Responses of Thai rice cultivars to water saving system

The development of a water saving rice growing system was stemmed from an attempt to manage efficient water usage, whereby reducing level of water use but still maintaining acceptable level of yield. To be successful in implementing the water saving rice growing system, it is necessary to understand a suitable photosynthetic mechanism and photosynthetic efficiency of each rice cultivar to be grown in such system. An understanding of such knowledge will lead to a better selection of healthy and high yielding cultivars. As such, this study was aimed to compare responses of 10 Thai rice cultivars in terms of photosynthesis rate and growth in well-drained and water-logged systems. Our data indicated that almost all rice cultivars grown under either well-drained or water-logged condition were capable of increasing photosynthesis rate with increasing light intensity from 0-2000 mol m-2 s-1. This was with an exception of RD21, whose photosynthesis rate when grown under water-logged condition, was not increased after light intensity of 1400 mol m-2 s-1. When comparing rice cultivars grown in either condition, all cultivars grown under well-drained condition were more responsive to light intensity than when grown under water-logged condition. In particular, RD31 and RD35 were able to increase photosynthesis rate to more than 30% at light intensity of 2000 mol m-2 s-1 in well-drained condition compared to water-logged condition. In conclusion, response of rice, both in term of growth and photosynthesis rate, was influenced by both genetics and water availability. Results from this study lead to classification of rice cultivars into 3 groups; 1) those that prefer welldrained condition, 2) those that prefer water-logged condition and 3) those that were not affected by water availability