Submitted to: Joint Meeting of the American Phytopathological Society and Society of Nematology
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2007
Publication Date: N/A
Technical Abstract: Surface sources of irrigation water including the Kings River and three canals were assayed for Phytophthora spp. at six locations in the San Joaquin Valley within 30 km of Hanford, CA. Four nylon-mesh bags, each containing three firm, green pear fruits (separated by Styrofoam blocks) as bait for Phytophthora spp., were floated for 3 days in the water at each location. After removal of the bags from the water, pear fruits were rinsed, incubated 2 to 4 days at 20 to 24°C, and monitored for lesions. Tissue samples from 1167 lesions were cultured on PARP medium and yielded 363 putative isolates of Phytophthora, which were subcultured on V8JA, CV8, and CMA growth media to group isolates subjectively based on colony morphology. Thirty-two of these isolates representing the diversity among groups were identified by sequencing rDNA amplified with primers ITS1 and ITS4. BLAST searches identified the following: P. citricola (3 isolates), P. citrophthora (1), P. cryptogea (6), P. dreschsleri (1), P. gonapodyides (2), Pythium sp. (2), and unidentified Phytophthora spp. (17). The first four species are known pathogens of walnut and Prunus species, which are important crops in the region surveyed. The presence of pathogenic Phytophthora spp. in the sampled water sources reinforces the importance of careful soil water management and use of resistant rootstocks.