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Investigation of genetic variation in Phytophthora capsici

Zheng Pan, University of Massachusetts Amherst


Phytophthora capsici is a destructive pathogen of tomato, pepper and cucurbits worldwide. Its genetic variation has a significant impact on disease management. Morphological analysis, fungicide resistance, isozyme analysis, internal transcribed spacers (ITS) and random amplified polymorphic DNA (RAPD) analysis were used to investigate the genetic variation in the genome of Phytophthora capsici from Western Massachusetts, Long Island, New York and Quebec, Canada. Isolates from the first two locations contained both mating types: Al and A2. Only one mating type, A2, was present in Quebec, Canada. The morphological characters used in this study included length and width of sporangia, length of pedicel, length and width of antheridia, and diameters of oospore and oogonia of P. capsici. All morphological characters had significant variation among the three collections. Within each collection, there were significant differences between isolates and between characters. There were no significant differences in resistance to the fungicide metalaxyl among the three collections, but more fungicide resistance was observed in the collection from Massachusetts. Crosses between the most resistant and sensitive isolates were performed. The banding patterns of the isozymes: glucose-6-phosphate dehydrogenase (G6PDH), glucose-6-phosphate isomerase (GPI), Malate dehydrogenase (MDH) and Malate dehydrogenase NADP (ME) were examined. The results from isozyme analysis showed no difference among isolates. ITS analysis revealed no difference among isolates, and suggested that the isolates may have a very close genotype. In RAPD analysis, twenty 10-mer random primers were tested and the banding patterns were analyzed with MacClade 3.5.1. The results suggested that (1) isolates of the same mating type tended to cluster together; (2) Massachusetts isolates were spread throughout in tree, suggesting more genetic variation; (3) New York and Canadian isolates were relatively close, implying less variation; (4) progenies of metalaxyl resistant and susceptible isolates tended to cluster with one parental isolate, although some were widely divergent indicating that genetic variation arose from sexual reproduction. Canadian isolates, which lacked sexual reproduction, had less genetic variation, and less metalaxyl resistance. This research demonstrated that DNA recombination during sexual reproduction can generate genetic variation that can lead to increased opportunity of occurrence of fungicide resistance. The RAPD technique was used to develop a Phytophthora capsici specific probe and primers for pathogen identification and detection.

Subject Area

Plant pathology|Microbiology|Genetics

Recommended Citation

Pan, Zheng, "Investigation of genetic variation in Phytophthora capsici" (1997). Doctoral Dissertations Available from Proquest. AAI9809380.