Phytophthora capsici an Oomycete pathogen is a major challenge to the pepper (Capsicum spp.) production around the world. Control measures are proved ineffective, so breeding resistant cultivars are the most promising strategy against the pathogen. Resistance against P. capsici is governed by quantitative trait loci (QTL). According to previous studies on QTL detection, the QTL on pepper chromosome 5 is a major contributor to resistance. In this study, to exploit the involvement of this QTL and identify its contributing genes, the F2 population derived from a cross between ECW30R and CM334 was inoculated with a medium virulence P. capsici strain JHAI1-7 zoospores at the 6-8 leaf stage. Composite interval mapping revealed two major QTLs; QTL5-1 from 7 days post inoculation (dpi) and QTL5-2 from 16 dpi on chromosome 5. To characterize and detect interactions of the two QTLs, near isogenic lines (NIL) were constructed by crossing Tean and recombinant inbred line (RIL) derived from a cross between YCM334 and Tean. RILs were screened with P. capsici strain MY-1 and resistant lines were selected. Among the resistance RILs most closely related to Tean were selected using AFLP and SSR genotyping data. These RILs were named as YT39-2 and YT143-2. To develop more advanced NILs, two rounds of marker-assisted backcrossing were done using a high-throughput SNP genotyping system (EPI Fluidigm, USA). Among the NILs derived from YT39-2, YT39-2-64 contains only QTL5-1 whereas YT39-2-61 and YT39-2-69 were identified to have both QTLs. On the other hand, YT143-2-55-7 with the highest Tean genetic background contains QTL5-1 only. In the next step, the 3 different NILs having QTL5-1, QTL5-2 individually and both QTLs will be identified. Furthermore, phenotyping and fine mapping will be done for the analysis of individual and interaction effects of QTLs.

• Hyeon-Seok Jeong(Department of Plant Science, Plant Genomics and Breeding Institute, and Vegetable Breeding Research Center, College of Agriculture and Life Sciences, Seoul National University)
• Muhammad Irfan Siddique(Department of Plant Science, Plant Genomics and Breeding Institute, and Vegetable Breeding Research Center, College of Agriculture and Life Sciences, Seoul National University)
• Jeong-Tak An(Department of Plant Science, Plant Genomics and Breeding Institute, and Vegetable Breeding Research Center, College of Agriculture and Life Sciences, Seoul National University)
• Ki‑Taek Kim(The Foundation of Agricultural Technology Commercialization and Transfer)
• Gyung Ja Choi(Chemical Biotechnology Research Center, Green Chemistry Division, Korea Research Institute of Chemical Technology)
• Darush Struss(Biotechnology group East West Seed, Hortigenetics Research, Thailand)
• Byoung-Cheorl Kang(Department of Plant Science, Plant Genomics and Breeding Institute, and Vegetable Breeding Research Center, College of Agriculture and Life Sciences, Seoul National University) Corresponding Author