Possible increases in yield potential of rice using low-panicle (LP) rice plant types

Most carbon required for yield is assimilated during grain filling in rice. Optimized canopy architecture during this stage is thus crucial for high yield potential. During grain filling, most current cultivars have particles on the top of the canopy and suffer from the limitations: (1) leaves shaded by panicles reduce canopy photosynthesis for supplying carbohydrates to the grain, and (2) plants have a high center of gravity and are susceptible to lodging. A simple solution to both problems is to lower the panicle height in the canopy. This study demonstrates the benefits of a new, low panicle (LP) rice plant type by presenting results with "artificial panicles" and simulation modeling. Artificial panicles are dried panicles which are attached to sticks and positioned in the canopy at different heights to evaluate effects on canopy photosynthesis. The effects of artificial panicles were most pronounced at high yield conditions at 90 and 180 kg N/ha applications. When panicles were place at 60 percent of canopy height, canopy photosynthesis was 150-240 percent of rates for plants with panicles placed at 100 percent of canopy height. Even at low yield conditions, at 0 kg N/ha there was a 32 percent increase in canopy photosynthesis for LP relative to high-panicle plants. Modeling predicts that lowering panicles within the canopy from 90 to 40 percent canopy height will increase yield by 18, 26, and 41 percent at a panicle area index (PAI) of 0.4, 0.6 and 1.0 respectively. This implies that the higher the yield, the greater the benefits of LP rice. Increasing yields with LP rice will likely be more sustainable because theoretically either higher yield may be achieved at the same N application of the same yield at lower N application. Plant breeding is now required to develop LP rice to confirm the benefits of the new, LP rice plant type