QTL Mapping and Correlations Between Leaf Water Potential and Drought Resistance in Rice Under Upland and Lowland Environments

The aim of this study was to show the role and genetic mechanism of leaf water potential (LWP) to japonica rice (Oryza sativa L. subsp. japonica) under various water status parameters. To achieve the above, 120 recombinant inbred lines (RILs), derived from a cross between IRAT109 (an upland japonica cultivar) and Yuefu (a lowland japonica cultivar) were planted under both upland and lowland environments for mapping quantitative trait loci (QTLs) associated with high LWP. The LWP was measured at predawn and midday. Drought resistance was evaluated with index of drought resistance (IDR), which was the ratio of grain yield of upland treatment to that of lowland treatment at maturity. Significant variations of LWP were observed in RILs in both upland and lowland treatments. Correlation analysis indicated that LWP at midday in upland (WPU) was positively correlated with IDR (r = 0.256, P < 0.01) and yield per plant (YPU) (r = 0.259, P < 0.01), and water potential difference in upland (WDU) negatively correlated with IDR (r = −0.280, P < 0.01) and YPU (r = −0.260, P < 0.01). For LWP, 6 additive QTLs, i.e., 2 for LWP at predawn in upland (WPIU), 1 for WPU, 2 for WDU, and 1 for LWP difference in lowland (WDL) and 5 pairs of epistatic QTLs, i.e., 1 for WPU, 1 for WPIU, 1 for LWP at predawn on lowland, and 2 for LWP at midday in lowland (WPL) were detected. Among the 6 additive QTLs, the 2 for WPIU (wpiu1 and wpiu4) and 1 for WPU (wpu6), all donated by IRAT109, explained 5.4%, 7.9%, and 10.0% of the phenotypic variances, respectively. For IDR, 3 additive and 2 pairs of epistatic QTLs were identified. The broad heritability of LWP was low for direct selection in the field, but might be effective through marker-assisted selection.