The Number and Distribution of Incompatibility Factors in Schizophyllum

Abstract

A world-wide sample of 114 homokaryotic strains of the tetrapolar mushroom, Schizophyllum commune, was analysed to determine the extent of the "multiple-allelic" series of A and B incompatibility factors. The sample contained 96 distinct and interfertile A factors and 56 different B factors. No evidence was found for non-random geographical distribution or for any departure from numerical equality of specific factors either in the A series or in the B series. Assuming random distribution and equal frequency of factors of both series, these data indicate 339 with 5 per cent limits of 562 and 216 A factors and 64 with 5 per cent limits of 79 and 53 B factors in the natural population. Since sexual fertility between strains depends upon heterozygosity of both A and B factors, the outcrossing efficiency in the natural population is 98.15 per cent.