Effects of Age on the Survival and Recovery of Submerged Rice (oryza Sativa L.) Seedlings

Post-submergence (about 100 cm water depth for ten days) survivality and recovery of rice seedlings were studied in a greenhouse experiment. Irrespective of varieties, 10 and 15-day-old seedlings barely could recover from the shock. More than 80% of 20-day-old seedlings of variety FR13A survived. With the increase of seedling age, elongation of plants decreased during submergence. The variety FR13A and BRRI dhan32 recovered considerably at the seedling age exceeding 20-day, whereas BR6110-10-2-1 and BR11 performed the same not below 40-day-old seedlings. At the higher seedling age, all the varieties maintained higher level of soluble sugar and starch both before and after submergence. During the submergence, the depletion rate of soluble sugar was more or less similar in all the varieties, but the rate of starch depletion was the lowest in FR13A. Therefore, the amount of total carbohydrate both preand post-submergence was higher in tolerant variety FR13A that might contribute to the better survivality and recovery ability. Introduction Rainfed, lowland rice transplanting aman covers an area of 4.5 million hectares in Bangladesh (Islam et al.1997) during June-September. As a result the crop is often submerged by flash flood as well as onrush of flood water. Such flood may continue for a week or more. Resulting severe decrease in yield (Zeigler and Puckridge 1995). Sarkar et al. (2006) reported that flashflooding and submergence adversely affect at least 16% of the rice lands of the world (= 22 m ha). Sometimes it causes total crop failure. So, flooding is an important constraint in T. Aman rice. Submergence tolerance and recovery ability both are equally important for lowland T. Aman rice. Moreover, submergence tolerance and recovery ability is affected by turbidity, water temperature, duration of submergence, solar radiation, and plant characters like seedling age, seedling quality, etc. (Ito et al. 1999, Sauter 2000). Pande et al. (1979) reported that grain yield of rice increased with the increase of seedling age in intermittent flooded area. Older seedlings, which have greater submergence tolerance, also contain more carbohydrate (Chaturvedi et al. 1993). The tolerant varieties are able to retain their stored carbohydrate which is used during the recovery period. The susceptible varieties cannot either produces enough carbohydrate to store or cannot retain their carbohydrate and, therefore, cannot recover until the period of submergence is over. The present study was undertaken to find out the contribution of seedling age as well as reserved carbohydrate on the survival and recovery of submerged seedlings and identify the most tolerant varieties of T. Aman. Material and Methods The experiment was conducted in the greenhouse of Plant Physiology Division, Bangladesh Rice Research Institute (BRRI) during T. Aman season, 2004. Three varieties (FR13A, BR11 and BRRI dhan32) and an advanced breeding line (BR6110-10-2-1) were used. Uniformly sprouted Corresponding author. Email: [email protected] Crop Botany Department, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh.