Varietal screening for drought resistance in rain-fed lowland rice in the Loa PDR

Abstract

Drought is recognized as a primary constraint for rainfed rice production. A series of experiments were conducted in rainfed lowland conditions to identify drought resistant rice varieties at the Agricultural Research Center (ARC) in Vientiane municipality and Tasano Research and Seed Multiplication center (Tasano) in Savannakhet province in Lao PDR. The study consisted of sixty-six rice genotypes grown under two water treatments, well water (WW/Irrigated control), and water-stress (WS/ imposed drought) conditions. The rice seed were sown on July 25th 2004 and transplanted on August 25th 2004 which is somewhat later than the normal sowing date. The late sowing aimed to increase the likelihood of drought occurring during grain filling. The water was drained from the WS field 25 days after transplanting (DAT) to impose the drought treatment. A large genotypic variation existed for grain yield under both WW and WS conditions, depending on timing, duration and severity of plant water deficit. Grain yield of rice genotypes under WS, in relation to that under WW conditions was reduced approximately 80%, and 60% at ARC and Tasano, respectively. Rice grown under WS reduced leaf water potential (LWP) and delay in flowering at both locations. The genotypic variation in LWP ranged from -0.73 to -2.43 MPa in WW and -1.65 to -3.88 MPa in WS at ARC and -0.80 to -1.70 MPa in WW and -1.53 to -2.73 MPa in WS at Tasano. Some genotypes were able to maintain high LWP and low drought response index (DRI) of grain yield ranged from -0.01 to -1.92 at ARC and 0.01 to 1.71 at Tasano are also an indicator of drought tolerance and associated with other drought tolerance traits during the drought stress period that developed just before flowering produced higher grain yield, and yield components. When water stress occurred prior to flowering, the onset of flowering was delayed. A long delay in flowering is generally considered a disadvantage for rice genotypes grown under WS environments. Therefore, genotypes have a short delay in flowering during WS are one indication of drought tolerance in rice.