|Rice Experiment Station Variety
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
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.
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.
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.
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 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.
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.
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