Four QTLs control stigma exsertion rate by changing stigma size in rice

The stigma exsertion rate (SER) is a key trait for the outcrossing ability of hybrid rice, which directly affects the yield of hybrid seeds in hybrid seed production. In previous studies, we have located 18 QTLs for SER using single-segment substitution lines in rice. In this study, we found that 4 of 18 QTLs for SER controlled stigma size (SS). On chromosome 1, a QTL qSL-1 controlling stigma length (SL) was located at the same interval of qSER-1b. On chromosome 2, two QTLs for SS, qSS-2a and qSS-2b, linked closely within a 1288.0 kb region, were at the same positions of qSER-2a and qSER-2b, respectively. A QTL qSL-12 controlling SL on chromosome 12 was at the same location of qSER-12. Additive effects of four QTLs for SS ranged from 0.12 mm to 0.38 mm, showing significant effects on SS. In pyramiding lines of QTLs for SS, SS enlarged with the increase of QTLs. The effect of QTLs on SER was consistent with their effect on SS, and SL had a greater positive effect on SER than the stigma width. Our findings demonstrate that SS is one of the important factors affecting SER in rice.