SELECTION OF HIGH-YIELD STRAINS AMONG REG ENERANTS FROM MUTAGENIC PROTOPLASTS OF PLEUROTUS-OSTREATUS

The relationships between mutagenic conditions for protoplasts and cul tural characteristics of mycelia regenerated from protoplasts were exa mined to clarify the optimum conditions for selecting high-yield strai ns among the regenerants. The protoplasts released from the mycelium o f Pleurotus ostreatus (Jacq.: Fr.) Kummer were treated with a germicid e lamp with various survival rates from 100% to less than 0.1% by mean s of changes of irradiation times. About 50 colonies regenerated from protoplasts from each survival rate were tested for cultural character istics such as the weights of the fruiting bodies. The characteristics of the regenerants were inferior to those of the parent for every ave rage, accompanied with declines in the survival rates of protoplasts. However, the standard deviation of each characteristic showed a tenden cy to increase at the same time. Consequently, the optimum conditions for selecting high-yield strains among regenerants was considered to b e when the survival rate of protoplasts was about 10% in view of both the average and standard deviaions of the regenerants at each step. Fo ur strains, yielding more than 15% as compared with parent, were selec ted out of 313 colonies regenerated from protoplasts treated under suc h conditions. One of them yielded 35% more than that of the parent in a reexamination. Furthermore, this strain was found to be stable and t he reason why the strain isolated from the tissue of a fruiting body a lso showed similar characteristics in yield. Therefore, the method of cell selection using mutagenic protoplasts was considered to be useful for the breeding of P. ostreatus.