The writer, during recent years, has been engaged in the study of the disease of the insect-powder plant (
Chrysanthemum cienrariifolium (Trev.) Bocc.) in Okayama prefecture, and found out that following six kinds of diseases exist on the host: the blight (
Diplodia chrysanthemella), the small sclerotium disease (
Sclerotinia minor), the large sclerotium disease (
Sclerotinia Libertiana), the sclerotium wilt (
Hypochnus centrifugus=Sclerotium Rolfsii) the fusarium wilt (
Fusarium sp.) and the septoriose (
Septoria chrysanthemella)., All fungi causing these diseases except the last one, were isolated and cultured purely, and their pathogenisities were proved respectively by the inoculation experiments. Among the diseases, however, more extremely prevalent are the blight, the small sclerotium disease, and the large sclerotium disease. The fusarium wilt may be serious but not so prevalent, other diseases being minor importance.
(1) The blight. This disease caused by a species of
Diplodia, which is hitherto undescribed and named here the writer as
Diplodia chrysanthemella nov. sp.. The description of this species is as follows.
Pycnidia immersed or erumpent, flaskshaped or irregular, black, 60 to 141μ usually about 100μ in diameter. Pycnidia prodaced on pure cultures are somewhat larger, being on acid standeard agar 81 t0 360μ on boild potato 200 to 340μ, and on mannit agar 115 to 300μ. Pycnospores ellipsoid unicellular and hyaline when young, but usually two or rarely three celled and brown or light olive when matured; 6-13μ×3-6μ, generally 6-9μ×3μ in average 11μ×3.6μ. The measurements of pycnospores produced on the culture media do not differ from natural ones. Conidiophores are very short and slender. The fungus flourishes well in various media and produces pycnidia.
It attacks the leaves, leaf-stalks, flowers and stems and causes leaf, stem or ray blight of the host.
(2) The small sclerotium disease This disease caused by the attack of
Sclerotinia minor Jagger, a species which is known to be found the lettuce, celery and other crops causing their decay disease in America. It is very interesting to know its occurrence in Japan. No report ever appeared on this fungus from this country. Sclerotia are very small, having onion seed appearance; 0.2 to 4mm. mostly 0.5 to 2mm. in diameter, irregular. Apothecium produced usually one, rarely two from single sclerotium; disc saucer shaped, 0.5 to 2mm. in diameter: stalks slender 2 to 5mm. long, 0.3 to 0.5mm. in diameter. Micro-conidia formed on the culture media but not in nature. The measurements and the morphological characters of the asci and ascospores agree with Jagger's original description. The inoculation experiments proved that this fungus attacks the insect-powder plants, and also
Artemisia vulgaris, Gnaphalium japonicum, Lactuca brevirostris, Asteromaea indica Erigeron linifolius, lettuce and celery. It attacks the host in the parts of the stem and the leaf tauched to the soil at first, so that the plant soon began to wilt and to decay or dry out, and finally forms numerous sclerotia on the decayed area.
(3) The large scleroatium disease. This disease caused by a welt known fungus
Sclerotinia Libertiana Fuck. The symptom of the disease is very alike to that caused by
Sclerotinia minor, but the shape and size their sclerotia, produced on the host plants or the culture media are very different. The measurements of the size of naturally produced sclerotia of this species are 2×2mm to 12×7mm., in average 6×3.6mm. So both species can easily be distinguished even on the host plant.
(4) The sclerotium wilt. It caused by
Sclerotium Rolfsii Sacc.=
Hypochnus centrifugus (Lév.) Tul., a fungus which is very widely distributed and attacks many other cultivated plants in this country.
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