Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 9, 2010
Publication Date: October 1, 2010
Citation: Roberts, D.P., Maul, J.E., Mckenna, L.F., Emche, S.E., Meyer, S.L., Collins, R.T., Bowers, J.H. 2010. Selection of genetically diverse trichoderma spp. isolates for suppression of phytophthora capsici on bell pepper. Canadian Journal of Microbiology. 56:864-873. Interpretive Summary: Soilborne plant pathogens, such as Phytophthora capsici, cause diseases that result in major economic losses to farmers in the United States. These plant pathogens were controlled in many cases with the broad spectrum biocidal fumigant methyl bromide. Alternative control measures for P. capsici need to be developed due to the phase-out of use of methyl bromide as a pre-plant soil fumigant. Biological controls, using plant-beneficial microbial biological control agents, offer promise for control of soil-borne pathogens especially when used in integrated disease management strategies. In total, we screened twenty-six isolates of the plant-beneficial fungus Trichoderma spp. for suppression of P. capsici on bell pepper in greenhouse pot assays. Isolates GL3 and Th23 provided the most consistent experiment to experiment disease suppression. Isolates GL12, GL13, and GL21 also provided disease suppression. Phylogenetic analysis based on the ITS region of the nuclear rDNA cluster and the tef1 gene was performed on a subset of these twenty-six isolates. These disease suppression assays and the phylogenetic analysis indicate that we have a number of genetically distinct isolates of Trichoderma with disease suppression capacity for potential use in integrated pest management strategies targeted against P. capsici on pepper. This information will be useful to scientists devising strategies to improve biological control consistency.
Technical Abstract: Environmentally compatible control measures are needed for suppression of Phytophthora capsici on pepper. Twenty-four isolates of Trichoderma were screened for suppression of this pathogen on bell pepper in greenhouse pot assays. Of these twenty-four isolates, GL12, GL13, and Th23 provided significant suppression of P. capsici on pepper in at least two assays. These isolates were then compared with T. virens isolates GL3 and GL21 for suppression of this disease in the presence and absence of the bioactive natural product Messenger®. Isolates GL3 and Th23 provided significant disease suppression in three of four assays while GL12, GL13, and GL21 provided significant suppression in two of four assays. There was no apparent benefit from the application of Messenger. Phylogenetic analysis (based on the ITS1 region of the nuclear rDNA cluster and tef1) of these five isolates, and an additional nine isolates that suppressed P. capsici in at least one assay, separated isolates into two clades, one clade containing GL3, GL12, GL13, and GL21. There were also two unrelated isolates, one of which was Th23. We report here the identification of genetically distinct Trichoderma isolates for potential use in disease management strategies employing isolate combinations directed at suppression of P. capsici on pepper.