Identification of quantitative trait loci for grain yield and its components in response to low nitrogen application in rice

Increasing grain yield with high nitrogen (N) use efficiency and less N application is an important objective in rice genetic improvement. A total of 127 rice recombinant inbred lines derived from Zhenshan 97  Minghui 63 (Oryza sativa L.) were used for detecting the quantitative trait loci (QTLs) of grain yield and its components (panicle per m 2 , spikelets per panicle, grain filling ratio, and 1000-grain weight) under low (LN) and normal nitrogen (NN) applications in 2006 and 2007. Among 68 QTLs detected across the two years under LN and NN, 33 QTLs were identified under LN (18 in 2006 and 15 in 2007), and 35 QTLs under NN (18 in 2006 and 17 in 2007). Only ten of 33 QTLs (30.3%) under LN and 14 of 35 QTLs (40%) under NN were detected simultaneously in both two years. A total of 18 of 36 QTLs (50%) in 2006 and 16 of 32 QTLs (50%) in 2007 were simultaneously detected under the two N applications, respectively. The results showed that environments over the two years and N applications had their significant effects of QTL expressions. The seven regions (RG532-G359-R753 on chromosome 1, RM53-R1738 on chromosome 2, RZ403-C1087- RG393 on chromosome 3, RM26-C246-C624 and C734b-RG360 on chromosome 5, R1440-C1023 and RZ471-RG678 on chromosome 7) were found to have their effects simultaneously under LN and NN in a year or two years. Eight regions were only detected under LN. Our results may provide information for genetically improving rice NUE by keeping yield stability when decreasing N application, and by increasing yield under current level of N application. Those regions that are stable across various nitrogen applications and responsive to LN would be useful for improving grain yield formation with high N use efficiency and less N application in rice breeding.