Agronomic performance and genetic analyses of resistance against Xanthomonas oryzae pv oryzae in rice mutant lines (Oryza sativa L.) / Aliif Ihsaan Akmal Shukri

Rice (Oryza sativa L.) is the third main staple food of the world. Over the years, the demands for rice are increasing but denied by the decrease in global and local production. The great fall of production is caused by multiple factors including the outbreak of bacterial leaf blight (BLB) disease which reduced the production by up to 60%. Mutagenesis is one method applied to develop a resistant line with great yield rate and better agronomic performances. In this study, a preliminary selection on six Malaysian rice varieties namely MR84, MR219, MR284, MR297, MR303 and MR307 was done based on twelve agronomic traits. MR297 was selected as the parental line for the development of rice mutant lines as it recorded the shortest days to flowering, shortest days to maturity, shortest plant height, highest number of tiller, highest number of panicle, highest weight of 1000 grains, lowest number of unfilled grains per panicle and highest yield rate per plant in parental screening. Post of preliminary selection, the seeds of MR297 were exposed to ten different treatments of acute gamma irradiation for identification of lethal dose (LD50). A total of 10 000 seeds were irradiated at 450 Gy (lethal dose, LD50) and developed as Mi generation. Throughout the observation on Mi generation, only one trait (day of maturity) showed a positive improvement among other traits as compared to parental line, MR297. In M2 generation, all twelve traits illustrated a better agronomic performance including days to maturity (104.23 days ± 0.52), plant height (95.23 cm ± 0.52) yield rate (81.97 % ± 2.61) as compared to parental line, MR297. Phenotypic screening against pathotype oiXanthomonas oryzae pv oryzae revealed that 1370 M2 plants were identified as resistant with lesion score between 1 and 3 whereas most of the plants in MR 297 were classified as susceptible with lesion score > 5. Chi-square test (%2) for a single gene model in M2 generation did not show a good fit on the test cross of 3R:1S (3 resistant: 1 susceptible) ratio at (x2=7.46; p= 0.063).