Progress 09/15/03 to 09/14/05
P. capsici from Florida and other geographic regions were characterized. Isolates that date back to the 1980s were all fully sensitive to mefenoxam. In the 1990s, isolates that were resistant to mefenoxam did not grow at more than 70% of the non-amended control plates when tested at the high concentration. Isolates from the years 2000-2003 were either strongly resistant to mefenoxam or strongly sensitive to this fungicide. A survey conducted in vegetable production fields in Puerto Rico in May 2004 failed to recover any Phytophthora species. Host specificty assays found, in general, some isolates were highly virulent on their primary hosts and less virulent on the other ones while other isolates proved to be highly cross-pathogenic on several hosts. P. capsici were recovered from Carolina wild geranium (Geranium carolinianum), American black nightshade (Solanum americanum), and common purslane (Portulaca oleracea). All but one of the twelve isolates tested were of A1
compatibility type. The only A2 compatibility type was found on Carolina wild geranium. All isolates of P. capsici from weeds were resistant to mefenoxam. Studies demonstrated that the longevity of oospores and other propagules, including mycelia and sporangia, was sufficient to span the relatively short fallow season (June through mid-August) and environmental conditions in South Florida. Plots fumigated with methyl bromide did not have viable inoculum. Weeds may also play an important role as a potential source of inoculum in the absence of vegetable hosts. Recovery All isolates from weeds originally identified as P. capsici from common purslane (Portulaca oleracea), nightshade (Solanum sp.), and Carolina wild geranium (Geranium carolinianum)indicating potential sources of inoculum. Formulate and test components of an integrated, multi-tactic management program including cultural, chemical, and biological control methods in greenhouse and field studies. Several compounds including
fungicides, biologicals, and other materials were evaluated for efficacy and did show a reduction in disease incidence after applications of phosphorus acid (K-Phite), biological amendments, compost, SAR inducers (other than Actigard) and Actinovate and Actino-Iron (biological fungicides). In one trial only SA-110201, Ridomil, Amistar, or Actigard treatments significantly reduced disease incidence (< 35% DI) compared to the untreated control (68% DI). Breeding lines of Capsicum spp., from a local seed company were compared with commercial bell pepper plants in their susceptibility to an aggressive isolate and were found resistant by comparison.
Information regarding the epidemiology of Phytophthora capsici in a subtropical and tropical climate is critical to formulate novel control measures and manage disease outbreaks. Information from these studies will yield important information on the pathogen and its behavior in this climate. Information on isolate variability can be used to determine the potential that resistance has a means for control of this disease. Screening for resistance and the development of a screening tool can be help to identify sources of resistance to P. capsici. An area of management utilizing non-traditional techniques such as the systemic acquired resistance inducers for plant defenses, biological agents with proven abilities, compost that suppresses pathogen population and combined with soil fumigation, ontogenic resistance, and other commercial disease management practices may help to manage the disease. Information such as survival studies confirm that fields infested with P. capsici
can have residual inoculum and should utilize additional management techniques such as crop rotation and P. capsici from weeds and irrigation water may account for the both the survival and dispersal of this pathogen.
- Roberts, P.D., Urs, R.R., French-Monar, R.D., and McGovern, R.J. 2004. Recovery of Phytophthora capsici and phytopathogenic oozmycetes from irrigation water in Florida. Fitopatologia 39:102.
- French-Monar, R.D., Braun, E.L., Jones, J.B, and Roberts, PD. 2004. Characterization of Phytophthora capsici isolated from weeds in Florida. Fitopatologia 39:100.
- French-Monar, R. D., Roberts, P. D., and Jones, J. B. 2004. Reduction of Phytophthora capsici populations in Florida by soil solarization in autumn. Phytopathology 94:S144.
Progress 10/01/03 to 09/30/04
The cooperating scientist from Puerto Rico visited the cooperators at the Univerisity of Florida and was trained in isolation techniques for Phytophthora capsici, field identification of symptoms, DNA isolation, and maintainence and purtiy of cultures. Cooperating scientists from UF traveled to Puerto Rico and collected data on field incidence of Phytophthora blight and examined commercial production of susceptible hosts. Isolates were added to the culture collection to include about 120 isolates of P. capsici, where approximately 90 are from all around Florida from 1983 to 2002. Experiments were conducted to determine the differential pathogenicty of isolates on diverse hosts. Isolates were found that were more virulent on a particular host. Isolates were further characterized by by pathogenicity, host specificity, mating types, and resistance to mefenoxam. Field studies were conducted to retrieve P. capsici from weeds after the host crop has been harvested. Weeds
were sampled, identified and brought and root and crown samples plated on semi-selective media for the presence of P. capsici as well as other potential pathogens. Oospores may be the source of inoculum in subsequent outbreaks. Oospores were found to persist for prolonged periods and their survival in fields in Florida is much longer than previously reported and easily spans vegetable production seasons in Florida. In addition, P. capsici isolates were characterized for sensitivity to mefenoxam (Ridomil Gold EC), the active enantioner of metalaxyl, the old chemical formulation. Out of 71 isolates tested, eight isolates showed intermediate resistance to this fungicide; what was more interesting is that this type of resistance was found in three isolates from Florida, one from 1982, one from 1983, and one from 1984. Resistant isolates accounted for 16 isolates, most of them from the years 2000 and 2001. What was even more interesting was that two isolates from 1987 were resistant to
mefenoxam, ten years before this fungicide was used, and probably only a few years after metalaxyl (Ridomil) had started to be used. A field trial was established to compare two field inoculation methods for reproducibilty of P capsici infection with peppers characterized with different leveles of resistance. Field trials evaluating methods of mangaement will continue and others established in 2005.
Information regarding the epidemiology of Phytophthora capsici in a subtropical and tropical climate is critical to formulate novel control measures and manage disease outbreaks. Information from these studies will yield important information on the pathogen and its behavior in this climate. Information on isolate variability can be used to determine the potential that resistance has a means for control of this disease. Screening for resistance and the development of a screening tool can be help to identify sources of resistance to P. capsici. An area of management utilizing non-traditional techniques such as the systemic acquired resistance inducers for plant defenses, biological agents with proven abilities, compost that suppresses pathogen population and combined with soil fumigation, ontogenic resistance, and other commercial disease management practices may help to manage the disease.
- ROBERTS, P.D., FRENCH-MONAR, R.D., URS, R.R., MCGOVERN, R.J. 2004. Recovery of Phytophthora capsici and phytopathogenic oomycetes from irrigation water in Florida. Fitopatologia 39: (In press).
- ROBERTS, P.D., URS, R.R., FRENCH-MONAR, R.D., HOFFINE, M.S., SEIJO. T.E.,MCGOVERN, R.J. 2005. Survival and recovery of Phytophthora capsici and oomycetes in tailwater and soil from vegetable fields in Florida. Annals of Applied Biology (in press).
- French-Monar, R., Jones, J., McGovern, R., and Roberts, P. 2004. Identification of inoculum sources in the field for Phytophthora blight and rot of pepper in Florida. (Abstr.) Book of Abstracts: The 17th International Pepper Conference. p. 5