Evaluation of Selected Bacterial Endophytes for Biocontrol Potential against Phytophthora Blight of Bell Pepper (Capsicum annuum L.)

Phytophthora blight, caused by Phytophthora capsici, is the most destructive disease of bell pepper in the United States.The effectiveness of current management strategies is limited by the long-term survival of oospores, wide host range, aggressive fungicide-resistant isolates, and lack of resistant cultivars with acceptable agronomic traits.Biological control is a viable alternative, and the use of endophytic microorganisms as biological control agents (BCA) has attracted widespread attention because they colonize the same ecological niches as plant pathogens.Seven isolates of bacterial endophytes in three genera Serratia (B17B), Enterobacter (E), and Bacillus (IMC8, Y, Ps, Psl and Prt), isolated from papaya, snap bean and flowering dogwood were evaluated for effects on P. capsici mycelial growth in vitro, and on disease severity and plant growth in greenhouse environment.All isolates significantly inhibited the mycelial growth of P. capsici with Ps, Psl and Prt having superior inhibitory effects.Seed treatments with Ps, Psl and Prt followed by plant inoculation with P. capsici reduced disease severity, and significantly increased plant shoot height, fresh weight, and fruit yield (number and weight) with Ps and Prt being slightly superior to Psl.Compatibility tests between isolates showed that only B17B and Y were compatible with each other.Sensitivity tests to different levels of mefenoxam (Ridomil Gold SL) showed that Ps, Psl and Prt were tolerant to the fungicide, while P. capsici was highly sensitive.Thus, Ps, Psl and Prt can be used in rotation with mefenoxam to reduce the frequency of fungicide usage for a more environmentally friendly, long lasting, consistent, and effective control of phytophthora blight.Overall, all isolates tested are potential BCAs against P. capsici, but more greenhouse and field studies are required to confirm in vitro results for all isolates that showed good potential in in vitro studies.