DEVELOPMENT OF DNA MARKERS LINKED TO BACTERIAL LEAF SPOT RESISTANCE OF CHILLI

Abstract

Bacterial leaf spot disease (Xanthomonas campestris pv. vesicatoria; Xcv) causes severe damage to chilli (Capsicum annuum L.) and has been a major yield constraint. An introduced chilli accession 3-25-27 derived from Florida XVR 3-25 has a dominant gene, Bs2, which confers resistance to Xcv races 1, 2 and 3. To identify RAPD markers linked to Bs2, bulked segregant analysis (BSA) and random amplified polymorphic DNA (RAPD) analysis were performed. Isogenic DNA pools were made from 10 resistant and 10 susceptible plants in a BC 1 F 1 population derived from crosses between 3-25-27 and Early California Wonder. Two RAPD markers, OPD05 and OPF10, were identified from a total of 460 10-basepair primers. From the linkage analysis it was found that two markers were located on either side of the Bs2 gene. OPD05 was located 5.3 cM away from Bs2 gene and OPF10 was located 4.9 cM from the Bs2 on the opposite side to OPD05. For practical use, identified RAPD markers were converted to sequence characterized amplified regions (SCARs). Primer sequences with various lengths were designed and examined for their ability to detect a resistance marker. SCF10, originating from the RAPD marker OPF10, was amplified using a 24-basepair primer set, and it showed polymorphism between resistant and susceptible individuals. The initial SCARs developed from OPD05, however, showed monomorphism between resistant and susceptible plants. After trials with various primer combinations, it was possible to develop a polymorphic SCD05 marker. These markers enable the identification of the Bs2 gene on segregating progenies for marker-assisted selection.