|Rice Breeding Program-91
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
California rice growers produce some of the highest grain yields in the
world. The statewide average yield on the 325,000 acres of rice grown in
1991 was more than 7,800 pounds per acre.
Much of this high productivity can be attributed to the improved public varieties developed by the Rice Experiment Station. Breeding objectives such as improved grain quality, cold tolerance, and yield remain high priorities. Development of improved rice varieties presents continuing challenges.
The California rice industry is undergoing considerable change in response to environmental regulation and grain quality requirements. Increased emphasis is being placed on seedling vigor, disease resistance and plant type because of pesticide regulation and the phasedown of rice straw burning. Development of premium quality and specialty rices - such as M-401, Southern long-grain types, aromatic types etc. is being emphasized because of marketing trends and in anticipation of new rice markets. This section of the annual report highlights the major activities of RES during 1991.
General Research Activities
Last year's activities included 837 new crosses and 80,000 progeny rows grown in nurseries at the RES facility, San Joaquin County, UC Davis and Hawaii. These are the first steps in selection, purification, generation advance, evaluation for seedling vigor, cold tolerance, disease reaction, grain quality, seed increase and seed maintenance. Several thousand pots of plants were grown in the greenhouse to screen for disease resistance and cold tolerance and for use in crossing and generation advance.
More than 20 new foreign germplasm lines to be used for varietal improvement were introduced through an approved quarantine procedure conducted by the pathologist at RES. Considerable effort is being made to incorporate genetically diverse material into California rice to reduce the risk of genetic vulnerability. The plant introduction permit issued to the RES pathologist in 1988 has dramatically increased the introduction of foreign germplasm. Previously it had taken years to get new material from foreign sources. Researchers are also using induced mutation on a limited scale to improve California rice. This technique helped to develop the premium quality medium grain varieties M-401 and M-203. An early maturing mutant of S-301 is scheduled for yield testing this year.
UC Cooperative Extension conducts agronomic performance and adaptability testing of advanced experimental lines in yield tests at several locations throughout rice growing areas. This is an essential activity to identify superior lines that may become new varieties. Preliminary yield tests at RES included 503 entries and check varieties. (See section on variety trials for more detailed information on test results.)
Long Grain Breeding
The major focus in long-grain breeding continues to be development of well adapted California varieties with Southern U.S. long-grain cooking characteristics. RES scientists are using more sophisticated cooking quality testing techniques, including tests for amylose content and alkali spreading, and starch pasting characteristics.
Advanced long-grain lines with "Newrex quality" are under evaluation. Incorporation of Newrex cooking characteristics into agronomically adapted long grains is an important objective. This quality type has distinct flour pasting characteristics and produces superior parboiling and canning products, as well as table rice.
Several promising long-grain entries performed better than either L-202 or L-203 in 1991 yield tests. These experimentals will be evaluated for possible special use or be used as parents in crosses with lines that have improved cooking characteristics.
Medium Grain Breeding
The medium-grain breeding program emphasizes incorporation of important agronomic characteristics such as high yield potential and seedling vigor, and resistance to lodging, and diseases into California varieties and blanking. Breeding activities directed toward grain quality, lodging resistance and incorporation of more exotic germplasm have also increased. A new medium grain, M-204, will be released to growers this year.
Short Grain Breeding
Improved yield potential, resistance to lodging, and improved grain and milling characteristics were the main focus of the short-grain breeding effort. California short grains have typically not performed as well as California medium grains. Also, short-grain markets have declined in recent years. The combination of these two factors has led to a decline in the already relatively small short-grain acreage.
However, RES plant breeders will continue to focus on developing productive short grains with good kernel characteristics and milling yields. Emphasis includes improvements in yield potential, lodging resistance, cold tolerance and grain and milling quality.
One experimental line, 89-Y-103, produced high yields at RES and other locations, and will undergo more extensive milling and yield tests in 1992.
Premium Quality Breeding
Premium prices for M-401 (public) and Kokuhorose (proprietary) varieties and the potential opening of the Japanese rice market have generated much interest in producing more California-grown premium quality rice. The premium quality medium grains are preferred by certain ethnic groups. RES researchers note that combining the desirable cooking quality of successful premium quality rice with good agronomic characteristics has :proven to be a difficult breeding challenge. The first short-grain entries selected from the premium quality crosses have reached the yield testing stage and many more will be forthcoming.
Because of the difficulty and rime required to develop these premium quality varieties, extensive field testing and quality evaluation of the Japanese premium quality varieties Koshihikari and Akitakomachi were conducted in 1990 and 1991 to determine their adaptation and commercial potential for California. Results of agronomic performance tests showed the yield potential of these varieties is significantly below the California premium quality medium-grain varieties M-401 and M-203.
Specialty Rices Breeding
A wide diversity of grain types and cooking quality exists in special purpose rice suitable for a number of small markets that require special varieties with unique characteristics. This work is performed as an adjunct to the total breeding program. In the area of aromatic long-grain rice, RES researchers emphasized development of traditional "basmati" (scented with extreme elongation of grains after cooking) and "Della" types (similar to traditional long-grain with characteristic scent). Work on other specialty types, including waxy (mochi) varieties like Calmochi-101, continues with efforts to improve agronomic and quality characteristics.
Screening and evaluating breeding material for grain quality is a primary part of the rice breeding program. Kernel size, shape, breakage and translucency are the physical characteristics used to select approximately 90,000 panicles each year.
Milling yield, physico-chemical tests and micro-cooking tests were conducted on several thousand long-grain lines to select for improved rice quality. Milling evaluations have been increased in medium and short grains. Milling yield determinations over a range of harvest moistures were performed on 35 advanced experimental lines and commercial varieties.
Improving disease resistance in California rice requires intense selection for important agronomic traits because sources of resistance to stem rot and aggregate sheath spot (AS) diseases have a wide range of undesirable characteristics. Progress has been slow and difficult but an increased breeding effort is being made to transfer resistance into California rites.
Efforts continue to transfer disease resistance from the wild species Oryza rufipogon to adapted California varieties. A cooperative project has been established with a plant pathologist at IRRI to make crosses between the highly resistant Oryza officinalis and M-202, and then backcross to produce fertile plants. Offspring from these crosses will eventually be returned to RES for quarantine introduction and screening. In 1991 an additional nine crosses were made to transfer AS resistance from Oryza fatua into adapted California materials.
UC Davis researchers report that bordered sheath spot seems to be spreading, and that it is more virulent in greenhouse tests than AS. Tests will continue in 1992 to compare varietal resistance to both AS and bordered sheath spot. An encapsulation technique has been adopted for production of bordered sheath spot inoculum for use in disease screening.
Good levels of seedling vigor enhance stand establishment, provide competition with early weed growth, may reduce the adverse effect of seedling disease, and may permit the use of deeper water during stand establishment for weed suppression.
Plant breeders made 23 crosses to incorporate good seedling vigor, as well as water mold resistance, from a Hungarian variety, "Italica livorno" into adapted breeding material. Of these, approximately 600 seedlings were selected and transplanted to the field for further screening for maturity and height. The advanced generation selections appear to have high vigor, short stature, and improved lodging resistance.
Water Weevil Tolerance
Crossing, selection and screening activities are also continuing to transfer rice water weevil tolerance to adapted California varieties. However, plant breeders note that blanking is a major problem with much of the breeding material used to tap into RWW tolerance. Sources of tolerance also tend to be leafy, of intermediate height and susceptible to lodging. Breeders are selecting against these undesirable traits.
New Medium-Grain Variety
The newest addition to the family of improved public varieties is the experimental line 88-Y-317, which was released to California rice growers during the 1992 season as M-2Q4. This variety is a smooth, early maturing semidwarf medium-grain rice with seed size, shape, weight and cooking quality similar to M-201 and M-202. It is similar to IVh201 and M-202 in maturity and has lodging resistance similar to M-201. The new variety, also appears to produce higher and more stable grain and milling yields than M-~1 and M-202. Seed of M-204 should be widely available in 1993-94.