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Title:   Author  item
                                            BHAT, R.G. - UCD - PLANT PATHOLOGYitem
                                            Colowit, Peteritem
                                            Tai, Thomasitem
                                            Aradhya, Mallikarjunaitem
                                            Browne, Greg
  Submitted to: Plant Disease
                                    Publication Type: Popular Publication
                                    Publication Acceptance Date: 8/16/2005
                                    Publication  Date: 2/1/2006
                                    Citation: Bhat, R., Colowit, P.M., Tai, T., Aradhya, M.K., Browne, G.T. 2006. Genetic and pathogenic variability in Phytophthora cactorum affecting fruit and nut crops in California. Plant Disease. 90: 161-169.Interpretive Summary: Isolates of Phytophthora cactorum and 15 other species of Phytophthora were characterized according to their genomic DNA, pathogenicity, and sensitivity to mefenoxam. Amplified fragment length polymorphism (AFLP) analysis was completed for 132 isolates of P. cactorum (30 from almond, 86 from strawberry, 5 from walnut, and 11 from other hosts) and 22 isolates of 15 other Phytophthora spp. from various hosts. All 16 Phytophthora spp. were distinguishable by unique AFLP banding patterns. Cluster analysis of the AFLP data revealed high coefficients of genetic similarity (>0.9) among all California isolates of P. cactorum. Analysis of molecular variance indicated that, among all 132 isolates of P. cactorum, 30.8 and 24.5% of the AFLP variation was associated with hosts and geographical sources of isolates, respectively, whereas 15.0% of the variation was associated with isolate niche (i.e., an aerial plant part, portion of the root system, or soil). Among the 86 isolates of P. cactorum from strawberry, characterization by source in the production system (i.e., fruiting field or plant nursery) did not account for a significant proportion of the variation (0.6%, P = 0.204). In pathogenicity tests on strawberry plants (cv. Diamante) in a greenhouse, isolates of P. cactorum from hosts other than strawberry and an isolate from a strawberry fruit caused only negligible amounts of disease, but isolates from strawberry root systems were highly aggressive. On excised shoot segments of almond (cv. Drake), all isolates of P. cactorum originally from almond were pathogenic, and 8 of 17 isolates of the pathogen from other hosts caused significantly less disease than the almond isolates. All 132 isolates of P. cactorum were sensitive to mefenoxam at 1 ppm. Populations of P. cactorum in California apparently are mefenoxam sensitive and exhibit host specificity with relatively minor variation in genomic DNA. The genetic variation observed in P. cactorum included significant geographical and host origin components, which has implications for disease management approaches.
                                Technical Abstract: Isolates of Phytophthora cactorum and 15 other species of Phytophthora were characterized according to their genomic DNA, pathogenicity, and sensitivity to mefenoxam. Amplified fragment length polymorphism (AFLP) analysis was completed for 132 isolates of P. cactorum (30 from almond, 86 from strawberry, 5 from walnut, and 11 from other hosts) and 22 isolates of 15 other Phytophthora spp. from various hosts. All 16 Phytophthora spp. were distinguishable by unique AFLP banding patterns. Cluster analysis of the AFLP data revealed high coefficients of genetic similarity (>0.9) among all California isolates of P. cactorum. Analysis of molecular variance indicated that, among all 132 isolates of P. cactorum, 30.8 and 24.5% of the AFLP variation was associated with hosts and geographical sources of isolates, respectively, whereas 15.0% of the variation was associated with isolate niche (i.e., an aerial plant part, portion of the root system, or soil). Among the 86 isolates of P. cactorum from strawberry, characterization by source in the production system (i.e., fruiting field or plant nursery) did not account for a significant proportion of the variation (0.6%, P = 0.204). In pathogenicity tests on strawberry plants (cv. Diamante) in a greenhouse, isolates of P. cactorum from hosts other than strawberry and an isolate from a strawberry fruit caused only negligible amounts of disease, but isolates from strawberry root systems were highly aggressive. On excised shoot segments of almond (cv. Drake), all isolates of P. cactorum originally from almond were pathogenic, and 8 of 17 isolates of the pathogen from other hosts caused significantly less disease than the almond isolates. All 132 isolates of P. cactorum were sensitive to mefenoxam at 1 ppm. Populations of P. cactorum in California apparently are mefenoxam sensitive and exhibit host specificity with relatively minor variation in genomic DNA. The genetic variation observed in P. cactorum included significant geographical and host origin components, which has implications for disease management approaches.


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