California's rice breeding program at the Rice Experiment Station, Biggs, was enlarged after the California Rice Marketing Order was approved in 1969. Increased funds made possible through grower assessments permitted enlargement of the breeding staff to a team of three full-time rice breeders. The expanded budget provided for support personnel and facilities to accommodate the expanded and accelerated breeding efforts. A plant pathologist was added to the team in 1980.

In 1969, California's rice production was based on two short grain varieties (Colusa and Caloro) and a single medium grain variety (Calrose) along with a very limited production of privately developed varieties. During the last 16 years, 17 new and improved publicly developed varieties have been released and grown. Rice growers now have a choice of growing short, medium, and long grain varieties as well as a sweet or mochi variety.

Among the medium grains are varieties with very early, early, intermediate and late maturity. All are shortstatured. A short-statured variety is less than 38 inches tall at average soil fertility. The shorter and stronger straw has reduced lodging, increased yields, and has made harvesting easier. Less straw per acre also has reduced particulate emissions associated with burning.

Figure 1 shows the release year of all publicly developed California varieties since 1917 and the production of certified seed from 1974 through 1983.

Figure 1: Release year and certified seed production of publicly developed California rice varieties

The market, including relative demand for different rices, and rice growers ultimately determine the success of a new variety. An indicator of variety acceptance is the amount of foundation, registered, and certified seed produced. The rise and decline of seed production also is influenced by the release of new varieties. For example, S6 replaced Colusa and Caloro. S-201, in turn, replaced S6. Similarly, M-201 is replacing much acreage previously seeded to M9. None of the varieties released before 1976 are still produced. Late maturing varieties that require about 110 days to 50 percent heading are being replaced by earlier maturing varieties despite reduced milling yields for the earlier maturing varieties. This shift was accentuated by the wet springs that delayed seeding in 1982 and 1983.

California yields increase

Rice yields statewide were generally stable during the 10-year period from 1966 to 1975, averaging 5,451 pounds per acre. Concurrent with the release and adoption of new short-stature varieties, the statewide average yields increased (Figure 2). The three-year average for 1981 to 1983 was 26 percent above the 10-year average from 1966 to 1975. New experimental lines promise further substantial yield increases.

Figure 3 compares California state average yields with those of the other rice-growing states.

California is relatively free of serious disease and insect pests compared with other rice growing areas. However, diseases and insect pests do detract from yields in some fields every year. The rice breeding program includes efforts to increase tolerance to the rice water weevil and to reduce susceptibility to stem rot and sheath blight diseases.

Other breeding objectives include good seedling vigor, reduced height, lodging resistance, tolerance to low temperatures and herbicides, and good quality. Quality indicators are grain shape, translucency of kernels, amylose content, gelatinization temperature of the starch, head rice yield and cooking character. Increased emphasis has recently been given to milling quality.

Breeding techniques vary

Combining all the desired heritable characteristics into a new rice variety is tedious and time consuming. The plant breeding team uses a combination of breeding techniques. Most of the varieties were developed through hybridization followed by selection. M5 was a natural mutation. Calrose 76 (by USDA), Calmochi-201 and M401 were mutations induced by cobalt radiation. (Only a few acres of Calmochi-201 were grown, and the variety was discontinued in favor of a more promising line later released as Calmochi-202). The popular medium grain varieties M9 and M-201 were developed by introgressive hybridization which entailed the transfer of the short stature gene from an indica tropical variety into a japonica background.

Figure 4. Rice Experiment Station rice breeders S.T. Tseng, C.W. Johnson, and H. L. Carnahan examine experimental lines of rice in a county yield plot.

The new long grain variety, L-202, is a major rice breeding achievement. It took many steps to convert the indica subspecies adapted to the subtropics to a high yielding, cold tolerant variety adapted to our climate that still retained satisfactory milling and long grain cooking quality.

New methods help

Recognizing the importance of numbers in plant breeding, the rice breeders have mechanized where possible and have modified procedures to enhance accuracy and increase efficiency. Using two seeding dates for yield trials at the Rice Experiment Station provides an economical way to sample environments and their effects on yield performance. Techniques developed for efficient screening of breeding materials include:

• a controlled environment facility to screen large numbers of selections for blanking at cool temperatures,
• a rapid and efficient laboratory procedure for screening for tolerance to grass herbicides,
• an effective micro-sample cooking test to evaluate the cooking characteristics of thousands of long grain rices that otherwise possess the necessary physicochemical properties.

Special nurseries

Special nurseries help achieve certain objectives. For example, disease inoculum is added to the disease nurseries to insure disease development. The cold nursery in San Joaquin County aids in the classification and selection of blanking resistant materials that will help produce higher, more stable yields in the future varieties. The Hawaii winter nursery provides for rapid generation advance and some selection for cold tolerance.