|Rice Breeding Program-93
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
Jeffery J. Oster, plant pathologist
|The 1993 season was another good year for California rice
growers Statewide yields matched the previous years record-setting level of 8,300
pounds per acre. The number of fields in production took a dramatic leap from 370,000
acres in 1992 to 437,000 acres last year. Much of what enables Californias rice
growers to sustain this high level of production is the result of a quarter century of
research into improved public rice varieties developed by the staff of the Rice Experiment
Station. The following narrative summarizes the highlights of 1993 research
Plant breeders made 735 new crows for varietal improvement, bringing the total since the program began in 1969 to just under 20,000. About 60 acres of the Rice Experiment Station at Biggs were devoted to nurseries in 1993. F, populations from 1992 crosses were grown in precision-drilled plots on about 12 acres. Approximately 60,000 progeny rows were grown for selection, purification and generation advance. The nurseries contained about 4,100 small plots and 2,500 large plots in various water-seeded yield tests. Thirty- one experimental lines were headrowed for seed increase and purification and five advanced lines were grown in small breeder seed increases. Breeder seed for the foundation seed program was also produced for several current varieties.
The cold tolerance nursery at UC Davis contained two acres of precision-drilled F2populafions and 5,000 dry- seeded progeny rows. The San Joaquin county cold tolerance nursery consisted of 13 acres of precision drill- seeded F2 populations and three acres containing just over 8,300 dry-seeded progeny rows. The cold tolerance nurseries are essential for developing blanking resistance. Approximately 300,000 panicles were selected from the various F2 populations in these nurseries.
Last year we reported on the devastating impact of Hurricane Iniki and other torrential rains on the winter nursery on the island of Kauai, Hawaii. This nursery, which allows breeders to speed up variety development by taking advantage of an "extra" growing season, suffered major damage to buildings and equipment. Late in 1993 the University of Hawaii announced its intention to rebuild the Kauai Branch Research Station where the nursery is located. More than 5,000 progeny rows were grown there last winter and will be seeded into RES nurseries in 1994.
Breeding research continues to incorporate genetically diverse materials into the breeding program. introduction of new traits and maintenance of a broad germplasm base reduces the risk of genetic vulnerability of California varieties.
Plant breeders obtain new materials from cooperating programs, germplasm exchanges and other rice collections. Many new varieties and germplasm lines have been received in exchanges with scientists from Japan, Korea and the International Rice Research Institute and brought through quarantine for use at the RES. In 1993 the RES grew and evaluated 200 entries from Southern U.S. public rice breeding programs. Induced mutation, which was used to develop the premium quality medium grains M401 and M-203, continues to be used on a limited basis.
Preliminary yield tests are the initial step of large plot testing for experimental lines. These tests included 532 entries and check varieties last year. Top experimental lines compared well with the highest yielding standard variety. Agronomic and quality information will be combined with cold tolerance and disease screening information to identify superior entries for further testing and advancement into the statewide yield tests.
RES researchers in collaboration with scientists from UG Cooperative Extension study the agronomic performance of current varieties and advanced selections in statewide yield tests. New entries that performed well during 1993 will be further evaluated during 1994. More details on this work is in the "Variety Trials" section of this report.
The main effort of long grain breeding research is to develop new varieties that have the cooking qualities of Southern long grains yet produce well under California conditions. one of the biggest obstacles plant breeders are encountering is that promising new lines with those cooking characteristics typically do not yield as well as the current public rice varieties L-202 and L-203. However, one entry (92-Y-93) in the 1993 yield tests showed promising yield potential and milling test results. This line will be tested in 1994.
Development of long grains with higher yield potential - regardless of quality characteristics - is also part of an ongoing effort. One entry to be used as a parent for improving yield potential was derived from a cross with a high-yielding introduction from China called "Qui-zhaw."
The medium grain component of the rice breeding program continues to focus on high yield potential, seedling vigor, improved milling yields and resistance to lodging, disease and blanking.
There are increased efforts to add seedling vigor from the Hungarian plant introductions M- 16 and Italica livorno to California medium grains. The genetic base of medium grains is being broadened by hybridization of California long grains and by promising plant introductions.
RES scientists are also emphasizing improved head and total milled rice yields in future varieties. Advanced experimentals were evaluated for head and total milled rice; 18 experimental entries showed improved head and tow milled rice yields over M-201 and 10 of them had higher milling yields than M-202.
Researchers also report that efforts to select for earlier maturity, improved lodging resistance, seedling vigor, and milling yield are effective.
Although the market for short grains has declined and acreage devoted to short grains has decreased, development of short grains with improved yield potential, resistance to lodging, milling yields and quality is a major objective of the breeding program.
Researchers report that 89-Y- 103, an early maturing short- grain experimental line has very high yield potential. In fact, it was the leading advanced entry - about 1 1,000 pounds/acre - in both the early and very early statewide yield tests. However, due to unfavorable results on its grain quality, work on this experimental will be discontinued to make room for testing new selections.
Another very early experimental short grain, 91-Y-171, also yielded well and has shown high milling yields. It will be tested further and seed will be increased in 1994.
Premium prices received by growers, strong demand by consumers and the market success of varieties such as M-401 and Kokuhorose, as well as the likelihood that the Japanese rice market will now open, are the main reasons why interest in premium quality rice remains strong. Premium quality medium grains have unique cooking characteristics - glossy after cooking, sticky with smooth texture, remains soft after cooling, and aroma and taste - that are preferred by Korean and Japanese consumers.
Major challenges exist in identifying and screening experimental lines for cooking and taste characteristics in lines with the needed straw strength, milling yield and high, stable yields. Cooking tests currently serve as the only screening tool available. Unfortunately, it is "quite common" for premium types that perform well in cooking tests to possess agronomic weaknesses and perform poorly in yield tests. Scientists are examining several laboratory tests to aid in their evaluations and hasten progress in this important area of research.
Special Purpose Types
A number of small, very specialized markets exist for rice with unique characteristics. breeders are working on specialty long-grains that include aromatic, soft-cooking and waxy type varieties. Special emphasis is on the traditional Basmati type - aromatic varieties with extreme kernel elongation after cooking. Work is also continuing to improve the agronomic and quality characteristics of other specialty ", including short-grain waxy or "mochi" varieties like Calmochi-101. Crosses have also been made to a number of new waxy germplasm introductions. Breeding for large-seeded types similar to the Italian "Arborio type" is included in the special purpose breeding program.
Kernel size, shape, breakage and translucency are the grain quality characteristics that plant breeders evaluate from initial crosses until an experimental line is released as a new variety. Only 20 percent of the 90,000 panicles evaluated by a visual screening procedure each winter are seeded into nurseries and evaluated for agronomic characteristics. Milling yield is a particularly important yet difficult quality to improve. Researchers conducted 31 milling tests at a range of harvest moistures in 1993.
One of the most important measures of cooking, processing and taste characteristics are the physicochemical tests conducted as a service by the USDA-ARS Rice Quality Research Laboratory in Beaumont, Texas. More-than 2,000 milled long-grain samples were evaluated for RES by the tab during 1993. Such tests, which give amylose content and alkali spreading values, are not routinely conducted on medium grains. RES plant breeders are concerned whether this evaluation service will continue.
With the increasing emphasis on rice quality, the RES breeding program is incorporating new techniques and laboratory equipment to help in quality evaluation of breeding lines. In 1993 a Rapid Visco Analyzer (RVA) was purchased with a donation from the Rice Research Trust. This laboratory instrument is used to determine starch pasting properties. More than 1,800 samples were evaluated in 1993. In 1994 plant breeders will evaluate about 6,500 long-grain samples. The RVA is also being used to evaluate waxy and premium quality breeding lines.
A near-infrared (NIR) scanning spectrophotometer, which offers researchers a rapid method of chemical analysis of factors such as amylose content, is being purchased and installed for 1994.
Plant breeders work in tandem with the RES plant pathologist on what continues to be a long, difficult challenge: improved resistance to stem rot. During 1993 researchers screened 1,900 rows of advanced experimentals in the statewide and preliminary yield tests for stem rot resistance.
Forty-two new crosses were made to transfer disease resistance derived from Oryza rufipogon to adapted California varieties. Since several backcrosses have already been made, emphasis now is on evaluation. The disease nursery consisted of 6,650 water-seeded rows. Evaluations were also conducted on 4,000 greenhouse plants. Only a very small percentage of the lines screened showed better levels of stem rot resistance than M-201. A cooperative study with the International Rice Research Institute (IRRI) in the Philippines continues. IRRI has made crosses between the highly resistant Oryza officinalis and M- 202. Scientists have also found that other wild species are highly resistant to stem, rot. IRRI has also found that certain other wild species are highly resistant to sheath blight, a possible source of resistance to aggregate sheath spot. The wild species will be processed through quarantine in 1994 and evaluated under California conditions.
Efforts to identify stern rot resistant fines with good agronomic characteristics has been, in a word, "frustrating." But plant breeders hope that a new cooperative project with the USDA geneticist at UC Davis may improve their ability to identify and select stem rot resistant lines. Molecular genetics techniques are being used to identify and map stem rot resistance genes. A stem rot resistant line, 87-Y-550, is a high yielding long-grain that was released as germplasm in 1993. It was not released as a variety because of other deficiencies.
The impact of fertilization on disease incidence was also studied last year. Researchers found that the incidence of both stem rot and aggregate sheath spot increased with increasing nitrogen levels, although those increases were small. Stem rot severity decreased slightly with increasing potassium levels (across all nitrogen rates), but aggregate sheath spot increased slightly. Researchers also determined nitrogen rates appear to have a greater influence on stem rot severity than variety. In contrast, however, nitrogen rates had less influence on aggregate sheath spot than did certain varieties.
California varieties currently have good levels of seedling vigor but plant breeders are, nonetheless, attempting to find new sources of even higher seedling vigor. This will improve stand establishment help compete against weeds and fight disease. As mentioned previously, scientists are continuing their efforts to incorporate more seedling vigor into California varieties from the Hungarian varieties M- 16 and Italica livorno. Incubator tests were used to screen 30,000 seedlings in 1993 involving backcrosses from the two varieties. Approximately 1,500 seedlings were selected and transplanted to the field for further evaluation. Advanced generation selections from M-16-derived backcrosses appear to have high seedling vigor, short stature, improved grain quality and yield potential, and better stem rot resistance.
Rice Water Weevil
The germplasm line showing resistance to rice water weevil (RWW) is PI 506230. Although blanking is a problem with this material, researchers are attempting to select out this and other agronomic deficiencies from offspring in order to take advantage of its RWW resistance.