The complementary reaction through heterokaryon formation between nitratenonutilizing (nit) mutants of Fusarium moniliforme was studied to understand the development mechanism to benomyl resistance. A benomyl resistant isolate with MIC value of 1600ppm showed the complementary reaction with less resistant ones (50≤MIC≤800) obtained from the same location in Tochigi, The complementary reactions between isolates obtained from different locations were rare. This result suggests that F. moniliforme may acquire benomyl resistance through heterokaryon formation and isolates from different origin do not belong to same vegetative compatibility group.
Three strains of Colletotrichum gloeosporioides and three strains of C. acutatum were tested concerning their ability to give rise to chlorate-resistant nitrate non-utilizing mutants (nit mutants) when they were cultured on a minimal medium containing 1.5% KClO3. All strains gave rise to mutants that could be placed in phenotypes of nit mutants. C. gloeosporioides mainly gave rise to nit1. While C. acutatum gave rise to nit1 and Nit3. All six strains did not give rise to nit2. Three nit mutants tested were pathogenic to strawberry.
The capillary watering system raising nursery in pot mechanically inhibited the dispersal of the conidia and successfuly depressed the spread of strawberry anthracnose. It was demonstrated that the conidia of Glomerella cingulate (=Colletotrichum gloeosporioides) were effectually dispersed in the water droplets and the wind. The conidia were hardly blown off by the wind in the absence of water. When the conidia on the diseased leaves were contacted with the water, they were immediately suspended into the water droplets which was splashed and blown by the wind.
Rhizoctonia rot/blights of muskmelon Cucumis melo var, reticulatus, scarlet plume Euphorbia fulgens, stock Matthiola incana and parsley Petroselinum crispum caused by Rhizoctonia solani AG-4, and balloon flower Platycodon grandiflorus, Boston fern Nephrolepis exaltata var. bostoniensis hort, and bishop's weed Ami majus caused by R. solani AG-2-2 occurred in Chiba Prefecture. Inoculation experiments showed that the fungi were the causal agents of the diseases.
To study the resistance of cucurbit crops against cucumber mosaic virus (CMV) by aphid transmission, a field test was performed. Numbers of plants showing symptoms were checked at successive days. Infection and concentration of CMV were checked by ELISA. The results showed that cucumber cultivars were generally resistant against CMV but that CMV concentration varied depending on cultivars. “Sachinari” revealed to contain CMV in high concentration, but out of ten plants, only two showed mosaic symptoms. “Natsusango” showed strong resistance in both symptomatology and virus concentration. Each melons showed low levels of resistance against CMV infection, however generally CMV concentration was not high.
Of 54 isolates tested, 4 isolates of Phytophthora cactorum from udo and 10 isolates of unidentified Phytophthora species, each one from Rhoeo discolor and Brodiaea and 8 isolates from gerbera, showed distinct pathogenicity to udo by artificial inoculation test. Nine isolates of P. cactorum from six different crops except udo were clearly inferior to the isolates from udo in virulence to blanched stem of udo.
Phytophthora rot developed on blanched stem of udo in the temperature range of 10 to 30°C, with the optimum temperature at 20°C and the second best at 15 or 18°C. Sclerotinia rot developed at 10 to 25°C with the optimum temperature being 20°C and southern blight developed at 15 to 35°C, with the optimum temperature at 25°C. The optimum temperature on the development of Phytophthora rot and Sclerotinia rot obtained by artificial inoculation test agreed with the optimum room temperature in blanching culture.
Infection degrees of tested cultivars were remarkably influenced by the soil temperature, and increased with rising temperature. Temperature over than 25°C was necessary for effective screening of resistant cultivars. In general, infection degree of middle resistant cultivars to race 2 increased quickly under the optimum soil temperature and high inoculum concentration, and the resistant level was evaluated to be near susceptible.
Race differentiation of Fusarium oxysporum f. sp. dianthi isolates from carnation growing areas in Japan were investigated with differential cultivars mainly used in Holland. Most isolates tested were considered to belong to race 2 by the reactions to the differential cultivars. It is difficult to say that a dominant race in Japan is race 2 with the results of only 18 isolates, But it could be suggested that race 2 is distributed widely in Japanese carnation growing areas.
Leaf blight of Gazania×splendens and web blight of Conteaster salicifolius occurred in Tokyo Metropolis in 1992. A Rhizoctonia species isolated from diseased plants was identified as R. solani AG-1. Inoculation experiments showed that the fungus was the causal agent of these diseases.
Sclerotium southern blight of Peperomia caperata, Ophiopogon japonicus f. nanus and Ajuga reptans occurred in Tokyo Metropolis in 1992, 1992 and 1983, respectively. The causal fungus isolated from diseased plants was identified as S. rolfsii by morphological observations and inoculation tests.
Two Pythium species were isolated from rotted secondary roots of collapsed plants of Eustoma grandiflorum during 1987-1992 in Kanto district and identified as P. irregulare and P. spinosum. An inoculation experiment showed that the fungi were the causal agents of the disease. Granular applications of metalaxyl were significantly effective for control of the disease. Soil drenches of benomyl, captan or hymexazol did not reduced the damage.
In 1992, Sclerotium rot of Alstroemeria spp, . Nerine bowdenii, Phalaenopsis hybrids, Solanum mammosum and Tulbaghia fragrans occurred in Chiba Prefecture. A Sclerotium species isolated from diseased plants was identified as S. rolfsii Sacc. Inoculation experiments showed that the fungus was the causal agent of the diseases.