Rice Breeding Program-90




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Rice Experiment Station Scientists

D. Marlin Brandon, director and agronomist

Carl W. Johnson, plant breeder

Kent S. McKenzie, plant breeder

Shu-Ten Tseng, plant breeder

Jeffrey J. Oster, plant pathology


Shu-Ten Tseng, one of the Rice Experiment Station plant breeders, makes a point during the growers' annual field day at Biggs.


In the last 20 years, the plant breeders at the Rice Experiment Station have developed 25 public varieties that have greatly increased average yields and, consequently, grower returns. Approximately 97 percent of California rice acreage is seeded in varieties developed by the RES-92 percent medium grain, 3 percent long grain and 4 percent short grain. Last year's activities included 900 new crosses and 90,000 progeny rows grown at nurseries in Biggs, San Joaquin County, and Hawaii. Several thousand pots of plants were also grown in RES greenhouses. These are only the first steps in the plant breeding process. The breeding process involves selection, purification, generation advance, evaluation for seedling vigor, cold tolerance, disease reaction, grain quality, seed increase and seed maintenance.

More than 90 new foreign germplasm lines were introduced through quarantine. These new sources of germplasm will be used for varietal improvement by reducing the risk of genetic vulnerability of existing California rice varieties. Work is also continuing on material generated by mutation breeding and biotechnology techniques.

UC Cooperative Extension evaluated the agronomic performance and adaptability of 118 advanced selections in statewide yield tests (see section on variety trials). Preliminary Yield Tests at RES included 582 entries and check varieties.

Long-grain breeding continues to focus on the development of varieties adapted to California with the cooking characteristics of Southern long grains. An early-maturing, high-yielding long grain, 88-Y-774, with. cooking characteristics similar to `L-202' was released in 1991. More sophisticated cooking tests have also been developed.

Medium-grain breeding continues to incorporate important agronomic characteristics such as high yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to blanking. An early maturing medium grain, 88-Y-317, is scheduled for Foundation seed increase and further testing in 1991. Increased emphasis will be placed on identifying the characteristics necessary for improved milling yields.

Short-grain breeding efforts are geared toward correcting some of the deficiencies found in current varieties. Emphasis is on improving yield potential, resistance to lodging, and grain and milling quality. `S-301', an intermediate-maturing short grain, has given good experimental and field yield performance and high milling yields. Foundation seed was available in 1990 and 1991, but `S-301' is grown on only a small acreage. Its performance in the market is unknown.

A strong effort is being made to improve premium quality rices similar to M-401 and Japanese premiumquality short grains. However, problems have been encountered in combining the unique cooking and taste characteristics with desirable agronomic traits. Over 600 lines were evaluated in 1990 cooking tests. Koshihikari, a high quality Japanese short-grain variety, lodged completely in statewide yield tests, S "difficult" breeding challenge to overcome. Other developments in specialty rices include:

  • An anther culture project begun in 1990 is expected to increase in 1991.
  • Specialty long-grain, rice development continues as a small portion of the long-grain program.
  • Basmati rice varieties from India and Pakistan were used in the long-grain breeding program to incorporate fluffiness into adapted varieties.
  • Research into other specialty long grains include the aromatic basmati, jasmine and della types and rices with colored bran.
  • Efforts to develop high-protein lines with biotechnology have been hindered by poor agronomic performance.
  • Work is continuing on other specialty types, including waxy (mochi) varieties like `Calmochi-101' and large grain (arborio) type rices.

Selection for grain quality-translucency and kernel size, shape and resistance to breakage-remiins a critical part of the breeding program. Milling yield tests, physico-chemical tests and micro-cooking tests were conducted on several thousand lines to select for improved rice quality. Milling evaluations have been increased in medium and short grains, including analysis of 15 advanced experimental lines and commercial varieties over a range of harvest moistures.

Development of long grains suited for California conditions took another step forward this year with release of L-203

Efforts to incorporate disease resistance have been slow because sources of disease resistance have a wide range of undesirable characteristics. Nonetheless, intensified breeding efforts are required because of the importance of disease resistance:

  • Seventy-four crosses were made to transfer stem rot resistance derived from the wild species Oryza rufipogon to California adapted varieties.
  • Efforts to develop aggregate sheath spot resistance included 20 crosses to transfer resistance from a rice-grass hybrid and 39 crosses to transfer resistance derived from Oryza fatua.
  • Analysis of different stem rot isolates detected no races of the fungus and only minor specialization of variety response to the fungus.
  • Field studies examined the relationship between plant density in innoculated rows and stem rot severity. Optimum seeding rate for stem rot resistance screening was shown to be 1 gram of seed per 4-foot of row under water-seeded conditions.
  • A field test to see whether different combina tions of herbicides and nitrogen rates had different impacts on the incidence of stem rot was inconclusive.

Good seedling vigor enhances stand establishment, provides competition with early weed growth, may reduce severity of seedling diseases, and may permit the use of deeper water for weed suppression. Breeders continue to evaluate seedling vigor of foreign germplasm for breeding purposes. A Hungarian variety, Italica livorno, showed both high levels of seedling vigor and water mold resistance. Work is under way to incorporate these characteristics into adapted breeding materials.

An experimental line showing resistance to the rice water weevil did not perform well agronomically. PI 506230 is tall, lodges severely and is susceptible to blanking. Further agronomic improvements must be made while maintaining the high levels of RWW tolerance before this character can be incorporated into adapted varieties.

The experimental line 88-Y-774 was released this year as `L-203: It is a smooth, early maturing semidwarf long grain. Days to maturity is similar to `M-202' and 5-7 days less than L-202. Milling and cooking characteristics are also similar to L-202. This new variety also shows about a 10 percent yield advantage over L-202. The area of adaptation appears similar to M-202, thus permitting long grain production in areas where L-202 would mature too late.

Foundation seed increase is planned this year for 88-Y-317, a smooth, early maturing medium grain. Compared to M-202, it shows superior straw strength, higher and more stable yields, more stable head and milling yields, similar kernel size, shape and seed weight, similar blanking resistance and cooking quality similar to the Calrose market type.

A new set of about 10 of the most promising entries will undergo breeder seed increase this year. Outstanding performers are then in a position for Foundation seed production in 1992.

Results of a three-year study indicate that nitrogen fertilizer efficiency is greater in fields treated with Londax® than in those treated with Basagran® or MCPA. This greater efficiency is attributed to the virtual elimination of broadleaf and sedge weed competition with Londax®. Consequently, growers are advised to reduce nitrogen rates by 20 to 30 pounds per acre in those fields where Londax® is used for broadleaf weed control in water-seeded rice.

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