A novel hybrid fungus culture, designated J9277, of the mushroom species Agaricus bisporus produces crops of mushrooms having white, rounded, thick-fleshed caps and proportionally long stems in a relatively short interval of time. Diverse additional strains can be developed from J9277 by various means including somatic and tissue culture selection, basidiospore selection, and hybridization to other strains of Agaricus bisporus, and the resulting derivative strains can be screened for desirable commercial characteristics.