High Genetic Diversity, Phenotypic Uniformity, and Evidence of Outcrossing in Sclerotinia Sclerotiorum in the Columbia Basin of Washington State

Abstract

Sclerotinia sclerotiorum, the causal agent of potato stem rot, is prevalent and poorly managed on potatoes in the Columbia Basin of Washington. Because of the ubiquitous nature of the fungus and high crop diversity within the Columbia Basin, understanding the population structure and the potential for outcrossing of the pathogen would be helpful in developing disease management strategies. The population structure of S. sclerotiorum in the Columbia Basin from potato was examined using microsatellite markers and mycelial compatibility. Analysis of molecular variance revealed that 92% of the variability among 167 isolates was found within subpopulations, with limited, yet statistically significant impact of the collection date, but not the year or location of collection. Linkage disequilibrium and index of association analyses noted a potential for outcrossing in two locations, which was substantiated by the discovery of recombinant ascospores in three field-generated apothecia from the 12 apothecia examined. Microsatellite haplotypes were not correlated with mycelial compatibility groups. This high haplotypic diversity did not seem to impact pathologically important phenotypes. Greenhouse inoculations of potato plants exhibited no significant differences in aggressiveness on potato stems. Moreover, in vitro studies of response to fungicides and temperature stimuli yielded no significant differences among studied isolates. These findings illustrate the potential for outcrossing in warm temperate regions of North America, where a diversity of crops are planted simultaneously and in neighboring fields. This study also indicates that the unsatisfactory management of potato stem rot is likely not directly attributable to genetic factors, but to gaps in agricultural practices.

Mycelial compatibility and aggressiveness of Sclerotinia sclerotiorum isolates from Brazil and the United States

“…Both aggressiveness differences (experiment one) and lack of difference (experiment two) were reported in former publications. Differences in isolate aggressiveness have been reported for soybean (Kull et al, 2004), canola (Kohli et al, 1995), and sunflower (Ekins et al, 2011;Marciano et al, 1983), while lack of significant differences in aggressiveness was reported among isolates collected from Canada and inoculated in soybean (Auclair et al, 2004), or collected in the USA and inoculated in potato (Atallah et al, 2004). The overall lesion lengths measured in the experiment two of this study were shorter than in experiment one, possibly due to growing conditions in the greenhouse related to planting dates throughout two years.…”

“…MCGs identified Set 1 18 12 BR1; BR2, BR3, and BR5; BR4 and BR8; BR6; BR7; BR9; US1, US3, US4, and US7; US2; US5; US6; US8; and US9 Set 2 17 4 BR9 and BR23; BR10-BR21 and BR24; BR22; and US1 accumulate mutations and generate new genotypes, as reported elsewhere (Atallah et al, 2004;Kohli & Kohn, 1998;Malvárez et al, 2007;Wu & Subbarao, 2006). In experiment two, 81% of the isolates from Brazil belonged to a single MCG, even though these isolates were sampled over an extensive area with the furthest isolate separation of about 2,000 km.…”

“…Other reports indicated lack of common MCGs in S. sclerotiorum isolates from North Carolina and Canada or North Carolina and Louisiana (Cubeta et al, 1997), and Canada, China, and England (Li et al, 2008). This lack of common MCGs may result of specific selection of MCG genotypes, due to differences in their adaptability to environmental conditions (Atallah et al, 2004;Kull et al, 2004). The ability of certain S. sclerotiorum genotypes to adapt to different environments may explain their presence over large areas.…”

“…Mycelial compatibility groups (MCGs) and DNA marker systems have been used to characterize the genotypic diversity in populations (Kohli & Kohn, 1998;Atallah et al, 2004;Gomes et al, 2011;Litholdo Júnior et al, 2011). The method to determine MCGs is broadly adopted for being a macroscopic assay of self/ nonself recognition controlled by multiple loci common in fungi (Kohn et al, 1990).…”

Genetic Diversity among Different Isolates of Sclerotinia sclerotiorum in North of Iran

“…Mycelia were harvested by vacuum filtration, lyophilized, and stored at -20°C. Fifteen to 20mg of dried mycelia were powdered, and transferred to 1.5 Eppendorf tubes for DNA extraction following the method of Liu et al, 21 with the slight modifications. The DNA pellets were dissolved in 30μl of 1X TE (10mM Tris-HCl, 1mM EDTA), and stored at 5°C.…”