Phenotypic, genotypic, and biochemical assessments of ion beam-derived rice mutants for drought tolerance under reproductive stage

Drought stress is one of the most critical abiotic constraints to rice productivity, particularly at the reproductive stage where yield losses are most severe. With the help of mutation breeding, new rice lines that are tolerance towards drought can be developed. Despite the development of four advanced mutant lines in Malaysia demonstrating improved field performance, the molecular characterization of drought-tolerance markers in these lines remains limited. Integrating molecular data is crucial to confirm their genetic basis of drought tolerance and to enhance their value in breeding programs. Hence, study was carried out to evaluate the performance of seven rice genotypes, including four ion beam–induced mutants (NMR191, MINT1, MINT3, and MINT9), two tolerant checks (NMR151, NMR152), and a susceptible check (MR219), under well-watered and drought stress conditions across two growing seasons. A randomized complete block design was used, and data were collected on morpho-physiological, complemented by molecular marker analysis of qDTY loci using SSR markers and biochemical tests involving Catalase, Guaiacol Peroxidase and Ascorbate Peroxidase. Significant genotypic differences (p < 0.05) were observed with drought stress reducing yield-related traits overall. However, MINT3 maintained higher spikelet fertility, filled grain numbers, and chlorophyll content with lower unfilled grain per panicle under drought stress compared to MR219. Molecular screening confirmed that NMR151 carried three qDTY loci associated with drought tolerance, MINT1 and MINT3 carried two qDTY loci, while NMR191 and MINT9 carried one qDTY, validating their genetic potential for resilience. Biochemical testing on antioxidant and proline shows that both NMR191 and MINT3 performed better under drought stress compared to other advanced mutant lines and MR219. The integration of agronomic performance, physiological stability, and molecular evidence and also biochemical parameters highlight ion beam induced mutants as promising genetic resources for breeding programs especially MINT3 and NMR191. These lines, together with tolerant checks, demonstrate enhanced drought adaptability and contribute to strategies for achieving yield stability under water-limited conditions.