XVI International Botanical Congess

Mutant colony colors are determined by genes forming a closely linked (>0.5 cM) cluster: orange (o) pumpkin (p) yellow (y) white (w) and magenta (m). Pink is determined by a dominant allele (+) and the w mutation is epistatic for all colony colors. The linkage map is o-p-y-centr-wA-wB-m.. Crosses involving field strains with different color phenotypes yield meiotic segregants with the same nonparental color with frequencies ranging from 25% to 100%, depending on the combination of strains. The most plausible explanation proposes the transcentric transposition of an element (TE) yielding an insertional color mutation. Genetic evidence indicates that for one combination of field strains a TE may be responsible for teliospores yielding mostly only a-1 or only a-2 sporidia, crossing over between the haplo-lethal mutant locus and the centromere is responsible for the few teliospores yielding both a-1 and a-2 sporidia. Sporidia of mutant laboratory ow stain grown on chlorate-nitrate minimal medium yielded 100% pink sporidial colonies and ca 0.3% chlorate-resistant mutants. Again, one plausible explanation proposes that a TE functioning during mitosis may be responsible for insertion mutations at loci in different chromosomes.