Rice Biology-75
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Project Leader and Principal UC Investigators D.S. Mikkelsen, Nutritional and Environmental Factors Affecting High Yield PotentialB.R. Hewitt D.M. Brandon S. Kuo J.A. Hardy E. Graetzer M.L. Peterson, Genetic and Physiological Determinants of Yield and Quality J.N. Rutger D.B. Jones R.C. Buckman Jose Galli Robert Barham C.C. Li K. Foster Y.C. Teng Tran Vat Dat Beatriz Pinheiro |
Projects in this category relate to the development of basic knowledge needed to support and expedite production research projects. For example, project RB3, led by UC Davis scientists, has contributed information on the physiology and genetics of rice plants that is of key use to plant breeders at the Rice Experiment Station. NUTRITIONAL AND ENVIRONMENTAL FACTORS AFFECTING YIELDPlant functions interrelated to fertilizer program. Each tiller on the rice plant produces about 15 leaves. As the leaves on each tiller develop in sequence, each leaf reaches a peak in nutrient content, then declines as the nutrient supply is translocated to the next new leaf in succession. This process is repeated with the development of each new leaf, so that each takes a turn as an "active center," the most important contributor to growth and yield at the various stages of development. Carbohydrate analyses reveal that the major portion of the carbohydrates deposited as grain comes from the uppermost leaf and its sheath. A single basal application of nitrogen can sustain California varieties for full growth and yield because the nitrogen is translocated to the active center from the soil and older tissues. þ Soil temperatures below 68OF adversely affect nutrient uptake, and therefore retard growth, yield, and maturity. Soil temperature is a major factor also in affecting the availability of zinc. Larger corrective applications of zinc are required in cool seasons. Phosphorus-induced zinc-deficiencies do not appear to be a significant problem in rice. Data are being accumulated toward developing a computer model of California rice management systems. GENETIC AND PHYSIOLOGICAL DETERMINANTS OF YIELD AND QUALITYContinued studies of low-temperature effects on sterility (blanking) have led to improved ways of determining sterility; to the identification of genetic sources with very low levels of sterility (5 to 6%, compared with 14 to 16% for standard varieties); and to the conclusion that temperature effects on sterility are highly localized rather than on the entire plant. Rice yields are being analyzed in terms of the components of yield: a) number of panicles per unit area, b) kernels per panicle, c) kernel weight, and d) percent of sterile kernels. Such data should make it possible to identify the more important factors affecting yield. With this information, genetic and physiological studies can be aimed at the most critical limitations to higher yields. Programs are in progress on each of these components. Stand establishment can be increased through improved seedling vigor. It now appears possible to combine seedling vigor with short-stature rice, but developing this characteristic will take a little more time. þ Solid evidence obtained in 1975 shows that short stature alone (independent of other associated characteristics) will improve rice yields at high fertility levels. Although that has been supposed for a long time, the 1975 studies gave the first solid evidence. An associated study of pubescent and smooth leaves shows that this characteristic has no effect on yield. Studies of panicle filling rates show surprising differences, though their importance is not fully established yet. Genes known to have beneficial effects on yield are being added to adapted California varieties.
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