USE OF MOLECULAR TOOLS FOR IMPROVING THE EFFICACY OF BIOLOGICAL CONTROL STRATEGIES FOR CACAO DISEASES
Title: Endophytic Trichoderma isolates from tropical environments delay disease onset and induce resistance against Phytophthora capsici in hot pepper using multiple mechanisms
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 17, 2010
Publication Date: March 1, 2011
Citation: Bae, H., Roberts, D.P., Lim, H.S., Strem, M.D., Park, S., Ryu, C., Melnick, R., Bailey, B.A. 2011. Endophytic Trichoderma isolates from tropical environments delay disease onset and induce resistance against Phytophthora capsici in hot pepper using multiple mechanisms. Molecular Plant-Microbe Interactions. 24:336-351.
Interpretive Summary: The plant pathogen Phytophthora capsici causes severe yield losses in many crops resulting in lost profits for farmers and reduced produce availability for consumers. Biocontrol is an environmentally friendly technique for controlling plant disease by using beneficial fungi. We are developing biocontrol strategies for plant diseases using the beneficial fungus Trichoderma. The Trichoderma strains we are using are unique in that they were isolated from tropical environments and they grow inside the root and stem tissue of plants. Trichoderma strains from the tropics were shown to delay disease caused by Phytophthora capsici in hot pepper. The mechanisms used by Trichoderma in delaying disease development included the production of compounds that limit the pathogens growth, the ability to use the pathogen as a food source, and the ability to stimulate the plant to protect itself. By providing farmers with environmentally friendly biocontrol strategies for control of diseases, crop yields may be increased resulting in increased profits to farmers and increased food supplies for consumers in addition to benefits to the environment through reduced use of pesticides.
Isolates of several Trichoderma spp., were collected from tropical environments as potential biocontrol agents for cacao (Theobroma cacao) diseases. The diversity of isolates collected, including new species, and there endophytic nature on their host plants, led us to consider if these isolates have endophytic and biocontrol activity in an unrelated crop, Korean hot pepper (Capsicum annuum), against Phytophthora capsici. Six Trichoderma isolates were tested for their mycoparasitic and antimicrobial activity against P. capsici, and their endophytic and induced resistance capabilities in Korean hot pepper. Isolates DIS 70a, DIS 219b, and DIS 376f were mycoparasites of P. capsici while isolates DIS 70a, DIS 259j, and DIS 320c produced antimicrobial compounds that inhibited growth of P. capsici. Isolate DIS 320c also produced metabolites that damaged pepper roots. All 6 isolates efficiently colonized pepper roots internally but were inefficient stem colonizers. Isolates DIS 256f, DIS 320c, and DIS 376f consistently induced plant defense related gene/ESTs in leaves and roots of 32 day old peppers. Although isolate DIS 376f provided the most consistent protection against P. capsici, isolates DIS 70a and DIS 259j also delayed disease development significantly. Microarray analysis of pepper gene expression 48 h after inoculation with isolates DIS 259j and DIS 376f identified a large group of highly induced ESTs putatively involved in plant defense. Early colonization of pepper roots by isolates DIS 259j or DIS 376f resulted in the shared induction of many pepper ESTs but the timing and intensity of induction varied between the 2 isolates. More important, some ESTs were only induced by specific isolates indicating divergent signal transduction pathways toward induced resistance may be involved. The divergent pattern of induction was apparent for many ESTs with potential to impact both Trichoderma endophytic colonization of pepper and disease development in response to P. capsici infection, not the least of which encode specific members of the lipid transferase-like protein family. The described screens identify multiple mechanisms for protection of Korean hot pepper by endophytic Trichoderma species of tropical origin.