Marker stability throughout 400 days of in vitro hyphal growth in the filamentous ascomycete, Sclerotinia sclerotiorum

Abstract

The stability of routinely used, population genetic markers through approximately 1 year of continuous laboratory growth was investigated in the common, plant pathogentic ascomycete Sclerotinia sclerotiorum. Given reports of accelerated mutation rates at higher temperatures, both a permissive temperature, 22°C, and a temperature at the high end of tolerance, 30°C, were employed. Because mycelial growth rate was tracked among mitotic lineages established for each strain, a subsidiary objective was addressed, testing the stability of a 30°C-competent phenotype. Twelve laboratory strains of S. sclerotiorum, including the genome sequence isolate, 1980, were propagated serially for up to 400 days at 22°C. Five of these strains were also propagated at 30°C. No mutations were observed in mycelial compatibility groupings (MCGs), DNA fingerprints, alleles at 7 microsatellite loci, or alleles at 56 AFLP loci. All of these markers show variation in field populations, which are likely much larger and influenced by different and more stochastic environmental processes. In S. sclerotiorum, population genetic markers were stable over time through serial transfer and growth of laboratory strains at both 22°C and 30°C. The strain isolated after extended drought and capable of infecting plants at 28°C demonstrated the stability of its high temperature-competent phenotype, in addition to its stable growth rate at 22°C. This observation has implications for modeling pathogen tolerance or adaptation under conditions of environmental stochasticity, including climate warming.