Raising the yield potential of rice
1988
Vergara, B.S. (International Rice Research Inst., Los Banos, Laguna (Philippines))
With the introduction of the modern high yielding rice varieties and appropriate cultural practices, yields have increased in the last two decades. Subsequent efforts to improve yielding ability by increasing photosynthetic rate increasing biomass production and increasing harvest index have not resulted in significant increase in yields. An approach being pursued to achieve this is the manipulation of the weight of single grains. Results of studies have shown the following. Increasing the number of high density (HD) grains can increase yield potential. HD grains result in better milling recovery and higher head rice recovery. Varietal differences in the number of HD grains per panicle exist. With a panicle, certain spikelets invariably developed into HD grains. Most spikelets on the secondary branches have low grain weight. Leaves near the panicle are more important in grain filling. Removal of the fourth leaf from the top increased grain weight and number of HD grains. Lower temperature or higher photosynthetically active radiation after anthesis results in higher number of HD grains. Applied nitrogen fertilizer had no effect on the number of HD grains. Limitations in grain filling may be the result of several factors. Although sufficient carbohydrate is available not all spikelets develop into HD grains. Factors limiting grain filling include structure of the pedicel, the spikelets and growth regulators. In view of the above findings a new plant type is proposed to break the yield ceiling. Further studies are being conducted to identify the limitations of the current varieties in order to develop the new plant type being proposed.
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