen h o u se bench.

Four and 8 days l a t e r ,

2 p e t s from ea ch s e t v/ere r e - e x p o s e d f o r 48 hours to c o n tin u e d w etn ess a t
30° C.

I n f e c t i o n was heavy on a l l o f th e p l a n t s (T able 2 2 ) .

There was

a r e d u c t i o n i n th e s e v e r i t y o f b l i g h t developm ent on t h o s e p l a n t s which
r e c e i v e d 4 days o f d r y in g , r e g a r d l e s s o f the i n i t i a l e x o o su re p e r io d .
Those p l a n t s which were kept d ry f o r 8 days d e v e lo p e d more s e v e r e head­
b l i g h t than th o s e e x p o se d to 48 hou rs o f c o n tin u e d w e tn e ss im m ed iately
a f t e r in o c u la .t io n .

L ess s e v e r e h e a d b lig h t d e v e lo p e d on th o se p l a n t s which

r e c e i v e d a sh o r t ex p o su r e p e r i o d .
in th e p r e v io u s e x p e r im e n t.

The r e s u l t s a g r ee w ith th o se o b ta in e d

This i n c r e a s e in h e a d b lig h t s e v e r i t y a f t e r

8 days o f d r y in g may be due to th e in c r e a s e d s u s c e p t i b i l i t y o f p l a n t s to
i n f e c t i o n in the l a t e r s t a g e s o f d evelopm ent.

I t ap p ears, t h e r e f o r e ,

t h a t a s h o r t e x p o s u r e p e r io d t o c o n tin u e d w e tn e s s a t tem p eratu res from
2 0 -3 0 ° C ., f o l l o w e d by a dry and a. second wet p e r io d , w i l l te n d to reduce
the s e v e r i t y o f h e a d b lig h t developm ent by H. s a tiv u m .

T a b le 2 2 . — The e f f e c t on r e s u l t i n g h e a d b l i g h t , on p l a n t s
i n o c u l a t e d i n th e f l o w e r i n g s t a g e w i t h H elm in th o sp o riu m s a tiv u m , o f
no e x p o s u r e and a b-hour i n i t i a l e x p o s u r e to c o n tin u e d w e tn e s s a t
3 0 ° C. f o l l o w e d by U and 8 days o f d r y in g and a seco n d w e tn e s s p e r ­
i o d o f U8 h o u r s a t 3 0 ° C.

E xposure
p e r io d

D rying
p e r io d

Heads

S p ik e le ts
T otal

In fected a

K ille d ®

Hours

Days

Number

Number

P er c e n t

P er c e n t

0

U
S
U
S
0

20
15
19
IS
13

185
128
igU
17U
189

36.3
100.0
100.0
100.0
100.0

2U.9
S 3 .b
S.2
5 1 .7
U0 . 2

b
US

6-

R ecorded 1C days a f t e r i n o c u l a t i o n .

I n f lu e n c e o f A ir Temperature and M oisture on S n o r u ln tio n
G -lb b erella zene

The p r e c e d in g s e c t i o n d e a l t p r i n c i p a l l y w ith the i n i t i a l
e s t a b lis h m e n t o f i n f e c t i o n and subsequent d i s e a s e development as in ­
f l u e n c e d by tem p erature anu m o is t u r e .

T h is s e c t i o n i s d ev o ted to a

s tu d y o f the r e l a t i o n o f t h e s e f a c t o r s to s p o r u la t io n on wheat heads,
a f e a t u r e which i s

important to th e secondary spread of the fu ngus un­

der f i e l d c o n d i t i o n s .

In the f i r s t s e t o f e x p e r im e n ts , the p l a n t s were

i n o c u l a t e d and ex p o sed f o r U8 hours t o c o n tin u e d w e tn e ss a t 25° C. and
th e n in c u b a te d on th e g reen h o u se bench f o r a week u n t i l the symptoms
were w e l l d e v e lo p e d and some o f th e s p i k e l e t s k i l l e d .

At th e end o f

t h i s p e r io d , s e v e r a l o f th e p l a n t s were r e - e x p o s e d to c o n tin u e d w etn ess
fo r in d e f in it e p e r io d s.

Wheat heads were removed a t r e g u la r i n t e r v a l s ,

washed i n w a te r, and c o n i d l a l c o u n ts made to determ ine the number o f coni d i a p r e s e n t on the h e a d s .

The r e s u l t * from one o f chese ex p erim en ts

a re p r e s e n t e d in T able 23*

The seco n d s e t o f e x p e rim en ts c o n s i s t e d o f

p l a n t s which were in o c u l a t e d and p l a c e d im m ed ia tely in the t e n t s f o r
i n d e f in it e p e r io d s.

Heads were removed from t h e s e p l a n t s a t f i x e d i n ­

t e r v a l s and th e number o f c o n i d i a were d e te r m in e d .

The r e s u l t s from a

r e p r e s e n t a t i v e experim en t a r e p r e s e n t e d i n Table 2 b .

In t h i s way reason­

a b le e s t i m a t i o n s o f the number o f d a ys r e q u ir e d f o r c o n id i a to be pro­
duced and the r a t e a t which th e y were produced were o b t a in e d .
D i f f e r e n c e s i n s p o r u l a t i o n were e n co u n tered on the heads o f
wheat which a lr e a d y had i n f e c t i o n w e l l e s t a b l i s h e d when th ey were p la c e d
in th e hum idity t e n t s and e x p o sed to c o n tin u e d w e tn e ss f o r v a r io u s per­
i o d s a t te m p e r a tu r e s o f 15°» 2 0 ° , 2 5 ° , and 30° C.

(T able 2 3 ) .

A few

- 77 -

T able 2 3 . — S p o r u la t io n o f G ib b e r e l l a z ea e on i n f e c t e d heads
o f p l a n t s exp osed f o r d i f f e r e n t l e n g t h s o f tim e t o c o n tin u e d w e tn e ss
a t 1 5 ° . 20°» 25° and 3O0 C. i n th e h u m id ity t e n t s . a

Temperature
d e g r e e s C.

Hours o f exposure to m o istu re
2Ub

1+8

72
2.62

15

0.00

O.3I+

20

0 .2 3

3 -1 0

11.88

25

0.63

1+.27

lU .ll

30

0.31

I .63

5 -1 1

V a lu e s r e p r e s e n t a v e r a g e number o f c o n i d i a , in m i l l i o n s , from 3 h e a d s.
b

No c o n i d i a v/ere -present on t h o s e heads removed a f t e r 12 h ou rs e x p o su r e.

T able 2 4 . — S p o r u la t io n o f G i b b e r e l l a z ea e on heads o f
wheat i n o c u l a t e d in t h e f l o w e r i n g s t a g e and e x p o s e d to c o n tin u e d
w e tn e s s a t 2 0 ° , 25°»
30° C.
th e h u m id ity t e n t s . a

Temn.
0 C.

Hours o f e x p o su re to m o is tu r e
7?b

9b

120

144

20

0.00

0.00

0 .1 5

5.00

25

0.58

l.c O

8.19

30.82

30

0 .2 7

1.51

13.44

1 7 .6 4

a V a lu e s r e p r e s e n t a v e r a g e numbers o f c o n i d i a , i n m i l l i o n s , from
3 wheat h e a d s .
^ No c o n i d i a were p r e s e n t on t h o s e h e a d s removed a f t e r 48 h ou rs
o f expo s u r e .

- 79 c o n i d i a v/ere p r o d u ce d a f t e r 2U h o u rs o f e x p o s u r e a t th e t h r e e h ig h e r
tem p era tu res.
a t 1 5 ° C.

C o n id ia w ere p r o d u c e d in US h o u rs on the h ea d s e x p o sed

I n a p r e v i o u s e x p e r im e n t i n w h ich h e e d s w ere removed from

p l a n t s a f t e r 1 2 , 1 8 , and 2U h o u rs e x p o s u r e ,
on t h o s e removed a f t e r 2*4- h o u r s .
C.

c o n i d i a w ere p r o d u ce d o n ly

The most c o n i d i a were p r o d u ce d a t 25°

The b e s t t e m p e r a t u r e s f o r s p o r u l a t i o n w ere 20° and 25° C.

At t h e s e

te m p e r a tu r e s an a v e r a g e o f 3- ! '(- m i l l i o n c o n i d i a were p r o d u ce d on e a ch
h ea d i n k S h o u rs and 1 2 - lU m i l l i o n in ~f2 h o u r s .
S l i g h t l y d i f f e r e n t r e s u l t s were o b t a i n e d in t h o s e s t u d i e s on
s p o r u l a t i o n i n v o l v i n g p l a n t s e x p o s e d c o n t i n u o u s l y to m o is t u r e from th e
tim e o f i n o c u l a t i o n (T a b le 2 U ) .

In t h i s s e r i e s o n l y th e 2 0 ° ,

3 0 ° C. te m p e r a tu r e t e n t s were u s e d .

25° and

I n i t i a l e x p e r im e n ts i n d i c a t e d t h a t

a t l e a s t U days w o u ld be n e c e s s a r y f o r c o n i d i a to be p r o d u ce d on wheat
h e a d s t r e a t e d i n t h i s manner and e x p o s e d a t any o f th e above m entioned
tem p era tu res.
a t 20

o

I n t h i s e x p e r im e n t (T a b le 2U) a fe w c o n i d i a v/ere o b s e r v e d

C. 3 d a y s a f t e r i n o c u l a t i o n ,

p e r h ead a f t e r 6 d a y s .

and an a v e r a g e o f 5 m i l l i o n c o n i d i a

At 25° C ., an a v e r a g e o f 3^ m i l l i o n c o n i d i a were

p r o d u c e d on e a c h head c days a f t e r i n o c u l a t i o n .

V ery s i m i l a r r e s u l t s

v/ere o b t a i n e d on a s e r i e s o f Cadet wheat p l a n t s w h ich r e c e i v e d s i m i l a r
treatm en ts.

I t i s e v i d e n t t h a t a. l o n g e r tim e was r e q u ir e d f o r c o n i d i a

t o be p ro d u ced on p l a n t s i n o c u l a t e d and e x p o s e d c o n t i n u o u s l y t o m o is tu r e
th a n on p l a n t s w h ic h a l r e a d y had d i s e a s e l e s i o n s p r e s e n t on t h e i r heads
a t th e tim e t h e y w e re s u b j e c t e d t o c o n t in u e d w e t n e s s .

T h is i s p r o b a b ly

b e c a u s e th e f u n g u s must e s t a b l i s h i t s e l f i n t h e h o s t t i s s u e b e f o r e i t
can b e g i n t o reproduce.

- 80 -

To o b t a i n f u r t h e r

i n f o r m a tio n on s p o r u l a ti o n o f G -lbberella

zeae on i n f e c t e d w heat heads u n d er d i f f e r e n t te m p e ra tu re c o n d itio n s ,
such h e a d s w ere rem oved from t h e p l a n t s and p l a c e d i n w a t e r .
were d i v i d e d i n t o

seven l o t s

b e r p r e p a r e d by l i n i n g a
covering i t

an d .each lo t

UooO-ml.

w ith a g la ss p la te .

v a l s f r o m 8° t o 3 ‘° °
hours and a t

C.

G.

In th is

th ere after for

m idity
than a t
cate

ten ts.
l o ° C.

the f i r s t

60

h o u r s and a t

The t o t a l num ber o f c o n i d i a p r e s e n t

2U° a n d 2 3 ° 0 .

respect

s m a l l h u m i d i t y cham­

The h e a d s w e r e i n c u b a t e d a t h ° i n t e r ­

on e a c h sample was d e t e r m i n e d ( T a b l e

w ere being- p r o d u c e d a t

a

b e a k e r w i t h m o i s t p a p e r t o w e l i n g and

2U-hour i n t e r v a l s .

w i t h i n Us h o u r s a t

in

T h r e e h e a d s w e r e r e m o v e d f r o m e a c h s e t a f t e r 12

12-hour in te r v a ls

two s u b s e q u e n t

put

The h e a d s

25).

A few c o n i d i a were p ro d u ced

A fte r 3 o r U days,

numerous conidia.

t e m o e r a t u r e s f r o m 2 0 ° t o 3 2° C. a n d a. f e w a t

these re s u lts

lv°

a g r e e w i t h t h o s e o b t a i n e d i n t h e hu­

M ore s p o r u l a t i o n o c c u r r e d a t

1 5 ° C. i n t h e h u m i d i t y t e n t

in the

The r e s u l t s ,

th e range o f

sm all m o is t cham ber.

however,

s p o r u l a ti o n w hich can b e e x p e c te d a f t e r

p e rio d s o f exposure to

high h um idity

Th e r e s u l t s p r e s e n t e d i n

at d iffe re n t

the p rec e d in g

indi­

differen t

tem peratures.
s e c tio n s i n d i c a t e the

i m p o r ta n t p o r t p l a y e d by m o is t u r e and te m p e ra tu re i n the developm ent o f
G ib b e re lla h ead b lig h t e p ip h y to tic s .

i'.To t o n l y do t h e s e

flu e n c e the e sta b lish m e n t of ix ifectio n ,
and the
It

but

they in flu e n c e

in­

t h e numbers

r a p i d i t y a t w hich c o n id i a e r e p ro d u ce d o n th e i n f e c t e d h e a d s.

would be d i f f i c u l t t o

estim a te the

a c t u a l numbers o f c o n i d i a which

would be p ro d u c e d w i t h i n 2-3 d ay s i n a f i e l d o f
optimum c o n d i t i o n s f o r
th at

two f a c t o r s

th is

i n f e c te d wheat under

s p o r u l a t i o n and b l i g h t d e v e lo p m en t.

f u n g u s wa s c a p a b l e o f e s t a b l i s h i n g

itself

The f a c t

in the h o st t i s s u e

T able 2 5 -— S p o r u la t io n o f G ib b e r e lla z ea e on i n f e c t e d wheat
h ead s removed from th e p l a n t s and in c u b a te d f o r d i f f e r e n t p e r i o d s i n
s m a ll m o is t chambers a t d i f f e r e n t t e m p e r a t u r e s .a

Hours o f ex p osu re to h ig h h u m id ity

Temp,
o C.
p'q."0
8
12
lb
20
2b

28
32

0.00
0.00
0.00
0.00
Few
0.02
0.00

3S

US

6o

8U

0.00
0.00
0.00

0.00
0.00
0.02
0.02
0.06
2.26
2.12

0.00
0.02

0.00

Few
o.oU
1.86
2.00

0.06
O.Oo
2 .9 8
U.22
2 .9 8

0.02
0.10
2.06
U.Oc
U.66
3 .8 2

108
Few
0.02
0 . 1U
5 -9 2
10.22
12.00
8.00

a D ata r e p r e s e n t s t h e t o t a l number o f c o n id ia , i n m i l l i o n s , from U
heads.
^ ITo c o n i d i a were produced i n 12 h o u r s .

w i t h i n ?U-36 hours a t 25° C. and, i n a d d i t i o n , was a b le to produce
o n e - h a l f m i l l i o n new c o n i d i a on each i n f e c t e d wheat head w ith in 72
hours,

i s a p a r t i a l e x p la n a t io n o f why t h e organism i s a c o n s ta n t

t h r e a t to wheat c ro n s th roughout the g r a m a r e a s .

H elm inthosoorium sativum

The e x t e n t o f s p o r u l a t i o n on wheat h eads a s i n f l u e n c e d by
tem p era tu re and m o is tu r e was d em on strated i n two s e r i e s o f e x p e r im e n ts .
In th e f i r s t s e r i e s ,

i n f e c t e d p l a n t s w ith w e l l d e v e lo p e d K elm in th osoo r-

iurn h e a d b lig h t symptoms were p l a c e d i n th e h u m id ity t e n t s and exposed
f o r s e v e r a l d a ys to c o n tin u e d w e tn e s s a t 1 5 ° , ? 0 ° , 2 5 °, and 30° C.
'wheat heads were removed a t 2^1—hour i n t e r v a l s and the number o f c o n id ia
p r e s e n t on the wheat heads were d e te r m in e d .
t h e s e e x p e r im e n ts a r e p r e s e n t e d i n Table 2b.

The r e s u l t s from one o f
C onid ia were produced on

th e heads i n Uf> h ou rs a t a l l th e te m p e r a tu r e s, w ith th e maximum number
a t 25° C.

In a s i m i l a r experim ent a few c o n id ia were produced w ith in

2h h ou rs a f t e r th e p l a n t s were e x p o s e d to m o is tu r e a t 25° C.

There was

no s t r i k i n g i n c r e a s e i n s p o r u l a t i o n from day to day a s was o b s e r v e d
v'hen G -ibberelle i n f e c t e d lie ads were g iv e n th e same t r e a tm e n t.
In the second s e r i e s of e x o e r im e n ts on s p o r u la t io n the p l a n t s
were i n o c u l a t e d and e x o o se a c o n t in u o u s ly to c o n tin u e d w e tn e s s a t 20° ,
2h°

30° C. i n th e hu m idity t e n t s .

Wheat heads were removed f o r ex­

a m in a tio n a t 2U-hour i n t e r v a l s from th e tim e o f i n o c u l a t i o n .

The r e ­

s u l t s from th r e e o f t h e s e e x o e r im e n ts v/ere p r a c t i c a l l y i d e n t i c a l i n
.

t h a t t h e f i r s t new s p o r e s were formed 4—5 &ay s a f t e r i n o c u l a t i o n a t 25
o r 30° C.

A lth o u gh abundant i n f e c t i o n was e s t a b l i s h e d , r e l a t i v e l y few

c o n i d i a were p rod u ced on the wheat heads even w ith b days exposure to
c o n tin u e d w e tn e s s a t 25° or 3 0 ° C.

o

T able 2 b .— S p o r u la t io n o f HelminthoBporium sativum on
i n f e c t e d heads o f p l a n t s exp osed f o r d i f f e r e n t l e n g t h s o f tim e to
c o n tin u e d w e tn e ss a t 15°» 20° , 25° , and 30° C*
the h u m id ity
ten t s . a

Temp.
o C

Hours o f e x p o su re to c o n tin u e d w e tn e ss
4 gb

72

96

120

15

0.09

0.09

1.02

1.03

20

0 .U7

0.88

1 .0b

1 .4 6

25

0 .S 3

1 .5 7

1 .5 7

2 .1 9

30

0.13

0 .3 2

O.Sb

1.22

a V a lu e s r e p r e s e n t a v e r a g e number o f c o n i d i a , i n m i l l i o n s , on 3 h e a d s.
b

i
No c o n i d i a were p r e s e n t on t h o s e removed a f t e r 24 hours e x p o s u r e .

A s tu d y wps made to d eterm in e the tem perature range f o r
s p o r u l a t i o n o f H. sa tivu m on i u f e c t e d wheat h e a d s .

The same methods

were u s e d as i n the experim ent w ith G. zeae e x c e p t t h a t fo u r heads
were removed from each s e t a t PH-hour i n t e r v a l s fo r 6 days (T able 27) .
I t to ok tw ic e as
as i t

d id i n

lo n g f o r o o n id ia t o be produced in the m o is t chambers

the hum idity t e n t s ,

ho c o n id ia w ere produced below l 6°

and above 28° C. du rin g the b-day p e r i o d .
a t 2U° and 28° C.

I-Caximum s p o r u l a t i o n occu rred

These r e s u l t s a g r ee c l o s e l y w ith th o s e o b t a in e d on

the e f f e c t o f tem p erature on s p o r u l a t i o n o f H. sativum on bean pod agar.
I t a p p ea r s from
sativu m

th e s e i n v e s t i g a t i o n s th a t Helminthosporium

does not nave th e n e c e s s a r y s o o r u la t in g p o t e n t i a l which appears

e s s e n t i a l f o r th e r a p id spread of the d i s e a s e i n the f i e l d .
be one reaso n why i t
grow ing a r e a s .

This may

seldom a t t a i n s e p i p h y t o t i c p r o p o r tio n s i n wheat

It is,

however, n o r m a lly found i n f e c t i n g a c e r t a i n

amount of g r a in e v e r y year in s u f f i c i e n t q u a n t i t i e s to lov;er the com­
m e r c ia l v a lu e o f th e c r o p .

T ab le 2 7 - — S p o r u l a t i o n o f K e lm in th o s t > q rium sa tiv u m on
i n f e c t e d wheat h ea d s removed from t h e p l a n t s and in c u b a te d f o r
v a r i o u s p e r i o d s i n s m a ll m o ist chambers a t d i f f e r e n t t e m p e r a t u r e s . a

Temp.
O C
r> .

Hours o f e x p o s u r e to h ig h h u m id ity
72°

95

120

144

16

0 .0 0

0 .0 0

0 .0 0

0 .1 1

20

0.00

Few

Few

0 .1 0

24

0.00

0.11

0 .1 8

1.10

22

Few

0.25

0.73

1 -7 9

a Data r e p r e s e n t s t h e t o t a l number o f c o n i d i a , i n m i l l i o n s , p ro d u ced
on 4 h e a d s .
D Ho c o n i d i a were p ro d u ced i n 24 and 4-8 h o u r s .

E f f e c t o f Mixed Inoculum on D is e a s e I n c id e n c e
Two e x p e r im e n ts were condu cted i n o rd er t o compare th e
amount oi s e e d i n f e c t i o n which would occu r wlien mixed s u s o e n sio n a
Cribberel l a

z ea e and Helm inthosporium sativum c o n id ia were m rolied

to p l a n t s in the p a s t - f l o w e r i n g s t a g e .

The approxim ate c o n c e n t r a t io n s

o f the c o n id i a u se d in t h e s e e x p e r im e n ts a r e g i v e n i n Table 2 8.

The

i n o c u l a t e d p l a n t s were e x p o se d to c o n tin u e d w e tn e s s f o r U-8 hours a t
two d i f f e r e n t te m p e r a tu r e s i n ea ch e x p e r im e n t.

In the f i r s t t e s t ,

th e te m p e r a tu r e s v e r e 2 k - 2 u ° and 29- 30° . , and i n the second , 2U -25°
and 2 7 -2 9 ° C ., r e s p e c t i v e l y .

At m a tu r ity the wheat was h a r v e s t e d ,

the s e e d s u r fa c e d i s i n f e c t e d in a 5 p e r c e n t C hlorox s o l u t i o n and
p l a t e d on 1 p er c e n t w a ter a g a r .

A l l the k e r n e l s showing i n f e c t i o n

were examined w ith th e 10X low p o w e r o b j e c t i v e of th e m icr o sc o p e in
o r d e r to determ ine i f one or b o t h f u n g i were o r e s e n t .

The p e r c e n ta g e

o f th e k e r n e ls i n f e c t e d w ith each fu n g u s i s p r e s e n t e d i n T able 28 .
Some i n h i b i t i o n i n i n f e c t i o n was n o te d w ith c e r t a i n c om b in atio n s o f
mixed c o n i d i a l in ocu lu m .

For exam ple. H. sativum a p p lie d to p l a n t s

a t 0 . 1 m i l l i o n c o n i d i a p e r p o t , r e s u l t e d in th e i n f e c t i o n o f 1 8 . 9 ,
2 2 . 0 , 2 2 . 0 and 2 1 .4 p er c en t of th e k e r n e l s , r e s p e c t i v e l y , a t each o f
the lev.' t e m p e r a t u r e s .

When th e came number of c o n iu ia were a p p lie d

mixed w ith 1 . 0 m i l l i o n G. zeae c o n i d i a , th e number o f s e e d s i n f e c t e d
were 0 . 0 , 1 0 . 0 , 1 0 . 0 and 6 . 0 p er c e n t r e s p e c t i v e l y , a r e d u c t i o n o f
o v er 50 per c e n t .

S im ila r r e s u l t s were o b t a in e d when low c o n c e n tr a ­

t i o n o f G. zeae was a p p l i e d t o g e t h e r w it h h ig h concent ra .tio n of H.
s a t iv u m .

Thus, 3 2 . 2 ,

l b . 6 , 6 b . 7 and l b . 6 per c e n t o f s e e d s became

i n f e c t e d when 0 . 1 m i l l i o n G. zeae c o n id ia were a p p lie d to p l a n t s a s
compared to 8 . 9 , 6 . 0 , lU .U , and l . U per c e n t i n f e c t e d k e r n e l s w ith

Table 2 8 .— E f f e c t o f i n o c u l a t in g p la n ts v-ith a mixed c o n i d i a l suspension o f G-ibberella
zeae and H eiaintho soorium sa tiv u m .a

P l a n t s in o c u la te d w ith
H. sativum

G. zeae

Temperature - D egrees C.
2U-25 C

27-29 b

25- 26c

Ho. c o n id ia per p ot

29- 30°

I n f e c t e d seed s - per cent
H. s_.

H .s .

G. z..

H.S.

G. z_.

i+s.o

1 0 .0

^7-7

6.0

5 2 .0

7 7 -^

5.0

5^ -5

1U.U

1+6 .0

l.U

k S .l

51 >

32.6

u7-7

17.8

2 6 .0

12.0

22.2

23 .3

20. b

2U.0

2U.U

30.0

2 2 .0

7 •U
V

0.0

8S . “

0.0

70.0

0.0

7 °-7

0.0

35.^

0.0

O.G

1.0

G. 0

7 1 .1

57 >

0.0

75 0

0.0

cc.O

a

0.1

0.0

1 8 .3

0.0

2 2 .5

0.0

22 .0

o .c

21.k

0.0

K

C.G

0 .1

0.0

32.2

0.0

lb .6

0.0

oc .7

O.G

16 .0

0.0

G.O

0.0

0.0

0.0

0.0

0.0

o .c

0.0

0.0

E .s.

M illio n s

l<i i l l i o n s

A

0.1

1.0

0.0

08.9

1 0 .0

£

1.0

0 .1

76.7

S .s

C

1.0

1.0

^8.3

D

0.1

C .l

S

l.C

F

Control

0 .G

a P la n ts in p a s t - f lo w e r in g s ta g e at i n o c u l a t i o n .

Exposed Ug hours to continued w e tn e ss .

^ F i r s t experim ent. Conducted i n t r i p l i c a t e - 50 seeds p la t e d from each not of n l a n t s .
£
Second experim ent. Conducted ir. t r i p l i c a t e - 30 seeds p la t e d from each pot o f p l a n t s .

- gg -

G. z e a e when th e same q u a n t i t y was a p p l i e d t o g e t h e r w it h 1 . 0 m i l l i o n
H. satlvujn c o n i d i a .

L ik e w is e , th e a p p l i c a t i o n s o f b o t h p a th o g e n s to

p l a n t s i n n i g h c o n c e n t r a t i o n s r e s u l t e d in a s i g n i f i c a n t d e c r e a s e in
th e number o f s e e d s i n f e c t e d w ith e a ch p a t h o g e n .

For i n s t a n c e , H.

sa tiv u m a lo n e i n f e c t e d 8 9 , 7 7, 77 and 55 per c e n t o f th e s e e d s , r e s p e c ­
t i v e l y , a t e a c h o f the 4 t e m p e r a t u r e s .

When a p p l i e d t o g e t h e r w ith an

e q u a l number o f G. z e a e c o n i d i a o n l y 4 9 , 5 1 , 4g and 26 p e r c en t o f th e
s e e d s became i n f e c t e d w it h H. s a t i v u m .

C o r r e sp o n d in g ly , G. z ea e a lo n e

i n f e c t e d 7 1 . 5 7 . 7^. and 66 p e r c e n t o f th e s e e d s , w hereas in combin­
a t i o n w it h 1 . 0 m i l l i o n H. sa tiv u m c o n i d i a 4 7 , 3 3 . 18 and 12 p e r c e n t
o f t h e s e e d s became i n f e c t e d .

In f a c t ,

in some i n s t a n c e s r e d u c t io n

was so g r e a t t h a t th e t o t a l number o f i n f e c t e d s e e d s was l e s s w ith the
combined inoculum th a n when e i t h e r was a p p l i e d a lo n e , even th ough tw ic e
a s many c o n i d i a v/ere n p n lie d p e r p o t .

Thus, i t a pp ears t h a t

the p r e s ­

e n ce o f a f a i r l y h eavy c o n c e n t r a t i o n o f c o n i d i a o f G. z e a e and H. s a t i ­
vum on p l a n t s .'nay r e s u l t in a r e d u c t i o n i n the i n f e c t i v i t y o f e i t h e r
o r b o t h o r g a n ism s,

depending o f c o u r s e ,

upon th e c o n i d i a l c o n c e n t r a t i o n

o f e a c h a t the tim e o f a p p l i c a t i o n or. th e h o s t .
There was t h e p o s s i b i l i t y ' t h a t th e tem p er a tu r e d u rin g th e
p e r i o d o f e x p o s u r e to c o n tin u e d w e t n e s s may have i n f l u e n c e d th e amount
o f s e e d i n f e c t i o n b y G i b b e r e l l a z e a e when mixed c o n i d i a l inoculum was
a p p l i e d to t h e p l a n t s .

T h is was e s p e c i a l l y n o t i c e a b l e when b o th p ath og en s

were a p p l i e d i n m ix tu r e o f 1 . 0 m i l l i o n c o n i d i a e a c h .

In t h i s c a s e , th e

number o f k e r n e l s i n f e c t e d w i t h G. zeae d e c r e a s e d from a h ig h a t 24-25°
C. to a low a t 2 5 - 3 0 ° C ., th e amount o f i n f e c t i o n b e in g 4 7 , 3 3 . 1 8, and
12 p e r c e n t , r e s p e c t i v e l y , a t th e v a r i o u s te m p e r a tu r e s .

In g e n e r a l ,

t h e r e was a te n d e n c y f o r a r e d u c t i o n i n th e number o f s e e d s i n f e c t e d by

- 89 b o t h o r g a n i s m s a t t h e h i g h e s t t e m p e r a t u r e s (.2 3-3 0° Cv.

T h is i s

fu rth er

i n d i c a t i o n t h a t 3 0 ° C* i s ao,t q u i t e a s f a v o r a b l e a t e m p e r a t u r e f o r i n ­
f e c t i o n b y e i t h e r H.
2 5-23°

C.

I t a lso

in w h ic h i t

s a tiv u m or G. ? e a e a s a r e t h o s e t e z r o e r n t u r e s from

c o n fir m s t h e r e s u l t s o b t a in e d i n p r e v io u s e x p e rim en ts

a p p e a r e d t h a t K. s a t iv u m wrs a more a c t i v e p a t h o g e n a t 29- 3 0 °

C. t h a n G. z e a e .
C h r i s t e n s e n and Stakman ( 1 5 ) fo u n d t h a t b a r l e y s e e d s i n f e c t e d
w i t h F u s a r iu m -were g e n e r a l l y i n f e c t e d a l s o w i t h H e l m i n t h o s o o r i u m .

In

t h e p r e s e n t s t u d i e s 1 9 2 0 'wheat s e e d s v/ere p l a t e d fr o m t h e m ix e d s u s p e n ­
s i o n s e r i e s t o d e t e r m i n e t h e p r e v a l e n c e o f G - ib b e r e lla
Of t h i s

to ta l,

z e a e and H. s a t i v u m .

3 ^+ n e r c e n t v/ere i n f e c t e d w i t h H e lm ln t h o s p o r iu m s a t i v u m .

? o p e r c e n t w i t h G i b b e r e l l a z e a e and 0 . 0 1 2 n e r c e n t w i t h b o t h f u n g i .
F u r t h e r m o r e , m o st o f t h o s e s e e d s w h ic h becam e i n f e c t e d w i t h b o t h f u n g i
w ere fro m t h e c l a n t s i n o c u l a t e d w i t h m ix e d s u s p e n s i o n c o n t a i n i x i g h i g h
c o n c e n t r a t i o n s o f b o t h f u n g i anc. w h ic h w ere e x p o s e d t o c o n t i n u e d w e t n e s s
a t 2 7 - 2 9 ° C. f o r hS h o u r s .
mum tem p eratvU ’e f o r

T h is ten rceratu re i s v e r y c l o s e

t o th e o p t i ­

th e g r o w t h o f b o t h p a t h o g e n s .

DISCUSSIOIT
A l t h o u g h G i b b e r e l l a z e a e and H e lm in th o s o o r ium s a t iv u m a r e v e r y
d i f f e r e n t m o r p h o lo g ic a lly , t h e ir b e h a v io r i n r e s p o n se to
a t u r e and m o i s t u r e c o n d i t i o n s w as v e r y much t h e sa m e .

s i m i l a r tem p er­

T h is

s i m i l a r i t y was

e v e n noted , i n t h e t y p e s o f symptoms p r o d u c e d o n p l a n t s w h ic h w e r e in o c u ­
l a t e d . i n th e d i f f e r e n t

s t a g e s o f d e v e lo p m e n t.

T h is l i k e b e h a v io r o f th e

two o r g a n i s m s may p o s s i b l y a c c o u n t f o r t h e i r f r e q u e n t o c c u r r e n c e t o g e t h e r
i n i n f e c t e d w h e a t s e e d l o t s and o n w h ea t h e a d s i n t h e f i e l d .

SO

-

-

But even th o u g h t h e i r g e n e r a l b e h a v io r in r e s p o n s e to v a r io u s
e n v i r o n m e n t a l f a c t o r s w as v e r y much t h e sam e,

th e r e w ere s m a ll d i f f e r ­

e n c e s i n t h e i r r e a c t i o n t o m o i s t u r e and t e m p e r a t u r e a s w e l l a s o t h e r f a c ­
t o r s w h ic h m ig h t p o s s i b l y e x p l a i n t h e d i f f e r e n c e s i n p r e v a l e n c e o f t h e s e
two p a t h o g e n s from s e a s o n to
and Stakm an ( 1 5 )

se a s o n a s n o te d b y P o r te r (57 )»

a n d H anson and C h r i s t e n s e n ( 3 0 ) .

C h r iste n se n

F iv e p o s s ib le fa c to r s

r e l a t i n g to th e p r e v a le n c e o f t h e s e fu n g i w ere e n c o u n te r e d d u rin g th e
presen t

s t u d i e s a n d may b e e n u m e r a t e d a s f o l l o w s :

(l)

d i f f e r e n t a m ou n ts o r q u a n t i t i e s o f c o n i d i a l in o c u lu m ;
in r e a c t io n a t th e h ig h e r te m p er a tu r e s;
lis h e d

d u r in g s h o r t w e t n e s s p e r i o d s ;

(U)

(3)

Tne e f f e c t s o f
(? )

th e a b i l i t y

th e d i f f e r e n c e s

th e d iffe r e n c e s

t o becom e e s t a b ­
in t h e i r snoru-

l a t i n g a b i l i t y u n d e r d i f f e r e n t c o n d i t i o n s o f t e m p e r a t u r e rnd m o i s t u r e ;
and ( 5 )

th e e f f e c t

o f o n e p a t h o g e n on t h e o t h e r when t h e two w ere a p p l i e d

t o g e t h e r on p l a n t s .
D i f f e r e n t a m o u n ts o f c o n i d i a l in o c u lu m w e re shown t o a f f e c t
t h e amount a n a t h e s e v e r i t y o f w h ea t h e a d b l i g h t .
w o u ld b e e n t i r e l y

s o il.

th e c o n tr o l m easures a p p lie d .

e lla

th is

d e p e n d e n t u p o n t h e p r e v a l e n c e o f t h e p a t h o g e n s on

d ea d c r o p r e f u s e and i n t h e

M a in e 8 ( 2 3 ) .

I n th e f i e l d

T h erefo re,

it

w o u ld be a f f e c t e d by

M a c ln n e s a n d F o g e lm a n ( ^ ) , D i c k s o n and

M uncie ( ^ 8 ) , K o e h l e r ( U l ) and o t h e r s s u g g e s t t h a t G-ibber-

h e a d b l i g h t c a n b e k e p t t o a minimum by u s i n g c l e a n s e e d , p r a c t i c ­

in g f i e l d

sa n ita tio n ,

p r a c t i c e s w o u ld a l s o

and b y u s in g p ro p er crop r o t a t i o n .

The same

t e n d t o r e d u c e t h e p r e v a l e n c e o f H e lm in th o s p o r iu m

h e a d b lig h t.
Tne t e m p e r a t u r e a t t h e t i m e o f i n f e c t i o n p r o b a b l y w o u ld i n ­
f l u e n c e t h e g e n e r a l p r e v a l e n c e o f t h e s e two p a t h o g e n s .

I t w as n o t e d

t h r o u g h o u t t h e p r e s e n t i n v e s t i g a t i o n s t h a t H e lm ln t h o s p o r iu m s a t iv u m

- 91 ap p eared to
th erefo re

te

a sim ilar
hot

tab lish m en t
iods
of

of

the

a m ore

did

a b ility

to

caused

in fect

th e

zeae

in

dews w ere

p lan ts

wheat

tiiat

these

which, new c o n i d i a

num bers

of

co n id ia

v'ould b e

when optim um

s p r e a d much m ore
co n d itio n s

F in ally ,

the

of

th e

stu d ies,

the

to g eth er
the

to

th e

in

tio n .

F u rth erm o re,

su p p ressio n of
the

of b o th p athogens

p ath o g en s.

It

a low

m ight

w ould be o f

tnan

r>er

-

in

it

G ibber-

and heavy

form ed on

in

iind s e v e r i t y o f
the

of

resu lt

in te rest

in

the

th e

of

the

inves­

sativum

these

the

inves­

field

developm ent

of

was
the

and g re e n ­

of co n id ia

of

t h e one

o t h e r p a th o g e n w ould

present

in a m arked

in

in

lab o rato ry

in

ap p ro x im ately

to

present

occurred.

im p o rtan ce

c o n cen tratio n s

p ath o g en

en v iro n m en tal

He 1 m i n t h o s p o r i u r n

path o g en upon
o b tain ed

in fected

z e a e w o u ld b e much m ore

developraeiil

c o n cen tratio n

presence

yjeriods,

abundant

w h ich was e n c o u n t e r e d

high

the

short

d ifferen ce

p rev alen t

o lt; ined

than

co n sid erab le

of

th is

prevalence

G ib b erella

rap id ly

one

es­

and p rev alen ce

exposure

w ere

the

resu lts

tliat

resu lts

presence
w ith

of

facto r

of

of

th e

th at

produced under d if f e r e n t

h ead b lig h t

last

oresence

resu lt

tio n s

for

a n d w h i c h may b e o f

A ccording

o ath o u en

expected

favor

m o istu re.

in flu en ce

On t h e b a s i s

to

appeared

was l e a s t

at

and

house

of

w ould p r o b a b l y a ls o

it

w o u ld b e m ore

rap id ity

o rev alen t

o th er.

source

fie ld .

appear

short

The

it

effect

rela tiv e ly

sativum

the

Because

p rin cip al

tig a tio n s

th e

K.

p ath o g en .

in

in

te m p e r a t'o r e a ;m d

tine e s t a b l i s h m e n t

s e a s o n s when r a i n f a l l

h ead b lig h t.

tig a tio n s

sativ u m , but

the

ana the

co n d itio n s

heads

h i-h er

tem peratures

w ould f a v o r

by t h i s

the

"be e x p e c t e d

a ir

H eln in th o sn o riu m

w ould be e x p e c te d
e lla

m ight

h ig h er

co n tin u e d w etness
disease

p ath o g en a t

response

only

of

n ativ e

the

low er

equal high
su p p ressio n

com pare t h e

co n centra­

concentra­
of both

o b serv atio n s

made I n

- y2 these

e x p e r im e n ts t o th e g e n e r a l p r e v a l e n c e o f b o t h o a th o g e n s i n the

field ,

e s p e c i a l l y d u rin g G ib b e r e lla h ea d b lig h t or scab e p i p l y t o t i c s

when i t

c o u l d be e x p e c t e d t h a t H e l m i n t h o s p o r l u m s a t i v u m i n f e c t i o n would

b e v e r y much s u p p r e s s e d e v e n i f

c o n d i t i o n s were f a v o r a b l e f o r

i t s develop­

ment .
Of e s p e c i a l , s i g n i f i c a n c e t o t h o s e i n v e s t i g a t o r s

in v o lv e d in the

c o n t r o l o f h e a d h l i g h t by b r e e d in g f o r d i s e a s e r e s i s t a n c e ,

was t h e v a r i o u s

amount o f i n f e c t i o n and t h e s e v e r i t y o f h e s a b l i g h t d e v e l o p m e n t u n d e r
d i f f e r e n t t e m p e r a t u r e and m o i s t u r e c o n d i t i o n s an d d u r i n g d i f f e r e n t
o f p la n t developm ent.

stages

Wheat v a r i e t i e s a r e o r d i n a r i l y t e s t e d f o r r e s i s t a n c e

i n t h e f i e l d where c o n d i t i o n s v a r y from day t o day and fr om s e a s o n t o
season.

Very s e l d o m ,

'under t h e s e

conditions,

are a l l p la n ts

i n t h e same

s t a g e o f d e v e l o p m e n t a t t h e t i m e t h e p l a n t s a r e i n o c u l a t e d and a t t h e
tim e t h a t f a v o r a b le
ex ist.

c o n d i t i o n s f o r i n f e c t i o n and h e a d b l i g h t d e v e l o p m e n t

Therefore i t

w o u ld b e e x p e c t e d t h a t v a r i o u s d e g r e e s o f i n f e c t i o n

may b e p r e s e n t and t h a t many p l a n t s may e s c a p e i n f e c t i o n e n t i r e l y .
a p p e a r s s i g n i f i c a n t t o ke e p i n m in d t h e c o n c l u s i o n o f C h r i s t e n s e n ,
man and Immer ( l o )

that

It
St pie­

" C o n s i d e r a b l e c a u t i o n i s n e c e s s a r y i n dr a w in g

c o n c l u s i o n s from t h e r e s u l t s o f v a r i e t a l t e s t s u n l e s s t h e y a r e c o n d u c t e d
for

s e v e r a l y e a r s u n d e r c a r e f u l l y r e p l i c a t e d and c o n t r o l l e d c o n d i t i o n s . "
A l t h o u g h t h e e x p e r i m e n t s on p a t h o g e n e s i s were c o n d u c t e d i n

the g reen h o u se,

t h e r e s u l t s s h o u l d p r o v e o f v a l u e to t h o s e e n g a g e d i n

c o n t r o l l i n g wheat h e a d b l i g h t th ro u g h the development o f r e s i s t a n t v a r i ­
e ties.

With a m ore t h o r o u g h k n o w l e d g e o f some o f

d is e a s e developm ent,

t h e p l a n t p a t h o l o g i s t and a g r o n o m i s t s h o u l d be a b l e

to judge, w ith g r e a t e r p r e c is io n ,
field

tests.

the f a c t o r s i n f l u e n c i n g

t h e r e s u l t s and o b s e r v a . t i o n s fr om h i s

- 93 -

SUMMARY

G -ibberella z ese

1.

The g r o w t h o f G i b b e r e l l a z e a e m y c e li u m a n a t h e g e r m in ­

a t i o n o f t h e c o n i d i a t o o k p l a c e a t t e m p e r a t u r e s from U—3 2° C . , w i t h
t h e m ost r a p i d r a d i a l growth o f

t h e m y c e li u m and the e l o n g a t i o n o f t h e

germ t u b e s o c c u r r i n g a t 2 8 ° C.

The m o s t r a p i d g e r m i n a t i o n o c c u r r e d a t

28 ° and 3 2 ° C.
2.
C.

The m os t r a p i d p r o d u c t i o n o f c o n i d i a o c c u r r e d a t 2 8 - 3 2 °

o n a g a r m e d ia ;

hut on l o n g e r

incub ation ,

mere c o n i d i a w e r e p r o ­

d u c e d a t 3 2 ° C. t h a n a t any o t h e r t e m p e r a t u r e .
d u c e d a t and b e l o w I t

o

Few c o n i d i a w e re p r o -

-o
C. and n o n e w e re p r o d u c e d a t 3 °
C-

M ainly 5 -

.o
s e p t a t e c o n i d i a were formed a t 2 0 - 2 4 C., w hereas 2 - s e p t e t e c o n i d i a
w e re -oredominant a t 3 - ° C.
3-

C o n i d i a were p r o d u c e d on i n f e c t e d h e a d s o f p l a n t s e x p o s e d

t o c o n t i n u e d w e t n e s s a t t e m p e r a t u r e s fr o m 1 5 - 3 0 ° 0 .
was p r o d u c e d on t h o s e h e a d s e x p o s e d a t 25
c u r r i n g a t 20

O

0.

At 2p

O

g.,

o

The maximum number

0 . w ith high p rou u ction oc-

\
c o n i d i a w e r e p r o d u c e d w i t h i n 24 h o u r s on

p l a n t s which a lr e a d y had i n f e c t i o n w e l l e s t a b l i s h e d at

the tim e th e

p l a n t s were e x p o s e d t o c o n t i n u e d w e t n e s s , w h e r e a s f 2 h o u r s o f e x p o s u r e
we re r e q u i r e d f o r

t h e f o r m a t i o n o f c o n i d i a on p l a n t s e x o o s e d t o c o n t i n ­

u e d w e t n e s s from t h e t i m e t h e y w e r e i n o c u l a t e d .
lio n

An a v e r a g e o f l 4 m i l ­

c o n i d i a p e r h e a d w e r e p r o d u c e d i n 3 d a y s a f t e r r e - e x n o s u r e o f the

i n f e c t e d p l a n t s and 3 & m i l l i o n w e r e u r o d u c e d i n 6 d a y s on p l a n t s e x ­
posed contin uously a ft e r
U.

in ocu lation .

The amount o f i n f e c t i o n and d i s e a s e

s e v e r ity increased

w i t h an i n c r e a s e i n t h e amount o f i n o c u l u m up t o 1 . 0- 2 . 0 m i l l i o n c o n ­
i d i a p e r p o t o f 10 w h e a t p l a n t s .

-

5.
to f l o w e r i n g .

3k

-

No i n f e c t i o n o c c u r r e d o n w h e a t h e a d s i n o c u l a t e d p r i o r
The o r d e r o f i n c r e a s e d s u s c e p t i b i l i t y o f whe at t o Gi b-

b e r e l l n h e a d b l i g h t was from t h e f l o w e r i n g t o t h e p a s t - f l o w e r i n g s t a g e s .
6.

The b e s t t e m p e r a t u r e f o r i n f e c t i o n and h e a d b l i g h t d e v e l ­

opment o n p l a n t s i n o c u l a t e d i n a l l
L ittle

o r no i n f e c t i o n o c c u r r e d a t 1 5 ° C.

a t 3 0 ° t h a n a t 2 0° C . , b u t a f t e r
ness

s t a g e s o f d e v e l o p m e n t was 25° C.
More r a p i d i n f e c t i o n o c c u r r e d

6 0 - 7 2 h o u r s e x p o s u r e to c o n t i n u e d w e t­

t h e amount o f i n f e c t i o n a n d d i s e a s e d e v e l o p m e n t was a p p r o x i m a t e l y

t h e same a t t h e s e two t e m p e r a t u r e s .
7.

The p e r i o d o f e x p o s u r e to c o n t i n u e d w e t n e s s f a v o r i n g maxi­

mum i n f e c t i o n and d i s e a s e s e v e r i t y v a r i e d w i t h t h e s t a g e o f h o s t d e v e l ­
opment and t h e t e m p e r a t u r e a t t h e t i m e o f e x p o s u r e .
posure necessary fo r

The p e r i o d o f e x ­

i n f e c t i o n was t h e s h o r t e s t a t 23° C . t b e c o m in g

p r o g r e s s i v e l y l o n g e r a t th e l o w e r and h i g h e r t e m p e r a t u r e s .
p e r i o d n e c e s s a r y f o r i n f e c t i o n was t h e s h o r t e s t

The e x p o s u r e

( a t any one t e m p e r a t u r e )

f o r t h o s e p l a n t s i n o c u l a t e d i n t h e p a s t - f l o w e r i n g s t a g e and l o n g e s t f o r
th ose in o c u la te d in the flo w e r in g s ta g e .
S.

The c r i t i c a l e x p o s u r e p e r i o d s f o r d i s e a s e s e v e r i t y were ,

f o r p l a n t s i n o c u l a t e d i n th e p a s t - f l o w e r i n g s t a g e , from h3-oQ h o u r s a t
2 0 ° C. and 3 0 -LS h o u r s a t 25° C.; f o r p l a n t s i n o c u l a t e d i n t h e f l o w e r i n g '
stage,

6 0 - 7 2 h o u r s a t 2 0° C. and
9.

h o u r s a t 25° C.

The s h o r t e s t p e r i o d o f i n c u b a t i o n was 2 d a y s f o r p l a n t s

i n o c u l a t e d i n t h e f l o w e r i n g s t a g e and e x p o s e d t o c o n t i n u e d w e t n e s s f o r
3 6 h o u r s a t 2 5 ° C.

The i n c u b a t i o n p e r i o d s were 6 da y s e a c h a t 20° and

3 0 ° C. w i t h t h e same e x p o s u r e o e r i o d .

In g e n era l,

longer in cu b ation

p e r i o d s were e n c o u n t e r e d a t t h e l o w e r and h i g h e r t e m p e r a t u r e s and w i t h
s h o r t e r p e r i o d s o f e x p o su r e to c o n tin u e d w e tn e ss a t any one o f th e s e
tem p eratures.

10.

95 -

The amount o f a e r i a l m y c e li u m p r e s e n t on t h e g l u m e s

i n c r e a s e d w i t h t h e t e m p e r a t u r e and th e l e n g t h o f e x p o s u r e a t a n y one
tem perature,
was v i s i b l e

b e i n g more p r e v a l e n t a t 3 0 ° t h a n a t 23° and 2 0 ° 0 .

It

in I S hours on t h o s e p l a n t s in o c u l a t e d i n the p a s t - f l o w e r ­

i n g s t a g e and i n c u b a t e d a t 3 0 ° C . , a s

compared t o 3 6 h o u r s on t h o s e

i n o c u la t e d in the flo w e r in g s t a g e .
11.

I n o c u l a t e d p l a n t s e x p o s e d f o r 6 - 1 2 hours to c o n tin u e d

w e t n e s s , f o l l o w e d b y a d r y n e r i o d o f 1 t o 9 d a y s and a s e c o n d w et
p e r i o d 01 5^ h o u r s a t 25° C . ,

developed l e s s

s e v e r e h e a d b lig h t than

t h o s e w h i c h r e c e i v e d no i n t e r m e d i a t e d r y i n g p e r i o d .

Those p l a n t s r e ­

c e i v i n g 18—3 c h o u r s o f i n i t i a l w e t n e s s b e f o r e d r y i n g showed no r e d u c ­
tio n in d isease

severity.

Those p l a n t s w hich r e c e i v e d a sh o r t i n t e r ­

m e d i a t e d r y i n g n e r i o d i . T m e d i a t e l y a f t e r i n o c u l a t i o n or a f t e r an i n i t i a l
w e ttin g p eriod of 6 hours,

developed l e s s

sev e r e head b ligh t than those

p l a n t s which r e c e i v e d a s i m i l a r tr e a tm e n t but were d r i e d f o r

several

days .
Helminth-0 s p o r iu m s a t i v u m

1.
g e r m in a tio n o f the

The g r o w t h o f Helm i n t ho s po r ium s a t i v u m m y c e l i u m and t h
c o n i d i a o c c u r r e d a t t e n p e r a t u r e s from *4—3 ° ° C. wri t h

t h e m o s t r a p i d r a d i a l g r o w t h o f t h e m y c e l i u m an d e l o n g a t i o n o f t h e germ
t u b e s o c c u r r i n g a t 28° C.
C.

The most r a p i d g e r m i n a t i o n o c c u r r e d a t $ 2 °

W i t h i n 5 h o u r s , most o f the

20-36°

c o n i d i a e x p o s e d t o t e m p e r a t u r e s from

C. had g e r m i n a t e d ; and a f t e r f P h o u r s a l l t h e c o n i d i a had ge rm in ­

a t e d a t t s n r p e r a t u r c s fr o m U-3 6 ° C.
2.

No c o n i d i a w e re p r o d u c e d on b e a n - p o d a g a r i n 20 d a y s a t

t e m p e r a t u r e s b e l o w l 6° and a b o v e 2 8 ° C.

The most r a p i d i n i t i a l

sp oru lation

- 9b o c c u r r e d , a t 28° C . ,
after

20 d a y s ,

a f t e r 1 ” d a y s more were p r o d u c e d a t ? k ° C . , and

t h e c u l t u r e s i n c u b a t e d at 2 0 ° C. -produced t h e most

co n id ia .
3*

C o n i d i a w e r e p r o d u c e d on i u f e c t e d h e a d s o f p l a n t s e x ­

p o s e d t o c o n t i n u e d w e t n e s s f o r ^8 h o u r s a t t e m p e r a t u r e s from 1 5- 3 0 ° 0.
A maximum o f 2 . 1 g m i l l i o n c o n i d i a was p r o d u c e d i n 5 d a y s a t 25° C.
Four t o 5 d a y s w e re r e q u i r e d f o r c o n i d i a t o be p r o d u c e d on whe at hea ds
i n o c u l a t e d and e x p o s e d c o n t i n u o u s l y to c o n t i n u e d w e t n e s s a.t 25° and
3 0 ° C.

ho c o n i d i a were p r o d u c e d b e l o w l o °

C. o r a b o v e 28° C. on i n ­

f e c t e d h e a d s rem oved from p l a n t s and i n c u b a t e d i n m o i s t c h a m b e r s .
U.

The amount o f i n f e c t i o n i n c r e a s e d -with i n c r e a s e d c o n i d i a l

i n o c u l u m up t o a p p r o x i m a t e l y 0 - 5 m i l l i o n c o n i d i a p e r p o t o f 10 whe at
p lan ts,

whereas th e

disease

s e v e r i t y p r o g r e s s i v e l y i n c r e a s e d w i t h ap­

p l i c a t i o n s up t o 1 . 0 - 2 . 0 m i l l i o n c o n i d i a p e r p o t .
5.

G e n e r a l l y no i n f e c t i o n o c c u r r e d o n w heat h e a d s i n o c u l a t e d

p r i o r to f l o w e r i n g .

The o r d e r o f i n c r e a s e d s u s c e o t i b i l i t y o f wheat to

H e l m i n t h o s p o r i u m h e a d b l i g h t was from t h e f l o w e r i n g to t h e p a s t - f l o w e r i n g
stages.
d.

In gen eral,

t e m p e r . - t i i r e s fr om 2 5 - 3 ^ ° C. were t h e b e s t f o r

i n f e c t i o n and h e a d b l i g h t d e v e lo p m e n t.

I t a p p e a r e d t h a t i n f e c t i o n was

more s e v e r e a t 3'd° t h a n a t 2 5 ° C. o n t h o s e p l a n t s i n o c u l a t e d i n the
past-flow erin g sta g es,

w h e r e a s t e m p e r a t u r e s o f 2 5 - 3 0 ° C. were a p p r o x i ­

m ately e q u a lly fa v o r a b le for the i n f e c t i o n of th o se p la n t s in o c u la te d
i n th e f l o w e r i n g s t a g e s .
w ere k i l l e d a t 1 5 ° C.
2 0 ° C.

L ittle

i n f e c t i o n o c c u r r e d and no s p i k e l e t s

I n f e c t i o n was much more s e v e r e a t 3^ ° t h a n a t

- 97 7-

The p e r i o d o f e x p o s a r f t o c o n t i n u e d v e t n s s s n e c e s s a r y

f o r maximum i n f e c t i o n end d i s e a s e
h e e d d e v e l o p m e n t e nd t h e

s e v e r i t y v a r ie d w ith the s ta g e o f

tem perature at the tim e o f exp osu re.

The

s h o r t e s t p e r io d o f exposure n e c e s s a r y fo r i n f e c t i o n o f p l a n t s inocu­
lated

i n tii e f l o w e r i n g to p a s t - f l o w e r i n g -

and 3 0 ° C. ,

2U h o u r s a t 2 0° C. ,

s t a g e s was 1 ? h o u r s a t 2 5 °

a n d U8 h o u r s a t lf>° C.

The s h o r t e s t

p e r i o d o f e x p o s u r e r e s u l t i n g i n th e k i l l i n g o f the s p i k e l e t s
n o u r s .'it 2 5° C . t 'j>o h o u r s a t 3 rJ ° C . ,
i n o c u l a t e d i n the f lo w e i'in g s t a g e ,
resp ectively,

for p lan ts

6.

p ast-flow erin g
in ocu la ted

stage,

?U and U& h o u r s ,

in o c u l a t e d in the p a s t - f l o w e r i n g s t a g e .
exposure periods" f o r d is e a s e

severity

2 5 ° and 3 0 ° C. f o r p l a n t s i n o c u l a t e d i n t h e

and h-3 t o bO h o u r s ,

r e s p e c tiv e ly , for p lan ts

in the flo w e r in g s t a g e .
9.

T h o s e p l a n t s i n o c u l a t e d and e x p o s e d to 3 C h o u r s o f c o n ­

t i n u e d w e t n e s s a t 2 5 ° and 3 ^° u . had t h e
(la

36

and J 2 h o u r s a t 20 ° C. f o r p l a n t s

as co mpared t o ?h,

The " c r i t i c a l

’ -ere f r o m 3 b-h& h o u r s a t

was

days).

s h o r t e s t in c u b a tio n period

Longer i n c u b a t i o n p e r i o d s were e n c o u n t e r e d at t h e lo w e r

t e m p e r a t u r e s and w i t h s h o r t e r e x p o s u r e p e r i o :1s t o c o n t i n u e d w e t n e s s .
10.
ued w e tn e s s ,

In ocu lated p la n ts,

exposed for

b

and 12 h o u r s t o c o n t i n ­

f o l l o w e d b y a dr y p e r i o d o f 1 t o 3 d a y s ana r

. - o s m e t o c o n t i n u e d w e t n e s s f o r 5 ^ h o u r s a t 3 ^° C . ,

second ex-

developed l e s s

s e v e r e h e a d b l i g h t t h a n t h o s e w h i c h r e c e i v e d no i n t e r m e d i a t e d r y i n g
p eriod .

T h o s e p l a n t s w h ic h r e c e i v e d 10 o r more h o u r s o f i n i t i a l w e t ­

ness before
A ll

the d r y in g p e r i o d

show ed no r e d u c t i o n i n d i s e a s e

severity.

t h o s e p l a n t s e x p o s e d i m m e d i a t e l y a f t e r i n o c u l a t i o n t o 2^ h o u r s o f

d r y i n g f o l l o w e d b y 5 ^ h o u r s o f c o n t i n u e d w e t n e s s and t h o s e w h i c h w ere
exposed im m ediately to

hours o f

c o n t i n u e d w e t n e s s were k i l l e d a s a

- 9*5 resu lt of in fectio n .

T ho se p l a n t s w h i c h r e c e i v e d a s h o r t i n t e r m e d i a t e

d r y i n g p e r i o d i m m e d i a t e l y a f t e r i n o c u l a t i o n o r a f t e r an i n i t i a l wettingp eriod of o hours,

developed l e s s

s e v e r e he ad "blight than t h o s e p l a n t s

w h ic h r e c e i v e d o s i m i l a r t r e a t m e n t

out w ere d r i e d f o r s e v e r a l d a y s .

A ssociation

1.

The m y c e l i a l g r o w t h o f G i b b e r e l l a z e a e was n o t i n h i b i t e d

by a n o t h e r l i k e
la rly ,

c o l o n y or by a H e l m i n t h o s n o r i u m s a t i v u m c o l o n y .

Si m i­

a h e a v y c o n c e n t r a t i o n o f G. z e a e c o n i d i a a l o n e or w i t h a h e av y

c o n c e n t r a t i o n o f H. s a t i v u m c o n i d i a
G. z e a e c o n i d i a .

d i d not p r e v e n t g e r m i n a t i o n o f t h e

How ev er, h e a v y c o n c e n t r a t i o n s o f G. z e a e c o n i d i a . a l o n e

p r e v e n t e d normal g r o w t h o f th e germ t u b e s .
71.

H e l m i n t h o spor ium s a t i v u m c o n i d i a

c e n t r a t i o n o f G.
alone

to g eth er w ith a l i k e

con­

z e a e c o n i d i a o r a h i g h c o n c e n t r a t i o n o f G. z e a e c o n i d i a

s t i m u l a t e d s e c o n d a r y c o n i d i a l p r o d u c t i o n and r e t a r d e d v e g e t a t i v e

d e v e l o p m e n t b y G. z e a e .
3-

The g r o w t h o f t h e m y c e li u m o f H e l m i n t h o s u o r i u m s a t i v u m

was i n h i b i t e d b y a n o t h e r l i k e c o l o n y or by a G i b b e r e l l a z e a e c o l o n y .
The c o n i d i a o f H. s a t i v u m g e r m i n a t e d n o r m a l l y and showed normal germ
tube growth in a l l c o n c e n t r a t i o n s ,

w h e r e a s t h e germ t u b e s w e re s t u n t e d

and knobby when m i x e d w i t h 0 . 3 P-nd 1 . 0 m i l l i o n / m l . G. z e a e c o n i d i a .
H.

The a p p l i c a t i o n o f 1 . 0 m i l l i o n G i b b e r e l l a z e a e c o n i d i a

mixed w i t h 0 . 1 m i l l i o n H e l m i n t h o s p o r ium s a t ivum

c o n i d i a to

wheat i n th e

p a s t - f l o w e r i n g s t a g e r e s u l t e d in a r e d u c tio n in

t h e number o f s e e d s i n ­

f e c t e d w i t h H. s a t i v u m but not w i t h G. z e a e when compared t o t h e r e s u l t s
o f applying a l i k e
la rly ,

number o f c o n i d i a o f e i t h e r p a t h o g e n a l o n e .

Si m i­

when a h i g h c o n i d i a l c o n c e n t r a t i o n o f H. s a t i v u m was m ix e d w i t h

- 93 a l o w c o n c e n t r a t i o n , o f G. z e a e c o n i d i a ,

t h e number o f s e e d s i n f e c t e d

w i t h G. z e a e was r e d u c e d a s compared to t h e i n f e c t i o n r e s u l t i n g from
t h e same q u a n t i t y a p x j l i c a t i o n o f G. z e a e a l o n e .
5-

The a p p l i c a t i o n o f a m i x t u r e o f 0 . 1 m i l l i o n c o n i d i a o f

e a c h p a t h o g e n r e s u l t e d i n no d e c r e a s e i n t h e number o f s e e d s i n f e c t e d
"by e i t h e r p a t h o g e n o s co mpared to t h e i n f e c t i o n r e s u l t i n g f r o m t h e ap­
p l i c a t i o n o f a l i k e num ter o f c o n i d i a o f e i t h e r p a t h o g e n a l o n e .
ever,
su lted

How­

the a p p l i c a t i o n o f a m ixtu re o f 1 .0 m i l l i o n c o n id i a o f each r e ­
i n a s i g n i f i c a n t d e c r e a s e i n t h e number o f s e e d s i n f e c t e d "by

e it h e r pathogen.

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________________ •

P h y siologic

Phytopath.

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________________ .

In flu en ce o f black p o in t d is e a s e ,

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19 3^ -

p a t h o l o g i c a l m o r p h o l o g y o f durum w h e a t g r a i n s a f ­

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treat­

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seed

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Sherbakoff,

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0 . A. R e i n k i n g , H. J o h a n n ,

Fundam entals f o r taxonomic s t u d i e s o f

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19^5*

PU T S I

Hum idity t e a b vvithout t h e c u t e r t e n t and t e m p e r a t u r e c o n t r o l
system*

Note St an da rd h u m i d i f i e r a t the end o f t e n b .

Plate I

PLATE I I

The r e l a t i o n o f th© stag© o f h o s t m a t u r i t y t o th© d e v e l o p m e n t
o f G i b b e r e l l a h e a d b l i g h t on h e w t h a t o h w h e a t .

Each s e t o f t h r o e h e a d s , from l e f t t o r i g h t , were f r o n p l a n t s
tr e a te d as f o llo w s :
the flow ering,
development.

( l ) }Ion-inooulated c o n t r o l ; ( 2 ) in o c u la te d i n

( 3) after-flow erin g,

and (I*.) p a s t - f l o w e r i n g s t a g e s o f

S e r i e s A was e x p o s e d t o c o n t i n u e d w e t n e s s f o r 36 ho u rs

a t 2 5 ° f * a f t e r i n o c u l a t i o n and s e r i e s 3 , ) j8 h o u r s a t 2 0 ° C«

B

Piste I I

FIATE III

The r e l a ti o n of* the stage of host m atu rity to th e development
of Helmintho sporium headblight on Hevrthatoh wheat*

Eaoh s e t of th ree heads, from l e f t to
tr e a te d as fo llo w s t
the flow ering;
development#

r i g h t , were from p lan ts

( l ) Hon—
inoculated c o n tr o l; (2) inooulated in

(3) a fte r-flo w e rin g ; and (1+) past—
flowering stages of
S eries A was exposed to continued wetness fo r 3^ hours

a t 25° C# a f t e r in o c u la tio n and s e rie s B, 1*8 hours a t 20° C#

PIATE IV

The relation of temperature and period of continued wetness
to the development of Gibberella headblight on Newthatoh wheat
inoculated in the past-flowering stage.

Each head, from left to right, represents the severity of
headblight development resulting from exposure of plants to continued
wetness at 30°# 25°, 20®, and 15° C,
B,

Series A was exposed 36 hours;

hours; and Cf } 60 hours to cont?.nued wetness.

Plate IV

PLATE V

Gibberella zeae myoolium growing over the surfaoe of the glumes
of Newthatoh wheat from infected extruded anthers*

Plants were inooul&ted in the past-flowering stage and exposed to
continued wetness for

hours at 30° C*