A near isogenic line of rice carrying chromosome segments containing OsSPS1 of Kasalath in the genetic background of Koshihikari produces an increased spikelet number per panicle

AbstractThe aim of this study was to analyze the yield characteristics of a near isogenic line (NIL) that carried chromosome segments containing OsSPS1, a gene encoding sucrose phosphate synthase (SPS), of the indica cultivar ‘Kasalath’ in the genetic background of the japonica cultivar ‘Koshihikari’ (designated as NIL-SPS1). To determine the growth and yield characteristics of NIL-SPS1, we compared NIL-SPS1 with the parental cultivar, Koshihikari, from field trials conducted over the course of a three-year period. The SPS activity in the source leaves of NIL-SPS1 was higher than that of Koshihikari at the transplanting and panicle formation stage. However, at the heading stage, no significant differences were observed in the leaf SPS activities. An analysis of the yield components revealed that the spikelet number per panicle in NIL-SPS1 was 38–47% higher than that in Koshihikari, mainly due to the larger number of secondary rachis branches. In the substituted chromosome region of NIL-SPS1, no quantitative trait loci (QTLs) for the number of secondary rachis branches have been reported, so far. Collectively, these results suggest that the chromosome segments of Kasalath in NIL-SPS1 contain a new putative QTL for the number of secondary rachis branches. Analysis of the distribution of dry matter revealed that a higher source-leaf SPS activity in NIL-SPS1 at the panicle formation stage might promote the distribution of dry matter to panicles and increase the number of secondary rachis branches