|Rice Breeding Program-96
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
|California rice acreage increased to 500,000 acres last year, a
35,000-acre jump over 1995. Medium grain varieties, led by M-202, continue to be the
growers' grain of choice with 96.4 percent of the acreage, according to the
Agricultural Statistics Service. Long grain and short grain acreage accounted for 1 and
2.6 percent, respectively. Estimated average yield continues a downward slide to 7,490
pounds/acre, compared to 7,600 in 1995 and 8,500 pounds/acre in 1994. The recent decline
in yields underscores the need for a strong rice breeding program to stabilize yields at
high levels over years and locations. A new threat, rice blast, has added a new objective
to the breeders' agenda. Transgenic rice is looming on the horizon. A new medium grain,
M-205, is slated for release in 1998. These and other significant developments in the rice
breeding program are detailed in this section.
Late spring rains and soggy ground last year delayed planting in the 60-acre breeding nursery at the Rice Experiment Station (RES). High temperatures and high humidity probably contributed to high disease levels observed in 1996. Weed control was generally good, although some grass problems popped up in one part of the nursery.
Plant breeders made 892 crosses for rice improvement during 1996, bringing the total since the program began in 1969 to 22,319. Approximately 70,000 progeny rows were grown for selection, purification and generation advance. The nursery contained 4,148 small plots and 2,600 large plots in various water-seeded yield tests. An estimated 200,000 panicles were selected from the F2 nursery for further screening and advancement. An additional 100,000 panicles and 10,000 rows were harvested from advanced generation rows for selection, advancement, quality evaluations and purification for progeny rows. Twenty-three experimental lines were grown in headrows for seed increase, quality evaluations and purification. Six advanced lines are undergoing breeder seed increase. Headrows of M-103, M- 401, L-204 and A-201 were also grown for foundation seed and production.
The Hawaii "winter" nursery, which allows plant breeders to speed up the selection process by growing an extra generation each year, contained 5,000 rows planted in late November and early December 1995. Seed production was good, cold-induced blanking occurred in susceptible materials and some bird damage occurred. Seed harvested from this nursery was shipped to California in April, inspected, processed and grown in different nurseries last summer. At the UC Davis nursery, where lines are screened for moderate levels of cold tolerance, two acres of precision drill- seeded second generation populations were grown. Good stands and water- grass control, a low level of blanking and a severe stem rot infestation were observed at UC Davis. Despite efforts to keep them out of the field, an indigenous flock of Canada geese caused considerable damage to the drill-seeded rice.
A nursery in the Sacramento-San Joaquin Delta is used to screen for greater levels of cold tolerance. Plant breeders drill-seeded second generation populations and 6,700 progeny rows. Problems in planting, seedling emergence and weed control occurred on this organic soil and many populations were unsalvageable. Nonetheless, the cold tolerance nurseries are essential to select for resistance to blanking.
Statewide Yield Tests
Researchers from the Rice Experiment Station in collaboration with UC Cooperative Extension specialists and county farm advisors annually conduct state- wide yield tests to evaluate the agronomic performance and adaptation of advanced experimental lines and commercial varieties. Results from these trials are reported in more detail in the "Variety Trials" section elsewhere in this report.
Preliminary yield tests - the initial step of replicated large plot testing for experimental lines - are performed at the RES. These tests included 532 entries and check or standard varieties in 1996.
Historically, the long-grain breeding effort at the Rice Experiment Station has focused on developing varieties with the characteristics of long-grain rice grown in the Southern United States. This rice typically cooks dry and fluffy. In more recent years, however, the program has broadened its effort to include varieties with "Newrex" type quality rice, which is considered superior for processing, and Basmati types popular with certain ethnic groups. Breeding efforts continue to incorporate many important agronomic characteristics into long grains. Currently, screening is most intensive for improved head rice milling yield.
Last year breeders released L-204, which has higher milling yield and better cooking quality than previously released long grains. Although L-204 cooks similar to Southern long grains, there are still subtle taste differences that need to be improved upon. L-204 has significantly improved head rice milling yields. Researchers are evaluating several advanced experimental lines for improved taste.
Development of Newrex-type long grain rice, with its dry cooking characteristics, is an important research objective. Incorporation of a higher amylose content into long grains is being pursued to overcome the softness and cohesiveness of California long grains. Breeders are encouraged by one experimental line, 94-Y-40, which has performed well and produced high grain yield and head rice percentage. Head- rows of 94-Y-40 were grown in 1996 for purification and initial seed increase.
Basmati rice is a class of aromatic rice primarily grown in the Punjab region of India and Pakistan. When cooked it produces long, slender kernels with very little stickiness and a distinctive aroma. It commands a premium in both international and domestic rice markets. Basmati varieties are poorly adapted to California, so a number of experimental lines are being tested to overcome problems with low temperature blanking, low yield potential and very low head rice milling yield. Aromatic long grains without the characteristic kernel elongation are also being developed. An aromatic long grain, A-201 was released in 1996 and is currently grown. Plant breeders are also looking at 94-Y-39, a soft-cooking long grain with high yield potential and adequate rice milling yield. Headrows of this experimental were grown for purification and seed increase. Further evaluation of consumer acceptability and market potential are needed.
Stem rot resistance from the wild species Oryza rufipogon is being success- fully recovered in several advanced long- grain breeding lines and scientists are especially enthusiastic about 96-Y501, which performed well in preliminary yield tests. 96-Y501 is being advanced in the Hawaii winter nursery for further evaluation and will be used as a source of stem rot resistance for short and medium grains.
To improve medium grain rice, the mainstay of the California rice industry, a wide range of agronomic characteristics - seedling vigor, high yield potential, resistance to lodging and disease, improved milling yields and resistance to blanking - are being targeted.
To enhance head rice and total milled rice yields, new techniques, evaluation methods and procedural modifications have been implemented. Researchers identified several advanced experimental lines that produced head rice yields superior to the highest Calrose check variety, even though high temperatures reduced milling yields in 1996. These will be further tested in 1997.
Nearly all of last year's work on medium grains was conducted on early and very early experimentals. Moisture at harvest is used as an important indicator of maturity. A number of Calrose-type experimentals in statewide yield tests had harvest moistures lower than M-202. Several of these are being eyed as possible replacements for current medium grains or show other promising features. Preliminary yield tests at the Hawaiian nursery also identified a number of entries that show promise over current medium grains with earlier maturity, greater yield potential, superior lodging resistance and/or improved grain quality. Although combining stem rot resistance with other agronomic improvements has been difficult, six of these preliminary entries show good stem rot resistance and are being advanced in Hawaii.
Efforts increased to improve stem rot resistance and enhance seedling vigor, these experimental materials are beginning to occupy a significant part of the medium-grain program. Agronomic performance is gradually improving as new materials evolve out of the back- crossing program. The greatest challenge so far has been improving stem rot resistance to at least that of M-201. An expanded effort is under way to harness seedling vigor from Hungarian and Russian rice varieties. Breeders note factors other than rapid leaf emergence through water are involved in establishing good stand density. Growth rate, leaf droopiness and other traits are being evaluated.
A new medium grain is planned for release in 1998. M-205 is an early maturing, smooth, large-seeded and high-yielding Calrose quality rice. Formerly tested as experimental 92-Y-624, its kernel weight is similar to Calpearl and is 4 percent heavier than M-204. Kernel shape is similar to M-401. It has the potential to serve rice cake markets and special niche markets for a larger-seeded Calrose rice. Agronomically, it is similar to M-202 in seedling vigor, height, lodging and resistance to blanking. Stem rot resistance is similar to M-201. In a yield test comparing it with Calpearl, the new variety had an 11 percent yield advantage, headed 8 days later and had 4 percent higher moisture at harvest. It is projected to do well in areas that can grow M-201 successfully - generally the northern half of the Sacramento Valley. Foundation seed production is slated for 1997.
"Premium quality" is a term used to describe short and medium grain varieties, such as M-401, with the unique cooking characteristics preferred by certain ethnic groups. These rices tend to be very glossy after cooking, sticky with a smooth texture and remain soft after cooling. Aroma and taste are also cited as important features. Premium quality is not clearly defined or well understood. Thus selecting for this characteristic poses a special breeding challenge. Nonetheless, the market success of premium quality medium grains, the opening of rice exports to Japan and other Asian countries and the limited production of California-grown Japanese varieties continue to fuel interest in this area.
Promising new breeding lines have been generated from conventional plant breeding techniques and from induced mutants of Koshihikari. However, it has proven unexpectedly difficult to find new experimental lines with the distinct cooking quality advantages necessary to set them apart from agronomically solid varieties such as M-401 and M-202. Improved quality evaluation methods, larger breeding populations and recurrent crossing of improved lines are being used to address this obstacle. Small-scale cooking tests and near-infrared spectroscopy are also helping select quality components. Samples of advanced lines were sent to California marketing organizations and Japan for quality evaluation in November, with additional testing scheduled in 1997.
A number of advanced premium lines are being evaluated through milling and cooking tests. One medium-grain entry, 94-Y-118, received positive preliminary evaluations in 1995 cooking tests and produced good milling yields. It continued to perform well last year. If its quality and late maturity prove acceptable, this advanced line could undergo additional seed increase. From statewide yield tests additional lines, developed from crosses to premium Japanese varieties such as Koshihikari and Akitakomachi, showed promising milling yield, kernel appearance and laboratory and cooking quality evaluations. The best performers will be advanced.
In statewide yield tests S-102, a new short grain released to growers in 1996, performed comparably to the industry's other primary short grain, S-201. Some of the problems with S-201 are its intermediate maturity, non-synchronous heading and low head rice yield. A number of early maturing short grains produced very high grain yields. Some of these lines with stemrot resistant parentage will be further tested in 1997.
Work on specialty purpose rice, including short-grain waxy varieties such as Calmochi-101, is challenging. For instance, one experimental line, 93-Y-195, has given inconsistent results, producing well in 1994, poorly in 1995 and then well again in 1996. This line will be replaced by a new waxy line that performed well last year in preliminary yield tests. In general, special purpose varieties often have unique or undefined cooking characteristics that make quality evaluation and selection difficult.
Another specialty purpose rice is the large-seeded "Italian types". Plant breeders reported that 96-Y-072, a new experimental line, performed fairly well in agronomic tests and is scheduled for further quality testing. Small plot yield tests contained additional large-seeded lines and several induced mutants of the Italian variety "Arborio." These will undergo further quality evaluation. It is very common to find the special purpose quality strongly associated with poor adaptation, low yield potential or low head rice yield.
Rice Water Weevil Tolerance
Tolerance to the rice water weevil is another important research objective. Rice water weevil tolerant lines have difficulties with blanking, lodging, and susceptibility to stem rot. Selections are made against these undesirable traits and the best new materials will be advance to the RWW nursery in 1997.
The discovery last year of rice blast, a potentially devastating new disease for the California rice industry, overshadowed other developments in rice disease research. The possible impact this discovery could have on California rice varieties is discussed in an adjoining sidebar.
Meanwhile, an intense effort continues to search for improved sources of resistance to stem rot and aggregate sheath spot. In addition to the extensive work in the RES disease nursery, the plant pathologist also cooperated with UC farm advisors in a disease survey of 17 sites in Butte County. Information from the survey will be used to track changes in disease incidence and severity as the burning phasedown continues.
One hundred fifty-eight new crosses were made to transfer disease resistance derived from 0. rufipogon to adapted California varieties. Nineteen crosses were made to transfer resistance from other wild species of rice that have even greater resistance to stem rot and/or aggregate sheath spot than 0. rufipogon.
More than 6,000 rows were grown in the disease nursery in 1996. Breeders exert heavy selection pressure against undesirable characteristics in resistant material - low seedling vigor, low tillering and susceptibility to blanking. Only a fraction of the lines screened show higher levels of stem rot resistance than M-201.
A large cooperative project is under way with the USDA-ARS geneticist at UC Davis to use advanced techniques in molecular biology to 'map" stem rot resistance genes in the resistant long- grain 87-Y-550 and in medium grain populations. If successful, stem rot resistance genes could be identified in the laboratory and transferred to all grain types. Researchers hope that these techniques in combination with a rapid generation advancement scheme will greatly accelerate development of stem rot resistant varieties for California.
Plant breeders also hope to tap into resistance to sheath spot from certain wild species of rice that are highly resistant to a similar fungus, sheath blight. These materials have been brought in through quarantine from the International Rice Research Institute and evaluated for sheath spot resistance. The best materials were crossed with adapted California materials.
In addition to enhancing stand establishment, good seedling vigor may also reduce the adverse effects of seedling disease. California varieties have relatively good levels of seedling vigor. Nonetheless, crosses are being made to transfer high levels of seedling vigor in rice germplasm from Italian and Hungarian varieties. Incubator tests screened 71,000 seedlings of Italica livorno and M-16 in 1996. Approximately 1,500 of these seedlings were selected and transplanted in the field to further screen for short stature and stem rot resistance. Seven Russian plant introductions were also evaluated.
Rice Blast Invades California
Rice blast, a potentially devastating fungal disease present in most other rice areas of the world turned up in Glenn and Colusa counties in early September 1996. The disease identified by researchers from the University of California, Rice Experiment Station and USDA. They quickly embarked on a proactive plan with industry groups to address this potentially serious problem.
The fungus was confirmed in 33 of 508 rice fields surveyed by a team of UC plant pathologists and a local UC farm advisor. The infection was confined to northern Colusa and southern Glenn counties. Many of the infected fields were burned under the "act of God" provision of the burning phasedown. Greenhouse studies and DNA "fingerprinting" have identified the race of this fungus as IG-1, which is present throughout the rice-growing regions of the world.
Rice blast is considered the most serious fungal disease of rice in the world. The fungus can infect rice plants at any stage of growth, attacking leaves, stems and/or panicles. Leaf blast is characterized by spot infections in the form of diamond-shaped lesions with a grayish center and a dark brown margin. Panicle blast (rotten neck) is considered the most damaging phase of the disease and occurs when the neck node of the panicle is attacked. Nutrient supply to the panicle is cut off and grains are partially or completely unfilled. The panicle may even break over on the stem.
The disease can complete its lifecycle in as little as a week, allowing it to produce several disease cycles in a growing season. Spores are produced in large numbers on the surface lesions and are spread to other plants by the wind. Conditions that favor infection are high humidity, warm temperatures, leaf wetness, and a susceptible host variety.
The blast fungus has hundreds of different strains or races that attack different varieties of rice. Especially virulent races may even develop and attack resistant rice varieties. California rice varieties are very susceptible to the major races of blast. Yield losses could be as high as 50 percent if left untreated.
The University of California, Rice Experiment Station, California Department of Food and Agriculture and county agricultural commissioners developed a plan for intensive control of the current outbreak. Measures include information and educational outreach, burning infested and adjacent fields, utilization of certified seed, the use of permissible seed treatments, and the registration of fungicides for use in control. A task force coordinated by the California Rice Industry Association has also been set up to develop a science-based strategy for control and containment of the disease.
Much of the initial research effort has been geared toward identifying the disease, its distribution and the conditions that allowed its development. Researchers have no way of predicting whether, where or when the disease could strike this year. Scientists will be monitoring the situation and surveying fields for signs of the disease, as well as conducting fungicide trials.
Although blast-resistant varieties are used in other parts of the world, they are not a viable option in California. These varieties are poorly adapted to California growing, conditions and lack the yield potential, cold tolerance, seedling vigor and grain quality characteristics of California varieties. Nonetheless, plant breeders have already begun efforts to incorporate acceptable levels of blast resistance into California varieties.
The RES plant pathologist has initiated a comprehensive search for single and multiple gene sources of blast resistance. Since blast has not been observed in Butte County, researchers will, as a precautionary measure, not conduct inoculations or screening work at the Rice Experiment Station. This testing will be done at infested sites, as well as in laboratories at UC Davis and the USDA-ARS facility in Texas. This is being done to prevent further spread of the disease and to protect the foundation seed at the RES.
Transgenic Rice Research
Genetically engineered rice with built-in resistance to broad spectrum herbicides may be on the way to California, but experiments at the Rice Experiment Station last summer indicate that it will be a few years before they are commercially available.
Genetically engineered herbicide resistance is already used in com, soybeans and canola. Development of herbicide resistant rice varieties could be very beneficial to California rice growers who face major problems with herbicides and weed control.
Rice Experiment Station researchers received transgenic lines containing a gene that confers resistance to the broad spectrum herbicide Liberty® (glufosinate). Provided by the LSU Rice Research Station and AgrEvo USA, these lines were developed from medium and long grains adapted to the South and from one Japanese variety. Experiments were conducted to determine the resistance of these genetically altered lines to Liberty®. Although these are varieties not adapted to California growing conditions, researchers were more interested in evaluating how they compared to an unresistant parent variety.
Reaction to the Liberty® application was "very dramatic". There were notable differences in the level of visual damage on different transgenic lines. Yellowing symptoms on the transgenic lines rapidly disappeared as the plants matured. Most of the susceptible parent varieties were killed, although a few escaped because of insufficient herbicide coverage or late emergence through water. These differences were statistically significant.
The results of this study confirm the plausibility of genetically engineered herbicide resistant rice varieties. They also show, however, some of the obstacles to the successful application of this technology. It's one thing to insert a gene into a rice plant; it's quite another to develop one that performs up to the agronomic quality and consumer standards the California rice industry has come to expect. Transgenic rice must be beneficial and acceptable to growers, marketers and consumers.
Intensive screening, testing and crossing programs will be needed to develop a well-adapted transgenic variety equal to its parent. This will require the expertise and involvement of plant breeders to select and "clean up" transgenic lines. In addition, all the research and testing required for any herbicide will be needed.
Success will involve the combined efforts of breeders, weed scientists, agronomists and the genetic engineering companies. Discussions are currently under way with major agrochemical companies to facilitate application of this genetic technology to the improvement of California rice varieties. AgrEvo USA is working on a Liberty®-Linked rice for California and Monsanto is developing Round-Up® Ready rice for California.
This is a new area for agriculture in general and there are many complex scientific, regulatory, consumer and ownership issues still unresolved. Thus, it may be years before this technology is ready for commercialization in California.