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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED STRATEGIES FOR ADVANCE MANAGEMENT OF FRUIT, NUT, AND OAK TREE DISEASES Title: Genetic Diversity in Populations of Phytophthora Citricola Associated with Horticultural Crops in California

Authors
item Bhat, Ravi - UNIV OF CALIF, DAVIS
item Browne, Greg

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2007
Publication Date: December 1, 2007
Citation: Bhat, R.G., Browne, G.T. 2007. Genetic diversity in populations of phytophthora citricola associated with horticultural crops in california. Plant Disease. 91:1556-1563

Interpretive Summary: California populations of the plant pathogen Phytophthora citricola were examined for amplified fragment length polymorphism (AFLP; a DNA fingerprinting technique), ability to cause disease on almond, and sensitivity to mefenoxam, an oomycete fungicide. The characterizations of AFLP variation and mefenoxam sensitivity were based on 86 isolates (44 from almond, 11 from avocado, three from strawberry, 18 from walnut and 10 from six other hosts). Cluster analysis of the AFLP data using the unweighted pair group method indicated a high level of genetic diversity among the isolates and four main clusters—one dominated by isolates from almond, another including all isolates from avocado, and two including isolates from several hosts other than avocado. Analysis of molecular variance revealed that 38.4% and 24.9% of the AFLP variation was associated with host and geographical grouping factors, respectively. Twenty-two of 24 isolates of P. citricola, including isolates from almond, avocado, strawberry and walnut, were aggressive on almond shoots; there was no evidence for host specificity. All but one of the 86 isolates of P. citricola grew at different rates on V8 juice medium amended with 1 ppm mefenoxam, indicating partial tolerance to the fungicide. In California, populations of P. citricola are genetically diverse, and much of the variation is associated with hosts and the geographical regions. These populations are all potentially pathogenic on almond and tend to be tolerant to mefenoxam.

Technical Abstract: California populations of the plant pathogen Phytophthora citricola were examined for amplified fragment length polymorphism (AFLP), pathogenicity on almond, and sensitivity to mefenoxam. The characterizations of AFLP variation and mefenoxam sensitivity were based on 86 isolates (44 from almond, 11 from avocado, three from strawberry, 18 from walnut and 10 from six other hosts). Cluster analysis of the AFLP data using the unweighted pair group method indicated a high level of genetic diversity among the isolates and four main clusters—one dominated by isolates from almond, another including all isolates from avocado, and two including isolates from several hosts other than avocado. Analysis of molecular variance revealed that 38.4% and 24.9% of the AFLP variation was associated with host and geographical grouping factors, respectively. Twenty-two of 24 isolates of P. citricola, including isolates from almond, avocado, strawberry and walnut, were aggressive on almond shoots; there was no evidence for host specificity. All but one of the 86 isolates of P. citricola grew at different rates on V8 juice medium amended with 1 ppm mefenoxam, indicating partial tolerance to the fungicide. In California, populations of P. citricola are genetically diverse, and much of the variation is associated with hosts and the geographical regions. These populations are all potentially pathogenic on almond and tend to be tolerant to mefenoxam.

Last Modified: 12/20/2014
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