A weakly virulent Fusarium sp. strain HPF-1 isolated from a Cymbidium leaf was suppressive to the occurrence of Cymbidium yellow spot on small plants of Cymbidium spp. Fusarium sp. strain HPF-1 was weakly virulent to Zygopetalum spp. and Cymbidium spp., and avirulent to rice, strawberry and asparagus. The strain caused small, irregular dark brown spots on Cymbidium spp. that were distinguishable with the naked eye, but it caused no damage to the production of Cymbidium. Yellow spot disease on Cymbidium spp. was suppressed by pre-inoculation with some other pathogenic Fusarium spp., but not by pre-inoculation with nonpathogenic Fusarium moniliforme. Strain HPF-1 was the most suppressive among the pathogenic Fusarium spp. tested. Spraying with a bud-cell suspension at a concentration of 105cells/ml was sufficient to reduce yellow spots. The suppressive effect was seen by 3 days after spraying and continued throughout the growing period. Strain HPF-1 spread over new leaves and lead leaves by systemically infecting the plant. An effective control of Cymbidium yellow spot can thus be made by pre-infection with strain HPF-1 of small mericloned plants.
Mechanization of rice cultivation has developed very rapidly, and transplanting machines have been adopted all over Japan. Rice seedlings grow very close together in the nursery boxes and under high humidity the close intra-row spacing. This method of cultivation creates favorable conditions for seedborne diseases. All the diseases, except sheath blight, are seedborne and cannot be controlled completely with seed disinfectants. For that reason, pathogen-free seeds (Gennmai seeds) have had the chaff removed so that fungal and bacterial pathogens cannot survive in the tissues of the seeds. The surfaces of hulled rice with healthy embryos have also been coated with a water-soluble polyacrylic resin and a powdery activated carbon. This study reveals that the Gennmai-seeds prohibit to a remarkable degree the development of seedborne diseases such as rice blast, bakanae disease, bacterial grain rot, and bacterial seedling blight. Pathogen-free seeds (Gennmai seeds) can effectively contribute to the eradication of seedborne diseases.
Races of 131 isolates of tomato leaf mold fungus, Fulvia fulva, collected from 30 prefectures of Japan during 1997-1998 were identified. Four races, race 0, 2, 2.4 and 2.4.11 were detected. Race 2 was predominant with 113 isolates identified as this race. All four races were found in Kanto district, but only race 2 was detected in Chugoku, Shikoku and Kyushu districts. Race 0 and 2 were thought to be identical to the known races in Japan. However, race 2.4 and 2.4.11 had a virulence pattern different from the known races in Japan.
Phytoplasmas were detected by PCR in vector leafhoppers Hishimonus sellatus and Macrosteles striifrons of onion yellows phytoplasma (OYP), and in a vector leafhopper H. sellatus of mulberry dwarf phytoplasma (MDP), respectively, after they fed on infected plants or were injected with the extract from infective insects. MDP was not detected by PCR in nonvector M. striifrons fed on infected plants, but was detected in preparations from whole bodies, headless bodies and heads of M. striifrons injected with the extract from infective insects. M. striifrons injected with infective MDP failed to transmit MDP to test plants.