Biological control of Phytophthora blight and growth promotion in sweet pepper by Bacillus species

Abstract

Phytophthora capsici is one of the most important pathogens impacting the production of horticultural crops including pepper (Capsicum annuum). Pepper growers rely heavily on pesticides, but toxicity hazards to farm-workers, consumers, non-target organisms as well as environmental contamination cause great concern. Furthermore, the development of pesticide resistance is problematic. The objective of this study was to evaluate isolates of three Bacillus spp. [B. vallismortis (Ps), B. amyloliquefaciens (PsL) and B. thuringiensis (IMC8)] as biological control agents for P. capsici disease management. These isolates inhibited P. capsici mycelial growth invitro and reduced P. capsici disease severity in plants grown in Phytophthora-infested soil in greenhouse environment. In addition, the three bacterial isolates promoted plant growth by increasing plant height, shoot weight, root length, root weight and chlorophyll content. Out of the three isolates, PsL displayed the best potential in reducing P. capsici disease severity and in promoting plant growth in Phytophthora-infested soil and both PsL and Ps were significantly better than the fungicide metalaxyl (Ridomil®, Syngenta, Greensboro, NC) in reducing disease severity and promoting plant growth in greenhouse environment. In addition, mixtures of IMC8 + Ps, IMC8 + PsL and IMC8 + Ps + PsL reduced P. capsici disease severity and promoted plant growth similar to the fungicide metalaxyl used at label recommended rates. These three isolates IMC8, Ps and PsL displayed potential as alternative products for disease management and C. annuum plant growth promotion.