Towards Improved Management Of Phytophthora Capsici: Biology Of And Management Tools For The Pathogen
Phytophthora capsici is a destructive oomycete pathogen of many vegetables, causing root, crown, and fruit rot, as well as foliar disease. Host resistance is an important management strategy in pepper, and the high levels of diversity in field populations of P. capsici have important implications for screening and selecting resistant cultivars. In order to better understand the changing structure of a field population, a previously-uninfested research field was inoculated with two single-spore isolates of P. capsici in September 2008. Isolates from this field were collected over the following four years and characterized with five microsatellite markers. A sexual population was established in the field, characterized by high genotypic diversity and no evidence of genetic drift. In addition, four novel alleles were detected, and characterization of F1 progeny from an in vitro cross between the same two parental isolates revealed evidence of non-Mendelian inheritance of alleles. In order to provide practical information to New York vegetable growers, commercial bell pepper cultivars were screened for resistance to P. capsici using a representative local isolate, over five years. In one year, yield and fruit quality were compared among commercial cultivars at three sites (one inoculated with P. capsici and two uninoculated). The cultivars Aristotle, Intruder, and Paladin were consistently most resistant to the isolate used, and while total marketable yields were comparable among resistant and susceptible cultivars, these more resistant cultivars tended to have smaller fruit and more problems with silvering than the susceptible cultivars. In order to better understand the P. capsici-pepper pathosystem, interactions between a P. capsici isolate (PcapG-a) tagged with green fluorescent protein and susceptible or resistant pepper cultivars were studied. Surprisingly, P. capsici zoospores attached to and germinated equally well on roots of resistant and susceptible cultivars within 120 minutes of inoculation. Differences in pathogen colonization of roots and crowns of resistant and susceptible cultivars were observed 3 days post inoculation. Although previous studies have implicated upregulation of plant defense genes in pepper host resistance to P. capsici, we did not see evidence of this at 8 or 24 hours post inoculation in either pepper stem or leaf tissue.
Phytophthora capsici; pepper; host resistance
Dillard, Helene RSmart, Christine Durbahn
Fry, William Earl; Smart, Christine Durbahn; Rangarajan, Anusuya; Reiners, Stephen; Fry, William Earl; Grunwald, Niklaus J.
Ph. D., Plant Pathology
Doctor of Philosophy
dissertation or thesis