Characterization of the relationship between vascular bundles features and indica-allelic frequency using a seventh filial generations of indica × japonica rice crosses

Abstract

The quality and yield of rice are influenced by vascular bundles and highly significant differences about size and number of vascular bundles can be found among rice subspecies. In this study, we divided a series of recombinant inbred lines, which were derived from a cross between the indica variety ‘Luhui 99’ and the japonica variety ‘Shennong 265’ into pre-indica, intermediate and pre-japonica groups using subspecies-specific markers. We completed an in-depth analysis of vascular bundles characteristics at different panicle positions. The results showed that the number of large vascular bundles (LVBs) and the ratio of the number of LVBs to the number of primary branches (V/R ratio) of the three groups was ranked as pre-indica > intermediate > pre-japonica. However, a large variation in the number of LVBs and V/R ratio was observed inside each group. Increases in the LVBs and the V/R ratio did not result in increased numbers of primary branches, but led to an increase in the number of secondary branches. With the increase in the frequency of indica-allelic markers, the differences in the grain setting rate and 1000-grain weight among the upper, middle and lower panicle sections became significant. Thus, we concluded that crosses between subspecies, followed by selection of the vascular bundle related traits and indica pedigree, can optimize the number of LVBs and the frequency of indica alleles. The simultaneous increase in both LVB and primary branch numbers, which might lead to greater rice yields, and may be a goal for breeders and scientists.