Hyphal morphology associated with strain instability in the commercial mushroom, Agaricus bisporus

Abstract

Light microscopy was used to examine the morphology of surface hyphae of strains of Agaricus bisporus that form “fluffy” or “stromatal” sectors on agar medium or in grain culture. Although differences were found between normal (U1 strain) and some sectoring isolates in the mean distance from the hyphal apex to the first branch, and in average internode length, these differences were not consistent under different growth conditions. Fluffy and stromatal isolates did show a high frequency of hyphae with irregular branching patterns. A correlation between high prevalence of hyphae with certain types of branching patterns and the ability to form sectors in grain culture was also observed in 35 single-basidiospore isolates derived from mushrooms produced by normal and sectoring cultures. It is suggested that the ability of any subculture to form a sector may depend on the prevalence of aberrent hyphae in the initial inoculum.

Key Words:

• Agaricus bisporus
• Agaricus brunnescens
• hyphal morphology
• sectors
• strain instability