TOOLS OF THE TRADE-One of the techniques geneticists use in their research to unlock the secrets of better rice varieties is anther culture, where "instant" pure lines are created in a petri dish.

Herbicide resistance

Progress in creating genetic resistance to a specific herbicide (American Cynamid AC499) resulted after resistant mutants were selected from a mutagenized seed population. Mutants from a tissue culture process had failed to hold up under repeated testing, but the different approach produced selections that performed well over time. Backcrosses are being made to increase the tolerance. The researchers expect that their objective of selecting tolerant rice lines will be met within one more year.

Promising male-steriles

Male-sterile lines of rice were selected from among 28 mutants, each with male sterility carried as a single recessive gene. More than 300 crosses were made to determine whether the same or different genes carry male sterility in the different lines. The results indicated that at least 20 different genes are involved.

Tests of viability, female fertility and outcrossed seed-set rate indicated that two lines appear to be most useful: M-201 no-pollen ms and M-101 ms #2. Both lines are completely pollen-sterile with normal female fertility, and show high rates of natural outcrossing.. Both are now available to the plant breeders.

Hybrid rice possibilities

California's rice breeders are not as optimistic as the Chinese are about the potential of hybrid rice, but they are looking for genetic tools that might make hybridization more efficient. High-yielding hybrid rice is grown on 20 million acres in China, but the high cost of producing hybrid seeds has thus far made it impractical in the U.S.

Tests continued on one experimental rice variety with male sterility that apparently is controlled by day length. Normally fertile in Hawaii's 12-hour days, this line showed the typical recessive gene pattern of male sterility at Davis with 15-hour days. The tests also indicated that a second male-sterile line is environmentally sensitive, but temperature rather than day length may be the trigger. Both lines are undergoing further tests in Hawaii.

Another area of research into hybridization is apomixis, or asexual seed production. Apomixis is currently unknown in rice, but it conceivably could create first-generation rice hybrids that breed true and retain their hybrid vigor. During 1988:

• The geneticists studied four rice lines from China that show high frequency of twin seedlings. Results indicate that most of the twins originated from fertilized two-egg or multiple-egg nuclei. However, about 3 to 5 percent were "adventitious" embryos, which may indicate apomixis at a low frequency.
• Following up on reports from China, the researchers also attempted to cross rice with a pearl millet species that contains apomixis. More than 10,000 rice florets were pollinated, but no true hybrid seeds resulted.

Anther culture

Culture of rice anthers-growing new plants by "planting" anthers on agar-can produce "instant" pure lines. If used on first-generation crosses, it could reduce the time needed to develop a new variety by two to three years.

In 1988 an economic analysis of anther culture expanded to include second-generation anthers. These could accelerate the recombination process and also reduce the number of pure lines required to develop a new variety. The need for fewer lines could make the anther culture process even less expensive than conventional single-seed descent. Tests also indicated that anther culture may be useful in genetic analyses.

Other studies

Rice geneticists also:

• Studied four new recessive tall mutants designated "eui" (for "elongated uppermost internode"). All proved similar to the original type reported in 1981, even sharing the same gene for "eui."
• Studied transposable genetic elements ("jumping genes"), which could be useful for genetic engineering. Results of this extremely basic research, so far, are inconclusive.
• Studied aspects of genetic diversity in more than 500 rice varieties from throughout the world.