|Rice Breeding Program-98
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
developments in personnel, new varieties, research activities and facility groundbreaking
made 1998 a "landmark year" for the Rice Experiment Station (RES). The 370-acre
RES near Biggs is acquiring an additional 95 acres of adjacent land for plant breeding,
agronomic and weed research and foundation seed production. Two new greenhouses are under
construction which will accelerate screening and breeding for blast resistance by RES
scientists and weed research by University of California scientists. A summary of these
and related developments is reported below.
Statewide yields plummet
California rice acreage remained robust at an estimated 478,00 acres. However, statewide yields plummeted to 6,840 pounds/acre from 8,300 pounds/acre in 1997. The weather was primarily to blame for this lowered productivity -- spring rain delayed planting, hot summer temperatures affected rice development and a much shortened growing season and a larger acreage of lower-yielding Japanese varieties added to lower yields. About 90 percent of California rice acreage is grown with public commercial varieties developed at the Rice Experiment Station.
Initial seeding of the RES breeding nursery began almost a month late on May 25. Seedbed preparation and fertilizer incorporation were less than desirable because of rain and wet soil. Weed control was good. Some tadpole shrimp damage was observed in the nurseries.
Plant breeders made 1,063 new crosses for rice improvement in 1998, bringing the total to 24,156 since 1969. Approximately 70,000 progeny rows were grown for selection, purification and generation advance. The nursery contained 4,337 small plots and 3,025 large plots in various water-seeded yield tests. An estimated 25,000 panicles and 10,000 rows were harvested for selection, advancement, quality evaluations and purification for progeny rows. Twenty-seven experimental lines were grown in headrows for seed increase, quality evaluations and purification. Eight advanced lines are undergoing breeder seed increase. Headrows of M-204, S-102, Akitakomachi and new varieties L-205, Calmati-201, Calhikari-201 and M-402 were also grown for breeder seed production.
The Hawaii winter nursery, which accelerates advanced breeding material and allows for cold tolerance screening, contained 5,000 rows planted Dec. 1-4, 1997. Rice blast disease was discovered in this nursery and confirmed as the same race in the current California infestation. All seed selections shipped back to California were inspected and treated to minimize risk of introducing blast at the RES. No blast was found on any of this material. The RES is working with the University of Hawaii to control the blast problem, as well as an increasing problem with bird depredation. Another 5,000 rows were seeded Nov. 12, 1998, transplanted Dec. 3, 1998 and were to be harvested in late March or early April 1999 for planting in California breeding nurseries.
Three acres of precision drill-seeded F2 populations and 6,906 dry-seeded progeny rows were grown in the UC Davis cold tolerance nursery. Stand and grass control were good and a low level of blanking was reported. The San Joaquin Cold Tolerance nursery was discontinued; an alternate site is being sought. However, a water-seeded planting of 701 rows of advanced breeding lines was grown at the San Joaquin location of the Statewide Yield Test to provide additional cold tolerance information. Two refrigerated greenhouses at RES are also used in selecting for blanking resistance.
Statewide Yield Tests
Statewide Yield Tests conducted annually in grower fields help scientists evaluate the performance of advanced experimental lines and commercial varieties. Late spring rain delayed seeding of some plots until the last week of May. Water-seeding and conventional management practices were used. Results from these trials are reported 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. These tests included 488 entries and check varieties. Top experimental lines performed well and will be advanced for further testing in 1999 Statewide Yield Tests.
Long grain breeding efforts have expanded beyond efforts to develop conventional long grains to include rice for processing and ethnic markets.
One of the oldest objectives of the RES breeding program has been to develop conventional long-grain varieties suited to California growing conditions. The first of these to be released, L-201, cooked softer and was more adhesive than typical dry and fluffy long grains grown in the Southern United States. L-202 and L-203 had similar problems with stickiness. The most recent variety L-204, released in 1996, and a new experimental line, 94-Y-40, are addressing concerns about softness and should enable California long grains to compete more favorably. L-204 continued to perform well in Statewide Yield Tests.
Newrex rice is used in parboiling, soup canning and rice noodles. The experimental long grain with Newrex cooking qualities, 94-Y-40, is scheduled for release as L-205 in 1999. This is an early maturing, semidwarf that heads similarly to other long grains. L-205 plants are awnless and have glabrous leaves and hulls. It is more likely to lodge than other long grains under excessive nitrogen fertilization. Grain and head rice milling yield are comparable to L-203 and L-204 (see table).
Basmati is an aromatic rice from Pakistan and India that is characterized by extreme kernel elongation and little width expansion during cooking. A short-stature basmati experimental line, 96-Y-90, is scheduled for release in 1999 as "Calmati-201." Plants of Calmati-201 have pubescent leaves and hulls and occasionally short awns. It heads about the same time as A-201 and an average of five days later than L-204. Seedling vigor is weaker than L-204 and A-201. Head rice milling yield is less than L-204 but better than A-201. Eighteen other aromatic experimental lines were included in 1998 yield tests.
Research is continuing on several other special purpose long grains. Six of seven "waxy" experimental lines out-performed L-204 and could be further developed for breeding purposes or as new cultivars.
Breeding for disease resistance is an important objective for all grain types. High-yielding stem rot resistant experimental lines have been developed from the wild species Oryza rufipogon. Some of them will be grown for purification and seed increase during 1999. Breeding for blast resistance has become a top priority since the disease was discovered in 1996. Elite long grain lines have been crossed and backcrossed to find sources of resistance. Approximately 200 individual plants from 31 F3 rows were harvested and screened for blast resistance. More than 100 F4 lines were being grown in the winter greenhouse for generation advance. A large number of F3 lines will be evaluated in 1999.
Calrose Medium Grains
Calrose medium grain breeding objectives focus on high stable yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to cold temperature blanking to improve varieties for current and future markets. An increased effort to incorporate blast and stem rot resistance was also made in 1998. Transgenic M-202 was evaluated at several locations. Improvements in medium grains are also being tapped from M-16, Italica livorno and several Russian varieties.
Work continued on two promising experimental medium grains scheduled for foundation seed production in 1999. They include:
A number of other promising medium grains with harvest moisture lower than M-202 are under consideration for 1999 Statewide Yield Tests. There are 23 Calrose medium-grain entries being grown in the Hawaii winter nursery from Preliminary Yield Tests. These entries have greater yield potential than their respective checks, lodging resistance superior to M-202 and/or improved grain quality. Further testing will be conducted on three of these entries, which showed better stem rot resistance than M-201.
Efforts to develop blast resistant Calrose have increased significantly. There were 1,197 blast rows from the 1997-98 Hawaii nursery grown at RES in 1998. Progeny from 26 percent of these should produce large plot yield entries in 1999. In addition, there are other Hawaii rows of F2 blast parentage that could produce as many as 3,000 rows at the RES in 1999. Domestic and foreign germplasm with confirmed resistance to the California blast race continue to be used in crosses to adapted California germplasm. Of the 366 Calrose crosses last year, 57 percent were blast related.
Transgenic M-202 lines with resistance to two different herbicides were evaluated under field conditions for the first time in 1998. Research included yield testing, headrows, transplants and a drill-seeded nursery, which required procedural changes and significant increases in land, equipment and staff time. Many uncertainties surround transgenic rice, such as potential yield reduction, changes in rice seed production and distribution systems, cost of transgenic seed, weed resistance potential and slower genetic improvement. Potential agronomic weaknesses, which are being investigated in varietal testing, include more lodging, delayed maturity, drought stress, height changes, negative grain size and symmetry changes and greater sterility. Other unknowns include cooking quality, consumer acceptance, marketing strategies, storage and potential herbicide limitations imposed by regulatory agencies. The "bottom line" is transgenic herbicide resistance may become a new tool for weed control but it will not be a cure all for every production field.
Highlights from other medium grain research includes:
Premium Quality/Short Grains
Premium quality rice, such as M-401, has unique cooking characteristics preferred by certain ethnic groups. This rice tends to be very glossy after cooking, sticky with a smooth texture and remain soft after cooling. An intensified effort to develop premium quality short grains and improved premium quality medium grains was initiated in 1988. Breeding efforts, cooking and milling quality testing and rice quality research have expanded extensively. This work has paid off with the scheduled release of two new premium quality lines in 1999.
The first is 94-Y-118, a semidwarf, late maturing medium grain with smooth hulls, proposed for release as M-402. Compared to M-401, it averages six days earlier heading, is slightly shorter and experiences half as much lodging. It averaged a 600 pound yield advantage over M-401 -- 9,160 pounds/acre vs. 8,580 pounds acre -- over five years. In other comparisons to M-401, the new variety has shown significant improved grain translucency, higher head rice milling yield, smaller kernel size and weight, similar cooking quality and improved milling yield.
The other premium quality variety is 96-Y-055, a semidwarf, early maturing, pubescent premium quality short grain proposed for release as Calhikari-201. Yield potential and resistance to lodging is significantly greater than Japanese varieties Akitakomachi and Koshihikari but still well below M-202. Over a three-year period it averaged 7,430 pounds/acre, compared to 6,290 for Akitakomachi and 5,700 pounds/acre for Koshihikari. Its milling yield potential is high but somewhat less than the Japanese varieties. It scored acceptably in taste tests. California rice marketing organizations also have expressed a commercial interest in Calhikari-201.
Improvements in yield potential, resistance to disease, and grain and yield milling characteristics continue to be the main focus of the short-grain breeding effort. S-102, the short grain released to growers in 1996, has become the predominant California short grain in commercial production. It also was the top yielding entry in the very early group of the Statewide Yield Tests. Several early maturing short grains performed well. One is being purified and advanced for further testing, while others are undergoing further evaluation.
Improvement in short-grain waxy rice is focusing on "glabrous" lines characterized by smooth leaves and hulls. Entry 96-Y-196 continues to perform well in comparison to Calmochi-101. Other special purpose rices under study include large-seeded Italian types. Several of these are showing grain and milling yield improvements and are being evaluated in preliminary and statewide tests.
Greenhouse screening confirmed blast resistance in several short and premium quality elite breeding lines. These materials are being rapidly advanced for yield testing and use as donor parents in blast resistance. Resistant lines from crosses with M-401 will be yield tested in 1999. Breeding for stem rot resistance continues, with several promising new crosses evaluated in small plot yield tests. Work is also continuing with the germplasm line PI 506230 to transfer resistance to rice water weevil.
Most rice pathology work is directed toward resistance to stem rot, sources of which also confer resistance to aggregate sheath spot and boarded sheath spot. Resistance to rice blast, however, is now a significant breeding objective.
Seventy-five new crosses were made at the Rice Experiment Station to transfer stem rot resistance from the wild species Oryza rufipogon. Another 338 first and second backcrosses were made from six other types of wild rice with even greater resistance to stem rot. There were about 9,000 rows grown in the 1998 stem rot nursery, only a fraction of which showed higher levels of stem rot resistance than M-201. RES scientists also completed a cooperative project with geneticists at UC Davis to identify molecular sources of resistance.
A few advanced lines with blast resistance in their pedigrees offer the greatest hope for rapid release of a resistant variety. Researchers made 251 crosses and backcrosses with lines having major genes for blast resistance in 1998. About 1,500 lines were screened at Chico State University. In addition, efforts to improve screening techniques are looking at fertilizer rate, timing and application method, as well as harvesting and evaluation of blast spores.
As previously noted, blast appeared in the Hawaii winter nursery in the 1997-1998 season. Seed was treated with chlorine bleach after being received in California and precautions are being made in 1999 with a fungicide to minimize the risk of future outbreaks. No blast has yet been found at the Rice Experiment Station.
Although only one race of blast has been identified, RES scientists feel it prudent to pursue genetic sources of resistance to multiple races of the disease and have begun a cooperative project with UC Davis geneticists with that objective in mind. A screening nursery will be started at the Rice Experiment Station when the disease spreads to Butte County, but until that time researchers will restrict field testing for additional sources of resistance to currently infested locations.
Research into the long-term effect of winter flooded field conditions and straw decomposition continued for a fourth year on a 25-acre plot adjacent to the Rice Experiment Station. A companion study is being conducted in Colusa County and is reported in the rice diseases and nitrogen availability/fertilizer recommendations sections of this annual report.
Rice straw from each harvest was flail chopped to reduce straw length in the soil incorporated and rolled methods. Rice straw was soil incorporated by chiseling two times followed by a few days of drying and then disking again before flooding. After straw was burned, removed and soil incorporated, winter flooded treatments were flooded to a depth of four to six inches. A cage roller donated to RES by Ducks Unlimited was used to roll the straw rolled treatments. Late spring rains resulted in poor conditions for seedbed preparation and may have affected rice performance in the test plots. M-202 was used in this study.
As in the first three years of this study, winter flooding did not influence rice grain yield in 1998. Rice straw management method, on the other hand, had a highly significant effect on yields. Grain yields were significantly reduced when straw was removed or rolled compared to when straw was burned or incorporated. A multi-year analysis shows that the straw removal method results in a highly significant average grain yield reduction of about 500 pounds per acre below burned or incorporated methods. The lower grain yields are linked to a potassium deficiency, as evidenced by firing and rust spotting on the tips of upper leaves. Soil potassium is marginal at this site, so removal of potentially recyclable potassium would exacerbate the problem. Thus, straw removal may induce mineral deficiencies that will necessitate increased fertilizer applications and significant cost increases. This study will conclude after 1999 unless new results and/or more financial support are generated to continue the research.