Genetic structure within Septobasidium colonies suggests outcrossing and frequent non-self-fusion

Fungi in the genus Septobasidium form colonies that envelop and infect multiple scale insects. Infection of each insect is thought to occur only via meiotic basidiospores. In this study, we investigated the genetic status of colonies by genotyping different phases of the Septobasidiumlife cycle including single spore isolates, mature colony tissue isolates, and infected insects. Meiotic analyses showed segregation of two alleles at multiple loci among the progeny from a single fungal colony. Genotyping of multiple tissue isolates demonstrated that individual Septobasidium colonies were composed of a single heterozygous dikaryotic mycelium. Fungi from insects fused to a colony of S. ramorum had identical genotypes to each other, but insects not yet fused to a colony sometimes had unique genotypes. Based on these studies, Septobasidium species are suggested to be predominantly outcrossing, with colonies maintaining their genetic identity despite frequent non self-fusions