Evaluation of Selected Endophytes for Phytophthora capsici Biocontrol and Plant Growth Promotion in Capsicum annuum L.
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 farmworkers, 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 (BCAs) for P. capsici disease management. These bacterial 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. The IMC8 BCAs have previously been shown to produce volatile compounds (Rotich et al 2019). This study evaluated four BCA isolates for their ability to produce volatile compounds and the effect of the volatiles on plant growth. Volatile compounds from PsL were most effective in increasing chlorophyll content and volatile compounds from Ps were best in increasing leaf area, while volatiles from a combination of IMC8 and Ps were most effective in increasing shoot weight. Because these bacterial isolates colonized plants internally without causing external symptoms, their movement inside plant was tracked to better understand their plant colonization and host-microbe interaction. A technique of fluorescence tagging was developed by transformation of selected bacterial BCAs using either a pANIC-10A vector that contains the ubiquitin promoter-reporter gene PvUbi1:pporRFP (RFP) and hygromycin B phosphotransferase II gene or pBSU101 plasmid that contains Green Fluorescence Protein (GFP). Four bacterial BCAs were tagged successfully with these reporter genes and internal plant colonization was confirmed through fluorescence microscopy and PCR analysis.
Plant sciences|Plant Pathology|Microbiology|Genetics|Horticulture|Agronomy
"Evaluation of Selected Endophytes for Phytophthora capsici Biocontrol and Plant Growth Promotion in Capsicum annuum L."
ETD Collection for Tennessee State University.