Chiang Mai Journal of Science

     One of the effective strategies for developing blast disease-resistant cultivars to mitigate the yield losses caused by Pyricularia oryzae is the discovery of new genetic resources containing resistance genes. In the present study, a Thai landrace glutinous rice cultivar Hahng Yi 71 (HY71) was used as a durable, broad resistance source to identify QTLs against blast fungus and crossed with a susceptible recurrent parent cultivar RD6, generating 56 BC₄F₅ lines. The BC₄F₅ population was tested with six blast isolates, including THL54, THL583, THL658, THL690, THL795, and THL1119, and evaluated with 161 SSR markers to identify resistance regions using modified bulk segregation analysis. Single marker analysis showed 7 markers linked to a resistance reaction located on chromosomes 2, 4, and 5, then tentatively designated as qBL2-RD6, qBL4-HY71, and qBL5-HY71, respectively. Two introgressed lines from the mapping population, KKN97057-7-1-1-2-5-NKI-4-1 and KKN97057-7-1-1-2-5-NKI-5-1, were the qBL5-HY71 donor for introgressing into two rice lines, RGD07123-MS12-MS22-MS1, and RGD07123-MS12-MS22-MS9, which generated two single crosses and a backcross population by marker-assisted selection (MAS) using the linked markers RM39 and RM164. Three improved lines, RGD10021-MS18-B-MS8-MS40, RGD10031-MS-MS3-B-MS9-MS42 (single cross), and RGD11086-MS-MS15-MS10-MS19 (backcross), carrying qBL5-HY71, were tested for their resistance against leaf and neck blast disease by 62 and 8 blast isolates, respectively. The disease screening results showed that qBL5-HY71 was very effective in controlling leaf and neck blast. This study demonstrates the effectiveness of resistance loci qBL5-HY71 from HY71 on chromosome 5 and their linked markers in improving durable blast resistance in rice breeding programs.