Dao Viet Bac  Postdoctoral Fellow, Department of Agronomy and Range Science, UC Davis

• Genetic resources - Maintenance of a diverse collection of commercial rice varieties and wild species; importation of useful new germplasm and the introduction of useful traits into California varieties.
• Identification of useful genes - Use of DNA markers to "tag" important genes conferring stem rot resistance, submergence tolerance, seedling vigor, cold tolerance and rice water weevil tolerance.
• Hybrid rice production - Development of the genetic mechanisms necessary for commercial hybrid rice production.

Significant developments from 1996 research - including notable efforts to sleuth genes conferring stem rot resistance - are summarized below.

Genetic Resources

To ensure future progress from plant breeding, a supply of useful genetic diversity is essential. Backcrossing is one of the techniques researchers use to tap useful traits from exotic species into well-adapted. Geneticists finished the backcrossing phase of a project to introduce genes from the wild species Oryza nivara into California cultivars. They also report an additional, significant cross with Oryza glumaepatula, a source of traits related to outcrossing.

Backcrossing, combined with the use of DNA markers to "tag" useful genes, is proving a powerful method to identify and transfer genes controlling a variety of agronomic characteristics. Researchers evaluated 117 previously tagged specimens to assess factors affecting their adaptation to temperate climates, including cold tolerance at seedling stage, panicle exsertion, and threshability.

Progress in Hunt for Stem Rot Resistance

Significant progress has been made in attempts to identify stem rot resistance. An effective level of stem rot resistance had previously been introduced from 0. rufipogon but has proven difficult to transfer into improved medium grains. Part of the difficulty is that resistance appears to be derived from several different rice genes.

In 1996 geneticists identified several different molecular markers associated with stem rot resistance inherited from the experimental cultivar 87-Y-550, which derives its tolerance from the wild species 0. rufipogon. With the identification of markers that appear to be linked to stem rot resistance, researchers say this improves the chances for making a successful transfer into California medium grains.

Last year these scientists reported the discovery of the gene that controls submergence tolerance in rice. The ability of this gene to imbue progeny with an ability to withstand submergence is "dramatic"-complete submergence for up to 16 days. Geneticists are refining their methods for transferring the gene and are backcrossing it into M-202. Seed increase at the Hawaii nursery was scheduled for winter 1996-97, with the best lines available for field testing in California during 1997.

Work is also in progress to map genes related to cold tolerance at booting stage, resistance to rice water weevil and seedling vigor.

Optimism on Hybrid Rice

Geneticists note exciting international developments in the production of hybrid rice bode well for similar prospects in California. India, which recently announced the release of 14 new hybrid cultivars, expects to have 5 million acres under cultivation by the year 2000. A Japanese company has developed high-yielding japonica hybrids with superior grain quality. And significant progress has also been made in developing hybrids for the southern U.S.

Geneticists believe these developments indicate that the barriers to the development of hybrid rice in California may not be as formidable as once thought. Their work continues to concentrate on development of the necessary genetic tools for hybrid seed production in California rice - restorer genes, wide compatibility trait, and photoperiod-sensitive genetic male sterility.