|Rice Breeding Program-95
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
|California rice acreage declined slightly last year to 465, 000
acres, a 20, 000- acre drop from 1994. Medium grain varieties, led by M-202, continue to
be growers' rice of choice with 96 percent of the acreage. The remainder was evenly
divided between long and short grains. The wet spring and comparatively cool summer took
their toll on rice productivity last year. Average statewide yields dropped down to 7,600
pounds/acre. Weather aside, the plant breeders at the Rice Experiment Station (RES) report
significant progress in 1995, including the release of three new varieties. Highlights of
their accomplishments are detailed below.
The record-breaking rainfall of spring 1995 delayed planting at the RES by nearly three weeks. This forced researchers to streamline or omit some land preparations. Below optimal nitrogen fertility manifested itself in short plant heights in the breeding nurseries.
Plant breeders made more than 900 crosses during the year, bringing the total since 1969 to 21,400. Approximately 100,000 progeny rows were grown in nurseries at the RES, as well as at UC Davis, San Joaquin and in Hawaii. Most of these rows (70,000) were grown on approximately 60 acres at the RES. Second generation (F,) populations from 1994 crosses were grown in precision drill-seeded plots on 12 acres. The nursery contained 4,000 small plots and 2,500 large plots in various water-seeded yield tests. An estimated 25,000 panicles and 12,000 rows were harvested for selection, advancement, quality evaluations and purification from these progeny rows. The nursery also produced headrows of M-204, M-202, L-202 and A-301 for breeder seed.
The Hawaii nursery, which allows plant breeders to speed up the selection process, reported a full nursery (5,000 rows) planted on schedule by December 5th. Seed production was good and cold-induced blanking was observed in susceptible material. Researchers report large differences in nitrogen fertility and plant height, as well as some damage from birds. Seed from this nursery was harvested and shipped to the mainland in April and grown out at the different California nurseries during the summer. An additional 500 rows were also being grown for the USDA geneticist at UC Davis.
The cold tolerance nursery at UC Davis contained two acres of precision-drilled F2 populations and 5,000 dry-seeded progeny rows. Stands and grass control in these progeny rows were reportedly good. A moderate level of blanking occurred; The space-planted F2 populations suffered considerable damage from Canada geese at both planting and harvest.
The cold tolerance nursery on an 11-acre tract on Staten island (San Joaquin) consisted of precision-drilled F2 populations and 20,100 dry- seeded progeny rows. The organic soil at this site caused problems in planting, seedling emergence and weed control. The San Joaquin nursery has allowed the identification of blanking resistant materials like Calmochi-101, S-101, M-103, S-301 and M-204.
The agronomic performance and adaptability of advanced selections are observed each year in Statewide and Preliminary Yield Tests.
The 1995 Statewide Yield Tests, conducted at the RES and at grower locations, included 116 entries and are reported in more detail in the section on Variety Trials. The preliminary yield tests, the initial step of replicated large plot testing for experimental lines, are performed only at the RES. These tests included 492 entries and check varieties last year. Top experimental lines compared well with highest yielding standard varieties. Superior entries will be advanced to State- wide Yield Tests this year.
The challenge for improving California-grown long grains has been to improve yield potential, head rice milling yield and cooking characteristics. Because of difficulty overcoming these obstacles, long grain acreage has declined in California. However, the release this year of L-204 may halt that trend.
L-204, known previously as the experimental line 92-Y-93, is an early maturing short-stature, variety derived from the cross Lemont//Tainun-sen-yu 2414/L-201. It heads an average two to three days earlier than L-203 and L-202; yields about 7 percent higher than L-202 and similarly to L-203 in the field; and it shows improved head rice yield in milling tests. In taste tests, panelists preferred L,204 over L-202 and L-203.
"Newrex" rice cooks up drier and fluffier than other long grains and is used in parboiling and canning. Plant breeders are monitoring 10 experimental entries for these qualities in 1995 Preliminary Yield tests. They yielded equivalent or superior to check varieties L-202 and L-203 and three showed superior head rice yield in milling tests.
"Basmati" rice is an aromatic long grain that shows extreme kernel elongation and little width expansion during cooking. These varieties are susceptible to low temperature blanking and are generally not well adapted to California. Nonetheless, researchers have developed several experimental lines with basmati cooking characteristics for California. Improvement of yield potential will be the focus of future work in this area.
An early aromatic line, 91-Y-631, is being released to growers this year as A-201. It yields similar to L-202 and A-301; heads about eight days earlier than A-301; and has better seedling vigor than A-301, the current dominant aromatic long grain in California. Evaluators liked the aroma and texture of A-201.
Breeding for stem rot resistance is another important objective for long grain development. Plant breeders continue efforts to incorporate resistance from the wild species Oryza ruflpogon and hope that one line, 94-Y-561, can be used as a 'bridge' to achieve that goal.
High yield potential, resistance to lodging and disease, seedling vigor, improved milling yields, resistance to blanking- these are among the high priorities in efforts to improve the quality of medium grain rice for California growers.
In field tests to improve medium grain milling quality, plant breeders sampled advanced experimentals twice a week at moisture levels decreasing from 25 percent to 17 percent. The immediate goal of this research is to eliminate all experimental lines in preliminary trials that have lower head rice values than M-201. Three entries - 93-Y-413, 94-Y-215, and 93-Y-421 - produced equal or greater head rice yield than M-103.
Early and very early experimental entries occupied 95 percent of the medium grain program. Harvest moisture values at cooler locations, along with heading uniformity and percentage of green kernels at harvest, help to identify superior early maturing experirnentals. Plant breeders report success in efforts to select for earlier maturity, improved lodging resistance, seedling vigor and milling yield. A number of entries had harvest moistures lower than M-202, resulting from earlier heading dates and/or more uniform heading and field dry-down rates.
Two entries look as if they're well on their way to becoming the next medium grain varieties. Both are under consideration for foundation seed increase. 91 -Y-3 81 is a very early to early maturing smooth medium grain that has shown high yield potential and high head rice yield. It heads three days earlier than M-202, has lodging and blanking resistance similar to M-204, and seedling vigor equal to M-202.
The other advanced medium grain experimental is 92-Y-624, an early maturing smooth medium grain. It has a larger seed size and weight, a good candidate for rice cake production. It is similar to M-202 in height, lodging and resistance to blanking. Seedling vigor is described as adequate- Stem rot resistance is similar to M-201.
In the Hawaii winter nursery, researchers grew 21 different medium-grain entries for purification, seed increase and additional agronomic evaluation. Some entries have greater yield potential than their respective highest yielding check varieties, lodging resistance superior to M-202 and/or improved grain quality. Researchers report agronomic improvement on some stem rot resistant lines.
Selection for improved stem rot resistance and seedling vigor is occupying a greater portion of the medium grain program. These objectives have been difficult to achieve simultaneously, since one of the most severe deficiencies of seedling vigor breeding material is stem rot susceptibility. But plant breeding takes place in a 'step-wise fashion,' researchers note. As new material evolves from backcrosses, the amount of improved adapted material continues to increase.
Premium Quality & Short Grains
'Premium quality' is a term used to describe rice, such as M-401, that has unique cooking characteristics and is preferred by certain ethnic groups (e.g. Japanese and Koreans). Premium quality medium grains are glossy after cooking, sticky with a smooth texture and remain soft after cooling. The opening of overseas markets and increasing domestic consumption of these types of rices have fueled interest in developing premium quality rice - both short and medium grain.
Plant breeders have intensified efforts through a crossing program to tap into elusive premium cooking characteristics while breaking free of undesirable characteristics, such as weak straw and low yields, that are inherent in much Japanese germplasm. Improved lines from the second cycle of this crossing program are now moving into the yield testing stage. Preliminary results indicate some very promising material has been generated.
Researchers have a new tool to help them identify premium quality characteristics - a near-infrared (NIR) spectrophotometer. This device analyzes breeding lines for important parameters, such as amylose and protein content, without the need for slower, more cumbersome wet chemistry.
Most premium quality medium- grain selections included in the 1995 Statewide Yield Tests were derived from crosses with M-401, M-203 and Kokuhorose. One entry that fared well in cooking tests and produced good milling yields is being advanced in the Hawaii winter nursery. A number of new premium quality short- and medium-grain experimental lines will enter the yield tests in 1996.
Short grain acreage has declined significantly in recent years. Plant breeders have been developing a new variety to overcome the shortcomings of S-201 (i.e. intermediate maturity and variable heading). The advanced experimental 91-Y-171, scheduled for release this year as S-102, may fill the bill. S-102 has consistently been one of the top producers in Statewide Yield Tests the last three years. Its strengths are very early maturity, high head and total milled rice yield, and a larger and more translucent kernel than S-201. The line is reportedly susceptible to stem rot.
Work also continues on 'special purpose' types of rice. Plant breeders are trying to improve the agronomic and quality characteristics of short- grain waxy varieties like Calmochi 101. Some large-seeded types similar to Italian varieties are in the small plot testing stage and one was a top yielding entry in one group of the Preliminary Yield Tests.
Plant breeders are continuing their work with PI 506230, the donor parent tapped for tolerance to rice water weevil. Blanking is a major problem with much of this breeding material. Several experimental entries showed more RWW tolerance than M- 201 in Statewide Yield Tests. They are being advanced and purified for further testing this year.
Breeding for disease resistance is directed primarily at improved resistance to stem rot. Last year 127 new crosses were made to transfer resistance from Oryza ruftpogon to adapted California varieties. More than 7, 100 rows were grown in the disease nursery in 1995. Only a fraction of a percent of the screened lines showed better levels of stem rot resistance than M-201.
A cooperative study with the International Rice Research Institute in the Philippines is continuing. In this study researchers are backcrossing highly stem rot- resistant Oryza officinalis with M-202. The best five of these crosses have been brought through quarantine and will be crossed this year into California materials.
The RES plant pathologist is also cooperating in a study with the USDA geneticist at UC Davis (see 'Genetics' section of report). Using advanced techniques in molecular biology, researchers are 'mapping' stem rot-resistant genes from 87-Y-550, a resistant long grain.
The plant pathologist screened 360 rows of crosses between 0. fatua and rice grass lines for resistance to Aggregate Sheath Spot. Researchers from IRRI have found some wild species to be highly resistant to sheath blight. This is significant because sheath blight is caused by a fungus similar to the sheath spot fungus. Resistance could be conferred from the same genes. Resistant materials have been brought through quarantine, evaluated for sheath spot resistance and will be incorporated in California materials this year.
Seedling vigor in California varieties is generally good, but greater seedling vigor would permit use of deeper water for weed suppression during stand establishment. Italica livorno and M-16, two Hungarian varieties, have high levels of seedling vigor. Thirty crosses were made in 1995 to transfer this enhanced seedling vigor. Additionally, incubator tests were used to screen 109,000 seedlings involving backcrosses with these varieties. Approximately 2,600 seedlings were selected and transplanted in the field to further screen for short stature and stem rot resistance.
The RES is collaborating with University of California scientists in a five-year project to study the long-term impact of various straw management systems on rice productivity.
The experiment, which is a companion study to similar research in Colusa County, is taking place on a 25-acre plot adjacent to the Rice Experiment Station. The straw treatments include burning, incorporation, rolling and removal with and without winter flooding. M-202 was water seeded May 30. Conventional agronomic practices for weed and insect control and water management were used through the season.
The plots produced relatively low grain yield which was probably caused by the late planting date and nitrogen deficiency. Because of the late planting date a relatively low rate of nitrogen fertilizer (122 pounds/acre) was used to reduce risk of blanking.
The only treatment in which a statistically significant yield reduction occurred was the winter-flooded, straw-removal plots. The cause of this reduction is not known. Firing of the upper leaves from the boot stage to maturation was persistent in plants in these plots. This may be caused by a nutrient deficiency. The experiment will continue.