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

Authors: Larkin, Robert - Bob

Submitted to: Biological Agriculture and Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2019
Publication Date: 1/6/2020
Citation: Larkin, R.P. 2020. Biological control of soilborne diseases in organic potato production using hypovirulent strains of Rhizoctonia solani. Biological Agriculture and Horticulture. 36(2):119-129. https://doi.org/10.1080/01448765.2019.1706636.
DOI: https://doi.org/10.1080/01448765.2019.1706636

Interpretive Summary: Potato growers face many challenges from soilborne diseases, including reduced plant growth and vigor, and losses in tuber quality and yield. Management of these diseases is particularly challenging in organic potato production, due to the lack of available effective control options. In this research, biological control treatments using selected fungal and bacterial treatments were evaluated, alone and in combination, as alternative or supplemental disease management practices in organic potato production over three cropping seasons in Maine. Varying summer rainfall over the three seasons resulted in substantial effects on crop growth, yield, and disease development, but multiple biocontrol treatments reduced multiple common soilborne tuber diseases under all environmental conditions. Combination treatments of multiple biocontrol agents generally improved overall disease control, and were the most effective treatments. Some biocontrol treatments also promoted plant growth and resulted in increases in tuber yield. This research demonstrated the usefulness of biocontrol using hypovirulent isolates and combinations of biocontrol treatments for reducing soilborne diseases and increasing yield in organic potato production. This research is useful for scientists, extension personnel, and growers, providing practical information on the use of supplemental management practices for enhanced sustainability and productivity in organic potato production systems.

Technical Abstract: 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 three 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 to 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.