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POSTERS: Population biology and genetics

Fumigation-induced shifts in Streptomyces populations in a potato cropping system
Lindsey Otto-Hanson - Univ of Minnesota-Twin Cities. Linda Kinkel- University of Minnesota, Epidemiology and Ecology of Plant Diseases, Nicholas Wornson- University of Minnesota, Ray Hammerschmidt- Michigan State University

Fumigation is frequently used in potato production, yet the long-term effects on soil microbial communities remain underexplored. The potential for fumigation to impose selective shifts on the competitive abilities of soil pathogens may exacerbate disease potential in fumigated soils. We studied the phenotypes of Streptomyces scabies, including pathogen competitive and antagonistic capacities and aggressiveness, following vapam or chloropicrin fumigation and in non-fumigated soils. Scab-susceptible potatoes were grown in fumigated and non-fumigated soil for two seasons, and S. scabies were randomly isolated from tuber lesions in year two. Nutrient use, inhibitory phenotypes, antibiotic resistance, thaxtomin production, and 16S sequence were determined for every isolate. Pathogen populations from different treatments varied in competitive and antagonistic phenotypes. Isolates from chloropicrin-treated soil were significantly less growth efficient than isolates from vapam (p=0.0109). In contrast, vapam isolates were significantly more resistant to antibiotics than isolates from non-fumigated or chloropicrin-treated soils (p=0.0002). These data suggest that pathogen populations in vapam-treated soils have significantly greater saprophytic competitive abilities than those in chloropicrin-treated soils. Variation in aggressiveness and fitness tradeoffs between saprophytic and pathogenic phenotypes are under investigation. By inducing shifts in saprophytic competitive abilities and pathogen aggressiveness, fumigation may contribute to the intensification of disease severities.