Genetic and Physiological Determinants
of Yield and Quality-81

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Project Leader and Principal UC Investigators

J.N. Rutger, USDA

R.L. Travis and M.L. Peterson,  Department of Agronomy and Range Science, UC Davis

R.K. Webster,  Department of Plant Pathology, UC Davis


A narrow-leaf mutant exhibited high seasonal trends of photosynthetic capacity . . .

The role of USDA and UCD scientists in the varietal improvement program is to provide basic information and genetic materials for the rice breeding program centered at the Rice Experiment Station. Goal of the project is to identify genetic and physiological factors that can raise yields. Emphasis in 1981 was on transfer of stem rot and sheath blight resistance from wild species, determination of the inheritance of male sterility systems and their use in hybrid rice production, and the significance and transfer of mesocotyl elongation to adapted varieties.

Basic Studies on Genetic and Physiological Factors that can Raise Yields

Two possible methods for raising yields are increased photosynthetic rates and increased storage capacity of the panicle. Past studies on increasing photosynthetic capacity have not been very promising. A narrow-leaf mutant exhibited high seasonal trends for photosynthetic capacity, but the leaf area was only 33 percent of normal leaf types. The yields were two-thirds those of standard varieties. So far, it has not been possible to transfer the high photosynthetic capacity of the narrow-leaf mutant to normal-leaf types.

Work on selection for large seeds and many seeds per panicle indicates that selection for many seeds is more promising. Further crossing and selection will be required to prove that yields can be increased by increasing the number of seeds per panicle.

Transfer of Stem Rot and Sheath Blight Resistance from Wild Species to Cultivated Rice

Previously, we showed that a wild species of rice, Oryza rufipogon, had greater resistance to stem rot than the most tolerant Oryza sativa variety, Colusa. In 1981 we continued the transfer of resistance from the wild species by narrowing our selections to 29 lines which partially recombine disease resistance and good plant type. These lines were released to breeders.

In hybrid rice studies we are attempting to obtain the Chinese cytoplasmic male sterile system. We are also studying two other cytoplasmic male sterile sources, the Birco source from California and the Boro source from Okinawa. Finally, we are trying to develop new cytoplasmic male sterile sources by crossing cultivated rice with wild species. These interspecific crosses are doing double duty: transferring disease resistance as well as searching for cytoplasmic male sterility.

The Significance of Mesocotyl Elongation

Elongation of the mesocotyl and seedling internode were studied. Mesocotyl elongation does not occur in water seeded rice, but is important for seedling emergence in drill seeded rice.

With California varieties, there does not seem to be any difference in mesocotyl elongation between short and tall varieties. However, in a cross with Labelle, a Southern variety which shows seedling internode elongation, mesocotyl elongation was associated with mature plant height. Nevertheless, some progress was made in recombining increased mesocotyl elongation and short mature plant height.


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