APS Homepage

Poster: Epidemiology: Population Biology Genetics


Sub-lethal fungicides induce microsatellite mutation in Sclerotinia sclerotiorum
B. Amaradasa (1), S. Everhart (1) (1) University of Nebraska, U.S.A.

Stress-induced mutations from sub-lethal fungicide exposure may be an important source of genetic variation for clonal plant pathogens. We used Sclerotinia sclerotiorum to assess the role of sub-lethal fungicide exposure in mutation at microsatellite loci. Nine sensitive isolates were exposed to long-term, sub-lethal doses of fungicides with different modes of action: boscalid, iprodione, thiophanate methyl, azoxystrobin and pyraclostrobin. Fungicides were plated in a logarithmic gradient and each isolate sub-cultured from the 50-100% inhibition zone for 12 consecutive generations and experiment repeated. Isolates at the first and twelfth generation from exposed and non-exposed lines were genotyped at six microsatellite loci. Control isolates showed no difference after 12 generations. Five of nine and two of nine fungicide-exposed isolates showed microsatellite mutations in both experiments. One locus did not mutate; all others range from 1 to 34 mutations per locus, with an average of 4.58 stepwise mutations. Most mutations were less than 20 bp, with one 80 bp mutation. The average mutation rate per locus among fungicide-exposed isolates ranged from 4-29 fold greater than the expected mutation rate of 1.3 x 10-5 estimated for microsatellites in Saccharomyces. All fungicides resulted in mutations, with iprodione- and azoxystrobin-exposed isolates showing the highest frequency. Results suggest long-term sub-lethal fungicide exposure increase mutation rates.