Jeffrey J. Oster, plant pathology

Breeding nurseries

Plant breeders are tapping into the genetic storehouse of rice varieities from throughout the world in hopes of tapping into desireable agronomic traits. Filipino workers pictured above planting rice seedlings by hand.

Plant breeders made just over 1,000 new crosses for varietal improvement. Approximately 80,000 rows were grown at the RES and nurseries in San Joaquin County, UC Davis and Hawaii. Here plant breeders evaluate, select, advance and purify for the agronomic characteristics so important to growers: seedling vigor, cold tolerance, disease reaction and grain quality. Several thousand pots of plants were also grown in greenhouses to screen for disease resistance and cold tolerance and for crossing and generation advance.

The nursery at Kauai, Hawaii, which allows breeders to speed up variety development by growing rice during the win-ter, was severely damaged in late 1991 by torrential rains and then again in the summer of 1992 byHurricane Iniki With help from the University of Hawaii, however, a full nursery and 5,000 rows transplanted on schedule and harvested in April 1993.

Last year researchers devoted 63 acres of the RES at Biggs to serve as a nursery for 60,000 progeny rows and 10 acres of F₂ populations. The nursery contained 4,000 small plots and 2,640 large plots in water-seeded yield tests. Twenty-two experimental lines were headrowed for seed increase and purification, and seven advanced lines were grown in small breeder seed increases.

RES staff also grew two acres of precision drill-seeded F₂ populations and 5,000 dry-seeded progeny rows to evaluate, select and advance breeding material for cold tolerance at UC Davis. Another 13,000 progeny rows for cold tolerance work were grown on 16 acres with a cooperating grower. These nurseries are essential to select blanking resistant sources of germplasm, such as that found in Calmochi 101, M-103 and M-204.

Germplasm

In efforts to incorporate genetically diverse material into California rice varieties, researchers, successfully introduced 52 foreign varieties through quarantine. Many new varieties and germplasm lines have been received in exchanges with scientists from Japan, Korea and the Philippines. A small amount of work continues on induced mutation; a successful breeding tool used in the past to create the premium medium-grain varieties M-401 and M-203.

Yield tests

RES researchers conduct statewide yield tests in collaboration with UC Cooperative Extension scientists. Last year they evaluated 124 advanced experimental lines and commercial varieties for agronomic performance and adaptability. Preliminary yield tests at the RES included 525 entries. (For more details, please see section called "variety trials")

Long grains

Long-grain breeding continues to focus on development of new varieties that bear the cooking qualities of Southern long grains yet produce well under California growing conditions. One of the problems researchers have encountered is that those lines possessing these cooking characteristics have not yielded as well as L-202 and L-203.

RES scientists are also evaluating rice with "Newrex" cooking characteristics. This is rice with a relatively high amylose content and is superior for parboiling and canning purposes. More than 1900 long-grain samples were tested amylose content and alkali spreading value, another indicator of cooking quality. Researchers also tested 1050 samples for starch pasting characteristics. About 7000 long-grain samples will be evaluated for cooking quality in 1993.

Medium grains

The medium-grain portion of the breeding program focuses on high yield potential, improved milling yield, seedling vigor and resistance to lodging, disease and blanking. Highlights include:

• Increased efforts to identify experimental lines with improved head rice and total milled rice yields.
• Harvest moisture rates at cooler locations were used effectively to select for uniform dry down to improve milling yields.
• Several advanced experimental lines have improved seedling vigor lodging resistance, grain yields and quality.

Short grains

Short-grain breeding activities focused on developing productive short grains with good kernel and milling characteristics. Emphasis includes improvements in yield potential, lodging resistance, cold tolerance, and grain quality and milling yields.

One promising early maturing experimental line is 89-Y-103, which averaged 10,000 pounds per acre in two years of statewide yield tests. it was the highest yielding entry in the very early group. Its heading date is about seven days earlier and its kernel size 12 percent smaller than S-201. Plant breeders will continue to evaluate agronomic and quality characteristics of this line.

Quality

Plant breeders continuously monitor grain quality characteristics - kernel size, shape, breakage and translucency - throughout the selection process. About 20 percent of the 90,000 panicle selections screened for quality each winter are saved for further evaluation.

A variety of cooking and chemical tests are used to ensure that new varieties will also perform well for consumers. Last year several thousand long grain lines were evaluated for improved quality. RES scientists also were involved in quality evaluation with several different Japanese and American scientists and marketing organizations.

Milling evaluations are increasing in all grain types. Researchers conducted detailed studies of the milling performance of 30 advanced lines and commercial varieties at different harvest moistures.

Disease resistance

Plant pathologist Jeffrey Oster is a key part of the scientific team at the Rice Experiment Station. It is his job to produce disease inoculum, operate a disease nursery, identify resistant germplasm and screen breeding lines and varieties for disease resistance.

Plant breeders team up with the RES plant pathologist in screening and selecting for disease resistance. Most of their work is targeted at stem rot disease, which has proven a long and difficult challenge. One of the problems is that the germplasm displaying disease resistance often contains undesirable characteristics, such as weak seedling vigor and straw strength.

Researchers have intensified work in this area because controlling stem rot is a very high priority. The battle against stem rot and other rice diseases will utilize emerging techniques in molecular genetics by USDA-ARS. This may improve both the identification and the selection of stem rot-resistant lines and hasten progress toward stem rot-resistant varieties.

RES scientists also made 42 new crosses in a continuing attempt to transfer disease resistance from the wild rice species Oryza rufipogon to California-adapted varieties. A cooperative study with the International Rice Research Institute is focusing on crosses between the highly resistant Oryza officinalis and M-202.

While stem rot is the main focus of disease work, researchers are also taking aim at sheath spot diseases. Eight sheath blight-resistant lines developed by IRRI from crosses with 0. officinalis were brought through quarantine last year and will be tested against two diseases in 1993.

UC Davis researchers report the bordered sheath spot disease seems to be spreading, and that it is more virulent in greenhouse tests than aggregate sheath spot disease.

Seedling vigor

California varieties currently have good levels of seedling vigor, but plant breeders are, nonetheless, attempting to find new sources of even higher seedling vigor. This is an important objective because seedling vigor improves stand establishment, strengthens competition against weeds, reduces effects of disease, and permits deeper water for weed control.

Plant breeders are continuing their efforts to incorporate this trait into California-adapted varieties from a Hungarian variety, Italica livorno. Incubator tests are being used to screen crosses of Italica livorno and M-16. Researchers report recovering higher seedling-vigor from advanced generation selections.

Rice Water Weevil

Crossing, selecting and screening for resistance to the rice water weevil is another significant area of the breeding program. A source of this resistance, PI 506230, was developed at RES. It is used as a donor parent but has a serious shortcoming, blanking, so researchers must exercise diligence in transferring tolerance to adapted varieties.

New varieties

No new varieties were released in 1992. About 10 promising new entries will undergo breeder seed increase in 1993. Any outstanding, performers would then be in a position for foundation seed production in 1994.

Plant breeders in 1992 did, however, announce two new germplasm releases - 87-Y-550 and 89-Y-235. The first, an early maturing long grain, is a superior source of stem rot resistance. However it is prone to blanking and is too sensitive to some herbicides. The second, a very early maturing short grain, is characterized by unusually large, chalky kernels. It suffers from lower yield potential and head rice yields than California varieties. These shortcomings kept these two lines from becoming new varieties, but their unique characteristics may prove useful in research or to the industry.