Increasing Rice Productivity by Manipulation of Starch Biosynthesis during Seed Development

Abstract

The small-grain cereals, wheat and rice, are two of the major crops grown in the world and are used mainly as food. As the world population is projected to increase by 40% by the year 2020, these cereals can be expected to assume a much larger role in providing the basic daily dietary requirements required for human growth and development. This is especially true for rice where this cereal provides many of the dietary calories for about 50% of the world’s population, most of whom live in Asia. In view of constraints caused by the amount of available arable land and the limitations in chemical inputs in the environment imposed by the increasing use of sustainable agricultural practices, new approaches to increase the genetic yield potential of crop plants must be developed and implemented. Although dramatic improvements in the genetic yield potentials of wheat and rice were achieved during the so-called green revolution, only relatively small annual increases (1-2%) in the genetic yield potential have been attained in recent years. This trend is even true for maize (Duvick, 1992), despite the employment of the most modern biotechnological tools and resources available to the maize plant breeder. If we are to meet the challenge of feeding 8 billion people in the year 2020, it is clear that a major increase in genetic yield potential of cereal crops must be achieved. In very general terms, the genetic yield potential is dependent on source-sink relationships (Ho, 1988; Turgeon, 1989). Source leaves capture light energy and fix carbon dioxide to produce sugars and other metabolites. These organic compounds are exported from the source leaves and transported to developing sink tissues, for example, young developing leaves and new root tissue, which utilize these basic precursors for growth and development. Because of the importance of the primary processes of photosynthesis in controlling plant productivity, considerable research effort has been directed to increasing the efficiency of the source leaves. Plant productivity is also influenced by the capacity of sink tissues to uptake and assimilate photosynthate produced by source leaves or reconverted from storage reserves (Ho, 1988).