Reduction of unproductive tillers did not increase the grain yield of irrigated rice

Tillering ability is one of the most important traits of the rice plant because it plays a major role in determining grain yield. However, it is not clear whether rice yield potential could be further increased if unproductive tillers were reduced or eliminated. Two field experiments were conducted to determine the effects of tiller reduction on plant growth and grain yield in two varieties with different tillering ability. Two methods were used to reduce tillers: the first was the removal of tillers manually at different crop growth stages and the second was to grow rice plants through holes in styrofoam slats, which provided a physical restriction on tiller emergence. Tiller number declined by 12-57% with the first method and by 18-47% with the second method compared with the control. Despite the significant reduction in tiller number and unproductive tiller percentage, none of the treatments with manual tiller removal and physical restriction of tillering resulted in a significant increase in grain yield compared with the control. Decreases in leaf area and biomass at heading and panicle number at maturity were observed when tiller number declined significantly, but grain yield was not necessarily reduced because it was compensated for by more biomass production after heading and increased spikelet number per panicle. The two varieties with different tillering ability had similar responses to tiller reduction. Based on the two methods of tiller reduction used in this study, we conclude that a further increase in rice yield potential may not be possible by reducing or eliminating unproductive tillers.