Biological control of soilborne diseases in organic potato production using hypovirulent strains of Rhizoctonia solani

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. Varying rainfall conditions over the 3 years significantly affected crop growth, tuber yield, and disease development. However, multiple biocontrol treatments resulted in significant reductions in black scurf and common scab under a variety of environmental conditions, reducing incidence and severity of each by 15-47%. Most biocontrol treatments reduced black scurf, but only specific treatments reduced common scab and silver scurf (by 15-40% and 16-24%, respectively). Combinations including both a hypovirulent strain and GB03 tended to be the most effective treatments overall. Although tuber yield varied greatly by year, Rhs1A1 and GB03 treatments, as well as combinations, increased yield by 11-37% over all three seasons. Use of hypovirulent R. solani, along with other biocontrol organisms, may provide reductions in soilborne diseases and enhanced yield in organic potato production.