Advanced Backcross QTL Analysis For The Whole Plant Growth Duration Salt Tolerance In Rice (Oryza Sativa L.)

To discover favorable “hidden” genes for salt tolerance (ST) from indica gene pool, six sets ofadvanced backcross introgression lines (ILs) derived from six different donors, Bg94-1, Budda,Gang46B, Guan122, IR64a and IRAT352, introgressed into a common recipient parent Huanghuazhan(HHZ) were evaluated for their ST over whole plant growth duration in Sanmen, Zhejiang. Also,quantitative trait loci (QTL) contributing to ST over whole-plant growth duration in rice were identifiedusing the three sets of advanced backcross introgression lines (ILs). Furthermore, three populationswere used to select for the extreme lines with grain yield per plant (GYP) significantly higher than thecheck. Three sets of GYP-selected lines were used for QTL mapping for ST and analysis of linkagedisequilibrium. The main results summarized as follows:1. Segregation presented in all the traits under normal irrigation and salt stress conditions. Most oflines showed lower PL than that of check under normal irrigation condition, the opposite was true forSNP, and the other traits showed different patterns. Six populations had different responses to stress, butall the lines showed greater GYP than that of check. Total of12,14and16lines were selected undernormal irrigation condition, and14,14and10lines were selected under stress condition. Among them,9lines were both selected under normal irrigation and stress conditions. It was indicated that thepopulations in general may have stronger ST than the check and development of backcross introgressionis effective to exploit the hidden variation in ST in rice. The extreme ST lines could be the bestmaterials for pyramiding breeding for improvement of ST.2. Total of17,15and15main-effect QTLs, and9,16and15pairs of epistatic QTLs were detectedamong three populations, respectively. Most QTLs showed clearly differential expressions in responseto salt stress, the donor alleles at most loci resulted in increased relative trait ratio, or improved traitstability between non-stress and stress conditions. Many QTLs clustered on chromosome withpleiotropic gene effect.3. The Chi-square statistical analysis showed that40loci affecting ST related-traits detected in thethree selected populations were all donor excessive introgression. Interestingly,23(57.5%) of the40loci were either identified as the main-effect or epistatic QTL under salt stress and the non-stressconditions, eleven overlapping QTLs affecting GYP were detected by X2test, these loci would be veryuseful for breeding because favorable genes were from donors. Besides, six pairs of overlappingepistatic QTLs affecting GYP were detected by LD analysis. This was consistent with the theoreticalexpectations. The large numbers of epistatic QTL pairs identified in this study indicate that epistasisplays a very important role in determining the genetic variation of rice yield traits.