A non-hypersensitive resistance in pepper to the bacterial spot pathogen is associated with two recessive genes

ABSTRACT The pepper genotype, ECW-12346, was developed with bacterial spot resistance derived from Pep13, PI 271322, and ECW123 (Early Calwonder containing Bs1, Bs2, and Bs3 genes). For genetic analysis of this resistance, ECW12346, ECW123, F(1), F(2), and backcrosses were inoculated with a pepper race 6 (P6) strain. Two recessive genes were identified that determined resistance. The genes are designated bs5 and bs6 for the resistance derived from PI 271322 and Pep13, respectively. In greenhouse and field studies, ECW12346 was highly resistant, whereas ECW123 had significant defoliation. In growth-room studies, electrolyte leakage and population dynamics were determined. Following infiltration of both genotypes with 10(8) CFU/ml of a P6 strain, there was no rapid increase in electrolyte leakage within 72 h, whereas a rapid increase in electrolyte leakage occurred within 24 h when a similar concentration of a P3 strain (containing the avrBs2 gene) was infiltrated into the intercellular spaces of the leaf. When 10(5) CFU/ml of a P6 strain was infiltrated into leaves, complete tissue collapse was evident in ECW123 10 days later as determined by visual assessment and electrolyte leakage data, but no confluent necrosis was detected in ECW12346. Internal populations were at least two logarithmic units higher in ECW123 than in ECW12346. Therefore, ECW12346 inhibits population build-up without inducing the typical hypersensitive reaction characterized by an increase in electrolyte leakage.