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Poster: Biology & Disease Mgmt: Biological Control


Biological control of soilborne diseases in organic potato production using hypovirulent strains of Rhizoctonia solani
R. LARKIN (1) (1) USDA-ARS, U.S.A.

Soilborne diseases are persistent problems in potato production and alternative management practices are needed, particularly in organic production, where control options are limited. Selected biocontrol organisms, including two naturally-occurring hypovirulent strains of Rhizoctonia solani (Rhs1a1 and Bs69) and a commercially available Bacillus subtilis (GB03), were evaluated, both individually and in combination, for control of soilborne diseases of potato under organic production practices over three field seasons in Maine. Overall, multiple biocontrol treatments resulted in modest but significant reductions in all three soilborne diseases observed (black scurf, common scab, and silver scurf), reducing incidence and severity of each by 10-32%. All biocontrol treatments reduced black scurf (by 15-32%), whereas only specific treatments reduced common scab and silver scurf (by 10-25%). Combinations including both a hypovirulent strain and GB03 tended to be the most effective treatments, although generally not significantly better than individual strains. Tuber yield varied somewhat by year, but Rhs1a1 and GB03 treatments, as well as combinations, increased yield by 10 to 24% overall. These results indicate that hypovirulent Rhizoctonia, along with other biocontrol organisms, may be useful for reducing certain soilborne diseases and enhancing yield in organic potato production.