Varietal Improvement Program-81



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Project Leader and Principal Investigators

Dr. Howard L. Carnahan, Director of Plant Breeding

Drs. S.T. Tseng & Carl W,. Johnson, Plant Breeders

Jeff J. Oster, Plant Pathologist, California Cooperative Rice Research Foundation


The objective of the variety improvement programs is to develop better-adapted high-yielding varieties that have superior grain qualities; early and uniform maturity within each maturity group; good seedling vigor; short stature and lodging resistance; and disease, insect and blanking resistance.

Largely because of improved varieties and cultural practices, growers produced a record 72 cwt per acre in 1981. Even more impressive is that these yield increases came when acreage was expanded from 522,000 acres to 605,000 acres. Such expansion is usually followed by a temporary decline in yield per acre.

New Varieties

In 1981 three new varieties were released for seed production and eventual paddy production in 1983. These were M-302, a replacement for M-301, with improved lodging resistance; M-401, a premium-quality, late-maturing variety with high yielding potential; and Calmochi-202, a short-statured sweet or waxy rice.

M-201, previously referred to as 78-Y-186, will be released to seed growers in 1982. Seed should be widely available in 1984. This early maturing, smooth, short-stature, medium-grain variety is of M9 maturity. In 12 statewide tests it has averaged 940 pounds per acre higher yield than M9, lodged 4 percent compared with 56 percent for M9, and is less susceptible to stem rot. Seed size of M-201 is similar to that of M7. In the statewide early variety trials, M-201 ranked first at 9,810 pounds per acre.

Eleven experimental entries in preliminary trials averaged over 10,000 pounds per acre at 14 percent moisture.

Generating and Identifying New Genetic Combinations

Over 900 new crosses and the second (segregating) generation from 854 crosses were grown for selection in 1981. More than 75,000 rows were grown for selection and evaluation for cold tolerance, water weevil, stem rot, quality, and other characteristics. Several thousand pots of plants were grown in the greenhouse to screen for blanking resistance and stem rot tolerance. Four thousand small test plots and 1,712 combine-size plots were grown on the Rice Experiment Station at Biggs for preliminary and advanced yield evaluations, respectively.

Largely because of improved varieties and cultural practices, growers produced a record 72 cwt per acre in 1981.


The short-stature segregates are selected from all crosses between short-stature and tall parents because reduced height is the primary reason for reduced lodging. In addition to the major gene for semi-dwarf height, there are modifying genes among the segregates that control height and straw strength. Productive lines with shorter and/or stronger straw are selected.


Many experimental lines that range in heading from 10 days earlier than Earlirose at Biggs to those that head as late as M7 are selected from the breeding program. Progress is being made in combining high yield and other necessary characteristics with very early maturity. It appears to be extremely difficult to obtain good milling characteristics in very early maturing rices.


Seed appearance - size, plumpness, translucency, shape, breakage and uniformity - is the basis for selecting 40,000 to 50,000 lines from the 250,000 to 300,000 lines examined each year. This selection, carried through several generations, has been reasonably effective. There is need for further improvement in large, translucent, good milling forms of each grain type.

In the long grains there is a continuing major need for lines with good physical, chemical, and cooking qualities. Repeated crossing and back crossing of long grains to Japonica rices is needed to incorporate cold tolerance. Excessively high temperatures during grain filling cause less plump and sometimes malformed kernels. These are more subject to breaking during milling. The combination of high temperatures, long days and low humidities during ripening of very early varieties makes it difficult to develop such varieties with consistent milling quality, but some improvement is possible.

Long Grain

Cooked samples of long grain experimental lines are examined at the Rice Experiment Station.

The long-grain variety, L-201, continued to yield very well in 1981 statewide tests - 9,070 pounds per acre, compared with 8,420 pounds for M9. Excellent progress is being made in the development of a long-grain variety with characteristics superior to those of L-201. Numerous experimentals now have adequate tolerance to both Ordram and Bolero. Progress is being made in developing lines that cook more nearly like the Southern long-grain rices. L-201 appears to be an excellent rice for parboiling.

Seeding Vigor

Seedling vigor and water depth management are critical to good stand establishment, successful weed control, and to obtaining high yields from short-stature varieties. We continue to select for improved seedling vigor. Most progress is being made in the long grains where the increased tolerance to herbicides has also been of value during stand establishment.

Sweet Rice (Glutinous)

The short-stature sweet rice variety, Calmochi-202, averaged 80 pounds per acre below M9 and 460 pounds per acre above the tall S6. It heads and matures 3 to 5 days later than S-201 and yielded nearly 1,000 pounds less than S-201 in 1981. An experimental sweet rice with more resistance to blanking will be included in 1982 statewide trials.

Tolerance to Low Temperature

The winter nursery in Hawaii was used for selection for resistance to blanking, particularly in the long grains. The new cold location in San Joaquin County provided the best conditions for effective selection for cold tolerance. The greenhouse tests permitted the elimination of some lines.

Resistance to Stem Rot and Tolerance to the Rice Water Weevil

Stem rot resistance from the weedy Oryza rufipogon parent is being transferred to several varieties for California. Results to date are cautiously optimistic.

This was a very good year in our continuing efforts to incorporate rice water weevil tolerance into adapted varieties. All California varieties are susceptible to the weevil. The 10 best experimentals averaged 97 percent higher yield than the California varieties under conditions of severe weevil infestation. Seed appearance and several agronomic characteristics are improving with each backcross. We should be able to select and purify some prospective new tolerant varieties for more extensive evaluation and possible release in 5 to 8 years.

Herbicide Tolerance

Several thousand long-grain breeding lines were screened for Bolero tolerance, which also provides tolerance to Ordram. Laboratory tests rating lines as either resistant or susceptible agreed perfectly with a field test. Thus, the more rapid and economical laboratory tests will be used routinely in the long grain breeding program to insure adequate herbicide tolerance in future varieties.


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