Development and validation of markers to improve heat tolerance in flowering stage of Laos elite rice cultivar

Importance of the work: Rice is sensitive to high temperatures in almost all its growth stages, with temperature being a major factor causing poor seed-setting rates. Objectives: To validate molecular markers linked to two quantitative trait loci associated with high-temperature spikelet fertility, namely qHTSF1.1 and qHTSF4.1 Materials & Methods: F2 lines were grouped as H1 and H2 with the HXBF2 allele at qHTSF1.1 and the N22 and HXBF2 alleles at qHTSF4.1, respectively, while groups H3 and H4 had the N22 allele at qHTSF1.1 and the N22 and HXBF2 alleles at qHTSF4.1, respectively. Stressing was done at 40–45°C for 6 hr from the booting to the harvesting stage. Pollen viability and spikelet fertility were used to assess tolerance to heat. Results: Parental lines were significantly different for pollen viability and spikelet fertility under heat stress. N22 was not affected by high temperatures, while HXBF2 showed a severe reduction in pollen viability (66%). N22 maintained 76% spikelet fertility under heat stress, making it moderately tolerant to heat stress with an 11% reduction against the 25% reduction in spikelet fertility of HXBF2. Under heat stress, the F2 lines of groups H1 and H3 had similar pollen viability scores to N22, while only the H1 group could be classified as heat-tolerant, maintaining good spikelet fertility. Main finding: The efficiency of marker-assisted selection was confirmed in the F2 3-way population phenotyped for pollen viability and spikelet fertility under heat stress conditions. The molecular markers, particularly qHTSF4.1, should be very useful for marker-assisted selection breeding.