| Phytophthora blight is one of the most destructive diseases that affects Capsicum pepper production around the world. One of the most effective control methods is the use of resistant cultivars. Pepper breeding programs have been unsuccessful in providing universally resistant cultivars. Explanations may be the use of different resistance sources, different pathotypes or races of Phytophthora capsici isolates, and different screening techniques. This dissertation compared the screening method for resistance to P. capsici used in the New Mexico State University chile pepper breeding program with the screening method used at Embrapa Vegetable Crops in Brazil. The two different screening methods produced similar and consistent results when different P. capsici isolates were used. Thus, either method would be successful in differentiating resistant and susceptible individuals.;In addition, 20 Brazilian P. capsici isolates were characterized using a set of 26 New Mexico recombinant inbred lines (NMRILs) of Capsicum annuum developed at New Mexico State University. A total of eight new physiological races were identified within the Brazilian P. capsici populations. The isolates Pca 33 and Pca 34 produced the same responses for the 26 NMRILs and were considered the same race. Likewise, Pcp113, Pcp114, and Pcp116 were considered the same race as they produced the same responses across the 26 NMRILs. A total of nine isolates were pathogenic only on the susceptible control 'Camelot.' The ability to identify physiological races of P.capsici in Brazil will allow a better understanding about race-specific resistance leading to better approaches in breeding for durable resistant cultivars.;The final objective evaluated the genetic diversity of Brazilian isolates of P. capsici using five single nucleotide polymorphism (SNP) markers. These markers were evaluated for 28 isolates from different regions of Brazil and from different host species (pepper, tomato, snap bean, eggplant, cucumber, pumpkin, and Solanum gilo). While many of the sequences examined lacked sufficient resolution to differentiate these isolates two SNP markers proved to be informative. Molecular characterization of the isolates found them all to be P. capsici. The molecular results demonstrated diverse genetic diversity among the current population of P. capsici from Brazil. |
