INHERITANCE OF STRAIN INSTABILITY (SECTORING) IN THE COMMERCIAL BUTTON MUSHROOM, AGARICUS-BISPORUS

The button mushroom, Agaricus bisporus, is a commercially important cu ltivated filamentous fungus. During the last decade, the button mushro om industry has depended mainly on two strains (or derivatives of thes e two strains). Using one of these highly successful strains (strain U 1) we examined the phenomenon of strain instability, specifically, the production of irreversible sectors. Three ''stromatal'' and three ''f luffy'' sectors were compared with a healthy type U1 strain and with a wild-collected isolate. Compost colonization and fruit body morpholog y were examined. The main objective of this study, however, was to exa mine the meiotic stability of the sectored phenotype. Single basidiosp ores were isolated and subjected to a grain bioassay in which the abil ity to produce sectors was measured. Our results were as follows: (i) basidiospore cultures obtained from a wild-collected isolate showed no tendency to produce sectors; (ii) approximately 5% of the basidiospor e cultures obtained from healthy type U1 strains produced irreversible sectors in the grain bioassay; (iii) the five primary sectors examine d produced basidiospore cultures, half of which produced normal-lookin g growth in the grain bioassay and half of which produced some degree of sectoring; and (iv) the one sectored isolate that represented the F 2 generation gave ratios similar to the 1:1 ratio observed for the F1 cultures.