Effects of high temperature on spikelet sterility in rice ( Oryza sativa L.): association between molecular markers and allelic phenotypic effect in field condition

Rice varieties are generally bred for higher yield but may possess genomic regions conferring tolerance to abiotic stresses. Climate change driven heat stress during reproductive stage of the crop affects spikelet fertility and yield. Though genetic regions associated with heat stress tolerance have been identified in rice, but response of rice varieties and allelic phenotypic effect favoring spikelet fertility during heat stress has not been comprehensively studied. Hence, the present study aimed at assessing the response of 198 rice varieties during the dry season (2016) followed by validation of selected 67 varieties in the second dry season (2017) through staggered sowing for high temperature. The analysis showed mean spikelet sterility of 21.82% and 33.81% for the first and second sowing, respectively. Further, average difference in spikelet sterility for unit increase in maximum temperature during the flowering period was observed to be 7.93%. Employment of nine heat stress associated markers for genetic analysis identified four sub-populations in the 67 varieties inferred through neighbor-joining phylogenetic tree and sub-structure analysis. Marker-trait association analysis showed two markers namely RM205, RM242 were significantly associated with spikelet sterility with phenotypic variance (R 2 ) of 7.7% and 6.0%, respectively. Allelic phenotypic effect of favorable alleles for both the markers reduced spikelet sterility by 14.49% compared to mean spikelet sterility (33.81%). Furthermore, four rice varieties showed spikelet sterility < 15%. Thus, predominantly moderate tolerance to susceptible response was observed for rice varieties in this study. Besides, favorable allele of RM205, RM242 could be effectively used for improving tolerance in rice varieties to heat stress.