Genetic analysis of Cochliobolus heterostrophus polyoxinresistant mutants

Abstract

Nine polyoxin-resistant mutants of Cochliobolus heterostrophus were isolated after ethyl methanesulphonate mutagenesis. All were highly resistant to polyoxin (MIC≥ 1,600 ppm). Crosses between the mutants and a wild-type strain revealed that the resistance trait was inherited to the offsprings in different fashions. Four of the mutant strains inherited polyoxin resistance in a 1 : 1 segregation ratio, indicating that the phenotypes in these strains were due to alteration at a single locus. Allelism tests revealed four new loci, Pol1, Po12, Po13 and Po14, for polyoxin resistance in these mutant strains. The genes responsible for the phenotypes of the other five mutant strains were not determined, because of extremely slow growth of progenies in one cross, sterility in another cross, and inexplicable responses to polyoxin of the progenies in the other crosses. No linkage was detected between the genes for polyoxin resistance and mating type.