QTL analysis of floral traits of rice (Oryza Sativa L.) under well-watered and drought stress conditions

Three floral traits, spikelet number per panicle (SNP), percentage of single exserted stigma (PSES) and dual exserted stigma (PDES) of a RI population with 185 lines under water stress and non-stress conditions for two years were investigated in a drought tolerance screening facility. ANOVA results showed high significance between years, lines, and water stress treatments, together with interactions among them in pairs. High phenotypic correlation was found between PSES and PDES (r=0.5424***). Based on a linkage map of 203 SSR markers, when under well-watered condition, six QTLs (qSNP-3b, qSNP-4, qSNP-11 qSNP-2, qSNP-5 andqSNP-9) were detected for SNP. Half of them had significant Q × E interactions. Three QTLs (qPSES-1, qPSES-2, qPSES-5) were found to influence PSES, including one locus (qPSES-2) having Q × E interaction. And three QTLs (qPDES-2, qPDES-5 andqPDES-8) were also detected to influence PDES.qPDES-5 was found to have Q × E interaction. The contribution rate of a single QTL varied from 0.80% to 8.83% for additive effect, and 1.86% to 15.25% for Q × E interactions. Under drought stress, six QTLs (qSNP-3a, qSNP-4, qSNP-7a, qSNP-7b, qSNP-8 andqSNP-9) were associated with SNP, includingqSNP-3a andqSNP-4 with Q × E interaction. Three QTLs (qPSES-1, qPSES-10 andqPSES-12) were located on rice chromosome 1, 10 and 12 for PSES. Four QTLs (qPDES-1a, qPDES-1b, qPDES-4 andqPDES-9) were detected for PDES, includingqPDES-9 with Q × E interaction. The additive effect of single QTL can only explain 1.16% to 5.84% of total variance while Q × E interaction of four loci can explain 4.25% to 11.54% of total variance for each locus. There were one to nine pairs of epistatic QTLs influencing SNP and stigma exsertion. The contribution rates of additive and epistatic effects seemed to be in a low magnitude for most cases (0.76%≈9.92%) while a few QTLs or QTL pairs explained more than 10% of total variance. Some main effect QTL and epistasis were commonly detected among PSES and PDES, explaining the high positive correlation between them. Few QTLs were detected under both water stress and non-stress conditions, indicating that drought had severe impact on the genetic behaviors of both spikelet number and stigma exsertion.