Yield advantage of hybrid rice induced by its higher control in tiller emergence

Tiller senescence occurs in most tillering crops since maximum tiller number produced during the vegetative phase is higher than the number of tillers that will be productive at maturity. The assimilate stored in senescent tillers are, however, mostly wasted as few translocation of assimilate between tillers of the same plant occurs. The opportunity to improve grain yield through an increase in tiller fertility rate was addressed in a high tillering crop like rice by comparing two genotypes, an improved inbred line and a hybrid rice with different tillering strategy but similar crop duration. Seedlings were grown in seedling trays and wet-bed nurseries and transplanted 7, 14 and 21 days after sowing at 25 or 50 pl m-2. Early plant development of both varieties during wet and dry seasons did not differ until mid-tillering, as plant tiller number and leaf and stem dry weight per plant were similar. From mid-tillering onwards, shoot dry weight per plant was again similar for both genotypes, but the tillering emergence rate of IR72 was maintained whereas the hybrid stopped its tiller emergence earlier. This reduced the number of tillers in hybrid rice that were likely to senesce as productive tiller number per plant at maturity was similar for both varieties. Grain yield was then significantly higher for hybrid rice as hybrid increased assimilate allocation towards productive tillers. The higher efficiency in assimilate partitioning reported for hybrid suggests that crop management that could improve control in tiller emergence will increase grain yield in rice significantly. (Résumé d'auteur