Genetic studies of the<i>b</i>incompatability locus of<i>Ustilago maydis</i>

Abstract

SUMMARY The b locus of Ustilago maydis is both an incompatibility locus and a pathogenicity locus. There are several different b factors, and they are randomly distributed and equally frequent in the natural population. A sample of 62 lines contained 18 b groups and permitted an estimate of no more than 25 b groups in the natural population. All lines within the same b group are indistinguishable in their mating behaviour. No linkage was detected between b and any of the four biochemical markers tested. No intrafactor recombinants at b were found among more than 6700 progeny. Differences in degree of pathogenicity between solopathogenic diploids and comparable haploid by haploid crosses were detected.