Adaptive traits associated with tolerance to flash flooding during emergence and early seedling growth stages in rice

Identification of adaptive traits associated with flash flooding tolerance during the initial growth stages is one approach to enhance seedling establishment in direct-seeded rice. To identify these traits, dry seeds of 53 contrasting genotypes were sown in soil and watered normally (control) or submerged with 10 cm of water for 17 days. Subsequently, the plants kept under normal rice cultivation conditions for a further 7 days. Among these genotypes, nine lines had been developed for anaerobic germination and submergence tolerance (AG + Sub1) by IRRI. The length of coleoptile and mesocotyl were measured at different times of submergence period. Length and dry weight of shoot and root were measured during submergence and recovery periods. Emergence date and percentage of plants reaching the floodwater surface were monitored during submergence period. The results showed that tested genotypes were classified into four clusters based on coleoptile and mesocotyl lengths at different times of submergence period using Ward'soleoptilemethodandmesocotyl. TheofIR06F561c genotype that placed individually in cluster 4 and AG + Sub1 lines in cluster 2 elongated more rapidly than other genotypes under control and submerged treatments. Rapid elongation of coleoptile under submergence conditions was significantly correlated with the rapid seed emergence and the percentage of plant reached the floodwater surface. Shoot dry weight during recovery period was significantly correlated with the traits of fast seed emergence, rapid coleoptile elongation and vigorous shoot growth under submergence conditions. In conclusion, the AG + Sub1 lines (IR06F561) were identified having adaptive traits that contribute to flash flooding tolerance during emergence and early seedling growth stages.