Rice Breeding Program, 2001

Statewide Yields on Upswing

California rice acreage declined from 548,000 acres in 2000 to 471,000 last year. About 90 percent of this acreage was seeded with varieties developed at the grower-owned Rice Experiment Station (RES) near Biggs. Statewide yields continue improvement over the last few years with a 2001 average of 8,200 pounds/acre.

Seed Production and Maintenance

The California public rice breeding program has developed 36 improved varieties since accelerated research began in 1969. In 2001 foundation seed of 14 public rice varieties and basic seed of two Japanese premium quality varieties were produced on 146 acres of the RES. The 478-acre facility, owned and operated by the California Cooperative Rice Research Foundation (CCRRF), expanded by 100 acres in 1998 to support weed research, breeding and foundation seed production.

Breeding Nurseries Report

Seedbed preparation in RES rice nurseries was again slightly delayed in 2001. Seeding began May 12, 2001. Water seeding and drill seeding went generally well, with the exception of strong winds causing some seedling drift, mixing of seed and poor stands in parts of the nursery. This had a negative effect on yield, increased variability in some experiments and required more roguing of the nursery. Weed control was good in the drill-seeded nursery. Weed control in the water-seeded nursery is a more serious problem, however, because of herbicide resistant arrowhead and the loss of aerial application of broadleaf herbicides due to regulatory restrictions.

A total of 955 new crosses were made for rice improvement at the RES in 2001, bringing the total since 1969 to 27,186. The nursery occupied approximately 60 acres and included 3,723 small plots and 3,011 large plots. Small seed-increase plots were grown on three acres and included 29 advanced breeding lines. Thirty-four experimental lines were grown in headrows for seed increase, quality evaluations and purification. The nursery included about 60,632 water-seeded progeny rows. Selections were made from about 12,000 of these rows.

Second generation (F2) populations from crosses made in 1999 and 2000 were grown in precision drill-seeded plots on 10 acres. An estimated 200,000 panicles were selected from these for further screening and advancement. Headrows of A-201, L-205, M-205 and M-401 were grown for breeder seed production.

The Hawaii winter nursery, which allows the advancement of breeding material and cold tolerance screening, contained 5,200 rows planted between November 20 and December 1, 2000. The fungicide Quadris has been used there the last few years to treat an outbreak of blast. This nursery was also netted to prevent bird damage. In April 2001, the University of Hawaii informed RES staff that it would be discontinuing the rice winter nursery and closing the research farm after 32 consecutive years due to retirements, funding shortages and administrative changes. A new winter nursery site was identified in September and, overcoming formidable challenges, 7,800 rows were planted in November.

A 3.5-acre cold tolerance nursery at UC Davis was planted with second generation precision-drilled populations and 16,000 dry-seeded progeny rows. Grassy weed control presented some problems. Blanking in the F2populations was moderate and thus useful for screening breeding lines. Canada geese continue to be a problem at this site.

While a more permanent location for the San Joaquin cold tolerance nursery is being sought, a location in the statewide yield tests has been used since 1999. A water-seeded nursery of 1,100 rows of advanced breeding lines provided a source of cold tolerance evaluation. Blanking at this location was reportedly at moderate to low levels in 2001. Cold tolerance nurseries are an essential part of the selection process used in conjunction with two refrigerated greenhouses at RES.

Statewide Yield Tests

Statewide yield tests were conducted in grower fields at eight locations to evaluate promising advanced selections in all three maturity groups. Water seeding and conventional practices were used at these sites. Entries that performed well will be advanced for further testing in 2002. More detail on the 2001 Statewide yield tests is in the Variety Trials section of this annual report.

Preliminary Yield Tests are the initial step of replicated large plot testing for experimental lines. This included 681 entries and check varieties in 2001. Superior entries will be advanced for further testing in the 2002 Statewide Yield Tests.

Long Grains

The long-grain breeding program continues to focus on four major quality types—conventional, Newrex, Jasmine and Basmati. Milling and cooking quality improvements are chief objectives, followed by resistance to cold-induced blanking and other agronomic and disease resistance traits.

California long grains have improved considerably in recent years. Extensive quality research is under way to improve upon the cooking softness of L-204 (released in 1996). Conventional California long grains possess superior agronomic traits yet improvements in milling qualities and cold tolerance are needed, so this has become a major area of emphasis.

During the 2001 season, a total of 118 advanced conventional long grain selections were tested in statewide and preliminary yield tests. Two entries, 99-Y-41 and 98-Y-511, yielded consistently higher than L-204 in 1999-2001 statewide yield tests. Over-location yields in the intermediate maturity group were 9,650 and 8,669 pounds/acre, respectively. Detailed quality evaluations of these lines are under way.

Newrex is a special quality rice well-suited for canned soups, parboiling and noodle making. The Newrex-type L-205 released in 1999 has superior processing qualities and excellent agronomic characteristics. Commercial production of this variety began in the year 2000. Estimated acreage last year was 6,400 acres. Several experimental Newrex-type performed well, with grain yields in the range of 9,100 to 10,570 pounds/acre.

A true basmati-type long grain was released in 1999 as Calmati-201. It is susceptible to cold-induced blanking and is not recommended for cooler regions. Heavy nitrogen fertilization should be avoided in areas where cold-induced blanking is likely. At RES last year Calmati-201 yielded 8,240 pounds/acre, and 7,190 pounds/acre off station. It promises to be a good performer in warmer areas for the basmati class.

A considerable number of basmati lines were evaluated in 2001. Four advanced selections with improved cooking qualities were tested in Statewide Yield Tests. Experimental line 01-Y-112 with higher elongation and a more slender grain shape was purified in a headrow block. Twenty-seven basmati selections were advanced in increase blocks for further milling and cooking quality evaluations.

Efforts also continued to develop jasmine types through pedigree and mutation-induced breeding.

One waxy long-grain line, 99-Y-494, was tested in 2001 Statewide Yield Tests. Waxy lines are being used as donor parents in cold tolerance and yield improvement efforts.

Efforts are under way to build upon milling quality improvements found in recent long grain releases. For instance, grain characteristics lending to greater yield stability under adverse weather conditions would allow a wider harvest window. The milling yield potential of 40 very early and early advanced long-grain lines from Statewide Yield Tests were evaluated in 2001 harvest moisture studies.

Stem rot resistance originating from a wild species source, Oryza rufipogon, has been transferred to a number of high-yielding long grains. Fifteen of these were tested in statewide and preliminary yield tests in 2001. Two of them have shown a significant improvement in their combined low stem rot score, low blanking and early maturity. In small plots 194 lines with various levels of resistance were evaluated last year.

Breeding efforts are also progressing to develop blast-resistant long grains. A considerable number of early generation blast resistant lines were selected and are currently being screened in greenhouse tests. A cross between L-204 and Kaybonnet, a Southern blast-resistant line, performed well and is being advanced.

Premium Quality

“Premium quality” is a term used to identify the California medium-grain varieties like M-401 that have unique cooking characteristics preferred by certain ethnic groups. Premium quality medium grains are very glossy after cooking, sticky with a smooth texture and remain soft after cooling. These types are similar to high-quality short-grain varieties like Koshihikari.

Intensified premium quality breeding efforts initiated in 1988 led to the development of Calhikari-201 and M-402. Commercial demand for premium quality short grains plummeted in California and, as a result, acreage of these two varieties has dropped to about 1,000 acres and 5,000 acres, respectively. The smaller kernel size of M-402 presents an issue for dryers, mills and marketers.

Calhikari-201, the first premium quality short grain for California, continues to show superior agronomic performance and yields, although not as strong as M-202. Statewide yield tests averaged 8,010 and 8,700 pounds/acre for Calhikari-201 and M-202, respectively.

Eight premium quality short-grain breeding lines were advanced for earlier maturity, smooth hull, different parentage, kernel size or better yield potential than Calhikari-201. Five preliminary yield test entries also showed performance advantages over the check variety and will be evaluated in cooking tests.

A parallel breeding effort is seeking to improve premium quality medium grains for the M-401 market. Thirteen entries were included in statewide yield tests. Emphasis is on larger kernel size, with M-202 grain and milling yields. Cooking tests will be conducted on these lines and others harvested from small plots.

Short Grains

S-102, released in 1996, was the top over-location yielding entry in the very early advanced group of the statewide yield tests the last four years. Two entries in the preliminary yield tests gave very high yields and will be further evaluated in 2002. A number of blast-resistant short grains will be tested in large plots this year. Yield potential, resistance to disease, and grain and milling characteristics are the main focus of short-grain breeding.

Special Purpose Types

Special purpose rice has unique or undefined cooking characteristics. Improvement of the short-grain waxy (mochi, glutinous or sweet rice) type, such as Calmochi-101, is focusing on agronomic and quality characteristics. Three entries performed well in statewide yield tests. New lines and pedigrees are being advanced, some derived from crosses with Japanese waxy varieties. Advanced quality testing will require new evaluations with marketing organizations.

Breeding for bold grain types, similar to the Italian variety Arborio, are focusing on agronomic and milling performance. However, interest by marketing organizations is weak.

Induced mutation has been utilized to help produce a rice low in amylose (starch) for improved eating quality and new products. Mutants of Calhikari-201—low amylose and waxy lines—were increased in the 2001 winter greenhouse. Two lines are being compared to similar low-amylose Japanese varieties Snow Pearl and Milky Queen. Selections are being advanced for further increase and agronomic and quality evaluations in 2002.

Disease/Pest Resistance

Blast resistance has been added as an objective for premium quality and short grain rice. Approximately 1,700 lines have been screened in the new RES greenhouse facilities. Linkages to undesirable agronomic characteristics such as late maturity and blanking will need to be broken by continued crossing, selection and screening. Poor seedling vigor, grain quality weaknesses and other difficulties present challenges in breeding for stem rot resistance, although some short-grain lines with improved stem rot resistance have been recovered.

Breeding efforts are also seeking to transfer rice water weevil (RWW) resistance from the donor parent line PI 506230 developed at RES. Crosses with new varieties are being made in an effort to overcome agronomic weaknesses. Four medium-grain entries, plus PI 506230 were tested in preliminary yield tests. One of these will be further evaluated in 2001, along with lines advanced from small plot testing.

Calrose Medium Grains

Calrose medium grain breeding is focusing on high yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to cold-temperature blanking. A significantly increased effort was made to incorporate blast resistance. Transgenic herbicide resistant M-202 was also evaluated.

Growers seem to be responding well to the two new Calrose medium grains—M-104 and M-205—released in 2000. M-104 occupied 29,199 acres and M-205 was grown on 37,594 acres in 2001. These new varieties are filling important niches at the expense of the long-time industry standard M-202, which was grown on significantly less acreage in 2001, 232,765 acres (compared to 353,879 acres in 2000).

M-104 is a very early Calrose for cooler regions like San Joaquin County. Yield potential, milling qualities, improved seedling vigor and lodging resistance are some of the attractive features of this new variety. Best areas for this variety are east of Highway 70 and south of Highway 20. M-104 is a good complement to M-202 in coolest production areas where there is a need to spread harvest dates and is the variety of choice for plantings delayed past the third week of May.

M-205 is an early, high-yielding Calrose medium grain that may take the place of M-204 in warmer production areas west of Highway 70 and north of Highway 20. Improved lodging resistance, less susceptibility to stem rot and a three to eight percent yield advantage over M-202 make this variety attractive. M-205 must be planted in the first three weeks of May and is not recommended south of the Colusa-Yolo county line or in cooler production areas.

A very early to early, high yielding experimental line, 98-Y-242, could replace M-202. Breeder seed was produced in 2001 and foundation seed increase is scheduled for 2002. Agronomic data show greater yield stability in challenging environments.

A fast-track effort to develop Calrose medium grain blast resistance continued with entries in statewide yield tests for the first time. Three entries will be tested again, along with cooking evaluations. These breeding efforts have overcome the 30 percent yield drag, higher blanking levels and poor milling yields that plagued earlier entries. Another yield test with selected entries from progeny rows is planned for 2002. The performance of these entries suggests that an acceptable Calrose medium grain with blast resistance will be in some stage of seed increase within the next five years. Molecular markers continue to be refined for detecting blast resistance genes.

Transgenic M-202 lines at various stages of development were evaluated in a water-seeded nursery. Results confirm previous results that regardless of technique, these lines do not perform as well as non-transgenic M-202. Experience with other crops indicates that direct transgenic descendants suffer yield drags of at least five percent and may become less stable in different environments. This has included more lodging, delayed maturity, height changes, grain characteristics and greater sterility. Nonetheless, herbicide resistant M-202 could provide an additional tool for weed control. Other issues, ranging from seed production to consumer acceptance need to be addressed.

Selection for grain quality factors that affect milling quality continue to be an integral part of the Calrose medium grain program. Harvest moisture, plant density and morphological characteristics are being examined to determine their effects on milling yield. There were 185 entries at this stage in 2001, 14 of which had head rice yields equal to or better than the best check. Thirteen of 29 saved blast entries had head rice equal to or better than M-202.

Stem rot resistance breeding efforts continue. Crosses made from wild species generated at least one line with excellent “stay green” ability at maturity and good plant yield. Selections with leaves and stems that remain green may provide improved disease resistance.

Rice Pathology

Breeding for disease resistance is a cooperative effort between plant breeders and the plant pathologist. About 2,000 rows a year are cycled through the disease nursery to advance resistant lines.

A major effort is directed toward resistance to blast, but stem rot continues to receive significant attention. Sources of stem rot resistance also confer resistance to aggregate and bordered sheath spot. Efforts are also under way to develop detection and control techniques for Bakanae Disease.

Seventy-eight new crosses were made at RES to transfer stem rot resistance derived from O. rufipogon into California varieties. Five thousand rows, a significant increase, were grown in the stem rot nursery. Another 2,200 second generation long-grain transplants were evaluated for the usefulness of stem rot genetic markers. Researchers also examined 384 rows derived from crosses with six wild species containing even greater resistance than O. rufipogon. At least one of them has blast resistance, as well. Several early generation lines show promise and will be retested from crosses with other wild species. A large molecular marker project with the USDA geneticist at UC Davis has been completed. Two markers were found that differentiate a resistant long-grain parent from the susceptible parent. These markers have not been useful in medium grains.

Work on blast resistance includes 135 new crosses and backcrosses with germplasm having major genes for resistance. About 8,500 lines were screened this past year. A cooperative project involving USDA scientists at UC Davis and in Texas is seeking to develop molecular markers for blast resistance. Markers are working reasonably well but need some fine-tuning. Development of blast resistance is a complex undertaking and thus is a longer term goal.

Good seedling vigor helps young rice plants fight off diseases and weeds, so this remains an important objective. Seedling vigor ratings were taken on all water-seeded progeny rows, small plots and preliminary and statewide yield tests at RES. Incubator tests were used to screen 15,000 seedlings. Incubator tests provide an important additional tool since field conditions are not always favorable for evaluating seedling vigor. Approximately 320 seedlings were selected and transplanted in the field to further screen at maturity. Crosses have been made with new Russian varieties to transfer higher seedling vigor into California varieties.

California’s newest rice disease, Bakanae, has spread throughout most rice-growing areas in 2001. Many fields had Bakanae but the incidence was usually less than half of one percent and has not been associated with measurable yield reduction to date. Bakanae disease does not usually affect yields significantly in other areas of the world, although some countries regularly treat their seed with fungicides to combat this disease.

Five observation plots were established in Butte and Yuba counties to track plant symptoms and seedling loss. A laboratory analysis showed that about 25 to 75 percent of the seeds that tested positive for the fungus would have developed symptoms in the field. These studies underscore the importance of seed-borne inoculum. The disease has the potential to spread rapidly if seed-borne inoculum is not eliminated.

Laboratory, greenhouse and field tests indicate that a five to 10 percent bleach solution will greatly reduce bakanae incidence, offering a relatively cheap and available seed treatment. Although seedling growth may be slowed initially by this treatment, test plot stands recovered as the season progressed. Field fungicide testing is scheduled for 2002.

In the meantime, the single most important thing growers can do to reduce Bakanae incidence is to minimize seed-borne inoculum. Seed should not be held longer than necessary after soaking. Draining fields during establishment encourages disease development. Efforts to promote straw decomposition, such as flooding, may help reduce inoculum. Fungicide seed treatments are being evaluated as a method of disease control for seed production.

Project Leader and Principal Investigators

Carl W. Johnson, plant breeder, Calrose medium grain program

Kent S. McKenzie, director and plant breeder, Premium Quality and Short Grain program

Farman Jodari, plant breeder, Long Grain program

Jeffery J. Oster, plant pathologist, Rice Disease program