Identification and validation of quantitative trait loci for a parameter associated with nitrogen partitioning to grain using a population derived from japonica- and indica-type cultivars of rice (Oryza sativa L.)

ABSTRACT Nitrogen (N) partitioning to grain affects productivity and grain quality in rice. The objectives of this study were to clarify the difference between the rice cultivars ‘Momiroman’ (japonica) and ‘Takanari’ (indica) in the relation between the amount of total N in aboveground parts per grain dry weight (TNA/GW) and grain N concentration (GNC), to identify quantitative trait loci (QTLs) associated with the coefficient characterizing this relation by using populations derived from a cross between Momiroman and Takanari, and to verify the effects of the detected QTLs by using near-isogenic lines (NILs). We used 156 F2 plants grown under high N in 2015 and 156 F3 lines grown under high or low N in 2016, and determined N concentrations and contents in grain and aboveground vegetative parts. We found a logarithmic relation between GNC and TNA/GW in Momiroman and Takanari. The regression coefficient (A) was higher in Takanari. Under each N condition, A was calculated for each population and QTL analysis was performed. QTLs for A were detected on chromosomes (Chrs.) 6 and 10 in all conditions; the Takanari alleles of both QTLs increased the value. NILs with the Takanari allele in each region had higher A than NILs with the Momiroman alleles. We conclude that the QTLs for A are associated with N partitioning to grain in rice. Abbreviations: GNA, amount of N in grain; GNC, grain N concentration; GW, grain dry weight; TNA, amount of N in aboveground parts Graphical abstract