STUDIES ON THE WHEAT SCAB， CAUSED BY

GIBBERELLA ZEAE (SCHW.) PETCH， AND ITS CONTROL

By

Yosikazu NISIKADO

INTRODUCTION

The present disease seems to have been known sin巴elong before， not only in Japan， but also in almost a11 over the world. As the rainy season， so called “Tsuyu"， in Japan sets u自uallyin the ripening period of wheat and other

cereals， the damage of thi自 diseasemight be sometimes especially severe， although it had been attributed to the rain damage. The disease was caused

by a parasitic fungus， which has a very wide range of host plants of Grami-

neae and other families. Among these， the damage on wheat， known as head blight， scab or seedling blight， was especia11y prominent. The disease was

studied by many plant pathologists of a11 the world， and great many numbers of reports had been published. But no suitable method to control this disease

had been shown. In 1913 the writer began to investigate the scab or head blight disease

of wheat fundamenta11y， hoping to ascertain some reliable method for the protection. After then the project was continuously supported by the Ministry

of Agriculture and Forestry. The results of the writers' investigations have

already been published in progressive annual reports to the Ministry of

Agriculture and Forestry and in other papers. Although further investiga-

tions must be done in many points， the writer thought it we11 to compile a11 the available data of his work田， as circumstances compe11ed him to do so.

Lately they were published in a paper in Japanese “Komugi no Akakabi-byo ni kansuru Kenkyu"， or Studies on the wheat scab caused by Gibberella zeae (SCHW.) Pet巴hand its control， published in the “Nogaku Kenkyu" or Report of the Ohara Institute for Agricultural Biology， Okayama University， Vol. 45 pp 59-86， 141-158， 159-220， Vol. 46， pp 1-47，1958， and also in the “Nogyd Kairyo Gizyutsu Shiryo" or Publications for the Impl'oving Agri-

巴ulturalTechnique of the Ministry of Agriculture and Forestry， No. 97， pp. i

ー玄， 1ー162，References: pp.144-153， English summary: pp.155-162， Plate I-XVIII， March 1958. The contents of the original paper in Japanese， above mentioned， and the summary and some of the Plates are given in this paper.

During the course of the investigation the wriもerhas been much obliged to Messrs. Hideo Nishigori， Director of the Resear巴hDepartment; Shinjiro Akimoto and Jiro Takeuchi， Former Heads of the Agricultural Production Section; Masaakira Hori， Head of the Plant Protection Section; Umenojo Bokura， Kazuo Goto， Project Leader of the Plant Protection; Yoshihisa

Iizuka， Chief of the Forecast of Disease Outbreak， and others of the Ministry

142 Berichte d. Ohara 1nstituts (Bd. 11， Ht. 2

of Agriculture and Forestry; Takao Nakayama， and many other former and

pressent members of the Plant Pathology Laboratory of the Ohara Institute

for Agri巴ulturalBiology， Okayama University. To these gentlemen the writer

wishes to express his sincere thanks. Thanks are also due色oDr. Shunsuke

Kusano， Professor emeritus of Tokyo and other professors and researchers in

the plant pathology laboratories of many National Universities and National

or Prefectural Agri巴ulturalExperiment Stations for their kind suggestion

and supply of research materials.

Contents of the Original Paper in ]apanese

1. 1ntroduction....・H ・..…....・ H ・..……...・H ・.......・ H ・.....・ H ・..…………...・ H ・H ・H ・........・ H ・.....・ H ・.1 11. Hi目t刀ricalreviews.……・….....・ H ・.....・ H ・........・ H ・.....・H ・.....……・ H ・H ・..……...・ H ・.....・ H ・....1 III. Name and distribution of the disease.…....・ H ・....・H ・...........・ H ・.....・ H ・........・ H ・.....・H ・....3

IV. Symptoms'"…H ・H ・...・ H ・.....・ H ・.....・ H ・...…・…...・H ・...・ H ・…...・ H ・H ・....・ H ・……...・ H ・H ・H ・..…..6 V. Causal fungus ....・ H ・..…-…… H ・H ・...… H ・H ・...… H ・H ・....・ H ・...・ H ・H ・.....・ H ・...…....・ H ・...・ H ・....8

1. Ta:'l:onomy and name.......・H ・..… H ・H ・....…・・…...・ H ・...…・・…...・ H ・.....・ H ・・ H ・H ・....・ H ・H ・H ・.8

2. Morphological characters …...・ H ・・ H ・H ・・ H ・H ・..…・・………………・…・・…… H ・H ・・ H ・H ・.......101 Pycnidium stage. y…...・ H ・・ H ・H ・.....・ H ・..… H ・....…..…・・・・・・・ H ・H ・..……...・H ・.....・ H ・....102 Peritheeium stage...…・…...・ H ・..…-…..……………・・・…...・ H ・..…...・ H ・.....・ H ・.....・H ・.12

3. Physiological eharacters.…...・ H ・.....・ H ・・・………...・H ・..………...・H ・..…….....・ H ・・ H ・H ・....131 Variation in character・sof colony and spores in relation ωthe origins

isolated..・・・…...…・・・・・・・・・……… H ・H ・…… H ・H ・H ・H ・…・・・……...………......… H ・H ・…・・・.132 Effect. of environments on the mycelial growth.……・…....・...……・ H ・H ・.....・ H ・.13

i) Temperature.…...・ H ・.....・ H ・...…...・H ・..… H ・H ・..…....・H ・..… H ・H ・.....…・ H ・H ・....13ii) Hydrogen ion concentration of the culture medium...…H ・H ・...・H ・.....・H ・..13

3 i) Effect of environments on the conidium formation'"・H ・..…・……...・ H ・..…・・14a) Temperature b) Moisture c) Age of culture d) Nutrients e) Light

ii) Effect of environments on the eonidium germination'…… H ・H ・...・H ・H ・H ・....17a) Temperature b) Moisture c) Nutrients d) Light e) Density of

conidium in suspesion f) Duration of drying the coniclium g) Age

of conidium or duration of conidium after the formation h) Effect of washing the eoating material of eonidium

4 Effect of environments on the formation and germination of aseospore'……・・21i) Variatien in peritheeium formation among various isolates...・H ・・ H ・H ・..…・・21

ii) Effect of environments on the perithecium formation...…H ・H ・-……，..・ H ・.22a) Temperature b) Moisture e) Moisture contents in air during the

preservation of peritheeium d) Duration of drying the peritheeium 5 Sexuality of the wheat scab fungus....・H ・..…............・ H ・....・H ・...….....・H ・.....・H ・.256 Considerations on the result渇・・H ・H ・…...・ H ・.....・H ・-…………・…...・H ・..… H ・H ・.....・ H ・.26

VI. Penetration and infection of the wheat scab fungus to host plants.......-唱・ H ・H ・H ・H ・.291. Fungus penetration to wheat heads.......・H ・H ・H ・.....・H ・..…...・ H ・....・ H ・…...・ H ・.....・ H ・....29

1 Penetration through the glumes..…・・……・ H ・H ・..…...・ H ・.....・ H ・.....・ H ・.....・ H ・..…・・292 Penetration through the anthjlrs・-……・・…...・ H ・........・ H ・.....・ H ・H ・H ・..…...・ H ・H ・H ・.30

2. Fungus penetration to wheat 回 edlings....・H ・-…・・…-…....・H ・-……… H ・H ・...・ H ・...・H ・-・・311 Penetration through young r∞ts......・H ・・・H ・H ・-……・…....・ H ・....・ H ・・・ H ・H ・....・ H ・....312 Penetration through cotyledon........・H ・....…...・ H ・..…....・H ・....・ H ・......・H ・.....・H ・-・・31

3. Consideration自 on the resul ts・………・・・… H ・H ・...・ H ・..…...・ H ・..…...・ H ・..…....・H ・.....・H ・32VII. Variation in pathogenicity of wheat scab fungus and in its resistance to fungicides"'33

1. Pathogenicity of various isolates of the fungus at the time of wheat germination...33 2. Pathogenicity of the fungus to young wheat plants....・・....・・・・ H ・H ・.....・ H ・H ・H ・H ・H ・....36

1 Pathogenicity variation of mycelil!m…・ H ・H ・..…・…-….......・....・ H ・.....・H ・-‘H ・H ・-・38

1959) Nisikado: Studics on the Wheat Scab 143

2 Pathogenicity of conidium'"・H ・...・ H ・.....・ H ・-“・…H ・H ・....・ H ・...・H ・.....・H ・-……'"・H ・.893 Pathogenicity of allCoopor蝿 H ・H ・...・ H ・._...・H ・-……・・・…… H ・H ・.....・ H ・...…… H ・H ・….39

4 Pathogenicity variation of an iliolate to the wheat variety， from which the isolate wa8 taken'"…..一…...・H ・....・ H ・.....・H ・.............・ H ・.....・ H ・...・H ・.....・H ・.40

5 Pathogenicity variation in regard to the kinds of medium， and to the repeating of transplant ・・…...・H ・.....・H ・.....・ H ・....・ H ・.........・H ・..… H ・H ・.....・ H ・.......41

6 Comparioon in the scab susceptibility between wheat heads and seedlings...…42

3. Resistance variation of the fungus to various fungicides.…...・ H ・H ・H ・.....・ H ・H ・-…・・.44

4. Considerations on the results....・H ・.........・H ・..…..，・H ・...・ H ・....・H ・....・H ・H ・H ・....・ H ・..…・・.44

VIII. Susceptibility of wheat varietieo to the scab'"・H ・..…・・…………...・H ・H ・H ・.....・H ・..….45

1. Effect of the maturity of wheat head on the scab ousceptibility"・H ・...・ H ・....・H ・...452. Effect of inoculation temperature on scab susceptibility'"・H ・..…...・ H ・..……H ・H ・...493. Reactions between various head characters of wheat varieties， and scab

susceptibility ....・ H ・・.......…・… H ・H ・...・H ・..… H ・H ・.....・ H ・H ・...........・H ・.....・ H ・.....・ H ・..…・・60

1 Relations in susceptibility to the length， thickness， width， and awn-length of wheat heads， respeotively....・H ・H ・H ・.....・ H ・...・H ・...・ H ・........・ H ・......…..51

2 Relations ωthe height of wheat plant and to the density of spike-Iet， respectively.............. ...…・・・・・・・・・…・・・・・・…・・・…・....................・・・・・・・・・….......・・・・・・・・・61

3 Relations to the color of wheat heads..…......・ H ・.......・ H ・…...・H ・.....・H ・H ・H ・..…・614. Relations in susceptibility between germination stage and maturation stage...…・・・53

5 Relations in susceptibility between seedling stage and maturation stage......・H ・..63

6. Relations in susceptibility between maturation periods and wheat varieties..'・H ・..54

7. Considerations on the results.....……...・H ・....・ H ・......・H ・..…・・…・…・H ・H ・H ・H ・..… H ・H ・....67IX. Disseminations of the wbeat scab........・H ・.....・ H ・..…...・H ・....・ H ・… H ・H ・...・H ・....・ H ・..…..59

1. R・lationsbetween the shape of scabbed grains and the germination...・H ・…...・ H ・-…591 Shape of scabbed grains.......・H ・..…....・ H ・H ・H ・.....・H ・..…...・H ・.....・H ・-…...・ H ・..…・・59

a) Size， weight of one thousand grains and specific gravity b) Width and thicknes目

2 Germination of scabbed wheat grains …・…...・ H ・...…… H ・H ・・ H ・H ・H ・H ・-…...・ H ・....60a)日ffectof temperature on 七he 1!'6rmination of healthy graino

b) Effect of soil temperature on the germination of scabbed grains

c) Soil moisture and the germination of scabbed graino d) Size of

scabbed grains and the germination e) Thickness of covering soil

and the germination

3 Seed selection for the sake of control of primary outbreak"・・・・H ・H ・-….....・ H ・..62i) Specific gravity of scabbed grains.....…・…-…...・…… H ・H ・...・H ・-…...・ H ・....63a) Specific gravity b) Specific gravity and germination c) Specific

gravity and the presence of hyphae inside the grains

ii) Size of grains and specific gravity..……...・H ・....・ H ・…...・H ・..…… H ・H ・...・H ・65a) Size of scabbed grains and specific gravity b) Size and specific

gravity of scabbed grains and the germination c) Size and specific

gravity of scabbed grains and the presene of phyphae inside the grains

iii) Winnowing selection of 即時bedgrains and the specific gravity'"・H・-…・66a) Specific gravity of winnowed grains b) Germination of the scab-

bed grains selected by the winnowing and by the specific gravity

c) Presence of inner hyphae inside the scabbed grains selected by

the winning and by the speci4'ic gravity

4 Considerationo on the results....・H ・..…・ H ・H ・...・・・ H ・H ・...… H ・H ・.....……...・ H ・..…・・70

2. Pri皿arydi回 emination...…....・ H ・...・H ・.....・H ・....・ H ・.......・H ・H ・H ・..…・H ・H ・.....・H ・...・H ・..…70

1 Course of primary outbreak........・H ・...・ H ・H ・H ・...・ H ・...・H ・-…....・H ・...・H ・H ・H ・....….71

i) Longevity of scab fungus......・H ・....・H ・.......・ H ・........・ H ・.....・H ・.....・H ・...・H ・...71a) On agar medium b) On ric6 straw mediu血

ii) Season of the formation and maturations of the fungus perithecium‘・・…72

144 Berichte d. Ohara Instituts (Bd. 11， Ht. 2

iii) Perithecium formation in fie1ds"…H ・H ・...・H ・....・H ・""・H ・.....・H ・...・H ・.....・・・・.73

a) Formation and maturation of the perithecium b) Formation and

maturation of the perithecium on straw of rice， wheat and bar1ey piled in fie1ds e) Formation of perithecium on weeds

iv) Dispersion of ascospor凹…・・H ・H ・.....・H ・..一...・H ・.....・H ・.....・H ・....・H ・.....・H ・-・78

v) Mechanism of ascospore dispersion from the perithecium......・H ・....・H ・...…83

a) Asoospore dispersion and moisture b) Heigh t of the ascospore

dispersion from perlthecium c) Length of time from the wetting of perithecium to the diHperoion of ascospores

vi) Outbreak of 1eaf blight of wheat by the scab fungus....・H ・..…・H ・H ・..…・・84

vii) Germination of ascostores on wheat ears....・H ・.....・H ・....・H ・-…H ・H ・.....・H ・.85a) Ascospore germination and temperature b) Length of time requir-ing for ascospore germination

viii) Outbreak of scab by ascospores....・H ・......・H ・..…・・…H ・H ・....・H ・....・H ・....・H ・..872 Period of primary iofection'"…....・H ・H ・H ・...・H ・...・H ・H ・.....・H ・H ・H ・....・H ・.......・H ・.873 Considerations on the results.…...・H ・..…...・H ・........・H ・..….....・H ・-……H ・H ・...・H ・89

3. Secondary dis田 mioation'"…H ・H ・...・H ・....・H ・...・H ・...............・H ・...・H ・..……H ・H ・...・H ・-・・90

1 Formation of conidium 00 scabbed ears'"…H ・H ・H ・.....・H ・........・H ・....・H ・....・H ・..902 Conidium germination in rain drops 00 ear and 1eaves of whe晶z・H ・H ・.....・H ・..913 Dispersion of the conidium produced on affected ears'"・H ・..…...・H ・.....・H ・..・・・924 Deta巴hmentof 巴onidiumfrom wheat heads by rain.......・H ・H ・H ・.....・H ・....・H ・..925 Conidium suspension in water drops from scabbed wheat heads・u ・H ・H ・...・H ・....946 Conidium dispersion from conidium su圃penoion......・H ・....・H ・...・H ・H ・H ・........・H ・..957 Considerations on the results...........・H ・-…H ・H ・....・H ・....・H ・...・H ・H ・H ・..…...・H ・...95

玄 Effec旬 ofenvironments .on the outbreak of wheat scab...・H ・...・H ・...・H ・....・H ・....・H ・..…96

1. Effects of rainfall on the scab susceptibility of wheat........・H ・-…....・H ・...・H ・...・H ・.962. Effe巴tsof soi1 moisture on scab outbreak...・H ・....・H ・...・H ・H ・.....・H ・.....・H ・H ・H ・..……97

3. Effects of manuring on scab outbreak..'・H ・....・H ・.....・H ・....・H ・.....・H ・...…H ・H ・.....・H ・.984. Outbreak of wheat scab in fie1ds in natura1 conditions ............・H ・H ・....・H ・....・H ・.1∞5. Effect of time of the rainfall after inocu1ation on scab outbreak …...・ H ・.....・H ・..1026. Outbreak of wheat s巴abin fie1ds and 1ength of time from infection to rainfall...104 7. Considerations on the results ..・H ・..…...・H ・.......・H ・..…・H ・H ・…・H ・H ・H ・H ・..…H ・H ・...….105

玄1. Toxicity or intoxication of scabbed grain箇 H ・H ・...・H ・...……・H ・H ・..…."・H ・...…H ・H ・....1071. Revie ws of li tera ture .....・H ・....・H ・...…...・H ・....・H ・H ・H ・-・……H ・H ・....・H ・....・H ・.....・H ・.1072. Experiment on white mouse…....・H ・H ・H ・...・H ・.....・H ・.......・H ・.....・H ・..…・H ・H ・.....・H ・.1093. ExperIment on white rabbit …H ・H ・.........・H ・..…H ・H ・-……、H ・H ・.....・H ・....o...・H ・..…・111

4. Experiment on chicken...・H ・..…...・H ・....・H ・..…H ・H ・..…....・H ・....・H ・......・H ・H ・........・H ・.1115. Studies on the intoxication to ox and ca1f・H ・H ・....・H ・....・H ・....・H ・...・H ・.....・H ・.....・H ・.1146. Considerations on the resu1ts ・H ・H ・-…H ・H ・H ・H ・...・H ・...・H ・...…...・H ・.....・H ・.....・H ・...・H ・115

玄II. Experiments on 倒的同巴ontro1by chemica1s ..・H ・...・H ・......・H ・....・H ・........・H ・...・H ・-…・・・116

1. Scab-contro1 by spray chemica1s ..・H ・...・H ・.....・H ・....・H ・...・H ・H ・H ・...・H ・...・H ・.....・H ・...1161 Experiments on slide glass ・H ・H ・....・H ・...・H ・H ・..…...・H ・....・H ・...・H ・.....・H ・.....・H ・..1162 Growth contro1 by sprlly chemica1s'"・H ・..…H ・H ・.....・H ・H ・H ・....・H ・...・H ・.....・H ・...1183 Experiment on wheat heads..........................・・・・・・........・H ・......・H ・...…H ・H ・..…・119

2. Duration of effectiveness of spray materia1s'"・H ・...…・H ・H ・.....・H ・..…...・H ・.....・H ・.1233 Se1ection of the time 8uitab1e to spray for scab contro1....・H ・..…...・H ・.....・H ・..…..125

4. Environments in the season of scab outbreak and time of Ipraying...・H ・.....・ H ・..…125

5. Loss of spray materia1s by rainfall ・H ・H ・..…H ・H ・...…H ・H ・...・H ・....・H ・...・H ・.....・H ・..1306. Seed treatments ・…...・H ・..................................................................................1337. Considerations on the resu1ts ・H ・H ・...・H ・....・H ・-…...・H ・.....・H ・....・H ・H ・H ・...・H ・..…H ・H ・.133

玄III. Summary ・H ・H ・H ・H ・..…・H ・H ・.....・H ・..…...・H ・.....・H ・.....・H ・..…....・H ・..…・・H ・H ・......・H ・..139Referrence図…...・H ・.....・H ・.....・H ・.....・H ・.....・H ・.....・H ・H ・H ・.....・H ・....・H ・...・H ・.....・H ・.....・H ・H ・H ・..144Eng1ish summary....…...・H ・...…H ・H ・....・H ・H ・H ・...・H ・.....・H ・….....・H ・H ・H ・....・H ・.....・H ・.....・H ・..154P1ates I-XVIII， Exp1anations of the p1ates.....!.・...・H ・-…...・H ・....・H ・....・H ・H ・H ・......・H ・...I-XIII

1959) Nisikado: Studies on the Wheat Scab 145

SUMMARY

1. NAME AND DISTRIBUTION OF THE DISEASE

1. Name of the Disease: A blight disease of head and seedling of wheat

was first called in England， Wheat scab. 1n America it was called variouly

as Head blight of wheat， Fusarium blight， Fusarial head blight， Ear blight， and on seedlings as Seedling blight. 1n Germany it is called Weizenschorf， and in Italy it is Go1pe bian巴ade1 frumento. 1n Japan such names as

Akakabi-byo (Red mou1d disease) or Kokuter山yo(B1ack spot disease) have

been used wide1y. 2. 1n years past， the disease was be1ieved to be the direct damage caused

by the rain. 1n Japan the disease was first recorded in 1902， whi1e in 1914 it made an e玄tensiveoutbreak and attracted attention as one of the most

serious diseases of small grains. The disease is now widely distributed

throughout the wor1d， but in the United States， its damage has been great and there are numerous reports published on this disease.

II. SYMPTOMS

3. The b1ight on the wheat normally oc巴urson the head w hen there is

rain during the heading period. 4. During the ear1y period of infection， a part or entire spike1et becomes

disco1ored brown. Then normally there appears a sa1mon co1ored fungus

growth between the 1ayers of glumes， which are the masses of conidia. When dry days follow after the infection， further spread of the disease is checked， but the portion of a head above the infected spike1et normally dies. When

the dise加 edhead is e玄posedto more rain， the disease progresses rapid1y and causes the entire head to rot. As the infe巴tedhead ages， there appears on the surface minute b1ack bodies whi巴hare the peri the巴iathat bear ascospores.

5. 1nfection 0巴cursa1so on the tender root and co1yopti1e of the young

p1ant， which appears as brown， reddish brown or dark brown spots. Some-

times b10tches of spots are produced on the b1ades of the weakened p1ant.

III. CAUSAL FUNGUS

6. The b1ight is caused by a fungus be10nging to the genus Gibberella.

As to its name， the authors have adopted G. z伺 e(Schw.) Petch (1936)， with G. saubinetii (Mont.) Sacc. as its synonym. 1n the as位 ualor巴onidia1stage of this fungus i t is called l!'usar仰mgraminearum Schwabe.

7. The causa1 fungus produ巴es巴onidia，ascospores， and to a limited

extent chlamydospores. Conidia are hya1ine， cresent shaped， normally 6・celled， point泡dat one end and with a distinct base or foot at the other end. Size averages 49.5 x 6.5，1.. Conidiophores are either simp1e or branched， and bear one conidium at the apex.

146 Berichte d. Ohara Instituts (Bd. 11， Ht. 2

Perithecia are b1ue-b1ack to b1a巴kin co1or，且earspherica1 and each pro-

vided with a beak having an opening or ostio1e. Size of the perithecia ave rages 272 X 218.1 fl..

As巴iare hya1ine， c1ub shaped， and ea巴h巴ontains8 ascospores. Their

size averages 99.8 X 1111・ Ascosporesare hyaline， spind1e-shaped， and consist of 4 cells. The size averages 21.4X4.111.

Ch1amydospores may be formed in the cells of the mycelium or the coni-

dium. They are usually imperfectly formed.

8. Variation 'in the morpho1ogy of the myce1ia and巴onidiamay be

influenced by the portion of the fungus body removed for the iso1ation of the

fungus. The fungus iso1ates those originated from ascospores normally exhi-

bi ted vigor and reprod u巴edreadi1y conidia. Those originating from conidia or myce1ia may yie1d perithe巴ia.

9. The optimum temperature for the growth of myce1ia is 270C. Maxi-

mum and minimum temperatures are， respective1y， 320 to 350 and 50C.

Optimum pH range for the growth of fungus is 5.0 to 6.0. The fungus will

grow at a wide range of between pH 2.7 and 11.7. For the formation of con-

idia， temperature higher than 150C and a re1ative humidity greater than 98 % are required.

The optimum temperature for the germination of conidia is in the neigh-

borhood of 250C. For an optimum germination a re1ative humidity of 100労

is required. There will be no germination at 93 % or 1ess. Aeria1 myce1ium is

produced most abundantly at 98 % re1ative humidity. 10. Formation of conidia is gradually increased after ea巴hcyc1e consist-'

ing of severa1 days. Light is required for the formation of conida and the

u1tra-vio1et light influences the most. An extreme1y intense 1ight is harmfu1

to the formation of conidia. Germination of conidia is best when they are

fresh and the density is 1ow. Addition of small amounts of glucose or mag-

nesium su1fate in the medium stimu1ates germination. Removing the adhesive

巴oatingof the conidia will not巴ausereduction in the germination.

11. For the formation of perithe巴iaa minimum re1ative humidity of

98労， a temperature of above 150C， diffused light， and a certain amount

of air circu1ation are required. A high nutrient 1eve1 is not essentia1 for the formation of perithecia.

12. From resu1ts of mi玄巴u1turingof the fungus iso1ates from sing1e

ascospore， the fungus has been determined homothallic. in its se玄ua1behavior.

IV. INVASION OF HOST PLANT BY THE CAUSAL FUNGUS

13. When invading the wheat head the fungus first infe巴tedthe anthers， then progressed into the outer and the inner glumes. It was rare that the

fungus penentrated the epiderma1 cells of the outer glume. The most巴ommon

mode of entrance was through the stomata. It appeared that the invasion of the inner glume was more common than the outer glume. The fungus reach・

1959) Nisikado : Studies on the Wheat Scab 147

ed endosp白rmand embryo of the developing kernel from the glumes by pro.

gressing through vascu1ar bund1es. 1nvasion into the kerne1 was made more

diffi巴ultas the tissues of the kerne1 deve10p and become thickened. 1nfection

of the kerne1 was therefore usually limited to the mi1k stage.

14. The causa1 fungus a1so atta巴kedgerminating seeds， young roots， sheath and hypo巴otyl. 1nvation of the young roots took p1ace by either di-

rectly penetrating the epiderma1 cells or entering between the epiderma1巴ells

and the root hairs. Mycelia1 mass was formed on the sheath by which infe巴-

tion occured through the seam of the cell or through the stomata. 1nfection

of th白 hypocotyla1so took p1ace by means of mycelia1 mass through stomata.

V. PATHOGENICITY AND VARIATION IN RESISTANCE

TO FUNGICIDES

15. 1n the 124 iso1ates of the fungu日 studied，the pathogenicity varied

wide1y from very weak to very strong.

16. 1n the six variants that were separated from the mother iso1ates as having distinct morphologica1 differences， the pathogenicity was found to have been changed. The direction of the change was in both directions-some

increased the pathogenicity whi1e the others decreased. Variation in the

pathogenicity among the conidia and ascospores was found to be very 1ittle.

Pathogenicity decreased by repeated transp1anting. Iso1ates made from wheat

having varying degrees of 8usceptibility to wheat scab， showed no distinct tendency in their degree of pathogenicity. 1n a study of reaction of different

iso1ates to copper fungicides， it was found that variation existed among the isolates in the resistance to copper fungicides.

VI. SUSCEPTIBILITY OF WHEA T V ARIETIES TO THE WHEAT SCAB

17. From the resu1t of tests conducted on some 70 varieties of wheat， it

was found that the susceptibiIity type of the wheat head to scab can be c1assi. fied in the following 3 1arge groups， in re1ation tり thep白riodof b100ming

and that of infe巴tion.

Group 1. Maximum infection oc巴ursduring the period of b1ooming.

Group 2. Maximum infection occurs during the period following the

b1ooming. Infection declines rapid1y after this period.

a. Uniform rate of infection occurs during the period of one

weeks after b1ooming. b. Uniform rate of infection 0巴巴ursduring the period of two

weeks after blooming.

Group 3. Rate of infection rises for a short time after b1ooming， whi巴his followed by a gradua1 dec1ine.

a. Rate of infection rea巴hesa maximum on 3 to 5 days

148 Berichte d. Ohara Instituts (Bd. 11， Ht. 2

after b1ooming， then it gradually dec1ines. b. Rate of infection reaches a maximum on 7 to 9 days

after b1ooming， the it gradually dec1ines. 巴. Rate of infection reaches a maximum on 11 to 13 days

after b1ooming， then i t grad ually dec1ines.

18. Most varieties of wheat showed higher rates of infection when ino-

巴u1atedand incubated at 270C or 300C than at 200C.

19. There were no significant corre1ation between the susceptibility of

wheat varieties and the 1ength， width， thickness of the head， 1ength of awn， ang1e of the opened glumes， hairyness， as well as pigmentation of the head.

20. Corre1ation was high on the susceptibi1ity of wheat between the

stages of seed germination and p1ant maturity， and r = 0.472土 0.085(Pく

0.01). A1so a certain degree of corre1ation was observed between the susce-

ptibi1ities of the varieties in the seedling and matured stages， and between seed germination and seed1ing infection.

21. From a 7 year study of wheat varieties on the susceptibility on the

wheat scab， it was found that there were no varieties that showed consistent resistance to the wheat scab. A1though the reaction varied somewhat from

year to year， such varieties as Soshu， Wase・Komugi，Homan， Homan No.1， Iwate-Soshu， Kinai No. 9， SanshιKotake showed comparative1y 1ess infected heads， whereas， Saikai No. 45， Kitakanto No. 14， Pusa No. 12， Mihara， Mubo-chiko， Shirage-Nankin， Norin No. 5， Yamaguchi・Komugiand Bei No.1 had

more infected heads from year to year， and were thus considered susceptib1e varieties.

VII. SHAPE AND GERMINATION OF DISEASED KERNEL

22. Hea1thy kerne1s passed mostly through sieves having openings be-

tween 2.5 and 2.7 mm; w hereas in the diseased kerne1s they were 2.2 and

2.5 mm. The diseased kerne1s a1so showed a genera1 re1ationship of width

being 1ess than thickness. The diseased kerne1s are thus more slenderer than

the hea1thy kerne1s and their weight of 1000 grains was 1ess than that of hea1 thy kerne1s.

23. Germination of wheat seed was best at temperatures between 150

and 170C. In the inocu1ated seeds the germination was best in the neighbor-

hood of 100C. At 100C damage from the disease was at a minimum. Germi-

nation of inocu1ated seeds decreased with the reduction in soi1 moisture up to 45.5 percent (percent of moisture in air dry邑oil).

24. Germination of diseased grain was better on 1arger grain than thc

smaller grain. The diseased grains germinated better when they were on1y

1ightly covered with soil. Those diseased grains that had a specific gravity

of more than 1.24 showed 1east effect on the germination. Lighter grains had poorer germination. Less fungus myce1ium was present in kerne1s with greater specific gravity.

1959) Nisikado: Studies on the Wheat Scab 149

25. When samples of diseased grains were blown by a current of air， a

majority of the heavier grains had the spe巴ificgravity of greater than 1.20.

In the healthy grains the percentage of germination had but little relation-

ship with the specific gravity.

VIII. PRIMARY AND SECONDARY INFECTIONS

26. The fungus survived on rice straw agar巴ulturmedium as follows:

36 months or more at 50C， 33加 36months at 100 to 150C， 14 months at

200C， 10 to 15 months at 250C， 4 to 7 months at 300C， and 2句 4months

at 350C.

27. Formation of perithecia was affected by the environmental tempera-

ture， but in pure culture， perithecium was produced at any time of period between late March and November. In nature， perithecia were produced on rice straw that were piled in the open and on rice stubbles remaining in the

field after the middle of April. These perithecia mature in May. They were

also produced and thriving in abundan巴eon other monocotyledonous plants.

28. Flight of ascospores was affected by environment. Ascospores oc・

curred mostly during the period soon after a prolonged rain. The spores were

shot out into the air when the humidity of the air was saturated or near

saturated. They may fly to a height of 1 to 3 cm. It was found that the

time between absorption of moisture by the perithecia and the flight of spores

was 4 to 9 hours.

29. On the wheat head， ascospores germinated best at 240 to 250C.

Between 200C and 300C， the latter temperature was more favorable for the germination. Ascospores germinated better on the head than in plain water.

Germination of ascopores took place within 3 hours， when the temperature might be between 200 and 300C.

30. Observations made on the infection of wheat head by the ascospores

produced in nature in the open showed that the wheat close to the source of

infection became diseased as much as 96 percent. This percentage decreased

in proportion to the distance from the source of inoculum. Plants in the

leeward direction showed greater percentage of infected heads. These obser-vations indicated that the as巴osporespossess high. degree of pathogenicity to

the wheat ear.

31. The time requiring for the infection of wheat head ‘by the fungus

spores under natural condition was studied， byexposing the wheat head to the source of infection at specified periods. It was shown that the head， becoming infected within one week after blooming， received the greatest damage from the disease. The infection was more自evere，when there was

rain or when the ascospore自 werein flight.

32. Studies were made on the conditions under which conidia are pro

duced on the diseased wheat head. It was found that the conidia are not

150 Berichte d. Ohara Instituts (Bd. 11， Ht. 2

produced in abundance when there is a pro10nged period of wetness or dry-

ness; but rather that， improvement in the weather conditions takes p1ace， after the fungus has made sufficient growth， by rainy weather.

33. The percentage of germination of conidia was greatly increased by

using the water adhering to the surface of the p1ant. The germination tube

was a1so observed to e10ngate rapid1y in this water.

34. Conidia produced on the diseased head were carried by the wind

much more， when there was rain and high humidity. 35. 80 far as observations were made， an infected head produced at

1east 16 X 106 conidia， which upon contact with water might yie1d suspension of the conidia in自hortperiod of time. As the conidia1 suspension flowed down

the side of the wheat head， the conidia adhered to the new surface. 1n this

manner considerab1e number of conidia were 1eft on the surface of the wheat head as a source of inocu1um.

IX. EPIDEMIOLOGY OF THE SCAB DISEASE IN RELATION TO ENVIRONMENTAL FACTORS.

36. Occurrence of rain prior to infection stage had 1ittle effect on the

susceptibility of wheat head to the scab. '

37. Wheat p1ants growing in soi1巴ontaining 60箔 soi1moisture， had the greatest number of scab deve10pment; and either an increase or decrease

in soi1 moisture from this content， caused reduction in the disease develop-ment.

38. 1ncreased use and 1ate application of nitrogen fertilizers巴ausedin-

creased scab deve10pment. Phosphorus and potassium fertilizers showed but

1itt1e effect on the deve10pment of the s巴ab，but appeared to have an opposite effect to that of the nitrogen fertilizers.

X. TOXICITY OF GRAINS AFFECTED WITH SCAB

39. Toxicity of the scabbed grain， as tested by feeding mice and rab-bits， disc10sed that these anima1s were not affected by the diseased grains. Further feeding tests using young巴hi巴kensa1so did not show significant

effect on the weight， body temperature， feca1 mater， and deve10pment of the birds.

40. Toxicity of the scabbed grain was observed in Okayama prefecture

on two ca1ves fed with a ration containing diseased bar1ey grain. As a resu1 t

of consuming the grains， the ca1ves exhibited such abnorma1 behavior as reduced appetite， difficu1ty in wa1king， a1so difficu1ty in the rising and sluggish in action， 10s8 in firmness of the feces， and 10ss in body weight. The mothers of ca1ves， however， did not show any effect from consuming diseased bar1ey grains. Ana1yses of the feed showed that it contained， in 1arge proportion， grain自 infectedwith Gibberella zeae， Alternaria sp.， Peni・

1959) Nisikado : Studies on tlie Wheat Scab 151

cill仰msp. and species of bacteria. Since Gibberlla z伺 ewas particularly

prevalent in the mixture it was believed that the to玄icityeffect， shown by the calves， was cau自edthe scabbed grains.

XI. CONTROL OF THE DISEASE

41. For preventing the seedling blight a seed sterilization by a 5 minute

soaking in hot water held at 500 to 520C， or in 1/2000 dilution of mercuric chloride; and a 3 hours soaking in 1/400 dilution of formalin or uspulun were

effective. Fumigation with 1/2500 formalin redu巴edthe viability of the

seed; whereas cbloropicrin at the same rate did not reduce the viability， when the treatment was made after allowing 2 weeks of after-ripening period.

42. Tests u日ingvarious fungicide compounds on slides showed that the

germination of conidia was che巴kedby fermate and bordeaux dusts. On

agar medium arasan and fermate at a concentration of 0.01 % effectively

checked the germination of conidia. In volatile materials， growth was checked most by spergon and phygon.

43. on the effectiveness of various fungicides on the wheat head in preventing the scab， arasan and dust and water dispersible fermate were found highly effective. A巴ertaindegree of effectiveness was obtained from

phygon and' PMF (1/2000). The efi'ectiveness was increased when dusting

was made while the dew still remained on the surface of the plant， as it increased adherance of the chemicals to the plant.

44. Using cover glasses to test the effect of elapse o'f time on the effec-

tiveness of fungicides， it was found that fermate retains effectiveness for at least 15 days which was equivalent to that of bordeaux mixture of 0.5%.

Using the wheat heads， farmate was still effective at 6 days after the appli-cation.

45. Application of fungi巴ideson the wheat head. was most effective

when it was made within one week after blooming. Effective control was

noted w hen fdngi巴ideswere a pplied 2 days after ino巴ulatingthe wheat head， whi巴hwas followed by favorable temperature and humidity con.ditions for

infection by the fungu日. Spraying after 3 day inoculation was still mode-

rately effective. Elapse of 6 days or more had but little effect in reducing

the damage on the head. The effectiveness of the fungicides was increased， if a period of dryness follows after appli巴ation of fungicides to the head.

46. Effectiveness of the deposit of fungicides was reduced by a 20 mi-

nu te rain; however， this redu巴tionwas巴omparativelyless on su巴hfungici-

des as arasan， fermate dust and phygon. Application of dust compounds

for wheat scab was more effective， when made at the time dew自tillremained

on the surfa巴eof the plant.

152 Berichte d. Ohara In目tituts (Bd. 11， Ht. 2

EXPLANATION OF PLATES

Plate 1 Symptoms of the scab disease of wheat caused by Gibberella zeae (Schw.) Petch.

(1) Wheat heads affected by the scab. At the left showing a seriously scabbed head， at the righ色ahealthy head， and between the two various grades of the scab.

(2) Leaf blotch of wheat caused by artificial inoculation with Gibberella zeae (Schw. )

Petch showing large irregular shaped blotche自.

Plate II. Hyphae of Gibberella zeae (Schw.) Petch.

(1)， (2) Showing thick-walled segments of the comparatively aged hyphae grown in

eulture.

(3) Showing ends of young hyphae grown on potato dextrose agar medium.

(4) Showing some conidium producing types of hyphae grown on potato dextrose agar.

(5) Fully grown hyphae.

(6) Vigorously growing young hyphae.

Plllte III. Conidia and conidiophores of Gibberella zeae (Schw.) Petch.

(1) Showing conidia produced on a scabbed head wheat. (X 800)

(2) Showing conidiophores produced on a scabbed wheat head. (x 450)

(3) Showing conidia produced on a leaf blotch caused by artificial inoculation. (x 900)

(4) Showing conidiophores produced on malt extract agar. (x 450)

Plate IV. Conidia， asci and ascospores of Gibberella zeae (Schw.) Petch.

(1) Conidia produced on scabbed wheat heads. (X 900)

(2) Conidia produced on potato-dextrose agar. (x 840)

(3) Asci a，nd ascospores produced on rice st1'a w. (Asci X 800， ascospores X 900)

Plate V. Formation， shape and con色enもsof perithecia and conidium germination of Gib-

berella zeae (Schw. ) Petch.

(1) Germination of conidia produced on a leaf bloωh caused by ar吐ficialino巴ulation.

(X450)

(2) Perithecia profusely produced on a scabbed wheat heads

(3) Perithecia broduced on germinating ri巴egrains， artificially ino巴ulated.(4) Section of a perithecium produced on rice straw. (X 120)

(5) Asci and ascospores of a perithe巴iumproduced on rice straw. (x 540)

Plate VI. Perithecium， asci and ascospores of Gibberella zeae (Schw. ) Petch.

(1) A perithecium produced on boiled rice straw medium， showing asci and ascospores. (X270)

(2) Asci and ascospore目. (X240)

(3) An ascus. (x 700)

(4) Ascospores. (x 1000)

Plate VII. Infection of Gibberella zeae (S巴hw.)Pet巴hto anther and glume tissue of wheat.

(1) Longitudinal section of a 'glume ino巴ulatedwith the s巴abfungus， showing fungus hyphae and pollen.

(2) Transverse section of anもhers.Showing hyphal attack to pollen. 24 hours after in-

oculation.

(3) Transverse section of a glume， showing maceration and collapse of leaf tissue near the stomata affected by色hefungus hyphae.

(4) The same as above， enlarged.

1959) Nisikado : Studies on the Wheat Scab 153

Plate VIII. Infeetion of Gibbe阿 llazeae (Sehw.) Peteh to wheat ti曲目.

(1) Transverse seetion of an outer glume， showing the fungu. hyphae in the host eella. (x6∞)

(2) Transverse seetion of outer glume，・howingthe hyphal penetration through stomata.

(3) Infeetion of hyphae to the ovary. (X 5∞)

(4) Infeetion of hyphaeωleaf tissues. (x 2∞)

Plate IX. Infeetion of Gibberella zeae (Sehw. ) Peteh to wheat tissues.

(1)， (2) Hyphal infectionωthe tip of tender r∞t. through epidermal cells.

(3) Hyphal infectionωtender root， through epidermal cells. (4)， (5) Hyphal infection to tender young r∞t， through the space between epidermal

cell and root hairs.

(6)， (7) Hyphal tips， somewhat s胃ellingon the epidermis of the host.

(8)， (9) Penetration of infeetion hyphae from am appressoria-like swelling tip of the

hyphae into the host tissue.

Plate X. Infection of Gibbe同 llazeae (Schw.) Petchωwheat tissues.

(1)， (2) Penetration of hyphal ma闘 inぬ theepidermal cells.

(3)ー (5) Penetration of hyphae through the stomata of cotyledon. Surface view of tlle

sωmata， 3-4 days after inocu1ation.

(6)， (7) Transverse section of the stomata of cotyledon， showing the hyphal 戸net~a­

tion and macerated chloroplasts.

Plate XI. Perithecium formation of Gibbe何 llazeae (Schw.) Petch.

(1) 'l'all beaker experiment for the peritheeium formation of Gibberella zeae (Schw.)

Petch. Pieces of rice straw sterilized in reagent glasseo， were inoculated with the 8cab fungu8. They were then kept in tall beakers under diffused sun light.

(2) Some of rice 8tubbs affected by the scab fungus in fields. Showing abundant

formation of perithecia.

(3) Scabbed wheat grains infected by Gibberella z師 e(Schw.) Petch. Scabbed grll.ins

are thinner and more wrinkled than the healthy ones.

Plate XII. Inoculation experiments of Gibbeγella zeae (Sehw.) Petch.

(1) Wheat plants in fields， showing inoculation experiment with Gibberella zeae (Schw. )

Petch， wheat heads beeing sacked with cellophllne to protect the heads from the

natural infection of the scab before the experimentB.

(2) Wheat plants in pots in a greenhou回， used for the inoclllation experiment with

Gibberella zeae (Schw.) Petch. Each h号adwas labelled to show the date of sh∞t-

ing and flowering.

154

Plate 1

•

( 2 )

155

Plate II

156

Plate III

( 1 )

• •

...

( 3 i

‘u，

安‘..4

ssfF' 2

グピグ~

;¥. (4 )

Plate IV

ドーー一ーー→10 f"

ドー--f

10λa

(1)

(2 )

。》bjL7

8 ~ トーーー-l'ー一ーーー『10ド

/01'- ( 3 )

157

同

MEZJ刊

158

Plate VI

""" 。

( 3 )

159

、

64 Fキご、旬開唱えb，，~唱えも~tt\ ~

ぷ;jd

，~Æ!事

( 4 )

160

Plate VII

c

~

( 1 ) (2 )

( 3 ) (生)

161

VIII

2

162

Plate IX

(1 ) (2 )

(3 ) (4 ) (5 )

( 6 ) ( 7 ) (8 ) (9 )

163

Plate X

( 1 ) ( 2)

，

( 3 ) (4 ) ( 5 )

( 6 ) (_7 )

164

Plate XI

、

d齢、

唾国， 、

165

Plate XIl