|Rice Breeding Program-03
Rice Experiment Station Scientists
Kent S. McKenzie,director
Farman Jodari, plant breeder, long grains
Carl W. Johnson, plant breeder, Calrose medium grain
Jeffry J. Oster, plant pathologist
California rice acreage and yield both declined in 2003. An estimated 507,000 acres of rice was grown last year, about 90 percent of it seeded with varieties developed at the Rice Experiment Station (RES) near Biggs. This compares with 540,000 acres grown in 2002. Statewide yields dropped to 7,620 pounds/acre, down from 8,200 pounds/acre more typical of previous seasons. The drop reflects planting delays caused by extensive wet weather in spring 2003.
Seed production and maintenance
The California public rice breeding program has now developed 37 improved varieties since accelerated research began in 1969. Foundation seed for 15 public varieties and basic seed for two Japanese premium quality varieties were produced on 174 acres at RES in 2003.
Breeding nurseries report
Late spring rain delayed planting of the 2003 rice breeding nursery until May 26th (compared to May 3rd in 2002). Water seeding and drill seeding of all the nurseries was completed in just five days, by May 31st. Stand establishment was good; however, high temperatures in July created a lodging problem. Milling yields were very high - something many growers noticed as well.
New crosses made in 2003 jumped significantly to 1,096, bringing the total since 1969 to 29,065. The 2003 breeding nursery occupied approximately 72 acres. Water-seeded yield tests included 3,716 small plots and 3,064 large plots. Small seed-increase plots and cooking samples were grown on three acres and included 55 advanced breeding lines. Twenty-nine experimental lines (2,770 headrows) were grown for seed increase, quality evaluations and purification. The nursery included about 60,620 water-seeded progeny rows. Selections were made from 10,000 of these rows.
Second generation (F2) populations from 2001 and 2002 crosses were grown in precision drill-seeded plots on 15 acres. An estimated 200,000 panicles were selected from these for further screening and advancement. Headrows of M-103, M-104, Calmochi-101, Calmati-201 and headrows for two experimental lines were grown for breeder seed production in 2003.
Work is continuing on a new winter nursery in Hawaii, a valuable resource that accelerates the breeding process. A new site was located in September 2001 after the University of Hawaii terminated its arrangement with the California rice industry. The past three seasons have focused on design, formation, preparation, seeding, and weed control at a new site. In the summer of 2002 a second new site was prepared and planted with 7,210 rows November 2-5. First generation lines were seeded for transplanting and an additional 460 rows were simultaneously seeded in flats. They were transplanted to the field December 3-5, 2002. Harvest of approximately 7,500 selections was completed in April 2003. Cool weather ensued during heading, which caused a very high level of blanking. The 2003-2004 site was seeded November 8-10 with 7,080 progeny, 500 transplanted F1 rows and 500 rows for the USDA-ARS geneticist. The winter nursery site is being monitored remotely with digital photographs and consultations with winter nursery staff. A successful harvest was completed by RES staff and advancing lines returned to RES for planting in summer 2004.
The 2003 cold tolerance nursery at UC Davis contained three acres of precision drill-seeded F2 populations and 10,000 dry-seeded progeny rows. Nursery management is now under the successful direction of Dr. Thomas Tai, the new USDA-ARS geneticist based at UC Davis. Blanking in the breeding rows and F2 populations was moderate, allowing for effective panicle selection. A new cold tolerance nursery in San Joaquin County was planted in cooperation with two local rice growers. The four-acre, drill-seeded nursery included 9,000 rows and 3.6 acres of F2 populations. Blanking was light to moderate but this location appears nonetheless to be a very suitable location to identify highly cold-tolerant material. Cold tolerance nurseries, in conjunction with two refrigerated greenhouse at RES, are essential for selecting resistance to blanking. In the past they've given rise to successful varieties such as Calmochi-101, M-103, S-102, M-104 and M-206.
Statewide yield tests
Statewide yield tests are conducted in grower fields each year to evaluate promising advanced selections from all three maturity groups. Conducted at eight locations in 2003, entries that perform well are advanced for further testing. More detail is reported in the variety trials section of this annual report.
Preliminary yield tests are the initial step of replicated large plot testing for experimental lines. These tests included 671 entries and check varieties in 2003. Superior entries were advanced to the 2004 statewide yield tests.
The long-grain breeding project continues its research and breeding efforts to develop superior long-grain varieties on four major quality types - conventional, Newrex, Jasmine and Basmati. Milling and cooking quality improvements of conventional long-grain and specialty types are a major aim of this program.
In the conventional long grain area, efforts continue to improve upon the starch characteristics of L-204 to more closely approximate those of Southern long grains. Improvements in milling quality, cold tolerance and cooking quality are also being sought. DNA marker technology is being used on a limited basis for identifying genes that confer improved starch characteristics in conventional and Rexmont-type long grains.
During the 2003 season, a total of 127 advanced conventional long-grain selections were tested in statewide and preliminary yield tests. Overall yields were lower than expected because of the late spring planting and mild weather the latter half of the season. Several experimental lines yielded significantly higher than L-204. Milling yields were high, something attributed to mild temperatures during grain filling. Two high-yielding entries - 99-Y-469 and 99-Y-041 - were headrowed last year, an important step on the road to varietal development. Cooking quality tests of both lines show a significant improvement over L-204. Experimental 01-Y-502 is a promising stem rot-resistant line with high yield potential.
Newrex is a special quality rice with high starch content that cooks dry with minimal solids loss and is thus a superior type for canned soups, parboiling and noodle making. L-205 has shown superior processing qualities along with excellent agronomic characteristics. Commercial production of this Newrex variety began in the 2000 season. Modifications in milling and storage procedures are expected to alleviate reported post-harvest milling yield reductions. This early maturing semidwarf variety is less susceptible to cold-induced blanking but may lodge with excessive nitrogen fertilization. Several experimentals yielded comparably to L-205.
Calmati-201, a true Basmati aromatic long grain released in 1999, is a variety well suited for the warmer growing regions in California. It is susceptible to cold-induced blanking and heavy fertilization should be avoided. In 2003 statewide yield tests it averaged 7,790 pounds/acre at RES and 7,340 pounds/acre off station. Basmati rice yields are inherently lower than standard varieties, even in their country of origin, primarily because of their small and slender kernels. A considerable number of new Basmati lines were evaluated in 2003 tests. Nine of them with improved cooking characteristics were advanced to statewide tests. Two experimentals - 02-Y-102 and 02-Y-720 - were purified in headrows. Increase blocks of 48 Basmati selections were grown for detailed evaluation and will be tested for yield performance in 2004.
Efforts also continued in 2003 to breed Jasmine types through pedigree and mutation breeding. Extreme photoperiod sensitivity has proven a significant obstacle. Irradiated mutants, a valuable germplasm source for further improvements, have been obtained and are being used in the crossing program.
A waxy long-grain line, 99-Y-494, has significantly outperformed L-204 and L-205 in statewide yield tests. Waxy lines are being used as donor parents in cold tolerance and yield improvement efforts.
Continued improvement in milling yield and milling stability of new long-grain varieties is another important breeding objective. One area of research is focusing on grain characteristics that lend milling yield stability to long grains under adverse weather conditions. This would permit a broader harvest window with sustained milling yields. Factors such as hull cover protection, grain formation or physiochemical properties that confer resistance to fissuring are being analyzed. Milling yield potential of 33 advanced long-grain lines from two maturity groups in statewide yield tests were evaluated in harvest moisture studies.
Stem rot resistance originating from Oryza rufipogon has been transferred to a number of high-yielding long grain lines. Eleven such entries were entered in statewide yield tests. One entry in particular, 01-Y-502, showed significant improvement for the third year in a row with low stem rot score, low blanking, early maturity and high yield potential. Other agronomic improvements are being pursued through crossing and backcrossing and in cooperation with the RES plant pathologist.
Efforts to develop blast-resistant long grains have yielded an encouraging performer in 00-Y-506. It is a cross between L-204 and the Southern variety Kaybonnet. Cooperative efforts are also continuing with USDA scientists in Texas and at UC Davis to develop genetic markers for blast resistance. A considerable number of early generation blast resistant lines were selected in 2003 and are currently being screened in greenhouse tests, as well as F2 and F3 lines at the Hawaii winter nursery and at the new San Joaquin cold tolerance nursery.
Premium quality is a broad term used to identify California varieties such as M-401 that have unique cooking characteristics preferred by Japanese, Korean and other ethnicities. This type of rice is typically glossy after cooking, sticky with a smooth texture and remains soft after cooling. Aroma and taste are also distinctive features. Developing high-yielding varieties of this type continues to be a challenge in California.
Intensified breeding efforts led to the creation of Calhikari-201 and M-402 in the late 1990s. The late start to the 2003 planting season hampered commercial production for premium quality varieties. Production of Calhikari-201 was estimated at 372 acres, while M-402 acreage was approximately 9,500 acres. Agronomic performance of Calhikari-201 continues to be superior to comparable Japanese varieties yet not as robust as M-202. Yields in statewide tests last year were 7,500 pounds/acre and 8,210 pounds/acre, respectively. Breeding efforts are targeting the new variety's susceptibility to stem rot and cool-temperature blanking.
Nearly a dozen other premium quality short grain experimental lines have been advanced in statewide testing. A parallel breeding effort seeks to improve premium quality medium grains for the M-401 market. Work is also continuing on conventional short grains such as S-102 to improve yield potential, disease resistance, and grain and milling characteristics. A number of experimental lines in all three areas performed well in statewide testing and are being advanced for further agronomic, cooking and laboratory analysis.
Incorporating resistance to blast and stem rot is an important objective for work in this class. Promising experimental lines are being advanced through statewide tests to screen for agronomic performance and milling yields. Initial reports are that the yield potential for blast-resistant lines is high and competitive with standard check varieties. However, improvements are needed in grain and milling quality and cold-induced blanking resistance. Pilot experiments are also under way with the USDA geneticist based at UC Davis and with the RES plant pathologist to determine the viability of marker-assisted selection for early generation blast resistance.
Stem rot resistance in short grain and premium quality lines is "challenging." Problems noted in statewide yield testing included poor seedling vigor, milling yield and grain quality.
Special purpose varieties often have unique or undefined cooking characteristics that make quality evaluation and selection difficult. Improvement of short-grain waxy types (i.e. mochi, glutinous or sweet rice) is focused on improved agronomic and quality characteristics. Four entries in statewide tests produced yields higher than Calmochi-101, one of them (00-Y-175) consistently over three years by more than 400 pounds/acre. Quality evaluations and marketing organization input are under way to determine the future of this line in the waxy breeding project. New lines and pedigrees, some from Japanese waxy varieties, are also being evaluated.
Breeding for bold grain types, similar to the Italian varieties like Arborio, continues with a few large-seeded experimental lines in the statewide yield tests. Agronomic performance thus far has been superior to Arborio but marketing organizations have shown only limited interest.
Amylose (starch) content is an important factor in the eating, cooking and processing quality of rice. A special project begun in 1999 is utilizing induced mutation technology to assist in the development of a low-amylose variety. Two such low-amylose experimental lines have undergone laboratory analysis both in California and Japan and are being field tested for agronomic performance. Overall, these lines have shown lower yield potential than Calhikari-201, as well as reduced grain weight and panicle size. Market demand and product feasibility will determine whether these lines are suitable for commercial production.
One of the additional project objectives is to transfer rice water weevil tolerance to California varieties. One medium grain entry and a donor parent developed at RES (PI 506230) were run through statewide yield tests. Early generation breeding lines were harvested from small plot tests and progeny rows for further testing. Another 400 selections were made from the RWW nursery for testing in 2004.
Calrose Medium Grains
Calrose medium grain breeding continues to focus on high-yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to cold temperature blanking. Efforts to incorporate blast resistance began in 1996. To reduce the risk of genetic vulnerability and to tap into new potential sources of blast resistance, 85 crosses were made with high-yielding Chinese introductions in 2003.
New variety released
M-206 was released to growers for registered seed production in 2003. A yield survey of 12 registered seed growers showed a broad range of harvest yield - 7,600 to 10,500 pounds/acre, with a mean of 9,100 pounds/acre. This new variety is a very early to early semidwarf, California glabrous, Calrose medium grain that heads four days earlier than M-202. It also shows improved lodging and blanking resistance, improved head rice yield and a small increase in seed size and weight. It is not blast resistant. Average whole grain milling yield of M-206 is higher than M-104 or M-202. Rice marketing organizations characterize M-206 as having cooking and taste characteristics similar to M-104 and M-202. It should prove a broadly adaptable variety - another alternative to M-202 and M-205 in both warm and cool production areas. In the coldest areas it becomes a full-season variety.
Other promising medium grain experimental entries are being examined. Harvest moisture values are one of the key factors under scrutiny, as well as lodging resistance, seedling vigor and milling yield. Increased emphasis has been placed on blast resistance, with the experimental line 00-Y-805 being the most promising and, pending yield and milling performance in 2004, may be released as the first blast-resistant Calrose medium grain.
Twenty-seven Calrose medium grain entries from 2003 yield tests are being grown in the Hawaii winter nursery for purification, seed increase and additional agronomic evaluation. Of maturities ranging from M-103 to M-205, these entries have high yield potential, superior lodging resistance and quality equal to or better than M-202.
Sources of blast resistance from RES, southern U.S. and foreign germplasm were crossed with California lines. Nearly half of the 360 Calrose crosses were blast related. Twenty-eight percent of 688 rows - representing 91 pedigrees - of Calrose medium grains in the Hawaii nursery were blast related. A special test for blast resistant entries was conducted at RES. Breeding efforts have overcome a 30 percent yield drag, higher blanking levels and lower milling yields and have produced improved experimental lines with blast resistance. Ten of these have sufficient merit to be further tested in Hawaii. Another yield test with selected entries from 923 rows is planned for 2004. A blast resistant Calrose medium grain should see seed increase within the next five years.
Several crosses made onto herbicide-resistant Clearfield® rice were advanced. No breeding research was conducted on transgenic herbicide resistant M-202 in 2003.
Selection for grain quality factors continues to be an integral part of the RES breeding effort. Good head rice yield is among the most important criteria for advancing a breeding line. There were 342 entries in preliminary yield tests for factors contributing to improved milling yield, 13 of which had superior head rice yield. Eighteen of 34 advancing blast entries had head rice yield significantly superior to M-202.
Advanced experimental lines in the second year of statewide testing or breeder seed increase were also evaluated for head and total milled rice. The environmental effects - dry-down rates, in particular - on head rice yield in some blast resistant entries are also being examined.
In spite of increased efforts to improve stem rot resistance in Calrose medium grains, only levels comparable to M-201 have been achieved. Sources of resistance are being tapped from both long-grain and short-grain projects. Unfortunately, good sources of stem rot resistance are also associated with poor seedling vigor, high floret blanking and low yield performance.
Efforts to transfer higher levels of seedling vigor have decreased because of greater emphasis on blast resistance. Progress is reported on improving straw strength relative to M-103 and M-202. Research on resistance to low-temperature blanking continues at cold tolerance nurseries and in RES greenhouses.
Breeding for disease resistance is a cooperative effort between plant breeders and the RES plant pathologist. About 2,000 rows a year are cycled through the disease nursery to advance lines resistant to stem rot, sheath spot and blast. Source of stem rot resistance also confer resistance to aggregate and bordered sheath spot. Bakanae is a relatively new disease that underwent significant research in 2003.
There were about 7,000 rows in the 2003 stem rot nursery. As part of an effort to identify useful molecular markers for stem rot work, 152 fourth generation long grain rows were rated for disease resistance. Another 104 rows derived from crosses with six wild species were also evaluated for disease resistance. Initially, it appears that superior resistance observed in some of these new wild species is related to late maturity.
Research is also under way to quantify yield loss with specific stem rot scores in current varieties and resistant lines. Resistant line 01-Y-502 showed a significant yield advantage over L-205 in both 2002 and 2003. Similarly, 00-Y-578 out yielded S-102, and all short grains out performed S-102 in 2003, which may have been due to a lodging issue. Only 01-Y-502 yielded more than L-205 in 2003.
Crosses have also been made to transfer bordered sheath spot resistance from the wild species Oryza rufipogon. This is also a source for resistance to sheath blight. A greenhouse screening program has been set up to test statewide entries for sheath spot resistance, especially important for medium grains that do not yet possess this resistance.
Rice blast was more prevalent in 2003 than in any year since 1998. About 5,000 lines were screened in the greenhouse in 2003 for blast resistance. Since only one known race of the fungus has been identified in California and others are known to exist elsewhere in the world, researchers have adopted a breeding strategy to incorporate a number of different genes with multiple sources of resistance. A cooperative project with the USDA lab at UC Davis is developing molecular markers for blast resistance. Markers would allow detection of multiple resistance genes in the same variety or breeding line without actually screening against the races necessary to differentiate these genes.
Incidence of Bakanae - a fungal disease that causes rice plants to grow erratically and then die with two to three weeks - was lower during the 2003 season. This may be due to widespread bleaching of seed, a cost-effective treatment. In an earlier test Bakanae incidence was reduced from 19.4 percent to less than 0.3 percent with a 5-10 percent bleach treatment in laboratory, greenhouse and field experiments. There is no residual protection of seed against seedbed inoculum with this treatment, however, and soak water disposal may be a problem. The treatment is registered for use in California at a rate of 3,000 ppm available chlorine (five gallons Clorox® Ultra per 100 gallons) to be applied during the first two hours of soak time. Other commercially available fungicides were tested alone and in various combinations. With the exception of Nusan, they were not as effective as ordinary bleach.
Varietal differences in susceptibility to Bakanae were also analyzed. Calmati-201 is apparently most susceptible. A-201 and L-205 were the least susceptible. Intermediate in susceptibility were the medium grains, with M-206 being most resistant and M-205 most susceptible. M-104 is as susceptible as M-204. S-102 was more susceptible than the medium grains but less susceptible than Calmati-201.
Researchers also looked at soak and drain times and found the latter to be more important in Bakanae spore and incidence increase. Somewhere between 24 and 48 hours, spores and therefore disease incidence, greatly increased. Experiments run in the greenhouse to test the effects of soaking, seed submergence and soil cover found Bakanae incidence highest in seed that was soaked and drained. Rice planted dry had very little Bakanae, whether rice seed was placed on top of the soil and submerged or covered with soil, allowed to emerge and then submerged. Delaying flooding did not have much effect on Bakanae. Increasing temperatures may also reduce Bakanae incidence. Straw decomposition should help control the disease and, as is the case with all California rice diseases, over fertilization should be avoided to limit conditions favorable to pathogens.
The building blocks for any breeding program are varieties with traits desirable in commercial production. In 2003, 15 entries passed through quarantine, including submergence-tolerant lines and new Australian varieties.