Impacts of biocontrol products on Rhizoctonia disease of potato and soil microbial communities, and their persistence in soil

Authors: Larkin, Robert - Bob; Halloran, John

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2016
Publication Date: 9/21/2016
Citation: Larkin, R.P., Halloran, J.M. 2016. Impacts of biocontrol products on Rhizoctonia disease of potato and soil microbial communities, and their persistence in soil. Crop Protection. 90:96-105.

Interpretive Summary: Soilborne potato diseases, such as Rhizoctonia disease, are persistent problems in potato production. The use of selected microbial biocontrol agents may be useful for reducing these soilborne diseases on potato. In this research, four biocontrol formulations (two fungal and two bacterial agents), a chemical seed treatment, and a combination chemical/biological treatment, were compared with a pathogen-treated and nontreated control, and monitored in two field seasons in Maine for their effects on the development of Rhizoctonia disease and soil microbial community characteristics. All treatments reduced the incidence and severity of stem canker (37 to 75% reduction) relative to the pathogen control over both years, with the best control provided by a Bacillus bacteria and the combination chemical/biological treatment. Both bacterial treatments reduced severity of black scurf in both years, and a fungal treatment reduced scurf in one year. Over both years, most treatments increased total and marketable yield by 11 to 15% relative to the pathogen control. Biocontrol treatments also affected soil microbial community characteristics, including microbial activity and substrate utilization. Substantial populations of the added fungal agents, but not the bacteria, were detected in bulk soil at the end of the growing season. Some effects on soil microbial communities were also observed the following spring (1 yr after application) using fatty acid profiles. This research indicates that biocontrol treatments can assist in the control of Rhizoctonia disease of potato, can persist in soil to some degree, and have significant effects on soil microbial communities long after application.

Technical Abstract: Four commercial biocontrol formulations (Bacillus subtilis GB03, Burkholderia ambifaria type Wisconsin isolate J82, Trichoderma virens Gl-21, and Trichoderma harzianum strain T-22), a chemical seed treatment (Topsin, mancozeb, and cymoxanil mixture, TMC), and a combination chemical/biological treatment, were compared with a pathogen-treated and nontreated control, and monitored in two field seasons in Maine for their effects on the development of Rhizoctonia disease of potato and soil microbial community characteristics. All treatments reduced the incidence and severity of stem canker (37 to 75% reduction) relative to the pathogen control over both years, with the best control provided by B. subtilis and the combination chemical/biological treatment (TMC/B.amb). Both bacterial treatments (B. subtilis and Bu. ambifaria) reduced severity of black scurf in both years, and T. virens reduced scurf in one year. Over both years, the B. subtilis, Bu. ambifaria, T. virens, and TMC/B.amb treatments increased total and marketable yield by 11 to 15%. Biocontrol treatments also significantly affected soil microbial community characteristics, with bacterial treatments resulting in higher activity and substrate utilization and chemical treatment in the lowest. Substantial populations of the added fungal agents, but not the bacteria, were detected in bulk soil at the end of the growing season. Effects on soil microbial communities were also observed the following spring (1 yr after application). This research indicates that biocontrol treatments can assist in the control of Rhizoctonia disease of potato, can persist in soil to some degree, and have significant effects on soil microbial communities long after application.