Objectives

The general objective of the rice genetics project is to combine conventional genetics with recent developments in biotechnology to improve germplasm and breeding methods. Procedures being used include:

• the transfer of genes for disease resistance from wild to cultivated species of rice,
• use of male-sterile facilitated crossing techniques to introduce desirable traits from Asian and African rice to California varieties,
• use of a chemical mutagen to induce genetic male sterility,
• genetic mechanisms that might make the production of hybrid rice seed possible,
• regeneration of rice plants from somatic cells and from rice anthers,
• searching for rice plants that will produce seed by asexual (without fertilization) reproduction,
• transferring foreign genes into rice.

Some of these are studies of basic biological mechanisms that have no immediate practical application but, in many cases, basic research leads to practical uses.

Interspecific Transfer of Genes for Aggregate Sheath Spot Resistance

Weedy relatives of cultivated rice (Oryxa sativa) were found to be good sources of resistance to aggregate sheath spot. The weedy donors used in crosses were Oryza rufipogon and Oryza fatua. The Oryza fatua line was a better donor source for aggregate sheath spot, and a larger proportion of resistant plants were obtained in the progeny of crosses between cultivated rice and Oryza fatua. Estimated gains in aggregate sheath spot resistance ranged from 5 to 11 percent. Lines with improved resistance will be made available to rice breeders.

Evaluation of Induced Mutations

A chemical mutagen (ethylmethyl sulfate) has been used to induce new genotypes of possible value in future breeding programs. In 1984, selections were made for early maturity in the variety M-201. In 1985, 25 lines which ranged from 5 to 13 days earlier than M-201 were selected from an initial population of 649 early maturing plants. Seeds of these lines have been turned over to rice breeders.

Other mutants selected were an early S-201 and a double dwarf M-201 which is only 28 inches tall. Neither of these mutants will be useful to the breeding program because of the grain shape of the mutant S-201 and excessive shortness of the mutant M-201.

Use of Asian and African Rice Introductions

Dr. J.N. Rutger, USDA geneticist, and his assistant Betsy Peterson look for promising selections among crosses with Asian and African rice introductions.

In 1983, about 400 collections of rice lines from Japan, Korea, and Taiwan were permitted to cross naturally with a male sterile M-101. The more than 2,000 selections made in 1984 were progeny tested in 1985. The number of lines has been reduced to 374. These will be used in another cycle of random crossing for population improvement in 1986.

A similar program is under way with African rice introductions. Seeds from the germplasm pool of the Asian selections have been provided to the breeding program.

Genetic Male Sterile Mutants From M-201

Genetic male sterility is a useful tool for making hybrids with less effort and cost and, therefore, has applications in subsequent breeding and genetic programs. Male sterility genes are needed in different varieties to maximize opportunities for genetic recombination among diverse parents. Fourteen genetic male sterile mutants were selected from M-201 which had been treated with the chemical mutagen ethylmethyl sulfate (EMS).

In 1985 four additional varieties were treated with EMS and gamma rays, 25kR in preparation for screening for additional male steriles.

Hybrid Rice Studies

Research is continuing on genetic mechanisms to make large scale hybrid seed production easier. Cytoplasmic male sterility is an essential part of this process. Studies include using chemical hybridizing agents, inducing additional cytoplasmic male sterility in California varieties, and the inheritance of fertility restoration. To date, none of these approaches is adequate by itself for hybrid rice production in California.

Seedling Screening for Herbicide Resistance

Resistance in rice to the broad-spectrum herbicide glyphosate (Roundup) would be extremely useful in weed control. After considerable effort, the conclusion has been reached that finding a mutant with resistance is highly unlikely, and efforts have been redirected to less difficult herbicides.

Somatic Tissue Culture and Anther Culture

Regenerated rice plant from a rice plant anther. The green plant on the left will develop into a healthy plant, but the albino one on the right will die.

The aim of the somatic tissue culture project is the regeneration of plants from single or small groups of cells grown in the laboratory. The initial cells for the rice project were taken from mature seeds and immature embryos. While being cultured as undifferentiated cells in the laboratory, the cells may mutate spontaneously. More than 200 plants have been regenerated from tissue culture of L202. Some of these were grown in the field in 1985.

More than 700 plants were regenerated from anther culture last year. Most of these were haploid plants (half the normal set of chromosomes). About 12 percent had the normal complement of chromosomes. This technique may shorten the variety development cycle by 2 or 3 years.

Searching for Asexual Seed Production

(Supported by the Rockefeller Foundation, except for use of land at the Rice Research Facility)

Asexual seed production, called apomixis, occurs in some plant species (Kentucky bluegrass and pearl millet are examples). If it could be found or induced in rice by advanced biotechnology methods, apomixis would offer the possibility of economically capturing the yield increases of hybrids.

Four approaches are being used or considered to produce an apomictic rice: 1) screening the world collection of rice for natural occurrence of apomixis, 2) looking or apomixis in weedy relatives of rice, 3) intergeneric hybridization between apomictic grasses and rice, and 4) transfer of genes for apomixis from forage grasses to rice by highly specialized techniques in biotechnology.

This is a "high risk" project which, if successful, could revolutionize world rice breeding.