STEM RUST OF OATS: IT'S EFFECT ON
YIELD AND THE (NHERITANCE
01‘ RESISTANCE 1‘0 PHYSIOLOGGC
RACES 2,. I7 AND E!

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STEM RUST OF OATS: ITS EFFECT ON YIELD AND
THE INHERITANCE OF RESISTANCE T0
PHYSIOLOGIC RACES 2, 7 AND 8

by
Paul G. Rothman

 

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree 0!

MASTER OF SCIENCE

Department of Farm Crops

1952

ACKNOWLEDGEMENTS

The writer wishes to express his thanks and apprecia-
tion to Doctor Kenneth J. Frey for his assistance during
this experiment and in the preparation or the manuscript,
and to other members or the Farm CrOps Department of

Michigan State College who aided in the study.

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TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . .
REVIEW; OF LITERATIIRE O 0 O O O O O
GREENHOUSE STUDY . . . . . . . . .
Materials and Procedure . . .
Experimental Results . . . .
Summary . . . . . . . . . . .
FIELD TESTS . . . . . . . . . . .
materials and Procedure . . .
Experimental Results . . . .
SW” 0 O O O O O O O O O 0

LITERATURE CITED . . . . . . . . .

“~10! 0'1 N P

INTRODUCTION

It has been realized for several decades that stem
rust or cats, Puccinia graminis avenae Erika. and Henn.,
can cause a serious reduction in cat grain yields, es-
pecially it the disease is present in epidemic or near
epidemic preportions. The damage to cats by rust is
usually measured in terms of bushels destroyed in rela-
tion to total production. Estimates of damage done by
the stem.rust disease have usually been empirical instead
of being derived from a yield comparison of diseased and
healthy material.

Since oat stem.rust is present in.Michigan in vary-
ing degrees of severity every growing season, it seemed
desirable to obtain some reliable estimate of the damage
which it could cause under the local environmental con-
ditions.

This paper is a report of an investigation into the
losses in yields of cats which can be attributed to dif-
ferences in strain reactions to Puccinia graminis avenae.
Also reported herein is an inheritance study, involving
two crosses between susceptible and resistant oat varie-
ties, of resistance to three of the most prevalent physio-

logical races of stem rust in Michigan.

REVIEW OF LITERATURE

Inheritance of resistance to Puccinia graminis avenae
has been reported in varietal surveys of cats by hackle (10),
Levine and Smith (8), and Newton, §3_§l (12), and in studies
of the progenies from crosses between known resistant and sus-
ceptible varieties by Gerber (4), Griffee (6), Hayes, g£_a£
(7), Smith (14), Cochran, gt'al_(l), Litzenberger (9) and
others.

Gerber (4) published preliminary results which indicated
that resistance to oat stem rust was dominant. Hayes, _e_t a;
(7) feund that inheritance was governed by one factor with
resistance dominant in seven crosses with Bond as the sus-
ceptible parent. Dietz (2) also showed that resistance was
dominant and determined by a single factor difference in the
crosses, National X White Tartar and Lincoln x White Tartar.
Welsh (16) in his varietal tests for reaction to eight dif-
ferent races of stem rust, found results which were in agree-
ment with those already mentioned. Others who confirmed the
single factor hypothesis were Griffee (6), Smith (14), Welsh
(l7), Torrie (l5), Cochran (l) and Litzenberger (9).

Results contrary to those quoted above were reported by
Dietz (2), who found that three genetically different and

susceptible strains of the Burt oats, when crossed with White

Russian, gave varying results. One cross behaved in agree-
ment with other reported investigations. However, in the
other two crosses the Fl was susceptible and the F2 segre-
gated in the ratio of one resistant to three susceptible
plants, and three resistant to thirteen susceptible plants,
respectively. Two factors, one an inhibitor, are necessary

to eXplain the results of the last cross.

GREENHOUSE STUDY

materials and Procedure

Three oat varieties were used in the study: Hajira X
Joanette (0.1. 4025), a pure line selection from Hajira
(G.I. 1001) X Joanette (0.1. 2660), which, as reported by
Welsh (17), has resistance or moderate resistance to all
known races of Puccinia graminis avenae; Wolverine, a silver-
mine type, of unknown parentage; and Huron (0.1. 5756), a
pure line selection from the cross Markton X Victory. Huron
and Wolverine are Michigan varieties which have proved to be
highly susceptible to all races of Puccinia graminis avenae.

Crosses involving these three parental varieties were
made at Michigan State College, East Lansing, Michigan, as
part of the oat breeding improvement program. The Huron X
HaJira-Joanette cross was made in the greenhouse during the-
winter of 1949, and the El seed was grown in the field. The
Wolverine X hajira-Joanette cross was made in the field during
the summer of 1949 and the 31 was grown in the greenhouse.

The F2 seeds of each cross were planted four inches
apart in sixteen-foot rows in the field in 1950, so that the
individual plants could be harvested and threshed individually.

One hundred and fifty and three hundred F2 strains were

obtained from the Huron X Hajira-Joanette (A-584) and the
Wolverine X HaJira-Joanette (A-587) crosses, respectively.
Each of the F2 strains was progeny tested in the greenhouse
for its seedling stage reaction to physiologic races 2, 7
and 8 of oat stem rust. Because it has been proved by
Newton, 33 a; (12) that varieties which are resistant to a
physiologic race in the seedling stage are also resistant
to it in the adult stage, it is possible by means of the
aforementioned tests to predict the field reaction of an
oat variety or strain with considerable accuracy.

Spore material of the three races was obtained from
Doctor E. C. Stakeman of the University of Minnesota. The
rust was increased on stock plants of Huron oats grown in
twelve-inch pots.

For rust reaction studies on seedling oat plants, about
six seedlings from each F2 progeny were grown in a four-inch
pot. Sand was used as the potting medium.and each progeny
was planted in triplicate for investigation with the three
races of stem rust. The pots were watered daily but were
never given nutrient solution, since the seedling plants
were discarded as soon as rust reaction notes were made.
Whenever the reaction of a strain to any race was doubtful,
the test was repeated.

Inoculations of the seedling plants were made prior to

the appearance of the second leaf. To avoid contamination

in handling and in the moist chamber, the three races were
tested at different times.

The inoculations were made by removing the uredinio-
spores from the stock plants with the thumb and forefinger
and rubbing them on the debloomed, moistened seedling leaves.
Deblooming was accomplished by rubbing the leaves between
moistened thumb and forefinger. Then all seedlings were
placed in a moist chamber and Sprayed with an oil Jet nozzle
attached to a garden hose to insure the presence of sufficient
moisture for spore germination. The incubation temperature
remained very near to 65° Fahrenheit at all times.

The pots of oat plants were held in the moist chamber
for twenty-four hours, after which time they were returned
to the benches. Classification into the resistance groups
was made ten days after inoculation. The resistant seedlings
were distinguished by a complete lack of necrotic areas on
the leaves or small uredia with hypersensitive areas surround-
ing them. All other seedlings were classified as susceptible.
Progenies containing both resistant and susceptible plants

were designated as segregating.

EXperimental Results

The F2 strains of the two oat crosses, A-584 and A-587,
are classified into two groups, resistant and susceptible,
for each physiologic race of stem.rust, according to the
greenhouse reaction of their progenies. Both the resistant
and segregating progenies are put into the resistant class
because of the difficulty of an accurate differentiation
between these two types when only six seedlings from each
progeny are used for the reaction studies. The results of
the inheritance studies are given in Table I. The observed
ratios are tested for their "goodness of fit” to expected

ratios in Tables II and III.
TABLE I

THE F2 PROGEHIES OF TWO OAT CROSSES GROUPED
ACCORDING TO THEIR REACTION TO RACES 2, 7 and 8 OF
' PUCCINIA GRAMINIS AVENAE

 

 

 

Physiologic Type 6? Reaction Tital No. of

 

 

 

Cross Race Res. Sus. Progenies
A-584 2 l 29 21 150
A-584 7 125 25 ' 148
A-584 8 114 54 148
A-587 2 270 27 297
A-587 7 287 11 298
A-587 8 249 16 265

 

TABLE II

CHI SQUARE TEST OF THE F2 SEGREGATION
FOR STEM RUST REACTION (RACES 2, 7 and 8) IN
THE OAT CROSS A-587 AGAINST A 15:1 RATIO

 

 

 

 

Groups Observed Calculated X2 P
Race 2

Res. 270 278.44

Sus. 27 18.56 4.095 0.02-0.05
Race 7

Res. 287 279.57

SUB. 11 18063 5.328 0.05-0010
Race 8

Res. 249 248.46

Sus. 16 16.56 .019 0.80-0.90

TABLE III

CHI SQUARE TEST OF THE F SEGREGATION
FOR STEM RUST REACTION (RACES 2, 7 and 8) IN
THE CAT CROSS A-584 AGAINST A 13:3 RATIO

W

 

Groups Observed Calculated X2 P
Race 2

Res. 129 121.87
Race 7

Res. 125 120.25

Sus. 25 27.75 1.001 0.50-0.50
Race 8

Res. 114 120.25

Sus. 34 27.75 1.732 0.10-0.20

 

In the Wolverine X Hajira-Joanette cross (A-587),

the F segregation of resistant and susceptible strains

2
for races 7 and 8 fit a 15:1 ratio very well. In neither

case is the chi square test significant. For race 2 the ratio
is significantly different from that eXpected on the basis
of a 15:1 segregation. The discrepancy is caused by an
abundance of susceptible strains. No other ratio can be
found to which the data for race 2 conforms. 0n the basis
of these data, it appears that resistance to races 7 or 8
of stem rust in the Wolverine X Hajira-Joanette cross is de-
termined by a dominant gene in either of two factor pairs.
No attempt was made to determine whether both genes in the
dominant condition gave a more resistant type of plant than
when only one was present. From the standpoint of the breeder,
the situation in which either of two gene pairs can determine
resistance to stem.rust is beneficial because a larger pro-
portion of the F2 segregates in a cross will be homozygous
resistant than in a cross in which only one factor is segre-
gating.

As can be seen from.Tab1e III, each of the F2 segregations
for reaction to the three races of oat stem.rust in the Huron
X Hajira-Joanette cross fit a 15:5 ratio. It would appear

offhand that two factor pairs, one acting as an inhibitor,

10

are determining the resistance to each of the races 2, 7

and 8. From.the scheme of segregation for two factor pairs,
shown in Table IV, of the nine possible genotypes contained
in the table, four, namely AABB, AABb, AaBB and AaBb, will
either breed true for resistance or segregate into resistant
and susceptible plants.' In any case, the progenies will
remain within the resistant classification. One progeny,
aabb, will breed true for susceptibility. Of the six re-
maining F2 progenies, two must breed true for susceptibility
and the other four must fall into the resistant category in
order to explain the 15:5 ratio. The question arises as to
which of the remaining four genotypes, aaBB, aaBb, AAbb or
Aabb constitute the susceptible classes. It must be remem-
bered that the F2 classifications given in Tables II and III
are based upon progeny tests and consequently the genotypes
aaBb and Aabb should show up as types segregating for resis-
tance and susceptibility rather than as susceptible. The-
genotypes which show up as susceptible in the F2 progenhas

must be derived from.homozygous F plants. The remaining

2
genotypes aaBB and AAbb fit this scheme, but the question
immediately occurs as to why aaBB and AAbb are susceptible
and aaBb and Aabb classed as resistant.

One possible explanation might involve heterosis as

described by East (5), in which each gene of a heterozygous

ll

combination actively affects the end result. Applying the
supposition of East (5) the effects of the heterozygotes,
through the probable production of some substance causing
resistance, are superior to the homozygotes. That is, in
the genotypes aaBb and Aabb, the heterozygous Aa and Bb
produce the substance for resistance in quantities which
cannot be neutralized by substances for susceptibility
produced by ea or bb genes. Consequently, the genotypes
aaBb and Aabb are resistant. Genotypes aaBB and AAbb, on
the other hand, are susceptible, for in the presence of the
homozygous recessives, as and bb, substances for resistance
produced by the homozygote dominant, AA and BB, are not
produced in sufficient quantities to counteract substances
produced for susceptibility as is the case with the hetero-
zygous types.'

Table IV summarizes inheritance based on the assump-
tion of heterosis in the heterozygote. The three genotypes
AAbb, aaBB, and aabb would be susceptible and the remaining
six genotypes resistant.

It seems safe to conclude on the basis of the data
reported herein, that the Hajira-Joanette parent contributes
two pairs of factors for resistance to each of the races,
2, 7 and 8, of oat stem.rust. In the Wolverine X Hajira-

Joanette cross resistance in either factor pair was completely

dominant.

12

However, in the Huron X Hajira-Joanette cross

it seems that the recessive genes, derived from the Huron

parent, may in certain genotypes be epistatic to the domi-

nant gene in the second factor pair.

F2 Progenies

TABLE IV

PROBABLE INHERITHNCE OF RUST RESISTENCE

 

Genonpes oI SegregatIon o? CIassITicaIIon
3; Seedlings of Prggegy
AABB All res. Res.
AABb 5 res., 1 sus. Res.
AAbb All sus. Sus.
AaBB 5 res., 1 sus. Res.
AaBb 15 res., 5 ans. Res.
Aabb 2 res., 2 ans. Res.
aaBB All sus. Sus.
aaBb 2 res., 2 ans. Res.
aabb All sue. Sus.

Ptol-‘NIFNHmH

 

13

Summary

The inheritance study of F2 progenies from the two

crosses of oats, each having a susceptible and a resistant

parent, were tested in the greenhouse for resistance to

the three physiologic races of stem rust most prevalent

in Michigan: namely, races 2, 7 and 8. From.the data ob-

tained, the following conclusions may be drawn:

1.

In the oat cross of Wolverine X Hajira-Joanette,
resistance to races 7 and 8 is determined by a
dominant gene in either of two factor pairs.

No known ratio could be found to indicate the

mode of inheritance for race 2 in the cross.

In the oat cross of Huron X Hajira-Joanette,
segregations for reaction to each of the three
races of stem.rust conform to a 15:5 ratio.

It is postulated that heterosis, in which the
heterozygous is superior to the homozygous con-
dition, might play an important role in the
explanation of the 15:5 ratio observed in the

Huron X HaJira-Joanette cross.

FIELD TEST

materials and Procedure

For investigation into losses in yields of oats caused
by stem.rust, races 2 and 8, in each of the three resistance
groups, a yield test was conducted under induced epiphytotic
conditions.

The thirty-three strains selected were as follows: six
resistant, nine segregating and six susceptible strains from
the Wolverine X Hajira-Joanette cross, and eight resistant
and four segregating strains from the Huron X Hajira-Joanette
cross. The selection of these progenies within each cross
was made at random.within the resistance groups. By such a
procedure it was felt that the average inherent yielding
ability of the three resistance groups would be approximately
equal, since they come from the same cross and therefore the
same genetic background. Consequently, any reduction in
yields could be attributed to losses from rust.

In addition to the thirty-three progenies selected from
the two crosses, the three parental varieties, Huron, Wolver-
ine, and Hajira-Joanette, were also included, making a total
of thirty-six entries. These entries were planted in a 6 X 6
triple lattice design with three replications.

Plots one row wide and four feet long were planted by
hand at a rate equivalent to two bushels per acre. Guard

rows of the susceptible parent variety, Huron, were planted

15

between plots to insure an even distribution of rust infes-
tation throughout the experiment.

The eXperiment was planted on May 5, 1951, and on June
12 the seedlings were dusted with a mixture of spores of
races 2 and 8, and talc which facilitates prOper distribution.
The dusting was carried out in the evening when the dew had
settled on the plants. After sori failed to appear in approxi-
mately ten days, it was assumed that the inoculum was washed
from.the seedlings by a heavy rain which fell during the night
following the first inoculation. A second application of
inoculum was then applied during the first week in July.

To designate intensity of stem rust develOpment and also
as a basis for comparison between oat strains, the modified
Cobb scale, as described by Melchers and Parker (11), was
employed. The individual plots were appraised for stem.rust
develOpment Just prior to ripening by reading ten randomly
selected plants in each plot. Where rust was present in
extremely small amounts, the readings were reported as traces.

The date of heading was recorded at the time when 50
percent of the heads had emerged above the flag leaves. In-
dividual plots were harvested by hand and threshed separately
'after which plot weights were recorded in grams. The relative
test weights were determined for each plot on the basis of

the weight of a 25 ml. beaker level full of grain.

16

Experimental Results

Data regarding date of heading, relative test weight,
and yield of the thirty-six strains and varieties included
in the rust infection eXperiment are given in Tables V and
VI, and the statistical analysis of the data for each of
these criteria are given in Tables VII, VIII and IX, respec-
tively.

Within cross A-587 the resistant strains headed four
'days earlier than the susceptible ones. This difference was
highly significant. No reason was apparent as to why sus-
ceptible strains headed later than the resistant ones.
Possibly the parasitic action of the rust organism inhibited
both vegetative and reproductive development of the susceptible
oat plants. Genetic linkage between susceptibility and date
of heading was discarded as a feasible explanation in view
of the fact that both parents, Wolverine and Hajira-Joanette
headed on the same day. The segregating group of strains had
an average heading date only one day later than the resistant
group. In the A-584 cross, both resistant and segregating
groups of oat strains headed on June 50.

The relative test weights were definitely reduced by
rust infection. This is shown clearly in Tables VI and VIII.
The average difference in test weight between the susceptible

and resistant classes in the A-587 cross was 2.5 or 6 percent.

TABLIY

HELD READINGS FOB rm VARIOUS STRAINS 01' OATS
TESTED IN THE RUST INFECTION EXPERIMENT

l7

 

 

 

H
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b. 8 4; 3 H s e C a '3
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4-D .4 H a §3 N H H
p m 3‘” 3 “’\' 5a a I 2 us III
a: a a . . .
3 3.25 s ’P “P '9
b58lt- 2: Res. 6/30 42.0 103.0 T/lOO r r 13/80
- 5 Res. 6/28 39.0 101.5 r/ho :- 1 1/20
- 19 Res. 6/30 37.0 98.1 13/! s r r/e
- 21 Res. 7/5 40.0 93.7 13/30 T/7O T/m
- 35 Res. 7/1 110.3 102.2 0/0 0 0 0/0
.. 69 Bee. 7/2 38.0 99.6 r/r 52/2 1/1
- 76 Bee. 6/27 u3.3 113.6 0/0 0 0 0/0
.434 Res. 7/2 111.3 87.1! 1/2 0/0 0/0
1-58a- n2 Sag. 6/25 37.7 108.9 1/2 r/io r/30
- 61 Sag. 6/27 39.7 116.3 5/100 5/100 35/100
-11u Sag. 6/30 36.3 69.0 52/100 r/ioo T/lOO
428 Sag. 7/6 38.0 92.9 10/100 8/100 T/lOO
1-587- 3 an. 7/2 38.7 103.7 sis/50 r/uo r/30
- 17 Res. 7/5 38.7 82.7 1/30 2]! 1/90
- 31 Bee. 7/8 . 39.0 106.2 2/2 0/0 0/0
- 35 Res. 7/5 39.3 10h.1 r/! r]: 0/0
- Lu Res. 7/3 39.7 99.9 0/0 0/0 0/0
- 1+2 Bee. 7/7 40.7 97.5 1]! 0/0 0/0
b587- 11 Seg. 7/5 40.0 79.6 T/lOO 5/100 T/T
- 58 Sag. 7/6 36.7 72.7 r/zo r/ho 0/0
- 82 Sag. 7/n 39.0 92.8 5/100 10/100 1/2
-238 Sag. 7/5 no.3 100.8 r/r 5/10 0/0
-280 Sag. 7/8 38.0 91.9 30/100 r/1oo 13/100
-256 Sag. 7/9 111.0 77.2 2/70 1/50 2]!
-266 Seg. 7/9 37.0 7u.9 10/100 13/100 2/100
-267 Seg. 7/6 37.3 93.1 5/100 two/100 5/100
-276 Sag. 7/1 111.0 111.0 1/50 r/ao r/uo
1-587- 36 Sue. 7/11 38.7 63.3 10/100 two/100 35/100
-202 Sue. 7/9 37.7 102.6 I5/100 5/50 '3/9
272 Sue. 7/9 37.0 82.6 r/uo r/ho T/lO
29 Sue. 7/9 38.3 99.». T/lOO e/9o r/r
-2t+7 Sue. 7/9 36.7 mm 52/100 15/100 5/50
-291. an... 7/7 35.7 66.1 15/100 90/100 25/100
siren Sue. 6/28 110.3 864 20/100 65/100 25/100
Wolverine Sue. 7/6 39. 93.2 5/100 35/100 20/100
Eajira-
Jeanette Res. 7/6 37.0 72.8 0/0 0/0 0/0

 

18

TABLE 71

am YIELD, TEST WEIGE', AND DATE 03' EADING 01' TI
RESISTANCE CLASSES AND VARIDTIDS OP OATS

 

 

 

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A-SBII» Res. 6/30 I40.]. 100.1
565. 6/30 3709 9608
1.587 Res. 7/5 39.2 99.8
Seg. 7/6 39.1 88.1
S“... 7/9 36o 7 76.“
Biron 511'. 6/28 “Oe3 86c“
Wolverine Sue. 7/ 6 39.7 93. 2
Redire-
Jeanette Res. 7/6 37.0 _ 72.8

 

19

 

 

 

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22

On this basis an oat variety which had a test weight of
34.0 pounds would be reduced about two pounds per bushel.
Further evidence that the rust epidemic caused the observed
reduction in test weight is shown in the statistical analysis
where the ”within resistance groups" source of variation,
in the A-587 cross was not significant, while the "among
resistance groups" source was highly significant. In the
A-584 cross, the average relative test weight of the segre-
gating group was significantly less than that of the resistant
group. Even among the strains within each resistance group,
the trend was for a low test weight to be accompanied by rela-
tively high rust readings. The three susceptible strains with
the lowest test weights also had the highest rust readings.
Similar reaponses were present among the segregating progenies.
It has long been recognized among cereal pathologists,
especially those working with wheat, that grain size and
weight are seriously affected by the rust parasite. One
cause for this is that the greater the plant surface area
covered by the fungus, the less food producing surface is
available. Furthermore, the fungus is maintained at the ex-
pense of the plant foods which would normally be stored in
the kernels. Also the girdling habit of growth of stem.rust

on the straw probably hinders passage of manufactured food to

the heads.

25

A highly significant difference was observed between the
yields of the two oat crosses as is shown in Table VII.
Within the cross A9584, the segregating group yielded 5 per-
cent less than the resistant group, a difference which was
not statistically significant. This result was different
from that expected on the basis of the data on test weight,
where there was a significant difference between the two
groups. In the A-587 cross, the rust epidemic caused a 12
percent reduction in the average yield of the segregating
class, and a 25 percent reduction in the susceptible class.
Both of these differences are highly significant when com-
pared with the yield of the resistant group. It is interest-
ing to note the straight line relationship between the yields
of the three resistance classes, as given in Figure l. The
segregating class yielded halfway between the other two
classes. On this basis it would seem that 50 percent of the
plants in the segregating progenies were susceptible and 50

percent were resistant.

Res. Seg. Sus.

Fig. l. Yields of the three resistance
groups in cross A-587.

24

In.Michigan the annual acreage of oats is 1,400,000
and the average yield is 37.0 bushels per acre. It has been
estimated that 40 percent of this acreage, or 560,000 acres,
is planted to stem rust susceptible varieties. The annual
oat production on this acreage, barring any disasters, should
be approximately 20,000,000 bushels and at the current market
price of 85 cents per bushel, the value would be $17,000,000.
If an epiphytotic of oat stem rust should occur, the loss to
Michigan farmers, on the basis of the test reported herein,
would be 25 percent of the $17,000,000, or about $4,000,000
in one year. Furthermore, the loss might be even more severe
if the stem rust epidemic should occur earlier in the growing
season. In this yield test the rust did not become severe
until near heading time. The possible loss to Michigan far-
mers that could be caused by oat stem rust further emphasizes
the need for wider use of oat varieties resistant to stem
rust.

In an attempt to measure the simultaneous effect d? stem
rust on the yield and test weight of the cat strains tested,
the intragroup correlation coefficient was calculated. The
correlation was found to be 4-0.55, a highly significant
value, showing that the rust disease had a dual effect of

reducing both test weights and yield in the cat strains which
it attacked. As would be eXpected the strains having the

lowest test weight and yield had the highest rust readings.

25

Both Huron and Wolverine oat varieties, while highly
susceptible to stem rust, outyielded the resistant variety,
Hajira-Joanette. From an oat breeder's standpoint, this
exemplifies the folly of introducing new varieties on the
basis of disease resistance alone. Even though in all
probability the resistant strains contain many genes from
the poorer yielding resistant parent, Hajira-Joanette, the
average yield of these strains from both crosses outyielded
the susceptible parent in each of the two crosses, A-584
and A-587, by 14 and 6 percent respectively. This indicates
that it is probably more advisable to incorporate disease
resistance into adapted varieties than to introduce exotic
varieties primarily on the basis of their resistance to a

particular disease.

Summary

Thirty-three strains, including resistant, segregating

and susceptible types from two oat crosses, were tested with

the parents in a yield trial to determine the effects of a

stem rust epiphytotic Upon yield, test weight, and date of

heading.
eluded:
1.

From the data obtained, the following may be con-

Resistant strains of oats in the Wolverine X
hajira-Joanette cross headed four days earlier
than the susceptible strains.

Relative test weights were definitely reduced

by 6 percent due to rust infection.

An average reduction of 25 percent in grain
yield of oats was caused in the susceptible

oat strains by the stem rust epidemic. Segre-
gating strains yielded halfway between the re-
sistant and susceptible classes.

Rust played a dual role of reducing both test
weights and yields in the oat strains it attacked.
It is shown that epiphytotics of oat stem rust

in Kichigan could cause losses amounting to four
million dollars in a single year.

It is suggested that stem.rust resistance alone
is not enough to recommend an oat variety because

in this test the adapted susceptible varieties

outyielded the unadapted resistant strain when
they were grown under rust epiphytotic condi-
tions. This shows the advisability of using
an adapted oat variety as the base into which
to incorporate rust resistance instead of re-

leasing exotic resistant varieties.

5.

10.

ll.

28

LITERATURE CITED

Cochran, W. 0., 0. 0. Johnston, and E. J. Heyne. Inheri-
tance of reaction to smut, stem rust, and crown rust in
four oat crosses. Jour. Agr. Res. 70: 45-61. 1945.

Dietz, 8. M3 Inheritance of resistance in oats to Puccinia
graminis avenae. Jour. Agr. Res. 57: 1-25. 1928.

 

East, E. My Heterosis. Genetics, 21:575-597. 1956.

Gerber, R. J. A preliminary note on the inheritance of
rust resistance in cats. Jour. Amer. Soc. Agron. 15:
41-45. 1921.

Gordon, W. L. A study of the relation of environment to
the development of the uredinial and telial stages of
the physiologic forms of Puccinia raminis avenae,
Eriks. and Henn. Sci. Agr. I4:I84-257. I955.

Griffee, F. Breeding oats resistant to stem rust. Jour.
Heredity, 15:187-190. 1922.

Hayes, H. K5, F. Griffee, F. J. Stevenson, and A. P. Lun-
den. Correlated studies in oats of the inheritance of
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tial characters. Jour. Agr. Res. 56:457-457. 1928.

Levine, M. M. and D. C. Smith. Comparative reaction of
oat varieties in the seedling and maturing stages to
physiologic races of Puccinia graminis avenae, and the
distribution of these races In e Un ted States. Jour.
Agr. Res. 55:715-729. 1957.

Litzenberger, S. C. Inheritance of resistance to Speci-
fic races of crown and stem rust, to Helminthosporium
blight, and of certain agronomic characters ofroats.
Research Bulletin 570, Ames, Iowa. December. 1949.

Mackie, W. W. and R. F. Allen. The resistance of oat
varieties to stem rust. Jour. Agr. Res. 28:705-720.
1924.

Melchers, L. E. and J. H. Parker. Rust resistance in
winter wheat varieties. U. S. Dept. Agr. Bull. 1046,

29

12. Newton, M., T. Johnson, and B. Peterson. Seedling reac-
tions of wheat varieties to stem rust and of oat varie-
ties to stem.rust and crown rust. Can. Jour. Res.

15. Parker, J. H. Greenhouse experiments on the rust resis-
tance of oat varieties. U. S. Dept. Agr. Bul. 629.
1918.

14. Smith, D. C. Correlated inheritance in cats of reaction
to diseases and other characters. Minn. Agr. Expt. Sta.
Tech. Bul. 102. 1954.

15. Torrie, J. H. Correlated inheritance in cats of reaction
to smuts, crown rust, stem.rust, and other characters.
Jour. Agr. Res. 59:785-804. 1959.

16. Welsh, J. N. The inheritance of stem rust and smut
reaction and lemma color in cats. Sci. Agr. 12:209-242.
1951.

17. . The synthetic production of oat varieties re-
sistafit to race 6 and certain other physiological races
of oat stem rust. Can. Jour. Res. Sect. 0, 15:58-69.
1959.

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