Rice (Oryza sativa L.) genotypes tolerance to flash flooding and stagnant flooding stress

Abstract

Flood is one of abiotic stress limiting rice production especially at rainfed area in wet season or at basin swampy area. The major constraint of rice cultivation in the flood-prone area is lack of tolerant varieties. The objectives of this research were to evaluate the tolerant level of several rice genotypes and reveal the mechanism of submergence tolerance in rice and to obtain rapid screening method. Green house experiment was conduct to screening rice genotypes under flash flooding condition. This experiment was conducted at Muara Experimental Station. The experimental design used was randomized complete design with three replication. There were four sub-experiment, grouping based on seedling age (10 days and 35 days) and duration of submergence (10 days and 14 days). Those sub-experiment in the green house correlated with experiment in the field. The Flash Flooding Experiment was conducted at Muara Experimental Farm of Indonesian Center of Rice Research, Bogor in wet season 2011/2012 and dry season 2012, while the Stagnant Flooding Experiment was conducted at Babakan Experimental Farm of Bogor Agricultural University in wet season 2011/2012. In both experiments, stress conditions were compared to optimum environment. Experimental design was randomized complete block design with three replications. For flash flooding stress, 35-day-old plants of 15 rice genotypes were submerged completely in water for 10 days. For stagnant flooding stress, 35-day-old of 22 rice genotypes plants were partially submerged in water (water depth 50-60 cm) until harvest. The result showed that B13138-7-MR-2-KA-1 genotype was tolerant to flash flooding stress. Rice genotypes tolerant to flash flooding stress (complete submergence) experienced reduced growth rate of plant height and maintained the carbohydrate content in rice stem remain unchange after stress period. Percentage of recovery after 10 days stress could be used as early selection indicator to flash flooding stress since it was easy to observed and had high correlation with grain yield. Stagnant flooding stress increased plant height, increased stem length, lengthen flowering and maturity date and increase the number of unfilled grain. Stem elongation ability didn’t correlate with grain yield under stagnant flooding stress condition (r=-0.29), but the number of filled grain has positive significant correlation to grain yield under both flooding stress condition. Genotype IPB107F-5-1-1 (5.47 t/ha) and IPB107-F-95-1-1 (4.61 t/ha) showed grain yield decrease less than 10% under stagnant flooding compared to flash flooding and optimum condition. None of the twelve genotypes has double tolerance under flash and stagnant flooding conditions, but B13138-7-MR-2-KA-2 had moderate grain yield under both flooding conditions, 3.61 t/ha and 3.72 t/ha respectively. This genotype can be developed as variety for longer flash flooding period (e.g. more than two weeks). Complete submergence at 10-day-old seedlings in green house could be developed as rapid screening method of rice tolerant to flash flooding stress.