Submergence tolerance of some modern rice cultivars at seedling and vegetative stages

Twenty five Sri Lankan modern rice cultivars were screened for submergence tolerance at seedling and vegetative stages. An experiment was carried out at the Faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, Sri Lanka during May to September, 2011 according to the randomized complete block design (RCBD) with 4 replicates and each replicate contained 20 plants to evaluate submergence tolerance of the rice cultivars were evaluated in two growth stages; seedling stage and vegetative stage. At seedling stage, germinated seedlings were grown for 2 weeks at normal growth conditions and 5-day, 9day and 14-day complete submergence stresses were given in separate experiments. Plants were allowed two-week-recovery period after each submergence stress. Plant height was recorded just before and after submergence stress, just after submergence stress and just after recovery period. Plant survival percentage was recorded after the recovery period. The experiment was repeated using 6 week old plants for vegetative stage. Among tested rice cultivars 100%, 32% and 24% of rice cultivars survived at 5-day, 9-day and 14-day submergence periods respectively at the seedling stage while 64%, 28% and 16% of rice cultivars survived at 5-day, 9-day and 14-day submergence periods respectively at vegetative stage. According to the Duncan’s multiple range test at 14-day complete submergence, Bg 379/2 was the best tolerant cultivar among the tested cultivars at both seedling stage (20% survival rate) and vegetative stage (17.5% survival rate). All the survived rice cultivars were elongated (100%) under 14-day submergence stress at both seedling and vegetative stages compared to that of control plants. Some survived rice cultivars reduced the plant height at 5-day and 9-day complete submergence stresses at both seedling and vegetative stages compared to that of control plants but none of the cultivars reduced the plant height at 14-day complete submergence stress compared to that of control plants was able to survive. There was a correlation between height gain during submergence stress and survival percentage of rice cultivars which depends on both growth stage and submerged period. The correlation between elongation ability of rice cultivars under control condition and under stress condition was also depends on the growth stage and the submergence period.