QTLs for Plant Height and Heading Date in Rice Under Two Nitrogen Levels

A recombinant inbred line (RIL) population derived from the super hybrid rice (Oryza sativa L.) cross between XQZB and R9308 was used to identify quantitative trait loci (QTLs) for plant height (PH) and heading date (HD) under low and normal nitrogen conditions. Under both nitrogen levels, 9 QTLs for PH were mapped on chromosomes 2, 3, 6, 7, and 8, and 8 QTLs for HD were mapped on chromosomes 4, 5, 6, 7, and 8. Another 4 QTLs were responsible for the differences of PH and HD between the 2 nitrogen levels. A single QTL explained 5.68–18.40% of the phenotypic variation. Two pleiotropic QTLs with high contributions to the phenotypic variations were located near RM5436 on chromosome 7 and between RM5556 and RM310 on chromosome 8, on which the positive alleles originated from R9308. One QTL for HD difference and one QTL for PH difference were involved in the intervals RM5916-RM166 on chromosome 2 and RM2366-RM5767 on chromosome 8, respectively. Both loci were inferred to directly contribute to nitrogen use efficiency in rice.