Rice Breeding Program, 2000

The year 2000 could best be described as a year of transition for the Rice Experiment Station. With the loss of RES Director Marlin Brandon and the appointment of Kent McKenzie to that position, a concerted effort was made by the entire staff to keep the breeding nursery on track. Project leader meetings, reassignment of program responsibilities and the support of an experienced staff made for successful and timely planting, management, selection and harvest of breeding material for testing, generation advancement and seed increase. Progress in the rice breeding program from last year is summarized below.

Statewide Yields Rebound

California rice acreage remained identical to the previous year, with 548,000 acres grown in the year 2000. More than 90 percent of this acreage is seeded with varieties developed at the Rice Experiment Station. Yields were up to more than 7,950 pounds/acre, a more normal level after two consecutive seasons of low productivity.

Breeding Nurseries

Seedbed preparation at the RES breeding nursery was delayed slightly to May 12, 2000 because of damp soil conditions. Only minor problems were reported with seedling drift; however, crawfish again damaged stands in small plots in the rice water weevil nursery. The only reported weed control problem was Londax®-resistant arrowhead. Alternative herbicides may be available in 2001 to provide better solutions.

A total of 1,078 new crosses for rice improvement were made in 2000, bringing the total to 26,231 since 1969. The nursery occupied approximately 69 acres and included 3,781 small plots and 2,844 large plots. Small seed increase plots were grown on 1.5 acres and included 92 advanced breeding lines. Thirty experimental lines were grown in headrows for seed increase, quality evaluations and purification. Selections were made from 20,000 progeny rows.

F2 populations from previous years were grown on drill-seeded plots on 10 acres. An estimated 200,000 panicles were selected from various F2populations for further screening and advancement. Headrows of Calmati-201, Calmochi-101, L-204, M-103, and M-202 were grown for breeder seed production.

The Hawaii winter nursery, which allows the advancement of breeding material and cold tolerance screening, contained 5,000 rows planted December 3, 1999; an additional 1,000 row transgenic nursery was planted in a separate field December 21, 1999. Rice straw residue was destroyed and the nursery sprayed with the fungicide Quadris® as a precaution against blast. Birds continue to hamper seed production in some trials; prompting nursery managers to explore netting for 2001. Harvest was completed, shipped back to RES and inspected by the Butte County Agricultural Commissioner in early May. No blast was found at the nursery or in any of the material.

The 2000-2001 RES winter nursery was seeded with 5,200 rows on November 2-3 and transplanted November 20-22, 2000. Selections were to be harvested in late March or early April for use in the 2001 breeding nurseries at RES.

A 3.5 acre cold tolerance nursery continued at UC Davis in 2000. It contained precision drill-seeded F2 populations and 10,000 dry-seeded progeny rows. Stands and grassy weed control were reportedly good; blanking in breeding rows was moderate and, therefore, useful in screening. Canada geese destroyed one basin of space-planted F2 short grain.

An alternative site for the San Joaquin cold tolerance nursery is still being sought. However, a water-seeded planting of 701 rows of advanced breeding lines was grown at a San Joaquin location in the Statewide Yield Tests. The site proved an excellent screening test for resistance to blanking. Cold tolerance nurseries are an essential part of the breeding program and are used in conjunction with two refrigerated greenhouses at RES.

Statewide Yield Tests

Statewide Yield Tests were conducted at eight locations in fields throughout rice country to identify and evaluate promising advanced selections in commercial production fields. Water seeding and conventional management practices were used in these experiments. Entries that performed well will be advanced for further testing in 2001. Complete results of the 2000 Statewide Yield Tests are discussed in more detail in the Variety Trials section of this report.

Preliminary Yield Tests are the initial step of replicated large plot testing for experimental lines. This included 776 entries and check varieties in 2000. Superior entries will be advanced for further testing in the 2001 Statewide Yield Tests.

Long Grains

The focus of the long-grain breeding program is to improve four quality types – conventional long grains, Newrex, Jasmine and Basmati. Milling and cooking quality improvements of conventional long-grain and specialty types remains a priority in this program, followed by resistance to cold-induced blanking and other agronomic and disease resistance traits.

Efforts continue to improve the cooking and milling qualities of conventional long grains so that California-grown varieties can compete more effectively with Southern-grown long grains, which are noted by their dry and fluffy cooking character. Research is evaluating amylose, gel temperature, viscogram, and small sample cooking information, in addition to kernel characteristics data, to improve conventional long grain quality. During the 2000 season, 113 advanced conventional long grain selections were tested in the Statewide and Preliminary Yield Tests. Some Southern long grains are being tapped for blast resistance and cooking quality improvements. Two entries are resistant to the strain of blast in California.

Newrex is a special quality type rice regarded superior for canned soups, parboiling and noodle making. Some major soup manufacturing companies have expressed considerable interest in the high-yielding Newrex variety L-205, released in 1999. Several experimental entries tested in 2000 performed well, with grain yields ranging between 9,800 and 11,200 pounds/acre, compared to 10,500 pounds/acre for L-205.

Specialty long grains include aromatics such as Calmati-201, a California-adapted basmati type released in 1999. Although not recommended for cooler regions, Calmati-201 is expected to be a good performer in warmer rice-growing regions of California. In 2000 Statewide Yield Tests, it averaged 8,180 and 7,340 pounds/acre respectively. Basmati rice yields are inherently lower than standard varieties, even in their country of origin, primarily due to their small and slender kernels. Twenty lines with improved cooking quality attributes, including excellent cooked kernel elongation, were grown in small increase blocks. Some of these are being advanced in the Hawaii Winter Nursery.

Several waxy long-grain lines were tested in 2000 large plot tests. Two of these lines significantly outperformed L-204 and are being used as donor parents in cold tolerance and yield improvement efforts. Research also continued in 2000 to breed for Jasmine types through pedigree and mutation breeding. Crosses were made with Jasmine lines from foreign sources and Southern U.S. long grains. An original Thai Jasmine variety was irradiated and is being advanced in the greenhouse.

Research is also under way to improve milling quality in long grains. Many factors affect rice milling quality, including grain formation, chalkiness and fissuring. The milling yield potential of 14 advanced experimental lines and varieties was evaluated in harvest moisture studies.

Stem rot resistance originating from the wild species Oryza rufipogon has been transferred to a number of high-yielding long grain lines. Fifteen entries with a wide range of resistance were tested. Improvement in yield, cold tolerance and early maturity of these lines in relation to L-204 and L-205 are being pursued through further backcrossing.

Considerable effort is also progressing to confer blast resistance to California long grains. Several of these were advanced through the Hawaii Winter Nursery and will be included in 2001 yield tests. A number of early generation blast resistant lines were also selected and are being screened in greenhouse blast tests.

Premium Quality

Development of improved premium quality short and medium grains is the primary focus of this part of the breeding program. These include varieties such as M-401 preferred by certain ethnic groups. Premium quality medium grains are characterized by being very glossy after cooking, sticky with a smooth texture, and remain soft after cooling. Aroma and taste are also important.

M-402, a premium quality medium grain, and Calhikari-201, a premium quality short grain, were released to seed growers in 1999 and were produced on several thousand acres in California last year. Calhikari-201 is the first release of a premium quality short grain for California. Its agronomic performance and yields are far superior to Japanese varieties Akitakomachi and Koshihikari. However, it is not as well-adapted and high yielding as M-202. Overall yield from eight locations in statewide yield tests last year were 8,220 pounds/acre, compared to 9,190 pounds/acre for M-202. Efforts are under way to improve stem rot susceptibility and cool-temperature blanking in Calhikari-201.

Work is continuing on other premium quality short grains that have traits of interest, including earlier maturity, smooth hull, different parentage, kernel size or better yield potential than Calhikari-201. Selected entries from premium quality medium grains were advanced from small plots to the Hawaii winter nursery to address concerns about improvements needed in quality, yield, cold tolerance and disease resistance.

Short Grains

S-102, released in 1996, is now the predominant California short grain in commercial production. It was the top over-location yielding entry in the very early advanced group of the Statewide Yield Tests for three years running. Further improvements in yield potential, disease resistance and grain and milling characteristics are the main focus of short-grain breeding.

Special purpose rices have unique yet undefined cooking characteristics that make quality evaluation a challenge. Most waxy type entries yielded very well in 1999 and again in 2000, a reflection of the cold tolerance of Calmochi-101 in their parentage. One entry – 99-Y-205 – produced significantly higher yields than Calmochi-101 at the Rice Experiment Station for the second year in a row. High-yielding sister selections will be tested for improved milling yield. Testing of waxy breeding lines will include some new cooperative quality evaluation studies.

Breeding for bold grain types similar to Italian varieties like Arborio continue in this breeding project. Some large-seeded experimental lines are showing promise. Quality samples were provided to three marketing organizations currently marketing these types.

Approximately 650 short and premium quality lines have been tested for blast resistance, with some of these being advanced for further agronomic and quality testing. A single large plot yield test was conducted in 2000 that included 12 blast resistant short-grain entries. Disappointing performance of these blast resistant lines illustrates the difficulty in developing adapted varieties containing resistance.

Breeding for stem rot resistance remains an important objective. However, recovering good agronomic characteristics and high levels of stem rot resistance in short grain premium quality germplasm is proving very difficult. New crosses with some of the resistant long grains have been made and are being evaluated. In 2000 Preliminary Yield Tests several entries showed acceptable seedling vigor and good cold tolerance, but problems persist with reduced head rice yields.

Another objective is tapping tolerance to rice water weevil. Fourteen medium-grain entries were tested in Preliminary Yield Tests in 2000, with three of them averaging respectable yields above 10,000 pounds/acre. They will be further evaluated in 2001. The area used for rice water weevil tolerance work continues to be plagued with heavy seedling damage from crawfish.

Calrose Medium Grains

High stable yield potential, resistance to lodging and disease, seedling vigor, improved milling yields, and resistance to cold temperature blanking are some of the main goals of the Calrose medium grain breeding effort. In addition, a significant effort was made to incorporate blast resistance into medium grains in 2000. Transgenic herbicide resistance in M-202 is also being extensively evaluated in yield trials and nursery rows.

As expected two new Calrose medium grains were named, released and foundation seed allocated for the 2000 growing season. M-104 is a very early medium grain that holds promise for replacing M-103 in the coolest rice production areas. Some of its comparative advantages include improved seedling vigor, lodging resistance and yield. Its earliness could limit its yield potential and head rice when planted early in warmer areas. Best areas for this variety are east of Highway 70 and south of Highway 20. Seed producers confirmed M-104’s superior seedling vigor and comparable yield to M-202.

M-205 is an early, high yielding medium grain that provides an alternative to M-202 and may take the place of M-204 in warmer production areas. It has improved lodging resistance, a lower stem rot score and an 11 percent yield advantage over M-202. Seed producers also commented on its excellent straw strength. It must be planted within the first three and a half weeks of May and is not recommended for cooler production areas.

A new experimental line, 98-Y-242, is a very early to early maturing, smooth, high yielding Calrose medium grain that could replace M-202 in both warm and cool production areas. Field observations and agronomic data indicate this line shows greater yield stability. A number of other promising entries were advanced in Statewide Yield Tests, showing attributes such as lodging resistance, good milling, stem rot resistant parentage and high yield. Thirty Calrose medium grain lines from the 2000 yield tests were also advanced to the Hawaii winter nursery for purification, seed increase and additional agronomic evaluation.

Efforts to incorporate blast resistance into California medium grains are on the “fast track.” Sources of resistant germplasm are being tapped from Southern U.S. and foreign lines. Scientists anticipate it will take two to four backcrosses to obtain a “respectable” high yielding medium grain with Calrose cooking qualities. Of the 283 Calrose medium grain crosses made last year, 38 percent were blast related. Selections for blast resistance were made this season from 1,288 of 4,607 rows that advanced from the 1999-2000 Hawaii winter nursery. Forty-four percent of Calrose medium grain 2001 Hawaii rows (762 rows) are blast related and include 84 pedigrees.

A special yield test of blast resistant varieties was conducted at the Rice Experiment Station. Breeding efforts have overcome a 30 percent yield drag, higher blanking levels and poor milling yields and have produced improved experimental lines with blast resistance. Another yield test with selected entries from 1,288 rows is planned for 2001.

Fifteen of the blast resistant entries have sufficient agronomic promise to be advanced in Hawaii and retested in 2001. Greenhouse tests confirm they have at least one gene for blast resistance. An acceptable Calrose medium grain with blast resistance should be in some stage of seed increase within the next five years.

There are also three cooperative projects in progress with the USDA and other cooperating scientists to develop molecular markers to assist in selection for blast resistant genes. Markers have been developed and are currently being used to evaluate the 15 Hawaii Calrose medium grain lines.

Work also continues under a grant to the Rice Experiment Station and the Monsanto corporation to develop an herbicide-resistant transgenic version of M-202. Confidentiality agreements forbid an in-depth discussion of the results. However, scientists report that evaluation on the experimental lines continued for a third year. Research included purification, evaluation for yield and other agronomic characteristics, as well as milling studies. Experience with other crops suggests that transgenic varieties show a “yield drag” of at least five percent and may become less stable in different environments. Problems that have emerged with the experimental transgenic lines of M-202 include more lodging, delayed maturity, height changes, grain characteristics and greater sterility. The 2000 lines, derived from backcrossing with M-202, showed improved milling and yield performance.

New techniques and procedures are being used to enhance the grain quality factors leading to improved milling yields. Milling tests for Calrose medium grains began on entries in the preliminary yield tests with 204 entries last year. Thirty of 76 entries saved had head rice equal to three points better than the best Calrose check. Nineteen of 57 saved blast-resistant entries had head rice equal to their respective Calrose check. Advanced experimental lines in the second year of statewide testing and/or at the breeder increase stage were evaluated for head and total milled rice.

Breeding for improved stem rot resistance and seedling vigor occupies a significant portion of the medium-grain program. Lines with resistance from new sources are being tapped. Breeding lines from the long-grain stem rot resistant source 94-Y-561 and other backcrosses to Oryza rufipogon have produced some entries with low stem rot scores. Unfortunately, many sources of stem rot resistance also perform poorly, plagued with problems such as poor seedling vigor. Efforts to transfer higher levels of seedling vigor are being affected by higher priorities, such as blast resistance and transgenic M-202.

Progress is also reported on other medium-grain objectives, including improved straw strength and resistance to low temperature blanking. A cooperative effort to study salt tolerance in rice is also under way between the USDA and scientists at UC Riverside and UC Davis.

Rice Pathology

Breeding for disease resistance is done cooperatively with plant breeders and the plant pathologist. About 2000 rows a year are cycled through the disease nursery to identify and verify resistant lines. Priorities are directed primarily at blast and stem rot resistance. Sources of stem rot resistance are also resistant to aggregate and bordered sheath spot.

Eighty-two new crosses were made in the RES breeding projects to transfer disease resistance derived from Oryza rufipogon into California varieties. Nine thousand early generation second backcross transplants and 1,700 rows derived from crosses with six wild species were evaluated.

These wild species have even greater resistance to stem rot and sheath spot than O. rufipogon. At least one wild species has blast resistance as well. About 9,000 rows were grown in the 2000 stem rot nursery.

One hundred twenty-two crosses and backcrosses were made in different projects to tap sources of blast resistance in 2000. About 9,000 lines were screened this past year at the Rice Experiment Station’s new greenhouse. Major resistance genes limit blast symptoms to small brown flecks – at most. But this resistance could be overcome by different races of the blast fungus. A project involving the USDA geneticist at UC Davis and Southern researchers is developing molecular markers to help identify genes conferring blast resistance. The severity of the blast infestation has been much lower than when the disease was first detected in 1996. Screening for blast resistance is being done only in greenhouse facilities during the off-season.

Good seedling vigor continues to be an important breeding objective that helps young rice plants compete more effectively against weeds and may reduce the adverse effects of seedling disease. It also allows for use of deeper water in weed suppression efforts. Although California varieties generally have good seedling vigor, a limited amount of work continues to tap into higher levels from Italica livorno and M-16 (Italian and Hungarian varieties). Three new crosses were made in 2000 with these varieties. Incubator tests were used to screen 19,000 seedlings. Approximately 265 seedlings were selected and transplanted in the field to further screen at maturity for short stature and stem rot resistance. Eleven crosses were made with new Russian varieties that have seedling vigor similar to Italica livorno.

The building blocks for any breeding program are varieties with traits desirable for commercial production. This past year, 132 entries were brought through quarantine and grown under revised procedures developed and approved by USDA and CDFA to prevent the accidental introduction of exotic pests and rice diseases.

Bakanae Disease

A new, yet not especially threatening, disease appeared in California rice fields in 1999 – Bakanae disease. It is caused by the fungus Gibberella fujikuroi. Thus far it has been identified in Yuba, Sutter, Butte and Colusa counties. It usually does not greatly affect yield elsewhere in the world, especially where seed is sown into standing water.

Affected plants appear about a month after seeding and display elongated, rolled, yellow leaf blades and sheaths. Plants are scattered throughout a field. Leaves droop as they elongate. Most plants die two to three weeks after symptom expression but then lesser numbers of other seedlings develop symptoms throughout the season. Very little grain is formed and panicles may turn gray as they age. The crowns of these plants are rotted by the bakanae fungus, which sporulates on dead tissue just above the waterline. Spore masses appear powdery and may be white to pale orange in color. Harvest operations distribute the fungus throughout the seed, which is superficially contaminated and may not exhibit symptoms. The fungus does not persist well in the soil, although overwintering is possible. Fallowing may be effective in greatly reducing any carryover inoculum.

In 2000 six observation plots were established in Butte and Yuba counties. Symptomatic plants were marked weekly as they appeared and died. Seedling loss ranged upward to just over three percent, an amount that should not affect yield. Blanked panicles ranged up to just over half a percent.

Laboratory tests were conducted to detect contamination of seed lots from each of the six plots. Inoculum levels generally corresponded with field incidence levels. This seed will also be planted in the summer greenhouse to determine transmission rates and to compare results with field observations and laboratory tests. The results will be used to predict future disease incidence.

Field and greenhouse experiments will continue this year to observe whether the disease is becoming more prevalent. Preliminary tests with a chlorine seed treatment were successful and may offer a cheap, effective remedy.

Project Leader and Principal Investigators

Carl W. Johnson, plant breeder

Kent S. McKenzie, plant breeder

Farman Jodari, plant breeder

Jeffery J. Oster, plant pathologist