Rice Breeding Report-97


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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

M202.jpg (95441 bytes)California rice acreage edged up slightly in 1997 to 513,000 acres, a 13,000 acre increase over 1996. Medium-grain varieties continue to be the growers' grain of choice, led by M-202 with 60 percent of rice acreage. Average statewide yield rebounded in 1997 to 8,300 pounds per acre, up from about 7,500 in 1996. Most of this acreage - 95 percent - is planted to public varieties developed by scientists at the Rice Experiment Station (RES). Highlights of their activities and accomplishments are detailed below.

Breeding Nurseries

Seeding of the 1997 RES breeding nursery began ahead of schedule on April 28. Weed control was good; however, phenoxy herbicide damage occurred in sections of the nursery.

Plant breeders made 774 crosses for rice improvement during 1997, bringing the total since the program began in 1969 to 23,093. Approximately 70,000 progeny rows were grown for selection, purification and generation advance. The nursery contained 4,075 small plots and 2,456 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 25,000 panicles and 10,000 rows were harvested for selection, advancement, quality evaluations and purification for progeny rows. Thirty-eight experimental lines were grown in headrows for seed increase, quality evaluations and purification. Eight advanced lines are undergoing breeder seed increase. Headrows of M-201, M-202, M-401 and S-201 were also grown to maintain the genetic purity of registered and certified seed.

The Hawaii "winter" nursery, which accelerates advanced breeding material and allows for cold tolerance screening, contained 5,000 rows planted Nov. 18-20, 1996. Seed production was generally good. Harvested seed was shipped to California, processed and grown out in summer nurseries. Another 5,000 rows at the RES winter nursery were scheduled to be harvested in March and April of 1998.

Two acres of precision drill-seeded F2, populations and 6,900 dry-seeded progeny rows were grown in the UC Davis cold tolerance nursery. Stands and grass control were good and a low level of blanking was reported. The San Joaquin cold tolerance nursery included precision drill-seeded F2, populations and 6,354 dry-seeded progeny rows. The nursery, located on organic soil, had to be abandoned because of problems in planting, seedling emergence and weed control. An alternate location will be used in 1998. Two refrigerated greenhouses at the RES are also used to screen breeding lines for blanking resistance.

Statewide Yield Tests

Researchers from the Rice Experiment Station in collaboration with UC Cooperative Extension specialists and county farm advisors annually conduct statewide 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 488 entries and check varieties in 1997.

Long Grains

Long-grain breeding efforts have expanded in recent years from selection for conventional characteristics to include Newrex and "basmati" qualities.

Field Day Trk.jpg (47158 bytes)Conventional or southern U.S. long grains typically cook dry and fluffy. Two years ago the CCRRF released L-204, a new long-grain variety with these characteristics that has significantly improved head rice milling yield over earlier long-grain releases. In nine tests conducted with UC Cooperative Extension last year, L-204 averaged 9,470 pounds/acre, comparing favorably with 9,660 pounds/acre for M-202. Emphasis is now being placed on cold tolerance, head rice milling yield and cooking characteristics. Experimental lines with good yield potential and head rice yield are also being examined.

Newrex quality rice is a special purpose long-grain rice used for parboiling, soup canning and rice noodles. Research at RES has developed an early maturing experimental line, 94-Y-40, that has Newrex quality. About 1,500 pounds of breeder seed was produced in 1997 and will be used for foundation seed increase in 1998. Seed of 94-Y-40 will be released in 1999 if it performs well in 1998.

Basmati rice is an aromatic long grain characterized by extreme kernel elongation and little width expansion during cooking. It commands a premium in both domes- tic and international markets but is poorly adapted to California. However, research is progressing well to develop a California-adapted basmati. The advanced basmati line 96-Y-90 is under evaluation for market potential. Headrows were grown in the Hawaii winter nursery for further purification and the seed was increased for foundation seed production in 1998.

Another special purpose rice under closer scrutiny includes the experimental 94-Y-39, which could be used as a basis for developing a Jasmine type aromatic long grain. It performed well in statewide yield tests.

A high-yielding long- grain experimental line, 94-Y-561, with confirmed resistance to stem rot and aggregate sheath spot unfortunately has not produced an acceptable head rice yield that is required for commercial varieties. It will be used as an improved source of stem rot resistance in the RES brccding program for transferring resistance to all grain types. Breeding cfforts are also under way to develop California long grains with resistance to rice blast.

Medium Grains

High yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to cold temperature blanking - these are some of the chief objectives that are being pursued to improve Calrose type medium-grain varieties. Three experimental entries will be advanced in 1998 pending continued acceptable quality evaluations. They include:

94-Y-615 - an early maturing, smooth, very high yielding medium-grain Calrose quality rice. It has shown an II percent yield advantage over M-202 and is being considered as a potential replacement for the industry mainstay.

95-Y-214 - a very early, smooth, high yielding Calrose- type medium grain. It has shown an 8 percent yield advantage over M-103, better lodging resistance, and equal milling quality. It could be an alternative for growers in the coolest production areas.

95-Y-356 - an early maturing, smooth, high yielding Calrose-type medium grain. It has shown a 2-4 percent yield advantage over M-202 and is characterized by excellent lodging resistance. With lodging resistance superior to M-201, it would be well-suited to harvest with stripper headers.

An advanced experimental line, 92-Y-624, intended for release as a new medium-grain variety this year has been dropped. Problems cited included increased lodging potential; the loss of a major rice cake producer from California; and variety identity, storage, commingling and milling output with its larger seed.

Several other experimental medium-grain lines will be considered for testing at RES in 1998. Their attributes include high yield capacity, lodging resistance, faster dry down rates and improved milling yield. Twenty-three Calrose medium-grain lines were grown in the Hawaii winter nursery for purification, seed increase and additional agronomic evaluation.

Finding genetic sources of resistance to blast has become an important objective in the medium grain effort. Medium grains with possible blast resistant parentage have been evaluated but no major gene resistance has been found. However, advanced experimental lines have been crossed and backcrossed with sources of blast resistance.

Increased emphasis has been placed on identifying experimental lines with improved head rice and total milled yields. Researchers implemented new techniques and modified procedures and are focusing on milling quality, harvest moisture, plant density and morphological characteristics. Advanced experimental lines in the second year of statewide testing or at the breeder increase stage were evaluated for head and total milled rice.

Progress is also being made to improve stem rot resistance and seedling vigor. New breeding material from a long-grain resistant source and new backcrosses with the wild species Oryza ruftpogon are beginning to enter the yield testing stage. UC Davis plant pathologists finished screening 12,400 entries from the USDA germplasm collection at the RES for stem rot resistance. Thirty-six selections will be further evaluated in 1998.

Priorities for 1998 include continued screening for blast resistance, development of herbicide-resistant M-202, and enhanced stem rot resistance in Calrose type medium grains.

Premium Quality/Short Grains

"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. However, premium quality is not clearly defined or well understood. Market success of premium quality medium grains, the opening of rice imports to Japan and other Asian countries and a recent limited production of California-grown Japanese varieties continue to fuel interest in this area.

A large volume of premium quality breeding material has been generated over the years. Nonetheless, tapping into premium quality characteristics is proving difficult and frustrating. Breaking the association with some undesirable characteristics such as weak straw and low yields inherent in much of the Japanese germplasm is proving to be very difficult. Expanded quality and cooking evaluations were initiated in 1997 on advanced premium quality experimental lines from RES and off- station yield tests.

One experimental premium quality medium-grain line, 94-Y-118, has performed well in statewide yield tests since 1994. Its strongest attribute is higher milling yields than M-401. Quality evaluations from marketing organizations have been generally positive. Headrow and breeder seed were produced in 1997, enabling further seed increase and foundation seed production in 1998. Several advanced experimental premium quality short-grain lines developed from crosses to the premium Japanese varieties Koshihikari and Akitomachi are being advanced and evaluated for agronomic and quality characteristics.

Improvements in yield potential, resistance to disease, and grain and milling characteristics are the main focus of the short-grain breeding effort. S-102, the new short grain released to growers in 1996, performed well in commercial plantings last year. A number of early maturing short grains produced very high grain yields in preliminary yield tests and will be further tested for quality, resistance to blanking, and tolerance to water weevil and stem rot.

Special purpose rice includes short-grain waxy varieties such as Calmochi-101. Entry 96-Y-196 produced very high yields the last two years and will be evaluated for quality by processors and tested further. Three other waxy lines with high yield potential are undergoing quality and milling testing. Breeding for large-seeded "Italian types" is continuing, with one experimental line performing well and set for further quality testing. Sources of stem rot and blast resistance are being advanced for confirmation of resistance and field testing. Work on tolerance to rice water weevil suffered a major setback when nursery plantings were completely eaten by crawfish.

Rice Pathology Jeff Oster 1.jpg (43885 bytes)

Until last year most work on breeding for disease resistance was directed toward stem rot. However, the discovery of rice blast disease in the fall of 1996 compelled the RES to broaden its research by including this potentially devastating disease.

Researchers made 124 new crosses to transfer stem rot resistance from the wild species 0. ruftpogon to adapted California varieties. Seventy-six crosses and backcrosses were made to transfer resistance from other wild species of rice that have even greater resistance to stem rot and/or aggregate sheath spot. Four new crosses were made with plant introductions having stem rot resistance. About 7,000 rows were grown in the 1997 disease nursery.

A large cooperative project with the USDA geneticist at UC Davis is using molecular genetic techniques to "map" stem rot resistant genes from the resistant long-grain line 87-Y-550, which was derived from the wild species 0. rufzpogon. A genetic marker associated with this resistance has been found. Work continues to develop marker- aided techniques suitable for large-scale screening. Initial plans have also been made to map resistance genes in other wild specics now in the crossing program.

Rice blast spread significantly last year. Two state- wide yield tests from the early maturity group and 2,700 rows in blast-affected areas were rated in 1997. Although no entries were completely resistant, there were differences among the entries. Advanced lines with resistant parents in their pedigrees were screened by the USDA pathologist in Beaumont, Texas. A few of these lines appear to have major gene resistance and offer the best hope for rapid release of a resistant variety. Plans are also to map and develop marker-assisted screening for blast resistance genes.

Although California varieties have relatively good levels of seedling vigor, strengthening this characteristic will help enhance stand establishment, provide competition with early weed growth, reduce seedling disease and permit deeper water during stand establishment. Work is continuing with material deriving vigor from the Italian variety Italica livorno and the Hungarian variety M-16 to incorporate higher levels of seedling vigor. Five new crosses were made in 1997 and 65,000 seedlings were screened in incubator tests. Approximately 1,500 seedlings were selected and transplanted in the field to further screen at maturity for short stature and stem rot resistance.

This past year 106 varieties were brought through quarantine, including four wild species with stem rot and aggregate sheath spot resistance, 27 varieties with blast resistance, 59 with specific yield-enhancing traits, six with salt tolerance and 10 for the USDA geneticist at UC Davis.

Straw Management

RES and UC scientists have completed three years of observations in a 25-acre plot adjacent to the RES for studying straw management methods under winter flooded and unflooded conditions. A companion study has been under way in Colusa County.

Preliminary findings show no difference in grain yields between the flooded and unflooded conditions. However, grain yield was significantly lower when straw was removed than when it was burned or incorporated into the soil. Straw rolled plots yielded slightly more than the straw removed plots.

Straw removal appears to be intensifying potassium (K) deficiency at the site and is linked to lower yield when straw is removed from the field. Eighty pounds of K fertilizer reasonably corrected the deficiency in the burned, soil incorporated, and rolled methods but 120 pounds was necessary to correct the deficiency when the straw was removed from the field. Thus, factors other than K deficiency may be at work, such as disease or other mineral nutrients. More definitive answers on K plant nutrition in relation to straw management will be sought in 1998.

Soil incorporation and rolling of straw caused the rice to mature two to three days later than when the straw was burned or removed. Later maturity may have been caused by more N and/or interaction with other mineral nutrients when the straw was returned to the soil.

Additional information on this study can be found in the sections "Cause and Control of Rice Diseases" and "Reassessing soil nitrogen availability and fertilizer recommendations under alternative rice residue management practices" elsewhere in this report.

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