When grown on a cellulose membrane laid on Czapek agar without sugars (CCMA), Rhizoctonia solani formed a specific mycelial structure under the membrane. The structure was also formed by Rhizoctonia spp., Sclerotium spp., Sclerotinia sclerotiorum, Corticium rolfsii, Nakataea sigmoideum var. irregulare but not by other fungi tested. The structure was not formed on media containing such sugars as glucose, sucrose or galactose, but was formed on media with trehalose or mannitol. The structure was not formed under filter membranes of cellulosic fibriform or polycarbonate. When a double layer of different membranes was put on agar medium, the structure was produced only beneath the cellulose membrane. However, when a polycarbonate filter membrane was set on the cellulose membrane, the structure was produced between the two. Validamycin A, an antibiotic for Rhizoctonia disease control, prevented the formation of the structure at 0.01 μg/ml in CCMA.

　Uninucleate oidia from 8 wild-type homokaryons of Flammulina velutipes were UV-irradiated with a lethal dose of more than 98%. In total, 4,624 mutagenized oidial mycelia were isolated, 187 (4.0%) of which were auxotrophic mutants. During incubation on complete medium for 7-50 days, however, 106 (56.7%) of the mutants recovered from nutritional deficiency. In the present study, 19 adenineless, 12 methionineless, 6 p-aminobenzoic acidless, 4 arginineless, 2 nicotinamideless, 2 histidineless, 1 leucineless, 1 isoleucineless, 1 lysineless, 2 adenine-histidineless, and 1 adenine-methionineless auxotrophic mutants were isolated. Complementation test detected 5 genes (ade 1-ade 5) responsible for adenine biosynthesis, 4 genes (met 1-met 4) for methionine, 3 genes (pab 1-pab 3) for p-aminobenzoic acid, 3 genes (arg 1-arg 3) for arginine, 2 genes (nic 1, nic 2) for nicotinamide, and 2 genes (his 1, his 2) for histidine. Based on genetic analysis of ade 1, ade 2, arg 1, pab 1, and c (gene for compact morphology), tentative linkage map consisting of 3 linkage groups was established.

　An experiment was conducted to establish empirical genetic rules for breeding high-optimum-temperature hybrids of Flammulina velutipes. Optimum temperatures of monokaryotic stocks from commercial strains showed a normal distribution ranging between 20.0°C and 25.7°C with a mean of 22.5°C. Monokaryotic stocks having A2 incompatibility factor showed a higher optimum temperature than A1 factored stocks. Optimum temperatures of hybrids between compatible monokaryotic stocks also showed a normal distribution with a mean of 23.4°C, which was 0.9°C higher than the monokaryon's mean. When the monokaryons were classified into high-(H), medium-(M) and low-(L) optimum-temperature groups, the results of H×H, H×M and H×L matings yielded high-optimum-temperature dikaryons at the rates of 64%, 58% and 42%, respectively. In the case of H×H mating, the A1B1×A2B2 hybridization produced more than 80% high-optimum-temperature dikaryons, but the A1B2×A2B1 hybridization produced only 50% high-optimum-temperature dikaryons. The rate of high-optimum temperature hybrids between reciprocal dikaryon isolates of A1B1×A2B2 and A2B2×A1B1 showed no significant difference in temperature characteristic. However, a difference in the rate of high-optimum-temperature stock production was recognized between A2B1×A1B2 and A1B2×A2B1 reciprocal isolates. As a result of this work, a dikaryon with an optimum temperature of 25.9°C was produced.