Prevalence of inversion positive and inversion negative mating type (MAT) alleles andMATheterokaryons inSclerotinia sclerotiorumin the United States

Abstract

Sclerotinia sclerotiorum is a yield-limiting pathogen of several economically important crops, and it reproduces sexually by self-fertilization. Based on the presence of an inversion in the mating type locus, S. sclerotiorum can be grouped as inversion negative (Inv– MAT) and inversion positive (Inv+ MAT) isolates. This study was conducted to determine the prevalence of Inv– and Inv+ MAT S. sclerotiorum isolates across the United States. In total, 164 isolates from 16 hosts and 22 states were evaluated, including 87 isolates from North Dakota and northern Minnesota and 47 isolates from soybean. PCR screening was performed separately for Inv– and Inv+ MAT with specific primers. Of the two kinds of MAT homokaryons, Inv– MAT isolates were the most frequent (31.7%) and were identified in 15 states. Another 12.8% of isolates were Inv+ MAT, and were identified in 8 states. The majority (55.5%) of isolates screened were MAT heterokaryons, and these were identified from 18 states and 11 hosts. The implications of MAT heterokaryons for the biology and management of S. sclerotiorum are discussed.