Objectives

The USDA rice genetics program is headquartered with the Department of Agronomy and Range Science at the University of California, Davis, and is a cooperative program with the department. The long term objectives of the project are to develop new germplasm useful in variety development and physiological studies and to investigate standard and innovative breeding methods which can raise yield levels and accelerate variety development. Project purposes are to provide useful breeding materials and methods to rice breeders rather than engage directly in varietal development.

Twenty-one genetic lines were selected for greater grain weight and/or more grains per panicle as possible methods for increasing yields. They were compared in spaced plantings in 1983, along with the three check varieties. Selection for increased grain weight was successful in 11 of 14 lines. Selection for more grains per panicle was effective in only five of 14 lines, and none of the selections produced increased yield per plant. In most cases, selection gains for grain weight increases were offset by a decrease in number of panicles per plant. These lines will be discontinued, but world collections will continue to be screened for these yield components.

In another study, the antibiotics streptomycin and mytomycin were used in attempts to induce cytoplasmic male sterility in the variety M201. Thirty-five sterile or near-sterile plants were selected and will be progeny tested in 1984 to determine if this effort was successful.

Dr. J. N. Rutger and A. O. Bastawesi make crosses to study interspecific transfer of sheath blight resistance from a weed species of rice to cultivated rice.

Four different marker-gene mutants have been found in the variety M-101. Marker genes are useful in variety identification and separation. Trials were conducted in 1983 to determine if these marker genes had any beneficial or detrimental effects on yield. Three of the four marker genes produced yields identical to M-101. Two of them, pale green hull and yellow panicle, are apparently neutral mutants and are available for use by rice breeders.

A study of the inheritance and interspecific transfer of sheath blight resistance from the weedy species Oryza fatua and Oryza rufipogon has continued in cooperation with Dr. R. K. Webster in Plant Pathology and with the rice breeders at the Rice Experiment Station. In a comparison made in 1983 that included sheath blight resistant lines from Louisiana, the Philippines and Arkansas, only the Oryza fatua parent and the F, hybrid between it and the check line were more resistant than the check line. Also, some apparently resistant segregates were found among F2 progenies of the cross Oryza rufipogon and the check line. These studies will be continued in 1984 to confirm resistance in progeny tests.

Research technician Jan Holcomb examines diverse African germplasm lines.

Semi-dwarf selections from crosses between California varieties and tall Egyptian varieties with large panicles showed no yield advantage over M-101. The large panicle size of the Egyptian donor parent was not expressed in the semi-dwarf progenies.

Thirty Chinese rice varieties not previously introduced to the United States were obtained by the project leader during a visit to China in September and October, 1983. They will be evaluated in 1984.

Improved Breeding Methods

The previously developed M-101 genetic male sterile mutant was planted in alternate rows with about 600 varieties from Japan, Korea and Taiwan. Pollen from this world collection was blown by the wind onto the M-101 male sterile plants. At maturity, seed was harvested from 1,926 male sterile plants from 431 rows adjacent to world collection entries. Seed from the crosses will be bulked to create a germplasm composite. The use of genetic male sterile to facilitate crossing offers a way to make large numbers of crosses with relatively little effort. This increases the opportunity to combine useful genes into materials adapted to California.

Reports of 14 million acres of hybrid rice in China have stimulated research on hybrids in other countries. The Chinese report yield increases of 15 to 25 percent from hybrids over standard varieties. Studies at Davis were continued in 1983 on the inheritance of the Chinese hybrid rice sources of male sterility in crosses with various United States lines. Information of this kind is needed to assess the feasibility of producing hybrids suitable for the United States.

Graduate student Shannon Pinson explains a laboratory screening technique for detecting herbicide resistant mutants to members of the Rice Research Board.

A concentrated effort is being made to obtain mutants with resistance to herbicides. This is being done through tissue culture selection as well as selection of induced mutants at the whole plant level. Techniques have been developed for growing callus and detached embryos on herbicide-containing agar. Large scale screening for useful mutants will occur in 1984.