IRRI Scientists Work to Increase Rice Plant's Yield, Sustainability By Getting More Sunlight to Leaves

The architecture of the rice plant places the panicles high in the canopy, which means that some of the leaves are in the shade -- not in the best position for maximum photosynthesis to occur. What was needed was to lower the panicles in the plant's canopy so they no longer shaded the leaves. The panicles are the parts of the rice plant that bear the spikelets, which in turn form the grain.

In addition, the scientists saw that such a step would solve a second major problem. When yields are increased on a plant with panicles high in the canopy, the extra weight of the grains causes the plants to lodge, especially when it rains and the wind blows. But if the panicles were lowered, this tendency would be reduced because the center of gravity of the plant would be lowered.

To test the theory that lowering panicle height would increase the amount of light reaching the rice plant's leaves and thus photosynthesis of rice, scientists used six approaches, from removing panicles completely from plants to simulate very low panicle heights, to the use of hormones to increase or decrease panicle height.

All methods confirmed the importance of lowering panicle height to increase photosynthesis and yield. All results were consistent with computer modeling predictions that lowering panicles from 90 to 35 percent of canopy height would increase photosynthesis by 25-40 percent.

However, placing panicles lower in the canopy might result in other undesirable effects. For example, the quality of the grains might be decreased due to high humidity. Therefore, IRRI scientists are continuing to examine to what extent the panicles can be lowered to achieve increased yield without producing other undesirable effects.

Measuring a plant's susceptibility to lodging is difficult, but by applying a mathematical formula scientists were able to determine that by lowing panicle height from 70 centimeters to about 50 centimeters there will no increase in lodging with up to a 50 percent yield increase.

The significance of these findings is that lowering panicle height is a technique that breeders worldwide can apply immediately to any plant type. The yield advantage can be obtained from cultivars that have been successfully adapted over many decades to local environments, and that incorporate locally desired eating qualities. The technique can be applied equally to modern plant types.

One further advantage is that a plant that can increase its canopy photosynthesis by 25-40 percent without requiring an extra nitrogen supply, displays a high level of nitrogen use efficiency. This means that plants with low panicles are more sustainable, scientists say.

(IRRI news release)