Environmental factors influencing release and dispersal of conidiospores of Mycovellosiella nattrassii Deighton, causal fungus of leaf mold of eggplant, were studied in the laboratory and greenhouse. In the laboratory, the average number of conidiospores released from lesions on artificially inoculated leaves was 468/cm2/24 hour under 50% of relative humidity, however, under 100% of relative humidity spores released few. At 20-25°C in the dark under 50% relative humidity, more conidiospores were released than at other temperatures and light exposures. But few conidiospores were released under 100% relative humidity, in spite of optimal temperature and light conditions. In field tests, the number of conidiospores released from three lesions on naturally infected leaves increased during the day with low humidity following days with successively high humidity. The dispersal of conidiospores also increased on fine days immediately after a change from high to low humidity. On the other hand, few spores were dispersed at night or on rainy or cloudy days. These results seem to indicate that relative humidity was the main factor influencing release and dispersal of conidiospores from lesions on of eggplant leaves.
In autumn 1994, we isolated Phoma lycopersici from brown lesions on tomato leaf, stem and fruit in Takachiho, Miyazaki, Japan. The fungus produced round lesions on tomato leaves, petioles, stems and fruits by artificial inoculations using adult and juvenile plants. In Japan, P. exigua, P. lycopersici and P. destructiva have been reported as the pathogen of tomato leaf spot, stem rot and fruit rot, respectively. We propose that P. lycopersici also causes leaf spot and fruit rot of tomato, and that the tomato diseases caused by Phoma species should be called by a unified name.
To clarify the effects of adding silica gel (99.8% SiO2, pH 5.0) to soil in a rice nursery box (30×60×3cm) on the incidence of seedling blast caused by Pyricularia oryzae, 250 to 1000g of silica gel was mixed into 3000g of soil before sowing naturally infested rice seeds (100g/nursery box). The incidence of seedling blast in the boxes with 250g silica gel (the lowest dose) was 80% lower than that in the control box without silica gel. The silicon content in rice seedlings grown in the soil with 500g of silica gel increased starting at 5 days after sowing. After 7 days, the level reached 235% of the value of the seedlings grown in soil without silica gel. The pH of the soil containing silica gel did not change and remained in the optimal range for nursery growth of rice plants. In contrast, in soil amended with other silicon materials, fused phosphate, calcium silicate and potassium silicate, with silicon contents of 20.0%, 30.0% and 30.0% respectively, the pH increased to over pH 6.5, which is unsuitable for nursery growth of rice plants. Also, the silicon content in the seedlings grown on soil with silica gel was higher than that of seeedlings grown on soil with other silicon materials. Furthermore, the nitrogen content in rice seedlings in the soil with silica gel did not decrease. From these results, silica gel application was an effective method for the control of seedling blast of rice plants.
During winter, the causal fungus of brown leaf spot of Humulus scandens, Pseudocercospora humuli (Hori apud Takimoto) Guo et Liu, was observed in the form of conidia and stroma on fallen diseased leaves. These conidia maintained high germinability at every time examined. Although most of the conidia had disappeared by April, numerous new conidia were soon produced on new stroma in early May. Therefore, some overwintered conidia and newly produced conidia on fallen diseased leaves may act as the primary infection source on newly germinated host plant. Mycelia grew at 10°C-30°C with an optimum of 25°C. They grew well on various natural agars, such as PSA, MA and CMA and poorly on Czapek's, Waksman's and Richard's agar composed of inorganic chemicals without sugar. Among the media tested, PSA was the most suitable for mycelial growth. Mycelia grew well at a pH range from 4 to 9, but quite poorly below pH 3. Effect of fungicides and herbicide on germination of conidia and mycelial growth was tested. Although both maneb and CuSO4⋅5H2O suppressed conidial germination and mycelial growth, maneb was more effective. Meanwhile, conidia germinated and mycelial growth was not sensitive to glyphosinate at practical concentrations. Sporulation experiments on agar media were not successful.
Shoots of nine rose cultivars, including cut roses and rootstocks, were inoculated in vitro with four strains of Agrobacterium tumefaciens to test their resistance. Disease incidence of susceptible R. canina and R. canina ‘Pfänder’ was 61% and 85%, respectively. Disease incidence of ‘PEKcougel’ and ‘Lifirane’, with strong resistance to tumor formation, was under 17%. GOU1 caused disease on the most cultivars, with over 73% disease incidence on six roses, with the exceptions of ‘Bridal Pink’ ‘Lifirane’ and ‘PEKcougel’. A208, G-Ag-27, C58clrif-R were weakly virulent, except against R. canina ‘Pfänder’. ‘Dukat’, ‘Fashion Parade’ and R. coriifolia froebelii were susceptible to GOU1, but not to G-Ag-27 and C58clrif-R. Tumors were largest in ‘Lifirane’, and statistically smaller in the other roses. The tumors induced by C58clrif-R were larger than those induced by the other strains.
An attenuated strain of Japanese yam mosaic virus, selected from the fields and referred to as JYMV-M, caused no symptoms on Japanese yam plants throughout the growing season. The purified virus preparation was highly infective, and the virus was easily transmitted by aphids. An RT-PCR-RFLP assay was used in cross-protection tests to discriminate JYMV-M from other severe strains. Pre-inoculation of yam plants with JYMV-M remarkably protected them from infection with severe strains. JYMV-M infection did not affect either the quality and quantity of yam production.
In April 1998, powdery mildew was found on two species of citrus (tankan mandarin and mandarin orange) in Kagoshima prefecture, Japan. White, powdery mycelial colonies appeared on leaves and young shoots. Young leaves specially were damaged severely, infected leaves eventually fell. Conidia were ovoid to cylindric, 25.0-41.6×12.5-18.7(-27.1)μm in size, borne singly on conidiophores erected on aerial mycelium. Appressoria on germ tubes were lobed. Cleistothecia were not observed. On the basis of the morphological characters of the conidial state, the fungus was proposed as an Oidium sp. of the Erysiphe polygoni type.
The pathogenicity and serological properties of Bean yellow mosaic virus (BYMV) isolates from both cultivated and naturalized gladioli in Kagoshima prefecture were investigated. According to the method of Sasaya et al. (1998), 64 BYMV isolates from gladiolus were classified as pathotype I or IV, whereas five BYMV isolates from broad bean were classified as pathotype II. The serological relationships among the BYMV isolates were determined with DAS-ELISA and the improved Ouchterlony double-diffusion test using antisera to isolates S-22N (pathotype I) and S-22C (pathotype IV) originating from a gladiolus source, and Sb-50C (pathotype II) from broad bean. The gladiolus isolates (S-22N and S-22C) differed serologically from the broad bean isolate (Sb-50C).