Genetic Analysis for Heat Tolerance and Early Morning Flowering Traits at Flowering Stage in Rice (Oryza sativa L.)

Genetic factors for heat tolerance and early morning flowering (EMF) in rice were evaluated as part of rice genetic improvement under heat stress condition. Quantitative trait loci (QTL) linked to heat tolerance and early morning flowering (EMF) were analyzed by selective genotyping of phenotypic extremes in 235 BC1F1 plants derived from the cross PSB-Rc82/PSB-Rc82/WAB56-125 under controlled high temperature and 684 BC1F2 plants under glasshouse conditions using single marker analysis (SMA). For heat tolerance, data of pollen fertility and spikelet fertility of BC1F1 plants under high temperature were gathered and analyzed. For EMF, four parameters of flower opening to closing were determined, namely: time when flowers start to open (FOT), time of peak flowering (PFT), time when most of the flowers are closed (FMCT), and time when all of the flowers are closed (FCT). SMA revealed three markers on chromosomes 2, 3, and 8 are possibly linked to pollen fertility, while two markers on chromosomes 7 and 8 are possibly linked to spikelet fertility under high temperature. SMA for EMF revealed three markers on chromosomes 5, 7, and 9 are possibly linked to FOT, while six markers on chromosomes 5, 7, 8, 9, and 11 are possibly linked to PFT, FMCT and FCT. In general, markers on chromosomes 7 and 8 could be linked to QTLs controlling both heat tolerance and EMF at flowering stage in rice. The results could be useful for further fine mapping and marker-aided selection for heat-tolerant and heat escape in rice genotypes in the future.