Phytophthora capsici is a destructive soilborne pathogen worldwide. P. capsici has a broad host range that includes members of more than twenty plant families that contain many economically important vegetable crops. Some vegetable growers in Michigan plant conifers for the Christmas tree market in fields infested with P. capsici. To determine the susceptibility of Fraser fir to P. capsici, stems or roots of seedlings were inoculated with each of 4 P. capsici isolates and incubated in growth chambers. In addition, Fraser fir seedlings were planted in two commercial fields naturally infested with P. capsici. All P. capsici isolates tested incited disease in the seedlings regardless of incubation temperature or inoculation method. Seedlings (72%) planted in P. capsici-infested fields developed disease symptoms and died. Identification was confirmed by species-specific direct colony Polymerase chain reaction. This study suggests that planting Fraser fir in fields infested with P. capsici could result in infection and that adjustments in current rotational schemes are needed.Phytophthora capsici causes root, crown, and fruit rot of tomato, a major vegetable crop grown worldwide. One objective of this study was to screen tomato varieties and wild relatives of tomato for resistance to P. capsici. Four P. capsici isolates were individually used to inoculate 6-week-old seedlings of 42 tomato varieties and wild relatives in a greenhouse. Plants were evaluated daily for wilting and death. All P. capsici isolates tested caused disease in seedlings but some isolates were more pathogenic than others. A wild relative of cultivated tomato, Solanum habrochaites accession LA407, was resistant to all P. capsici isolates tested. Moderate resistance to all isolates was identified in the host genotypes Ha7998, Fla7600, Jolly Elf, and Talladega. Amplified fragment length polymorphisms of tomato genotypes showed a lack of correlation between genetic clusters and susceptibility to P. capsici, indicating that resistance is distributed in several tomato lineages. The results of this study create a baseline for future development of tomato varieties resistant to P. capsici.Phytophthora capsici Leonian is a destructive soilborne pathogen that can infect economically important solanaceous, cucurbitaceous, fabaceous, and other crops in the United States and worldwide. The objective of this study was to investigate the genetic structure of P. capsici isolates assigned to predefined host, geographical, mefenoxam sensitivity and mating type categories. Isolates from 6 continents, 21 countries, 18 United States (U.S) states, and 26 host species were genotyped for four mitochondrial and six nuclear loci. Bayesian clustering analysis revealed population structure by host, geographic origin and mefenoxam sensitivity with clusters occurring more or less frequently in particular categories. Our findings of genetic structuring in P. capsici populations highlight the importance of including isolates from all detected clusters that represent the genetic variation in P. capsici for development of diagnostic tools, fungicides, and host resistance. This study provides an initial map of global population structure of P. capsici but continued genotyping of isolates will be necessary to expand our knowledge of genetic variation in this important plant pathogen.
Read
