Multiple physiological race characterization of Phytophthora capsici causing foliar blight, nonhost resistance; and genetic evaluation of a novel inhibitor gene affecting disease resistance in chile peppers

Phytophthora capsici Leon. is the causal agent of phytophthora blight that produces enormous damages in chile pepper and bell pepper ( Capsicum annuum L.) crops worldwide. This pathogen can infect every part of a Capsicum plant causing disease syndromes such as foliar blight, fruit rot, stem blight, and root rot. A successful characterization of the physiological races of P. capsici causing the root rot syndrome has been accomplished. However, the different physiological races of P. capsici causing foliar blight syndrome have not been fully documented. This study presents a novel and accurate technique that allows us to evaluate phytophthora foliar blight syndrome using multiple isolates of P. capsici on a single C. annuum plant. The screening technique proved to be fast, accurate, and replicable. Using the phytophthora foliar blight multiple-race disease screening technique, several P. capsici isolates from different locations were evaluated. The different races were characterized using a population of 26 New Mexico Recombinant Inbred Lines (NMRILs) as a host differential set. A total of 12 different isolates were characterized as 12 different physiological races of P. capsici causing foliar blight syndrome in C. annuum plants. The characterization of some of the isolates as different physiological races agreed with previous reported studies, and proved that the NMRIL population is a reliable host differential set to characterize physiological races of P. capsici. This study, also reported an Inhibitor (I) gene found in the susceptible C. annuum accession NMCA10399. When the P. capsici resistant material CM-334 was hybridized with NMCA10399, the resultant F 1 population displayed 100% susceptibility against the P. capsici race-1. The F2 population from the same hybridization displayed a 3:13 (Resistant:Susceptible) ratio. The backcross population using the CM-334 parent displayed 1:1 ratio, and backcross population using NMCA10399 displayed 100% susceptibility. These results suggest the presence of a single dominant gene affecting the resistant expression of CM-334. The gene has been given the provisional name, Inhibitor (I). Lastly, the accession NMCA10399 was tested for nonhost resistance against different Phytophthora species. This experiment evaluated whether or not I affected the nonhost resistance of NMCA10399 against other Phytophthora species as well.;When NMCAI0399 was tested against seven Phytophthora species, only P. capsici caused disease on the plant. These results suggested that I is interfering with the expression of specific resistance, but not the expression of nonhost resistance.