Quantitative trait loci for leaf inclination angle in rice detected using reciprocal mapping populations

The improvement of canopy architecture is a feasible way to increase rice productivity. However, its genetic control in rice cultivars in the field is not well understood. The high-yielding indica cultivar Takanari has more erect leaves (a larger leaf inclination angle: LIA) during ripening, and this contributes to its higher dry matter production than that of the widely grown but less productive japonica cultivar Koshihikari. To identify quantitative trait loci (QTLs) for increasing LIA, we used reciprocal mapping populations of backcross inbred lines (131 lines in 2009 and 143 lines in 2010) and chromosome segment substitution lines (80 lines in 2011 and 2012) derived from a cross between Takanari and Koshihikari. Six Takanari alleles increased LIA at least in two of the four years, but we could not detect any such Koshihikari alleles. Five QTLs for LIA were expressed in plants with both Koshihikari and Takanari genetic backgrounds. LIA of two near isogenic lines carrying only one Takanari allele reached the level of Takanari. The Takanari alleles of the QTLs decreased the length of parenchyma cells in the lamina joint on the adaxial side in plants with the Koshihikari background, decreasing the ratio of the lamina joint length on the adaxial side to that on the abaxial side (LJ ratio) and thus increasing LIA. Three Takanari alleles increased dry matter production in plants with Koshihikari background via decreasing the canopy extinction coefficient (k). However, any pyramiding effects of Takanari alleles on LJ ratio, LIA, k and dry matter production were not observed.