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THE ANTHRACNOSE COMPIEX ON SOYBEANS
Lola Hattery Tiffany
A D issertation Submitted to the
Graduate Faculty In P artial Fulfillm ent of
The Requirements for the Degree of
DOCTOR OF PHILOSOPHY
t
Major Subject Plant Pathology
rfead of Major Department
E ge
Iowa State College
1960
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UMI Number: DP12218
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TABIE OF CONTENTS
INTRODUCTION...................................................................................................... 1
PART I — HISTOLOGICAL STUDIES......................................................... 4
lite ra tu re R eview ............................................................................. 4
Materials and Methods ................................................................... 8
Observations .............................................. . . . . . . . 10a
Discussion .................................................................... 28
PART II — TAXONOMIC STUDIES............................................................. 28
Introduction ...................................................................................... 28
M aterials and Methods ........................................................ 30
Observations ............................................................................ 32
Dlsoussion • ...................................................................................... 61
SUMMARY............................................................................................................... 70
LITERATURE CITED............................................................................... . 72
ACKNOWLEDGMENTS................................................................................... 76
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INTRODUCTION
Soybeans, although a relativ ely new crop In this coun
try , are taking an Important place In midwest agriculture.
A wide range of plant varieties and selections have been
Introduced, and these are being worked with intensively in
an effo rt to obtain selections that are b etter adapted for
specific uses and for environmental conditions and growing
seasons in various sections of the country. At the present
time they are not a host to any extremely destructive path
ogenic organisms, but are attacked by a number of diseases
that are responsible for small losses in plantings of the
present standard v arieties. With changes in the genetic
composition of the host plant, pathogens that were formerly
of only minor importance may be able to develop rapidly and
destructively, thus a complete knowledge of a ll of the fungi
that are capable of parasitizing soybeans is a valuable tool
for the breeding program.
Among the minor diseases is anthracnose, which, although
not studied intensively previously, has been reported from
a ll major soybean growing areas. The development of disease
symptoms, as is true of other legume anthracnoses, Is depen
dent upon environmental conditions. This has made d iffic u lt
the evaluation of the destructiveness of the disease. Soy
bean anthracnose was originally considered to involve only
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the pods and stems of mature plants, but the causal agent has
la te r been found to cause a seedling blig h t also. Because
of widespread occurrence and pathological p o te n tia litie s,
the disease was chosen for a more Intensive study.
Collections of diseased field m aterial were made in the
f a ll of 1945. Three fungus en titles of the genus C olletotr-
iohum that were Isolated from stems of the variety Lincoln
In these collections have subsequently been isolated from a
wide range of soybean varieties in Iowa and also from d is
eased soybean plants from M ississippi. Of the three, one
was the form described as Colie to trlchum glycines Horl, which
has been accepted as the causal agent of soybean anthracnose,
one was identical with the ascomyoete Qlomerella glycines
(Horl) Lehman and Wolf but its conidlal form differed from
Colletotrichum glycines that had e arlier been connected with
I t , and the third was a straig h t spored conidlal form that
has not been studied on this host.
Subsequent work has been divided into two general
fie ld s: (1) histological studies of the development of soy
bean anthracnose and (2) comparisons of the soybean e n titles
with cultures of various Colletotrichum species that have
been described do other legume hosts.
As a resu lt of the comparisons discussed In d etail in
part two, the three en tities have been identified as
Colietotriohum truncatum (Schw.) Andrus and Moore, Qlomerella
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•3*
glycines, and ColietotrIohum deatruotlvum O'Qara. In pre
liminary pathogenicity te a ts, £• t rune a turn wan found to be
the moat active parasite of the group. It was successfully
isolated from brown areas on the underside of major leaf
veins, from pods, from stems, from both diseased and appar
ently normal seed, and is undoubtedly responsible for much of
the field loss due to anthracnose. Consequently the more
detailed studies on various phases of disease development
have been limited to work with this one species. The time
and mode of entry and the histological details of development
of the fungus after entry into the host plant were investi
gated. Such information is basic to the determination of
damage attributable to the disease and to the establishment
of effective control measures.
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