Rice Experiment Station Variety

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Project Leader and Principal Investigators

Howard L. Carnahan, director of plant breeding, RES

S.T. Tseng & Carl W. Johnson, plant breeders, RES

Jeff J. Oster, plant pathologist, RES


Variety Improvement Programs

Objective: To develop better adapted new high yielding varieties to replace present ones, that better resist blanking, are earlier maturing within each maturity group, have good seedling vigor, are short statured and lodging resistant, have disease and insect resistance, and have superior grain qualities.

In 1979 and 1980 California rice growers truly began to fully benefit from using improved cultural practices and new varieties flowing from the research accomplishments of the Comprehensive Rice Research Program. No doubt the excellent growing conditions in 1979 contributed in part to the new California rice yield record of 6,520 pounds per acre on 522,000 acres. But even with the adverse early season weather conditions of 1980, rice growers on 548,000 acres turned in an average yield of 6,440 pounds per acre. It is clear that the accumulating new rice production management alternatives function under difficult as well as good growing conditions. There is no doubt, however, that the foundation of the new high-yield era has been the productivity of the variety improvement programs.

The last two years are the only years in the history of California rice culture that yield exceeded 6,000 pounds per acre. In 1980 an estimated 70 to 75 percent of the total acreage was planted to new to new short-stature varieties. This contrasts with 51 percent in 1979 and only 10 percent in 1978. We project, with the availability of the new short-stature, short-grain S201, that 90 percent of the 1981 acreage will be planted to short-stature varieties.

The plant breeders and the new plant pathologist at the Rice Experiment Station have principal responsibility for the production of new improved varieties for California rice farmers. USDA and UCD scientists are contributing basic genetic and physiological research upon which the variety program is based.

In the spring of 1981 three new varieties will be released to seed growers. They are M-302, a replacement for M-301; M-401, a late maturing premium quality medium grain; and Calmochi-202, an early short-stature sweet rice, a replacement for Calmochi-201.

Additional higher yielding materials were identified in extensive preliminary trials at the Rice Experiment Station and in statewide yield trials conducted jointly with Cooperative Extension. In the statewide trials with very early varieties, M9 averaged 7,357 pounds per acre compared with 8,125 for the top yielding of 24 very early entries. In the statewide trials with early varieties, M9 averaged 7,317 pounds per acre compared with 8,701 for L201, the top yielding of 24 early entries. A medium-grain experimental, 78-Y186, of M9 maturity was free from lodging and again yielded significantly above M9. The highest yielding experimental was a long grain that averaged 8,480 pounds per acre. In the late maturity statewide trial, M7 averaged 9,503 pounds per acre. Four experimentals, including M-401, the new short-stature premium rice, averaged over 10,000 pounds per acre, with the top entry in the late maturity group averaging 10,557 pounds.

Generating and Identifying New Genetic Combinations

Eight hundred and fifty-eight new crosses and the second (segregating) generation from 653 crosses were grown for selection to fulfill the several objectives. More than 75,000 rows again were grown for selection, purification, evaluation for cold tolerance, water weevil, stem rot, quality, etc., and for seed increase and seed maintenance, Four thousand 4by 6-foot plots and 1,896 combine-size plots were grown for preliminary and advanced yield evaluations.

The Rice Research Board Liaison Committee met at the station to discuss progress on research to determine the environmental fate of pesticides used in rice culture. Looking at field experiments are (1. to r.): Mel Androus, board manager; Kathy Linton, research associate; committee chairman Fran DuBois; Dr. James E. Hill, Cooperative Extension agronomist; Dr. Don G. Crosby, UCD environmental toxicologist; Dr. ]. Basil Bower, research associate; and Dr. Don Seaman, UC agronomist.


From all crosses between short-stature and tall parents, the short-stature segregates are selected because reduced height is a primary basis for reduced lodging. In addition to the major gene for semi-dwarf height, there are modifying genes that condition varying heights and straw strengths among the segregates. Those productive lines with shorter height and/or stronger straw are selected.

Tolerance to Low Temperature

The relatively warm nights at Biggs and Davis during 1980 were not favorable for screening rice for resistance to blanking. The best results were obtained on advanced lines grown at the new cold location near the San Joaquin-Sacramento county line in the direct path of incoming ocean air. More severe blanking also was obtained in the refrigerated greenhouse, thereby permitting some effective screening of advanced lines.

Rice Experiment Station field day scene at Biggs, Sept. 2,1980, showing yield trial area involving superior new varieties of very early maturity and superior quality characteristics.

Tolerance to Stem Rot and to Rice Water Weevil

Two events provide a basis for considerable optimism in the prospects of breeding new varieties with additional stem rot tolerance. These are the obtaining of a cross by USDA's Dr. J. Neil Rutger and his graduate student, R.A. Figoni, between the resistant Oryza rufipogon and a California variety; and the addition of a plant pathologist to the Rice Experiment Station staff to work with the plant breeding team.

Efforts to incorporate rice water weevil tolerance into adapted varieties - a joint project with the Department of Entomology at UCD - are continuing. Weevil infestation in the screening nursery (untreated for weevil control) was so severe that the resistant parent was severely damaged. Several selections were made and further backcrosses were made to adapted California varieties and experimentals.

Herbicide Tolerance

To control weeds and identify differences in reaction to herbicides, all of our nurseries are treated with Ordram and MCPA. Methods were developed to screen long-grain rices for tolerance to Ordram. Some promising breeding lines with tolerance superior to that of L-201 were identified.

Seedling Vigor

Seedling vigor and water depth management are critical to good stand establishment, successful weed control and high yields of short-stature varieties. Short-stature selections usually emerge through the water a little slower than do tall or intermediate height selections from the same cross. Insofar as additional seedling vigor is compatible with reduced height and straw strength, we continue to select for improved seedling vigor. Most progress is being made in the long grains.


Rice station yield test area for late maturity varieties. The line M-401 may soon be released as a short-statured, high-yield, medium-grain variety with premium grain quality. Beyond is a yield test of very promising new long-grain varieties. L-201, now in limited commercial production, has proven to be exceptionally high yielding. Note the improved seed handling facilities in background.


Many experimentals have been obtained from the breeding program that represent a complete range in heading from 10 days earlier than Earlirose at Biggs to those that head as late as M7. Continuing progress is being made in combining high yield and other necessary characteristics with very early maturity.


Seed appearance - size, translucency, shape, breakage and uniformity - is examined and used as the basis for selecting about 40,000 from 250,000 to 300,000 rice lines each year. This selection has been highly effective. Even so, there is still considerable room for improvement in the development of large, translucent, good milling forms of each grain type.

In the long grains there is a continuing major need to screen evolving lines for both chemical and cooking quality. The need for repeated crossing and back crossing of long grains to Japonica rices to incorporate added cold tolerance accentuates the need for identifying quality factors.

The prevailing high temperatures and low humidity during grain ripening of very early maturing rices make it difficult to develop very early varieties with consistent milling quality.

Long Grain

The new long-grain variety, L-201, gave outstanding yields both in test plots and in the fields of the few growers who had it. L-201 and other long-grain materials in the breeding program still have a narrower range of adaptation than most short-and medium-grain varieties. To increase cold tolerance and resistance to Ordram, it is necessary to cross the long grains with adapted medium grains. To improve cooking quality, crossing of our long grains to unadapted long grains is necessary. Thus, much research work is ahead to develop an ideal long-grain rice for California. Progress is encouraging.

Sweet Rice (Glutinous)

One hundred and nine hundredweight of foundation seed of a high yielding short-statured sweet rice were produced for possible replacement of the tall variety Calmochi-201. It, like Calmochi-201, is not satisfactory to the trade for making mochi cakes. Additional crosses are being made in an attempt to increase the seed size, cold tolerance and cooking characteristics of sweet rice.


 Table 2. Characteristics of Publicly Developed Rice Varieties-1981
Grain Height* Maturity Seed
S6 Tall Early 1977 Replaced Colusa, wide adaptation but only moderate resistance to blanking. Has irregular maturity.
S-201 Short Early 1981 Very high yield potential, replaced S6; more resistance to blanking than S6; maturity like S6.
Medium Grain
M-101 Short Very Early 1981 Earliest variety; excellent seedling vigor; good resistance to blanking best suited for special conditions such as cold areas and/or late planting dates; head rice can be low, so harvest as near to 25% moisture as possible to enhance head yield. May not yield as well as other varieties at normal planting dates.
M9 Short Early 1979 Very high yield potential in warmer areas; not adapted to colder areas or to very early seeding because of poor seedling vigor; mixed maturity of seeds on panicles. Somewhat difficult to thresh cleanly - special harvest adjustment may be necessary. May be more susceptible to sheath blight.
M-301 Short Intermediate 1981 High yield potential, was replacement for M5; good seedling vigor and resistance to blanking, can be seeded 10 days later than optimum date for late varieties, or earlier to spread harvest season; straw strength not as good as M7.
M-302 Short Intermediate 1983 Replaced M-301; has better straw strength; more translucent grains; is about 2 days later; has good seedling vigor and resistance to blanking. Can be seeded 7 or 8 days later than late varieties to spread harvest season.
M7 Short Late 1979 High yield potential; good seedling vigor and resistance to blanking; very good straw strength. Replaced CS-M3.
Short Late 1979 High yield potential; good seedling vigor and resistance to blanking; rough hulls and leaves; long awns in warmer areas. Replaced Calrose.
M-401 Short Late 1983 Intended as a premium quality rice and not as a replacement for M7. Has high yield potential; 3 days earlier than M7 but lodges more and is more sensitive to blanking.
Long Grain
L-201** Inter-
Early 1981 Very high yield potential in warmer areas; not adapted to colder areas; injury by Ordram® has been observed at rates greater than 3 a.i. lbs/acre; threshes readily at low cylinder speeds. Harvest at moisture content as near to 25% as possible to enhance head yield; matures in 7 to 10 fewer days after heading than do short- or medium-grain varieties.
Short Early 1983 A sweet rice replacing Calmochi-201. Similar to S-201 in growth characteristics but 2 days later. Has smaller seeds. Yield much greater and lodges less than Calmochi-201.
* The varieties with short height are rapidly replacing the tall varieties. Proper management of the short-stature varieties to obtain high yield includes: (1) managing water depth and other factors to obtain a dense stand; (2) good weed control; (3) nitrogen fertilization of 20 to 40 units higher than has been used for tall varieties; and (4) drain as late as possible before harvest.
** L-201 and Calmochi varieties should not be grown unless arrangements have been made first with a marketing agency. Market acceptance is in the exploratory state.


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