Genetic studies of the phytopathogenic fungus Botryotinia fuckeliana (Botrytis cinerea) by analysis of ordered tetrads

Botryotinia fuckeliana (Botrytis cinerea) is a heterothallic ascomycete which produces linear 8-spored asci (tetrads) in apothecia. Ascospores were collected in their linear sequence from individual asci, and analysed to determine the segregation patterns of alleles at gene loci controlling mating type (MAT1), resistance to dicarboximide fungicides (Daf1) and resistance to benzimidazole fungicides (Mbc1). The alleles were present in their expected linear sequence in 58% of the asci; most irregular sequences (32% of the asci) were caused by single exchanges between adjacent spores. The MAT1 locus was ca 12 map units from its centromere, and the Mbc1 locus showed loose linkage with its centromere. The Mbc1 and Daf1 loci were ca 47 map units apart on the same chromosome and not linked with the MAT1 locus. Pairs of homothallic ascospores were found in seven out of 105 asci. Homothallism was not caused by inclusion of more than one nucleus in ascospores, and it occurred only in ascospores predicted to carry the MAT1-2 allele after meiosis.