Rice Breeding Report - 2010




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Project Leader and Principal  Investigators

Kent S. McKenzie, Director, Calrose medium grains

Farman Jodari, plant breeder, long grains

Virgilio Andaya, plant breeder, Premium quality and short grains

Jeff Oster, rice pathologist




The California public rice breeding program has developed 43 improved rice varieties since accelerated research began in 1969. Foundation seed of 13 public varieties and basic seed of two Japanese premium quality varieties were grown on 140 acres at the Rice Experiment Station (RES) in 2010.

The rice breeding program consists of four ongoing research projects developing California-adapted varieties for specific grain and market types. With the departure of Jacob Lage, the Calrose medium grain project is now led by RES director Kent McKenzie. Farman Jodari leads the long grain project. Virgilio Andaya is project leader for premium quality, waxy, and California short grains. He also now handles early generation stages for medium grains. Manage-ment of the DNA marker laboratory has been assigned to Cynthia Andaya. Plant pathologist Jeffrey Oster supports efforts to improve disease resistance in all projects. Progress highlights are reported below.

Breeding nurseries

Seeding of the 2010 breeding nursery began May 15 and was completed by May 22. A total of 1,305 new crosses were made for rice improvement, bringing the total to 39,713 since 1969. Crosses made in early spring 2010 were grown during the summer at RES to produce second-generation seed. Crosses made in summer were planted in the Hawaii winter nursery and/or in the RES greenhouse to accelerate the selection process.

The 2010 RES breeding nursery occupied approximately 74 acres. Water-seeded yield tests included 4,230 small plots and 3,500 large plots. Small seed-increase plots, cooking samples, and advanced breeding lines were grown on three acres.

The nursery included 51,000 water-seeded and 28,000 drill-seeded progeny rows. Second-generation and fourth-generation populations from 2008 and 2009 crosses were grown in precision drill-seeded plots on eight acres. An estimated 150,000 panicles were selected from various second-generation populations for screening and advancement. Approximately 2,400 head rows of M-206, M-208, 05Y471, Calmochi-101, Calmati-202, and Koshihikari were grown for breeder seed production in 2010.

Selection and harvest of the 2009-’10 Hawaii Winter Nursery was completed and seed returned to RES for planting in May. The nursery included 8,400 progeny rows and 584 first generation crosses. The 2010-’11 winter nursery, with 8,800 rows, was planted November 2, and 691 first-generation populations were transplanted to the nursery November 24. Selection and harvest was scheduled for April 2011, with seed to be planted in the 2011 RES breeding nursery.

The San Joaquin cold tolerance nursery was planted in cooperation with two local growers. This seven-acre, drill-seeded nursery included 6,800 rows and six acres of second-generation populations. Stand establishment was good, although some bird and herbicide damage occurred. Very little blanking was observed in the rows, but heavy blanking occurred in the second-generation populations. An additional yield test took place near Rio Vista on Twitchell Island, with high blanking levels and greatly delayed maturity. No RES material was planted at the UC Davis rice facility in 2010.

Statewide yield tests

Statewide yield tests were conducted in grower fields and at the RES in 2010 to evaluate promising advanced selections from all three maturity groups—very early, early, or intermediate-to-late. More detail is reported in the Rice Variety Trials section of this annual report.

Preliminary yield tests are the initial step of replicated large-plot testing for experimental lines. These tests included 1,126 entries and check varieties. Superior entries advanced to statewide yield tests.

The statewide average yield on the 553,000 acres harvested in 2010 was 8,020 pounds/acre, according to USDA statistics.

Calrose medium grains

Fundamental objectives for Calrose medium grains have not changed. These include yield potential and stability, high grain quality, cold tolerance, early maturity, lodging resistance, and disease resistance.

New variety

M-105, a very early, semidwarf, glabrous, Calrose medium grain, has been approved for foundation seed release in 2011. This new variety has significantly improved head-rice milling yield and stability over M-104 and is equivalent to M-206.

It is a very early selection that has been evaluated in large-plot yield tests since 2005 as the experimental 05Y471. It is a selection from a cross between widely grown M-206 and M-104, the very-early maturing, cold-tolerant medium grain.

Days to heading averaged three days earlier than M-206 and three days later than M-104. Yield averages are less than M-206 but greater than M-104. It favors cooler locations; however, its resistance to cool-temperature blanking is not as high as M-104.

By far, its greatest attribute is superior head-rice milling yield and stability—a significant improvement over M-104 and equivalent to M-206. Approximately 60,000 pounds of foundation seed have been allocated for seed growers through the California Crop Improvement Association.

Large plot yield tests

Medium grains that can outperform M-206 and M-205 are rare but some promising entries were in 2010 large-plot yield tests, including a blast-resistant entry. Three of these were very early, three early, and two in the intermediate-to-late group.

Herbicide tolerance

California rice varieties show differences in tolerance to various herbicides, which is reflected in performance in the RES breeding nursery and in weed control testing. Work with weed scientists is under way to characterize the differences among varieties.

A limited effort has been made to recover plants with increased tolerance to the ALS-inhibiting herbicide Granite® GR. In 2009-2010 approximately 250,000 mutagenized M-206 seedlings were screened in the greenhouse, with 250 selections advanced for further testing. Selections will be tested for enhanced levels of herbicide tolerance. Additional screening and seed production is continuing in 2011.

Hybrid rice

Hybrid rice continues to get the attention of Southern rice growers and researchers. Both Louisiana State University and the University of Arkansas are establishing hybrid rice breeding projects. RES began reexamining the potential for japonica hybrid rice for California in 2008. In a small-plot yield test at RES in 2009, one hand-crossed hybrid long grain showed less than a 5% yield increase. Crosses between two medium and long grain varieties showed no yield advantage.

In 2010 hand-crossed hybrids involving a long, medium, and short grain line with three Chinese introductions showed no yield advantage over the RES parent and sterility problems in two of the three crosses. Further meaningful evaluation will require acquisition of the male sterile and restorer genetic components. A decision to allocate significant resources to this area remains under evaluation.

Long grains

The long grain breeding project focuses on four major rice types—conventional, Jasmine, Basmati, and aromatics. Milling and cooking quality improvements of conventional long grains and specialty types remain a major priority, followed by resistance to cold-induced blanking and other agronomic and disease-resistance traits.

Conventional long grain L-206, released in 2006, has improved cooking quality, higher grain yield, and earlier maturity but slightly lower milling yield than its predecessor, L-204. Recent studies show, however, that L-206 is significantly more resistant to grain fissuring, indicating more stable milling yield at lower harvest moisture.

L-206 is a very-early to early maturing conventional semidwarf that has shown good yield stability and is well adapted for most rice growing regions of California, except the coldest areas of Yolo and San Joaquin counties. Average heading date is one day earlier than M-206. Lodging potential is significantly lower than M-206, although plants may lean because of excessive dryness after harvest maturity. Similar to Southern long grains, L-206 has intermediate amylose and gelatinization temperature types.

Grain yield of L-206 in 2010 statewide yield tests averaged 9,200 pounds/acre. Average yield for M-206 within the same tests was 9,400 pounds/acre. Yields of L-206 at colder locations have not been competitive with M-206. Average head-rice yield of L-206 during the 2005-2010 seasons was 62%.

Other promising conventional long grains being evaluated include 06Y513 and 06Y575. Because of excessive disease susceptibility observed in 2010, 06Y513 will not be tested further. Entry 06Y575 is a high amylose type similar to L-205, with high yield potential, good milling yield, and cold tolerance. This line has shown exceptional yield potential for three consecutive years in cooler location experiments, which have traditionally been harder for long grains to be competitive with medium and short grains. This line was tested in all eight on-farm tests in 2010 statewide trials.

Grain yield in all locations, except Yuba County, was within the highest two entries among all grain types, averaging 10,220 pounds/acre, compared to 9,210 pounds/acre for L-206. Yields of M-206 in six locations, in addition to RES, averaged 9,410 pounds/acre. Potential uses for 06Y575 include canning and parboiling, as well as table rice.

Specialty long grains

Expanded breeding efforts continued in specialty long grains, including Jasmine, Basmati, and conventional aromatics such as A-201.

Calmati-202 is a true Basmati variety released in 2006. It is an early maturing, semidwarf, pubescent, aromatic, elongating long grain. Because of its susceptibility to blanking, it is not suited for colder locations. Average yield of Calmati-202 in 2010 early and intermediate-to-late tests was 6,530 pounds/acre. L-206 produced 9,770 pounds/acre in 2010. Grain quality studies have shown that Calmati-202 is susceptible to fissuring at low harvest moistures. Therefore, timely harvest and proper handling is important to preserve milling and cooking qualities. Recommended harvest moisture is 18%.

A new series of Basmati-type selections with cooking quality improvement over Calmati-202 was tested in 2010 statewide and preliminary trials. A collection of these promising lines is included in rapid generation advance in the greenhouse. Some of these entries, including 10Y151 and 09Y1081, possess true Basmati qualities that are nearly indistinguishable from imported Basmati. Their primary features include higher elongation, flakier texture, more slender grains, and minimal curving of cooked grains. Grain yield and milling yield of these lines, however, are lower than Calmati-202. Further testing is under way to determine suitability for commercial production.

Efforts continued in 2010 on Jasmine types through pedigree and mutation breeding. Crosses and backcrosses were made with Jasmine material from Southern U.S. breeding programs and foreign introductions. Photoperiod sensitivity of the original Thai Jasmine variety Kao-Dak-Mali has been a significant breeding barrier. This variety was irradiated and a new population was grown in the greenhouse in winter 2010. Second-generation rows will be evaluated for early maturity or photoperiod insensitivity in summer 2011. Altogether, 58 Jasmine types were tested in 2010 preliminary and statewide yield tests. Breeding objectives for Jasmine types include low amylose, strong aroma, high degree of whiteness, and smooth cooked grain texture.

Hybrid vigor evaluations

A study was conducted to compare the agronomic performance of a long-grain hybrid population with its parents. Crosses were made between long-grain experimental line 06Y575 and a Chinese short-grain introduction, Liaojing 294. Because of incompatibility of the two genotypes, however, 60% of the kernels were sterile. In 2009 a similar study using two long grain genotypes, 06Y575 and L-206, indicated a 3% yield advantage over the higher yielding parent.

Milling quality

Continued improvement in milling yield and stability remains an important objective in the long grain program. Grain characteristics are being evaluated that will lend milling yield stability under adverse weather, and thus allowing a wider window of harvest. In 2010 all specialty long grains in the preliminary and advanced yield tests were evaluated in special plots for milling yield evaluation. Advanced lines were evaluated at six to eight harvest moistures. Preliminary entries were tested at two harvest moistures. The goal for long grains is to maintain a minimum 64% head-rice yield in advanced breeding lines.

Disease resistance

Stem rot resistance from the wild species Oryza rufipogon continues to be incorporated into an increasing number of high yielding long grain lines. Twenty-four entries with a range of stem rot resistance were tested in 2010 statewide yield tests.

Field screening procedures are being modified to evaluate stem rot resistance based on maturity state to increase selection efficiency.

Short grain and premium quality

The short grain and premium quality project includes conventional short grains, premium-quality short grains, premium-quality medium grains, waxy short grains, low-amylose short grains, and bold grains such as Arborio. Priority is on premium-quality short and medium grains over conventional short grains.

Molecular (DNA) markers screen lines for grain quality and blast resistance. Markers for stem rot are also being investigated. Markers for cooking or eating quality complement sensory evaluation, especially with premium quality and Japanese-type short grains.

Conventional short grains

S-102 is the dominant commercial variety because of its high yield potential and very early maturity, resistance to cold-induced blanking, and large kernel size. This variety is susceptible to stem rot, however, and is pubescent (rough leaves and hulls). The primary goal for conventional short grains is to develop a variety with improved yields, stem rot resistance, smooth hulls, and better cooking quality. The overall yield of S-102 in 2010 statewide yield tests was 8,890 pounds/acre, down slightly from its six-year average of 8,940 pounds/acre. Highest yields in 2010 were recorded in Yuba and Colusa testing sites, with yields in excess of 10,000 pounds/acre. Yields fell below 8,000 pounds/acre in Butte, San Joaquin, and Yolo sites.

In 2010, six lines, including two stem rot resistant lines, were entered in statewide testing and 33 lines were entered in preliminary yield tests at RES. Further yield and agronomic evaluations are planned for 2011.

Premium quality medium and short grains

Premium quality is a term used to identify California medium grains such as M-401 and the Japanese variety Koshihikari. Calhikari-201 (CH-201) was the first premium short grain public variety (released in 1999). It is high yielding, early maturing, has good seedling vigor, and is lodging resistant. In 2010, yields of CH-201 ranged from 3,800 pounds/acre at an eastern Sutter site to 9,250 pounds/acre at a western Sutter site, with an average across-location yield of 8,190 pounds/acre. This is slightly higher than the six-year grain yield statewide average (8,000 pounds/acre). Grain yield at RES reached an average 9,400 pounds/acre.

Seven premium-quality short grain lines were entered in the statewide yield test and 35 lines were in the preliminary yield test, with CH-201 as check variety. These lines will be evaluated further for grain quality and cooking characteristics.

Ten premium-quality medium grains were tested in the statewide yield test and 84 lines were tested in preliminary yield tests. Check variety M-402 averaged 8,970 pounds/acre in combined Biggs, Glenn, and Sutter (west) locations. Selected lines will undergo additional grain quality evaluation and cooking tests.

An entry under evaluation for several years is the advanced premium-quality short grain 04Y177. It has undergone seed purification in head rows since 2007 and has been approved for foundation seed increase in 2011. Derived from a cross made in 1995, it is a semidwarf, early maturing, pubescent line with Koshihikari and S-101 in its pedigree. Compared to CH-201, its strengths include better cooking and taste test scores, slight milling yield advantage, four days earlier maturity, higher stem rot resistance rating, and more synchronous heading. Its weaknesses include slightly smaller kernels, tendency to lodge, and lower seedling vigor. In the period between 2005 and 2010 its average grain yield across locations was 8,600 pounds/acre, compared to 8,060 pounds/acre for CH 201. Additional quality evaluations are planned in 2011.

Specialty rices

Specialty short grains are divided into three groups—waxy short grains, low-amylose short grains, and bold grains like Arborio. Calmochi-101 (CM-101) is a waxy short grain noted for high yield potential, excellent blanking tolerance, and large kernels. Its drawback is rough hulls. Calamylow-201 is the only low-amylose variety and was developed through mutation of Calhikari-201.

Advanced lines in the statewide and preliminary yield tests in 2010 included 30 waxy, 16 low-amylose, and 11 big-seeded entries.

Grain yields of CM-101 in the 2010 statewide yield tests averaged 8,410 pounds/acre and ranged from 6,770 to 9,500 pounds/acre. The six-year, all-location average is 8,250 pounds/acre.

A waxy short-grain entry, 05Y343, entered in both very early and early groups, registered a significant grain yield advantage over CM-101 in 2010. It is seven days later maturing, has slightly lower seedling vigor, and has comparable stem rot resistance and plant height. It has heavier and bigger kernels. Grain quality has yet to be evaluated. This entry will be tested again in 2011 in all locations of the statewide yield tests and will be further purified in head rows.

A low-amylose entry, 09Y2159, registered an average yield of 10,940 pounds/acre across four locations in statewide testing. Pending additional grain quality information, this entry was to be tested further in 2011.

Mapping stem rot resistance

The DNA marker laboratory has significantly increased the capacity to identify desirable traits for rice breeding, including stem rot resistance. Incorporating stem rot resistance into California rice varieties is an essential goal, especially in medium grains. Achieving this resistance has been elusive. The resistance gene from Oryza rufipogon was transferred into a long-grain line designated as 87Y550 and was subsequently used in crosses at RES. The genetic basis and location of stem rot resistance genes have not been fully determined. An advanced backcross population from the cross 87Y550/M-206 is being examined to locate stem rot resistance genes. Chromosomes of interest have been identified. Additional trials are scheduled to verify stem rot scores and results of initial mapping.

Rice pathology

Breeding for disease resistance is a cooperative effort between plant breeders and the RES plant pathologist. About 2,000 rows are screened in statewide and preliminary yield tests for stem rot resistance. Since 2005, the immediate backcross program has screened 1,806 crosses for blast, 1,195 crosses for stem rot, and 971 crosses for sheath spot resistance to transfer resistance genes into an M-206 background. About 2,520 rows of early generation materials from breeders’ crosses were cycled through the disease nursery in 2010 to identify and verify disease resistant lines.

A small percentage of lines show higher levels of stem rot resistance than current lines. In 2010 the stem rot nursery included 7,745 rows. Of these, 5,225 rows were drill-seeded to reduce seed drift, improve stand establishment, and increase disease severity for better screening.

Promising long grains and short grains are emerging, but progress in medium grains has been slow. To address that problem, an immediate backcross program was initiated in 2005. Three long grain and two short grain lines with resistance derived from Oryza rufipogon and two lines from Oryza nivara have been backcrossed with M-206. A total 144 crosses were made in this effort in 2010.

In efforts to develop molecular markers for stem rot resistance genes, 1,501 rows of a population derived from a M-206/87Y550 cross were grown and analyzed. Three candidate genes have been identified and will be tested again in 2011. A similar population has been developed for the O. nivara resistance source and 995 rows were evaluated.

Also, the immediate backcross program made 102 crosses to transfer sheath spot resistance genes from Teqing, Jasmine 85, and MCR10277 to M-206 and L-206. As in the past, some resistant progeny also showed stem rot resistance equivalent to that found in wild species.

Blast concerns return

Rice blast disease, first discovered in 1996, initially spread to many Sacramento Valley rice growing areas but severity has been lower in recent years. In 2010 severity increased, with M-104 appearing most susceptible, followed by M-205.

Importantly, blast infection was identified in M-208, which contains the Pi-z blast resistance genes. Laboratory analysis at UC Riverside is under way to determine whether a mutation to the current race of blast has occurred or whether a new race of the fungus is now present in California.

Lines with different blast resistance genes are being screened. Blast race tests are being conducted and different components of M-208 are being tested to determine susceptibility.

Seven backcrosses were made with lines possessing a wide spectrum of resistance and M-206 in its pedigree. An additional 49 crosses were made with lines possessing other sources of blast resistance and will be grown in 2011. Six molecular markers have been successfully developed to identify sources of blast resistance.


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