Quantitative trait loci for nonstructural carbohydrate accumulation in leaf sheaths and culms of rice (Oryza sativa L.) and their effects on grain filling

Quantitative trait loci (QTLs) that affect the accumulation of nonstructural carbohydrates (NSCs) in the leaf sheaths and culms of rice (Oryza sativa L.), enhancing subsequent grain filling, were analyzed in a population of back-crossed inbred lines (BCILs) from the cross Sasanishiki (japonica)/Habataki (indica)//Sasanishiki///Sasanishiki. QTLs affecting NSC accumulation were detected on chromosomes 1, 4, 5, 7, 11 and 12. Of these, the indica alleles of QTLs on chromosomes 7 and 12 increased NSC accumulation, but were detected for only one year in the two-year study. These loci also showed a strong effect on the number of days to heading, suggesting that their effect on NSC accumulation was linked to environmental conditions before heading. The QTLs on chromosomes 1, 4, 5 and 11 did not affect appreciably the number of days to heading. The QTL on chromosome 1 might be identical with the QTL that increases the number of spikelets per panicle in the indica allele, implying that it has pleiotropic effects. The indica allele of this QTL reduced NSC accumulation, which led to an increased percentage of incompletely filled spikelets. In contrast, the indica allele of the QTLs found on chromosomes 5 and 11 increased NSC accumulation and did not affect appreciably the number of spikelets. These indica allele QTLs also exerted some effect on the reduction of the percentage of incompletely filled spikelets, suggesting the possibility that the expression of these QTLs could improve grain filling in rice.