Detection of intrachromosomal recombination in Sclerotinia sclerotiorum populations

Abstract

Genetic structure and reproductive mode of the homothallic fungal pathogen Sclerotinia sclerotiorum have been widely studied using linkage disequilibrium (LD) tests with putatively unlinked molecular markers. We previously observed random association between linked loci in S. sclerotiorum populations suggesting intrachromosomal recombination or high mutation rates at these loci. This study was aimed at testing intrachromosomal recombination using 12 microsatellite loci distributed over four chromosomes. Two hundred thirty isolates sampled from seven populations in the USA and China from a variety of crops were genotyped. Each isolate carried a single allele for each of the 12 loci suggesting the isolates were haploid and homokaryotic. Pairwise LD tests of all the intrachromosomal loci showed relationship ranged from linked to random association, and in many cases LD declined with increasing physical distance between loci. Thus the random associations of alleles cannot be simply attributed to random mutation. Majority of the isolates were mycelially incompatible, likely minimizing the possibility of heterokaryon formation and mitotic recombination. Thus the observed high intrachromosomal recombination is most likely due to meiotic recombination following outcross in these populations.