Four nonpathogenic strains of fluorescent pseudomonads (Bf-2, Bf-10, Bf-11 and Bf-15) isolated from field soil were revealed to be antagonistic to Erwinia carotovora subsp. carotovora on King B medium. These bacteria were applied to control of bacterial seedling blight of rice caused by Pseudomonas plantarii. In pot experiment, the incidence of the disease was strongly reduced with immersion of infected seeds in suspension of fluorescent antagonistic bacteria (109cfu/ml). Soil injection of the bacterial suspension was also effective to reduction of the disease. It was suggested that a part of the mechanism of this suppression was responsible for chemotaxis of fluorescent pseudomonads toward the exudates from rice seeds, though the competition between pathogenic bacteria and antagonistic one for iron in nutrient substratum was significantly relevant.
To assess the effects of fungicides on enlargement of lesion lesions of rice blast and spore formation on the lesions, several fungicides were sprayed to rice plants after the appearance of the lesions. The fungicides used were isoprothilane, EDDP, IBP, kasugamycin, blastcidin-S and ferimzone. All fungicides inhibited lesion enlargement and spore formation. A linear relation was found between days after application of each fungicide and an area of a lesion during a particular period. A linear, quadratice, or exponential equation was fitted to the relation between days after the application and spore formation on a lesion.
Effects of soil moisture and inoculum density on the incidence of Phytophthora blight of red pepper were investigated. The disease appeared in wet soil conditions (pF 1.8 and 2.3), whereas no disease in dry soil (pF 2.8).
Attenuated strains of Watermelon mosaic virus-2 (WMV-2) (WI-9 and WII-5) showed strong crossprotection to the infection of severe strain of WMV-2, and did scarcely show the reduction of growth in bottle gourd.
A new elongated virus was isolated from symtomless wasabi (Eutrema wasabi M.) plants. The virus has a peak in length distribution at 750-780nm and was transmitted by sap but not by aphids (Myzus persicae and Lipaphis erysimi). The host range was restricted to wasabi. No inclusion body characteristic of potyvirus was observed in infected tissues of wasabi. The virus did not serologically related to turnip mosaic virus. The name of wasabi latent virus is proposed.
A new disease of strawberry was found in Tochigi Prefecture in 1988 and 1991. The base of petioles near the soil surface which changed initially into water-soaked appearance was covered with white and silky mycelia with sclerotia similar to mustard seeds in size. Fungul isolates obtained from the diseased strawberry were pathogenic to 7 species of plants including strawberry, tomato and chinese chive. Colonies of the isolates on PDA medium were white, rich in aerial mycelial strands. Clamp connections were observed on hyphae of the isolates. Sclerotia were nearly spherical and 0.9-2.1mm in diameter. The pathogenic fungus was identified as Sclerotium rolfsii Sacc. on the basis of these morphological and pathological characteristics.
A new causal fungus of strawberry anthracnose was found in Tochigi Prefecture in 1991. The symptoms of the disease appeared on leaves, petioles and runners in nurseries. The lesions are dark brown to nearly black and occur on the margins and tips of leaflets. Mycelia of the fungus are white, becoming pinkish grey, and conidial masses are salmon pink on PDA medium. Sclerotia and setae are absent. Conidia are hyaline, single-celled and fusiform with the dimensions of 8.9-16.2×3.2-4.9 (15.5×4.4)μm. Appressoria are dark brown, clavate and 5.9-8.9×4.1-8.1 (7.8×5.7)μm in dimensions. The fungus is pathogenic to tomato, sweet pepper and rocket larkspur. Optimum temperature for mycelial growth on PDA medium was about 25°C. Based on these morphological and pathological characteristics, the causal fungus was identified as Colletotrichum acutatum Simmonds.
Conidia of scab fungus (Venturia nashicola), produced on the Japanese pear leaves, were usually dispersed by rainfall. The number of conidia dispersed was greatest just after the start of rainfall and gradually decreased. The rate of dispersal of the conidia re-produced on the leaf lesions was similar to the rate observed during the first experiment. The number of conidia re-produced and dispersed in the second experiment was approximately 20% of the number existing at the start of rainfall in the first experiment.
A Phytophthora species isolated from crown rot of baby's breath, Gypsophila paniculata L., were identified as P. nicotianae var. payasitica. An inoculation test showed that pathogenicity of the 8 isolates to baby's breath was severe. Soil fumigation with chloropicrin, chloropicrin methyl bromide or methyl isothiocyanate D-D, soil application with metalaxyl or fungicidal soil drench with fosetyl were recommendable effective for control of the disease, and hymexazol metalaxyl, oxadixyl mancozeb, propamocarb hydrochloride or echlomezol reduced the damage of the disease.
An isolate of tobacco mosaic virus (TMV) was isolated from Physalis alkekengi L. var. franchetii (Japanese lantern plants, Houzuki) which is commercially sold as ornamental plants. The plants showed mosaic and distortion of fruits. The isolate was identified as TMV (tomato strain) by morphology, host range and serology.
Sclerotium crown rots of Delphinium elatum, × Solidaster luteus and Chlorophytum comosum occurred in Chiba Prefecture in 1991, 1987 and 1991, respectively. A Sclerotium species isolated from diseased plants was identified as S. rolfsii. Inoculation experiments showed that the fungus was the causal agent of the diseases.
A Rhizoctonia species isolated from crown rot of Delphinium spp. was identified as R. solani AG 2-1. An inoculation experiment showed that the fungus was the causal agents of the disease. Fungicidal soil drenches with pencycuron or tolclofos-methyl, and soil fumigation with chloropicrin, chloropicrin·methyl bromide, methyl isothiocyanate · D-D or dazomet were reduced the damage.