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A STUDY OF SOME HOMOTHALLIC
AND HETEROTHALLEC
ASCOMYCETES
Thesis. for the Degree of M. S-

LAWRENCE MARION AMES
1929

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A Study of Some

Homothallic and Heterothallic Ascomycetes.

A thesis submitted in partial fulfillment
of the requirements for the degree of

Master of Science

by

Lawrence Marion épes.

(Michigan State College. B. S. 1927)

1929.

THESKS

This thesis is hereby
approved for recommendation

to the Graduate Council.

Major BIDfessor
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Thesis Committee

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Introduction . . . . .
History . . . . . . .
Present Work . . . . .
Methods and Results .

List of Fungi Used . .

Cultural Notes on Species
Discussion and Comparison

Bibliography . . . . . . .

CONTENTS.

Page

14

17

INTRODUCTION. _1_/

The discovery of sexuality in the Mucors by Blakeslee (3)
has stimulated other workers to investigate this highly interesting
problem of sex in the Fungi, as well as to go over the work already
done on the.Mucors.

The work presented in this paper On some of the Ascomy-
cetes was stimulated, both indirectly and directly, by the ideas cf
sexuality as brought out in Blakeslee's work.

The number of Species in this paper includes only a part
of the fungi on which work is being done. It is the plan of the

writer to complete many of this group at a future time.

 

.1/ The present work was suggested by Dr. Ernst A. Bessey of’Michigan

State College, under whose guidance and direction it has been carried

on.

HISTORY.

Heterothallism and homothallism were described by Blakeslee
(3) in the Mucorales. Since then additional work has revealed that
the greater number of the Mucorales belong to the heterothallic group.
In the aquatic Phycomycetes Couch (5) has reported heterothallism for
Dictyuchus, a genus of the Water Molds. numerous investigations have
also been carried on in some cf the higher fungi.

Craigie (6) reports that the sporidia of the Wheat rust and
Sunflower rust are of two distinct sexes which must unite before the
social cups will be formed. Similar sexual differentiation for corn
smut was reported by Hanna at the 1928 meeting of the American Phyto-
pathological Society at New York.

In 1918 further light was thrown on the problem of sexuality
of fungi by the researches of Mlle. Bensaude (1) in which she showed
that qurinus fimetarius, one of the Basidiomycetes, resembles certain
of the Mucorales investigated by Blakeslee in that it is heterothallic.
When sub-cultures were made from two single spore cultures and grown
separately, they remained for eight months in the primary condition,
in which the mycelium branched irregularly, produced no clamp connec—
tions, and consisted of uninucleate cells; furthermore the mycelia
‘were completely sterile, producing no fruit bodies. Hewever, when
two mycelia of Opposite sex were brought together and allowed to fuse,
they soon developed a secondary mycelium which was characterized by
regular branching, the presence of clamp-connections, dicaryon cells,
and the production of fruit bodies.

Kniep (15) has shown that Schizophyllum commune is a hetero-

-3-

thallic species, but that in this species fruit bodies are sometimes
produced from monosporous mycelia. Thus it is seen that the phenomenon
of heterothallism is not necessarily associated with the sterility of
monosporous mycelia. Kniep found that spores originating from such
monosporous fruit bodies were all of the same sex, and that when sown
in polysporous cultures the mycelium to which they gave rise never
produced clamp-connections. Thus in a heterothallic species fruit
bodies may develop from monosporous mycelia; but such fruit bodies
produce spores which are all of one sex.

Both Mlle. Bensaude (1) and Kniep (14) have found that the
presence of clamp-connections is invariably associated with the con-
jugate division of the nuclei. It is thought, because of this then,
that a reliable criterion is thus established for determining whether
a given species of Basidiomycete is homothallic or heterothallic. If
on monosporous mycelia clamp—connections appear regularly, the species
must be homothallic; while if on monosporous mycelia.no clamp-connec-
tions or fruit bodies appear until two mycelia of Opposite sex fuse
together, the species must be heterothallic.

Miss Mounce (17 & 18) has shown that Coprinus sterquilinus
and C. stercorarius are homothallic, and that C. lagOpus and C. niveus
are heterothallic. Thus in a single genus there exist homothallic and
heterothallic species.

Hanna (12) carried the work on Coprinus lagopus further and
showed that sex in this fungus is determined by factors which segre-
gate according to Mendelian principles. Newton (19) duplicated

Hanna's work and obtained similar results.

A study of the sexual differentiation on coprOphilous
Pyrenomycetes has been reported by the Marchal Brothers (16) which
will be referred to later. Edgerton (9) reported the occurrence of
plus and minus strains in the genus Glomerella which is interesting
because it is hetero-homothallic. Reference will be made to this
later. Dodge (8) showed that two separate strains are necessary for
the complete formation of fruit bodies in éscobolus mggnigigus. Bette
(2) reports heterothallism for Ascobolus carbonarius. Miss Wineland
(25) caused the production of mature perithecia of a species of
Gibberella when she placed certain strains together. Kirby (13) re-
ports the occurrence of two strains in Ophiobolus cariceti. Shear
and Dodge (21) have demonstrated the heterothallic nature of Eggggr
spora_§itophila. Dodge (7) gives the cytological explanation for
this behavior in Neurospora. Wehmeyer (23) gives a historical summary
of sexuality in the Ascomycetes.

With the background so well outlined the present work was
begun with the hope Of adding a little more to the already available

data.

PRESENT WORK.
Methods and Results

Single spore cultures were made of all the species listed
below. The single spore cultures were obtained by the dry needle
method as described by Hanna (11). All Species of Chaetomium were
cultivated on potato dextrose agar except C. murorum which was grown
on agar made from horse manure water. Fimetaria fimicola was also
grown on potato dextrose agar. The remaining species, which includes
species of Pleurage, Ascobolus, and an unidentified Pyrenomycete,
were grown on horse manure agar.

These experiments were repeated several times always using
single Spore cultures.

The results 0f the experiments are as follows:

All species of Chaetomium studied were homothallic.

All species of Pleurage studied were homothallic.

Fimetaria fimicola was found to be homothallic.

Ascobolus gtgrgorarius was found to be hetero-homothallic.

Aggggbglg§_imm§z§u§ gave no results that are satisfactory.

One species of an unidentified Pyrenomycete was proven to

be heterothallic.

2.

3.

4.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

LIST OF FUNGI USED.

Chaetomium globosum Kunze.

C.

C.

C.

C.

C.

elatum;Kunze & Schmidt.
funicolum Cook.

spirale Zopf.

aureum Chivers.
trilaterale Chivers.
cochliodes Pallister.
angustum Chivers.
aterrimum Ellis & Everhart.
murorum Corda.

sp- 1/

Sp.

Sp.

Fimetaria fimicola (Roberge) Griffiths & Seaver.

Pleurage

anomala D. Griff.

arizonensis D. Griff.

anserina (Ces.) Kuntze.

decipiens (Wint.) Kuntze.

minute (Fuckel) Kuntze.

Ascobolus immersus Pers.

A.

stercorarius (Bu11.) Schrot.

Pyrenomycete of unknown genus and species.

.1/ Species No. 11, 12, and 13 of Chaetomium are as yet unidentified.

They are not included in Chivers' (4) monograph. These C. species are

all homothallic.

-7-

CULTURAL NOTES ON SPECIES.

.ghaetomium:glpbosum Kunze._l/
Origin: This was given to me by Mr. F. C. Strong, of
Michigan State College, who found it on.some straw which came from
Maryland.

2/

Single spore cultures' on potato dextrose agar gave rise
to mature perithecia after a period of two and a half weeks. Growth
is very rapid. Perithecia appear in great numbers. The union of

mycelia from single spore cultures gives no evidence of increased

fructification.

Chaetomium_g1§tum Kunze and Schmidt.
Origin: Found on straw from horse barn at Michigan State
College.
Single spore cultures on potato dextrose agar grew very
rapidly, producing mature perithecia after a period of two and a half
weeks. There is no evidence of increased fruiting by the union of

single Spore cultures.

Chaetomium funicolum Cooke.

52/

Origin: Found on straw from horse barn.

Single spore cultures on potato dextrose agar gave rise to

 

.1/ All species of Chaetomium studied had 8 spores per ascus.
.g/ In no case were there less than thirty single spore cultures of
each species of Chaetomium grown.

.Q/ When not otherwise stated the origin is at Michigan State College

or immediate vicinity.

~8-

mature perithecia after a period of three weeks. Perithecia occur in
great numbers. The union of mycelia from single spore cultures gives

no evidence of increased fruiting.

.ghggtgmium spirals ZOpf.
Origin: Found on straw from horse barn.
Single spore cultures on potato dextrose agar gave rise to
mature perithecia after a period of three weeks. Perithecia numerous
but not crowded. The union of mycelia from single spore cultures

gives no evidence of increased fruiting.

gpgptomium aureum Chivers.
Origin: This was sent to me by Mr. Edgar C. Tullis of the
University of Arkansas. This fungus was found on the hulls of rice.
Single spore cultures on potato dextrose agar gave rise to
mature perithecia after a period of three and a half weeks. The
perithecia are numerous and closely compacted, forming a dense mat.
The union of mycelia from single spore cultures gives no evidence of

increased fruiting.

Chaetomium trilaterglg Chivers.
Origin: This was given to me by Mr. Stanley Johnston of
South Haven, Michigan. This fungus appeared in cultures made by him
from roots of blueberry plants (Vaccinium sp.)
Single spore cultures on potato dextrose agar gave rise to

mature perithecia after a period of three weeks. Perithecia formed

-9-

abundantly. The union of mycelia from single spore cultures gives no

evidence of increased fruiting.

.thetomium cochliodes Pallister.
Origin: Found on paper which was in contact with straw and
horse dung.
Single spore cultures on potato dextrose agar grew rapidly,
producing mature perithecia after a period of two and a half weeks.
The union of mycelia from single spore cultures gives no evidence of

increased fruiting.

Chaetomium angustum Chivers.
Origin: Found on straw from horse barn.
Single spore cultures on potato dextrose agar gave rise to
mature perithecia after a period of three weeks. Perithecia formed
abundantly. The union of mycelia from single spore cultures gives no

evidence of increased fruiting.

.thgtgmigm aterrimum Ellis and Everhart.

Origin: Found on wheat straw from horse barn.

Single spore cultures on potato dextrose agar gave rise to
mature perithecia after a period of three and a half weeks. Growth
is much slower than in g. globosum, and the perithecia are moderately
abundant. The union of mycelia from single spore cultures gives no

evidence of increased fruiting.

-10-

ggetomium murorum Corda.

Origin: Found on horse dung.

Single spore cultures on agar made from horse manure water,
gave rise to mature perithecia after a period of three and a half
weeks. mycelial growth not conspicuous, but soon covers entire sur—
face of agar in petri dish. Perithecia few and scattered. The union

of mycelia from single spore cultures gives no evidence of increased

fruiting.

Fimetaria fimicola,(Roberge) Griffiths and Beaver.

Origin: Found on horse dung.

Single spore cultures on dung agar gave rise to mature
perithecia after a period of three weeks. mycelial growth is rapid.
Perithecia form in abundance over entire surface, ranging from sunken
to superficial. The union of mycelia from single Spore cultures gives

no evidence of increased fruiting. Ascus 8 spored.

Pleurgge anomala D. Griff.

Origin: Found on horse dung.

Single spore cultures grown on horse dung agar gave rise to
unature perithecia after a period of three and a half weeks. mycelial
egrowth scanty, perithecia few and scattered, mostly sunken or partly
imbedded in substratum. Mycelial union from single spore cultures

Egives no evidence of increased fruiting. Asci 4 spored.

-11-

Iglggragefiggizonensis D. Griff.

Origin: Found on horse dung.

Single spore cultures grown on horse dung agar gave rise to
mature perithecia after nearly four weeks. Mycelial growth scanty,
perithecia few and scattered, partially sunken in the substratum. The
union of mycelia from single spore cultures gives no evidence of in-

creased fruiting. Asci 4 spared.

P eur e anserina (Ces.) Kuntze.

Origin: Found on horse dung.

Single spore cultures on horse dung agar gave rise to mature
perithecia after a period of three and a half weeks. mycelium spreads
quite rapidly over surface of agar, but is scanty; perithecia few and
scattered, partly sunken in the substratum. The union of mycelia

from.single spore cultures gives no indication of increased fruiting.

.Asci 4 spared.

Plgggggg degipiens (Wint.) KUntze.

Origin: Collected on horse dung.

Single Spore cultures grown on horse dung agar gave rise to
nnature perithecia after a period Of three and a half weeks. mycelial
Egrowth scanty, perithecia few and sunken in the substratum. The union

(Jf'mycelia,from single spore cultures gives no evidence of increased

xfruiting. Asci 8 spored.

-1“-

.ggggrage minuta (Fuckel) Kuntze.

Origin: Found on horse dung.

Single spore cultures grown on horse dung agar gave rise to
mature perithecia after three and a half weeks. mycelial growth
scanty, perithecia few and scattered, superficial or with base slightly
sunken in the substratum. The union of'mycelia from.single spore cul-

tures gives no evidence of increased fruiting. Asci 8 spared.

Asgobolus immersus Persai/

Origin: Found on weathered horse dung.

Two single spore cultures were obtained after many attempts
to germinate the spores. These two single spore cultures produced no
fruit bodies. Mycelial matings of these two cultures produced no
fruit bodies. Ramlow (20) explains that plain manure agar gives very
weakzmycelial growth and almost never the fruit bodies of Ascobolus
immersus, but if filter paper is added to the manure agar the spores
produce vigorous mycelia and abundant apothecia.

No conclusion can be made from.my work.

Aspobolus stercorariig (Bu11.) Schrot.

Origin: Found on horse dung.

Single spore cultures gave rise to a very few scattered
apothecia after a period of four to five weeks. Of more than twenty
single spore matings, approximately fifty per cent gave rise to
abundant apothecia along the margin where the mycelia of the two
,1/ Species of Ascobolus were identified according to Seaver's (22)

recent work.

 

(Ills-ll? III" 1.11

—13-

strains met. In the other cultures no fruiting resulted from such
union of mycelia. It is concluded from the data obtained that this

species is hetero-homothallic.

Spherical Pyrenomycete.
Genus? sp.?

Origin: Found on old cultures of horse dung.

Single spore cultures produced no fruit bodies. mycelial
matings from nine single spore cultures produced perithecia in appro-
ximately fifty per cent of the matings along the margin where the two
mycelia met. The remaining'matings produced no perithecia. The
spores Of this fungus were induced to grow only after being treated
in dilute HCl (1/10 of 1%) and incubated in a hot air oven for twenty
minutes up to 70°C. The experimental data indicate that this fungus
is heterothallic.

Perithecia scattered or thinly gregarious, superficial,
spherical, non-astialate, covered on all sides when young with long
ribbon-like cream colored appendages of uniform dimensions throughout
their length. As the perithecium matures the appendages disappear,
leaving it naked. Perithecia reach diameter of 609*, Asci club-shaped,
75-90 x 20“, 8 spared, soon dissolving leaving ascospores loose in
perithecia. Spores lemon-shaped, apiculate at both ends 12-15.5 x 8-llft.

Ascospores escape by the decaying of the perithecia.

 

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-l4-

DISCUSSION AND COMPARISON.

The work of Marchal (16) on Chaetomium elatum Kunze and
Hypoc0pra fimicola Sacc. (Fimetaria fimicola (Boberge) Griffiths and
Seaver) is substantiated by the present work, in which like that of
Marchal a cytological investigation of the nuclear behavior was not
included.

Dodge (7) in his study of Neurospora found an interesting
phase of spare formation in the species N. tetrasperma. The ascus in
this species normally contains four spores. If several perithecia are
crushed in which spores are maturing there wdll probably be found one
or two asci with an abnormal number of spores such as three large and
two small spares, or even in an extreme case only one giant spore.
Shear and Dodge (21) found that monosporous mycelia fran such small
spores bore only sclerotia or bodies which resembled aborted perithecia.
No ascospores deve10ped in these structures. By preperly mating these
cultures, normal perithecia are formed containing asci which normally
have only four spores. The larger normal spores have two nuclei when
first delimited and thus contain muclei of both sexes. One might con-
ceive from the above data that in a genus which contains both four and
eight spared species he would find them to be homothallic and hetero-
thallic respectively.

Wilcox (24) found , in the heterothallic species Neurospora
sitophila which has 8 spared asci, that the spare haplonts may be
arranged in the ascus in either one of the four following combinations,
AA, BB, AA, BB: BB, AA, BB, AA; AA, BB, BB, AA; or BB, AA, AA, BB, where

A and B are reciprocal as to their sexuality.

 

(iv‘ ‘1“: 1.7 '1'il1) (I

-15-

In my work I found that the four and eight spared species of
the genus Pleurage were both homothallic. The nuclear condition in
these species has not been studied. However, if it is assumed that
the four spared species has two nuclei per spare and that the eight
spared species has one nucleus per spore it must be granted, at least
for the eight spared species, that the sex determiners are carried in
one nucleus. It is therefore clear that in a genus in which the num»
ber of spores varies with the species no prediction can be made that
one of the BpOCiBS‘Wlll be homothallic and the other heterothallic.

Edgerton (9) found in the genus Glomerella a condition which
approaches that found in the Mucorales. The peculiar trait of pro-
ducing abundant perithecia at one time and a scarcity at another time
in nature gave grounds for presupposing sexual differentiation. Sin-
gle spore isolations yielded two strains, a "plus" strain of floccose
growth and abundant aerial mycelium, and a "minus" strain with scarce-
ly any aerial mycelium. However, single spore cultures of each strain
produced abundant perithecia. When both strains were grown in one
petri dish there appeared a great mass of perithecia along the margin
where the mycelia of the two colonies met. To determine whether this
was truly sexual stimulation or due to chemical and food conditions
some of the perithecia on the border were crushed and separate asci
were removed and planted separately in petri dishes. Edgerton found
that segregation took place giving the two characteristic strains.
This segregation 0f strains gives definite proof that there was sex-
ual stimulation and therefore that there is sexual differentiation.

A similar condition was found in.my work with Ascobolus

 

-15-

stercorgrius. Single Spore cultures of this species gave rise to a
few apothecia. By mating single spore cultures it was found that
approximately 50% of the matings stimulated a great abundance of
apothecia along the margin where the mycelia of the two strains met.
In the other cases there was no such stimulation. This shows clearly
that whereas single spore cultures may produce a few apothecia there
is, however, a definite sexual differentiation. Such a species can
be designated as a hetero-homothallic form. Further work is in pro-
gress to discover whether the antherids are functional in all cases
or whether parthenogamy may occur to explain the production of the
occasional apothecia on single spore cultures. The two single spore
cultures of ggggbolus immersus produced no fruit bodies. These two
mated together also produced no fruit bodies. Difficulty was encoun-
tered in germinating these spores. I have not done enough with this
species to venture even a guess as to its sexuality. However, Ramlow
(20), who studied this species morphologically and cytologically,

has demonstrated that this species is parthenogamic (i.e. there is no
distinct antherid and the paired nuclei in the ascogonial cells and
ascogenous hyphae are all of ascogonial origin). Such a species would
necessarily be homothallic unless antherids are formed when two sexes
of mycelia are present, and no antherids if only one is present. He

further found that A. immersus fruited well when a portion of filter

 

paper is partly immersed in the manure agar. The manure agar alone
produced a weak mycelium and almost never the fruit bodies. In.my
culture media of manure agar no filter paper was added; this may ex-

plain the weakness of growth and the non—production of fruit bodies.

2.

4.

5.

8.

-17-

BIBLIOGRAPHY.

Bensaude, M; Recherches sur le cycle evolutif et la sexualité
chez les Basidiomchtes. Nemours,l-156. Pls. 1-13. Figs.
;;§Q. 1918.

Betts, Edwin M. Heterothallism in Ascobolus carbonarius. Ameri-
can Jaurnal of Botany.l§: 427-432. Tables I-II. 1926.

Blakeslee, A. F. Sexual reproduction in the Mucorineae. Proceed-
ings of the American Academy of Arts and sciences g9: 205-319.
215. 1-5. 1904.

Chivers, A. H. A monograph of the genera Chaetomium and Ascatricha.
Memoirs of the Torrey Botanical Club lg: 155-240. Pls. 6-17.
1915.

Couch, J. N. Heterathallism in.Dictyuchus, a genus of the water
molds. Annals of Botany.gg: 849-881. Pls. 35-38. Fig. 1-3.
1926.

Craigie, J. H. Discovery of the function of the pycnidia of the
rust fungi. Nature-129: 765-767. Figs. 1-2. 1927.

Dodge, B. 0. Nuclear phenomena associated with heterothallism and
homothallism in the Ascomycete Neurospora. Journal of Agricul-
tural Research.§§: 289-505. P13. 1-3. Fig. 1-5. 1927.

Dodge, B. 0. The life history of Ascobolus magnificus. Mycologia
.lg: 115-154. Figs. 1-28. Tables 1-2. Pls. 7—8. 1920.

Edgerton, C. W. Plus and minus strains in the genus Glomerella.
American Journal of Botany.1: 244-254. Fig. . Pls. 22-23.

1914.

10. Griffiths, David, and Seaver, Fred Jay. North American Flora .

p: 65-88. 1910.

wii‘ .Ih .11 ll

(fill!) .11." a?" r. ‘

 

-18...

11. Hanna, W. F. The dry-needle method of making monosporous cultures
of Hymenomycetes and other fungi. Annals of Botany 38: 791-795.
Fig. 2. 1924.

12. . The problem of sex in Caprinus lagOpus. Ibid. 32:
431-457. Tables 1-15. 1925.

13. Kirby, R. S. Heterothallism in Ophiobolus cariceti. (Abstract)
PhytOpathology.l§: 35. 1923.

14. Kniep, H. fiber morphologische und physiologische Geschlechtsdif-
ferenzierung. Verhandl. der Physikal-Med. Gesellschaft zu
Wurzburg.4§: 1-18. 1920.

15. . Beitrage zur Kenntnis der Hymenomyceten. Zeitschr.
f. Botanik_9: 101—119. 1917.

16. Marchal E1.et Em. De 1"”homothallism’J de quelques Ascomchtes.
Academic Royals de Belgique. Bulletins de la classe de Sci-
ence 5e Serie.. .9: 8-13. 1923.

17. Mounce, I. Homothallism and the production of fruit bodies by
monosporous mycelia in the genus Caprinus. Transactions of
the British Mycological Society. 1: 198-217. 1921.

18. . Homothallism and heterothallism in the genus Caprinus.
Ibid..§: 256-269. 1922.

19. Newton, Dorothy E. The distribution of spores of diverse sex on
the hymenium of Caprinus lagopus. Annals of Botany.gg: 891-
917. .ggbles 1-7, Diggrams 1-4. 1926.

20. von.Ramlow, G. Beitrage zur Entwicklungsgeschichte der Ascoboleen-
Mycologisches Centralblatt p: 177-198. Pls. 1-2. Figs. 1—20.

1915.

21.

22.

23.

24.

25.

-19..

Shear, C. L., and Dodge, B. 0. Red bread mold fungi of the Monilia
sitophila group, life history and heterothallism. Journal of
Agricultural Research pg: 1019-1042. Pls. 1-4. 1927.

Seaver, Fred Jay. The North American Cup-fungi (Operculates)
pp. i-vii. 1-284. Pls. 1-45. Figs. 1-15. 1928.

Wehmeyer, L. E. The perfect stage of the Valsaceae in culture, and
the hypothesis of sexual strains in this group. Papers of the
Michigan Academy of Science _4: 395-412. P1. 19. 1924.

Wilcox, Marguerite S. The sexuality and arrangement of the spores
in the ascus of {eurospora sitophila. mycologia.29: 3-17.

Pl. 2. Fig. 2. 1928.

Wineland, Grace 0. The production in culture of the ascigerous

stage of Fusarium moniliforme. (Abstract) PhytOpathology

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