Mating type distributions of Microsphaeropsis tanaceti isolated from pyrethrum fields in Tasmania, Australia

Tan spot disease, caused by the ascomycete Microsphaeropsis tanaceti, is a prominent disease in Tasmanian pyrethrum crops, which are grown for insecticide production. M. tanaceti reproduces profusely via asexual conidia, however ascospores haven’t been observed and the role of sexual reproduction in the field unknown. In many ascomycete fungi, mating type (MAT) genes govern mating between individuals. In this study, two mating types, MAT1-1 and MAT1-2, have been identified within M. tanaceti in a heterothallic arrangement. A PCR assay was developed to identify mating type and used to screen two hierarchically sampled, field populations in August 2012. Each field consisted of two 50 m transects, sampled at 0.5 m intervals (n = 101 per transect). Within each transect, M. tanaceti was isolated from 62 and 46 sampling units in field A, and 21 and 45 sampling units in field B. The ratio of mating types did not differ from a 1:1 ratio at either the field or transect scale (P ≥ 0.13). Ordinary runs analysis identified no spatial aggregation of M. tanaceti or of MAT1-2 genotypes (P ≥ 0.06) within transects. Spatially significant (P < 0.05) aggregation of MAT1-1 was only identified in a single transect in field B. This data indicates a heterothallic species with no evidence to preclude a sexual cycle occurring in the field. MAT gene functionality will be examined via in vitro crosses and RNA expression analysis.