A virus (M) causing mild mottle and flower colour breaking was isolated from Gymnaster savatieri (Makino) Kitamura (miyakowasure) plants. The virus was sap-transmissible and induced systemic symptoms on G. savatieri, Helichrysum bracteatum, Nicotiana benthamiana, N. clevelandii, N. occidentalis, Petunia hybrida, Zinnia elegans, and local necrotic lesions on inoculated leaves of Chenopodium amaranti-color, , C. quinoa, Sesamum indicum and Tetragonia expansa. Thirteen other plant species in seven families tested were not infected. Infected leaf sap of N. clevelandii showed longevity in vitro for 4-5 days at 23°C, thermal inactivation point 70-75°C. Purified virus preparations yielded slightly flexuous particles (680nm×13nm) and contained a major polypeptide of approximately 34 K and nucleic acid of Mr 2.4×106. Rabbit antiserum prepared with the purified virus had a titer of 1×105 in ELISA. By ELISA and immunosorbent electron microscopy, the virus reacted positively against antisera to chrysanthemum virus B-J and carlavirus from erigeron plants (E). On the basis of these studies, the virus was identified as a strain of chrysanthemum B carlavirus.The virus widely spread in miyakowasure plants.
Fusarium oxysporum f. sp. adzukicola and nonpathogenic F. oxysporum against adzuki bean were grouped using vegetative compatibility tests with nitrate non-utilizing (nit) mutants. One hundred and twelve pathogenic isolates collected from 20 areas in Hokkaido were classified into the largest vegetative compatibility group (VCG) including two subgroups, one small VCG, four self-vegetative incompatible isolates and three single self-compatible isolates.All three races of this fungus were grouped within the largest VCG. The 199 onpathogenic F. oxysporum isolates were incompatible with the VCGs of F. oxysporum f. sp.adzukicola mentioned above and the isolates examined except for 15 single self-compatible isolates were classified into 25 VCGs. Sixteen VCGs out of 25 VCGs of the nonpathogenic isolates contained isolates from soil samples of both non-infested and infested fields in Tokachi district. Moreover, 162 isolates (81.3% of all isolates tested) belonged to these 16 VCGs. No marked difference in the population structure of nonpathogenic F. oxysporum was observed between the infested and noninfested (Tokachi) district.
We monitored the appearance of new races of the rice blast fungus Pyricularia oryzae Cavara in paddy fields after the release of new resistant rice cultivars having the new true resistance gene, noting specific sites in the plants. We looked for new races on blast-infected panicles of the newly developed ricecvs. Haenuki and Domannaka after inoculation with incompatible races using an injection method. Fifteen isolates were collected from blast lesions on naturally infected panicles of the susceptible rice cv. Sasanishiki at eight locations including Tsuruoka city in Yamagata Prefecture. After single conidiaisolation, subcultured isolates were identified as incompatible races on newly developed rice cultivars. Conidial suspensions (105 spores/ml) of each isolate were injected into flag leaf sheath at the boot stage of the two new rice cultivars grown in 1/5000 a Wagnerpot. Each incompatible race of this fungus could infect and form brownish lesions on more than 95% of the panicles of cvs. Haenuki and Domannaka. Furthermore, sporulation was abundant enough to reisolate the fungus on hull lesion. Races of the single conidia reisolates from hull lesions of the two new rice cultivars were differentiated using Japanese differential rice varieties. About 75% of these reisolates changed to the original pathogenicity. Many of the isolates could overcome resistance of rice cultivars with true resistance genes, Pi-ta, Pi-i, Pi-z, Pi-k and Pi-km, individually or in combination. About 75% of the variants appeared in this study could break down the resistance the newly rice cvs. Haenuki and Domannaka. From these results, we concluded that the panicle of the new resistant rice cultivars was an important sites for new races appearance of the rice blast fungus.
A new disease occurred on loquat fruit with “Tate-boya” symptoms, several longitudinal lines with splashed patterns on the surface of the fruit from the bracts to the tips of fruit, resembling the appearance of an “abrasion”, hence the name of Tate-boya. Scanning electron microscope (SEM) examinations of the symptomatic fruit surface showed signs of suctioning by the loquat rust mite (Aceria sp.), as well as conidia and mycelia of various filamentous fungi. No such signs or symptoms were recognized on fruits from which the bracts were artificially picked off in early stage of development. In bracteate cavities on diseased fruits many loquat rust mites could be seen. A Botrytis sp. was most frequently isolated from the inside of the bracts as well as from the diseased parts of the fruit. Tate-boya symptoms were found only when both the Botrytis sp. and loquat rust mite were found together within the bracteate cavities. Tate-boya symptoms could be reproduced when conidial suspensions of the Botrytis sp. were injected into bracteate cavities which were inhabited by the loquat rust mite. No other species of isolated fungi could reproduce the disease. The Botrytis sp. was identified as Botrytis cinerea Pers.: Fr., the common gray mold fungus, on the basis of morphology and cultural and pathogenicity studies.
Fourty-one species of plants belonging to three genera of the family Crassulaceae, namely 21 species of Kalanchoe including three hybrids, two species of Orostachys and 18 species of Sedum, were inoculated with basidiospores of Puccinia benkei to clarify the host range of the rust fungus. Telia were produced on leaves of nine species of Kalanchoe, four species of Sedum and one species of Orostachys. Among them, K. daigremontiana (Shikorobenkei), K. laziflora (Kochounomai and Kochounomainishiki), Kalanchoe sp. (Raui), K. tubiflora (Kinchyou), K. × hybrida (Fushichyou), K. beauverdii (Kurokinchyou), K. thyrsiflora (Touin), K. longiflora (Myougi), S. makinoi, S. cauticolum and O. japonicus were recognized as new host plants. Kalanchoe species recognized as host plants belong to sections Laxiflora and Beauverdii in subgenus Bryophyllum and sections Thyrsiflora and Eukalanchoe in subgenus Kalanchoe.
Haplic and umbric andosols soils were treated in the field with different types of fertilizer and methods of application in an effort to improve field suppression of common scab of potato caused by Streptomyces scabies. Scab severity index of the plot treated with aluminum sulfate was the lowest of all the plots. The exchange acidity y1 in soil was the highest of all plots during the infective stage of common scab of potato. On the other hand, when only ammonium sulfate was fertilized to the rows, and phosphate and potassium were broadcasted to surface soil (fertilization amelioration plot), the ratio of tubers in the serious scab severity class significantly decreased. The electrical conductivity of the soil solution around the potato tuber in the fertilization amelioration plot was lower than that in the plots fertilized with nitrogen, phosphate and potassium to the row during the infective stage of common scab of potato. Aluminum ion activity in the fertilization amelioration plot is higher than in the plots fertilized with nitrogen, phosphate and potassium to the row. Common scab of potato in fields with haplic andosols soil treated with fertilization amelioration was controlled more effectively than in umbric andosols soil. The electrical conductivity of the haplic andosols was lower than that of the umbric andosols, although the concentration of soluble aluminum ions on the haplic andosols was lower than that in the umbric andosols. Common scab of potato may be suppressed by a low concentration of soluble aluminum when electrical conductivity of the soil solution around the potato tubers is low because activities of aluminumions remain high.