Phytophthora capsici is an oomycete plant pathogen that infects cucumber, squash, melons, pumpkin, pepper, tomato and eggplant and has recently been described on snap and lima beans. In the US, the incidence and severity of epidemics has increased dramatically. Once P. capsici is introduced into an agricultural area dormant inoculum in the form of thick-walled sexual oospores can remain viable for many years. Crop rotation and chemical applications often do not provide adequate control and losses can reach 100%. For many US vegetable producers P. capsici is the most important limiting factor.
Phytophthora capsici has unique attributes that make it an ideal model for detailed investigations of oomycete biology and host specificity. These include
- Rapid growth on simple media at room temperature.
- Lack of thick-walled asexual spores (chlamydospores).
- he ease of conducting laboratory crosses (wide crosses as well as sib-crosses).
- The ability to produce high concentrations of the swimming zoospores (>103/ul)
- Broad host range.
Sex is under strong selection pressure in many epidemic populations and field isolates/populations carry significant genetic diversity. A key objective for this sequencing initiative is to develop a P. capsici molecular marker resource to support high resolution population and molecular genetic mapping and association investigations
The project is being completed using a combination of Sanger di-deoxy terminator sequencing of random clones and a newer pyrosequencing technology (dubbed “454 sequencing”) that bypasses bacterial cloning and generates shorter sequence reads. The isolate used for the sequencing, LT1534, was produced by crossing field isolates from Tennessee (LT263) and Michigan (OP97) to produce an F1 population and then conducting two consecutive rounds of backcrossing to LT263 to achieve a moderate level of inbreeding.