Evaluation of heat tolerance in Thai lowland indigenous rice germplasm in seedling and grain filling stages

Abstract

High temperature stress in rice is likely to occur in all rice growing systems in Thailand. In wet season, rice cultivated by broadcasting at the late of April to early May would be affected by high temperature in the seedling stage. In the dry season, rice will be affected by high temperatures during the grain filling stage in March to April. The experiment was high temperature tolerance evaluation in 132 lowland rice varieties at seedling and grain filling stages. Heat stress treatment was set at 45±3°C during 11:00 a.m. to 2:00 p.m. for 14 and 30 days in seedling and grain filling stages, respectively. The result showed that three groups of varieties based on leaf dead and dry weight reduction percentage included of 30 cultivars in group 1 (G1) had high temperature tolerance comparable to the standard check (N22). There was a decrease in dry weight of 40.8% – 59.7%. In conclusion, LLR-072, LLR-146 and LLR-232 were resistance to high temperatures at seedling stage due to the slow leaf death. At grain filling stage, group 1 (49 cultivars) showed low seed weight reduction by 65% - 68%, high filled seeds per plant, 100 seed weight and 100% seed number. However, in G1 at grain filling stage, there was a high reduction in 100% filled seed number, but low reduction in 75% and 50% filled seed number. The result showed that this group maintained higher seed weight than other groups. At the grain filling stage, LLR-230, LLR-232 and LLR-262 showed low decreasing in seed weight, filled seeds per plant and 100 seed weight. Interestingly, LLR-232 was high resistance at both seedling and grain filling stages.