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United States Department of Agriculture

Agricultural Research Service

Research Project: Cool Season Grain Legume Genetic Enhancement and Pathology

Location: Grain Legume Genetics Physiology Research

Title: Genetic and phenotypic diversity and random association of DNA markers of the fungal plant pathogen Sclerotinia sclerotiorum from soil on a fine geographic scale.

Authors
item Attanayake, Renuka -
item Porter, Lyndon
item Johnson, Dennis -
item Chen, Weidong

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2012
Publication Date: July 25, 2012
Citation: Attanayake, R., Porter, L., Johnson, D., Chen, W. 2012. Genetic and phenotypic diversity and random association of DNA markers of the fungal plant pathogen Sclerotinia sclerotiorum from soil on a fine geographic scale.. Soil Biology and Biochemistry. 55:28-36.

Interpretive Summary: The ubiquitous fungus Sclerotinia sclerotiorum is soil-borne plant pathogen producing durable sclerotia enabling the pathogen to survive in soil for many years. It causes white mold and stem rot diseases on more than 400 plant species including many economically important crops. Studies on population genetics of this pathogen have been mainly focused on sclerotia produced on infected plants. The sclerotia residing in the soil have been largely ignored. In this study sclerotia of Sclerotinia sclerotiorum were collected from one square meter area of the top 1.27 cm layer of soil in an alfalfa field. Out of 272 sclerotia collected, 40 were randomly selected and analyzed for genetic and phenotypic diversity. The following markers and traits were investigated; microsatellite loci, mycelial compatibility groups (MCGs), fungicide sensitivity, oxalic acid production, growth rate, colony color and virulence. Among the 40 isolates sixteen distinct microsatellite types and 15 MCGs were found. The isolates showed three colony colors (beige, black and white) on potato dextrose agar and exhibited significant differences in growth rate, oxalic acid production, and sensitivity to three fungicides, benomyl, fluazinam and iprodione. In spite of the genotypic and phenotypic diversity among the isolates there was no significant difference in virulence in detached leaf assays. No apparent relationship among the neutral genetic markers and the phenotypic traits was detected. Results showed high levels of genetic diversity and frequent outcrossing within the population of S. sclerotiorum. Multilocus Index of Association analyses with and without specification of subpopulations suggested that frequent outcrossing occurs only within interbreeding subpopulations of S. sclerotiorum.

Technical Abstract: Sclerotia of the soilborne plant pathogen, Sclerotinia sclerotiorum, were collected from 1 m2 area of the top 1.27 cm layer of soil in an alfalfa field. Out of 272 sclerotia collected, 40 were randomly selected and analyzed for genetic diversity in terms of microsatellite loci, mycelial compatibility groups (MCGs) and phenotypic diversity using five phenotypic traits (fungicide sensitivity, oxalic acid production, growth rate, colony color and virulence). Sixteen microsatellite haplotypes and 15 MCGs were found among the 40 isolates. The isolates showed three colony colors (beige, black and white) on potato dextrose agar and exhibited significant differences in growth rate, oxalic acid production, and sensitivity to three fungicides, benomyl, fluazinam and iprodione. In spite of the genotypic and phenotypic diversity among the isolates there was no significant difference in virulence in detached leaf assays. No apparent relationship among the neutral genetic markers and the phenotypic traits was detected. Several lines of evidence show high levels of genetic diversity and frequent outcrossing within the population of S. sclerotiorum: 1) high likelihood of five genetic populations based on Bayesian probability; 2) random association of alleles between every pairwise linkage disequilibrium test among eight independent microsatellite loci, as well as in multilocus analysis when subpopulations were defined; 3) discordances between microsatellite haplotypes and MCGs, and 4) lack of correspondence among the genetic markers and phenotypic traits. Multilocus Index of Association analyses with and without specification of subpopulations suggested outcrossing occurs only within interbreeding subpopulations of S. sclerotiorum.

Last Modified: 9/23/2014