Abstract
To identify the adaptive traits responsible for flooding tolerance during the initial growth stages of rice, 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 were kept under normal rice cultivation conditions for a further 7 days. Cluster analysis showed that 53 genotypes were divided into three groups based on emergence date, percentage of plants reaching the water's surface, maximum coleoptile length, shoot elongation rate during submergence and increases in shoot dry weight after de-submergence. Twelve genotypes were placed in cluster 1 and characterized by fast emergence, rapid coleoptile elongation, and vigorous shoot growth under control and submergence conditions. The genotypes in cluster 1 attained also a higher increase in shoot dry weight at different time of submergence and de-submergence than the genotypes in clusters 2 and 3. A significant correlation was observed between the increase in shoot dry weight and traits related with fast and vigorous shoot elongation and coleoptile. In conclusion, flooding tolerance during initial growth stages were mainly due to major submergence avoidance or escape mechanisms, and crop establishment of direct-seeded rice in flood-prone areas is accomplished by harnessing reserves for fast shoot elongation.