Zhongmeng Bao, Post-graduate Researcher, Department of Agronomy and Range Science, UC Davis

Troy Thorup, Lab Assistant, Department of Agronomy and Range Science, UC Davis

• To build and maintain a diverse set of rice varieties and wild species, including germplasm imported from other countries.
• To identify useful genes with DNA markers that show the chromosomal locations.
• To develop the genetic mechanisms necessary for the commercial production of hybrid rice.

Genetic Resources

Geneticists greatly expanded their efforts to introduce germplasm into breeding nurseries. About 250 new introductions from the U.S. germplasm collection were grown and evaluated at Davis during 1995. More than 100 germplasm accessions from a previous study on genetic diversity in japonica rice were also grown. Geneticists also grew rice varieties from the South; made backcrosses to introduce new genes into M-202; and grew out 1,900 pedigree lines and 14 F₂. populations.

These scientists also report significant progress in the 'fingerprinting' of California rice cultivars with an advanced molecular technique utilizing RAPD (random amplified polymorphic DNA). Geneticists are investigating the application of two relatively new types of genetic markers used to study japonica rice. Genetic markers are easily detectable genes that help researchers identify the location of other agronomically important genes.

The first type, termed AFLP (amplified fragment length polymorphism), are abundant in rice and randomly distributed throughout the rice genome. These should be promising markers for tagging genes useful in rice breeding.

Microsatellite markers, the second type, differ from AFLP in that only a single marker or locus is examined at a time. The main limitation currently is that very few of these markers have been mapped and it is expensive and time consuming to identify the large number of loci needed for gene mapping. Nonetheless, geneticists believe that when enough of them have been identified, they will be valuable tools for gene tagging in japonica rice cultivars.

Useful Genes

Researchers report progress in the identification of seedling vigor-related traits from the japonica cultivar Italica livorno. This included a shoot length trait that appears to be an important characteristic of seedling vigor.

If deep water is used as a method of weed control near seeding, submergence tolerance will become increasingly important. Strong sources of submergence tolerance have been identified in indica rice cultivars. Geneticists are making crosses to transfer this gene into M-202.

Plant breeders from the Rice Experiment Station supplied geneticists with new crosses to screen for stem rot resistance. They are increasing their use of RAPD and AFLP techniques to identify loci that may confer stem rot resistance but have not identified any as of yet.

Researchers also continue attempts to identify cold tolerance but report inconsistent results from last year's experiments. A population for the study of water weevil tolerance is being advanced and will be ready for screening within two years.

Hybrid Rice

Researchers have developed lines containing the cytoplasmic male sterility (CMS) necessary for hybird rice production. The main limitation to exploiting these lines is lack of restorer genes in japonica rice. Researchers are attempting to intro- duce restorer genes from an indica cultivar.

In order to obtain fertile hybrids from indica-japonica crosses, geneticists are attempting to transfer the wide compatibility gene into California medium grain cultivars. This work is described in more detail in the report on marker- assisted breeding.

Photoperiod-sensitive genetic male sterility (PGMS) is another mechanism through which hybrid rice production could become a cost- effective reality. Researchers characterized a number of new male sterile mutants and some appear to be promising candidates. They report that selection of spontaneous male sterile mutants from growers' fields is an effective method of isolating new sources of sterility.