Rice Breeding Program 94

Rice Breeding Program-94
Project Leaders 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	Bolstered by rising domestic consumption and new markets overseas, California rice acreage remains at levels not seen in recent years - 485,000 acres in 1994. The vast majority of this acreage was medium grain (94 percent), followed by short grain (5 percent) and long grain (1 percent). Yields crept up another notch to 8,500 pounds per acre, due in large part to improvements made in public rice varieties developed at the Rice Experiment Station, coupled with integrated management by growers. Breeding Nurseries Plant breeders made more than 900 new crosses for varietal improvement during 1994, bringing the total since the program began in 1961 to 20,500. Approximately 100,000 progeny rows were grown in nurseries at the RES, UC Davis, San Joaquin County and Hawaii. Progeny rows included selected lines in the third through seventh generation after crosses were made. From these rows breeders select, purify, advance and evaluate promising lines for seedling vigor, cold tolerance, disease reaction, and grain quality and yield. Additionally, several thousand pots of plants were grown in the greenhouse to screen for disease resistance and cold tolerance, and for use in crossing and generation advance. The University of Hawaii nursery on Kauai - the "Paddy Crop Farm" - plays a critical role in accelerating the variety development process by enabling plant breeders to grow an additional generation of select lines each year. In 1993 research facilities were severely damaged from a hurricane but the University of Hawaii transplanted a full nursery of 5,300 rows on schedule for breeding and genetic research. Seed from this nursery was harvested, inspected, processed and grown in the mainland nurseries last summer. Another 5,300 selections from the RES nursery were transplanted in December 1994 and harvested in early April 1995. The 1994 RES nursery comprised about 60 acres. Second generation (F₂) populations were drill-seeded on 12 acres. The nursery contained 70,000 progeny rows, 4,000 small plots and 2,600 large plots in various water-seeded yield tests. In addition 40 experimental lines were headrowed for seed increase and purification, and three advanced lines were grown in small breeder increases. Headrow seed of all public California varieties and advanced lines to maintain pure seed will be stored in a cold storage facility enlarged and retrofitted in 1993. The cold tolerance nursery at UC Davis contained two acres of precision-drilled F₂ populations and 5,000 dry-seeded progeny rows. At the 11-acre cold tolerance nursery on Staten Island in San Joaquin County breeders planted more than 20,000 dry-seeded progeny rows and precision drill-seeded F₂ populations. An estimated 300,000 panicles were selected from the various F₂ populations in these different nurseries for further screening and advancement. An additional 25,000 to 30,000 panicles were harvested for selection and purification from progeny rows. Some of this material is being advanced in the Hawaii nursery; the remainder to be screened and processed for planting in 1995. Germplasm Germplasm is a broad term that refers to rice varieties, breeding lines, plant introductions, mutants and wild species of rice. From these diverse sources plant breeders can tap into genetic diversity to improve California rice. In 1994 RES researchers grew and evaluated the Cooperative Regional Uniform Rice nursery consisting of 200 entries from Southern U.S. public rice breeding programs. Induced mutation has been a successful breeding tool in the past - both M-401 and M-203 were developed this way. Selections were made from M₂ populations at RES, UC Davis and San Joaquin County nurseries. Seed from foreign sources started becoming more readily available with the advent of a plant introduction permit in 1988. Many new varieties and germplasm lines have been received from Japan, Russia and the Philippines. As required by quarantine procedures, materials are grown in the winter greenhouse when rice is not growing in the field and insect activity is minimal. Thirty-five new lines were successfully introduced for enhancement of grain quality and disease resistance. Yield Tests Rice Experiment Station and UC Cooperative Extension scientists annually conduct statewide yield tests to evaluate the agronomic performance and adaptation of advanced experimental lines and commercial varieties. Please see the section Variety Trials elsewhere in this report for the results of these tests. Preliminary yield tests, the initial step of replicated large plot testing for experimental lines are performed at the RES. These tests included 552 entries and check or standard varieties in 1994. Long Grains Improved milling and cooking characteristics remain the focus of long-grain rice breeding. Current long grains grown in California, L-202 and L-203, have good yield potential but are low in whole kernel (head) milling yield. In addition, the starch characteristics are different from Southern long grains. Plant breeders are trying to incorporate some of the cooking characteristics of Southern long grains into California long grains. They have identified an early experimental line, 91-Y-093, as a promising entry with similar traits. It also has yield potential above L-203 and promising head rice yield based on milling tests. Evaluation will continue in 1995. Another goal in the long grain program is to develop a variety with "Newrex type" cooking characteristics. Newrex rice cooks drier and fluffier than other Southern long grains and is considered superior for processing purposes. Plant breeders are looking closely at 93-Y-092, an early maturing experimental line, that yields similar to L-203. Milling yields tended to be on the low side for 93-Y-092 during preliminary evaluations. Researchers are also continuing studies of five stem rot-resistant long grains. Tests in 1994 showed a wide range of disease incidence. The nature of this variability will be studied again in 1995 to determine whether further selection can narrow the range to that of 87-Y-550, a stem rot resistant long grain germplasm line developed at RES. Medium Grains Some of the multiple goals of the medium-grain rice breeding program include higher yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to blanking. Selection for grain quality factors continues to be an integral part of the RES breeding effort. Increased emphasis is being placed on identifying advanced experimentals with improved head and total milled rice yields. Early and very early experimental entries occupied 95 percent of the medium-grain program. Harvest moisture values at cooler locations, along with evaluations of heading uniformity and green kernels at harvest were used to identify superior early maturing experimental entries. Two of those entries that will be retested in 1995 are of particular interest because they have improved lodging resistance, seedling vigor and milling yields. 91-Y-381 is a very early to early maturing smooth medium grain that has shown very high yield potential and high head rice yield. It has ranked first overall in three years of testing in the early group of the Statewide Yield Tests. It heads three days earlier than M-202, has and seedling vigor equal to M-202. Its strengths are good lodging and blanking resistance equal to M-204, early maturity, adequate straw strength and very high grain and milling yields. Breeder seed will be produced in 1995. The second advanced medium grain experimental is 92-Y-624, an early maturing smooth medium grain. It has a larger seed size and seed weight that averages 3.5 percent heavier than M-204. Results from tests in 1993 and 1994 show that it is a "very acceptable" candidate for rice cake production. Twenty-four different medium grains are being grown in the Hawaiian nursery for purification, seed increase and additional agronomic evaluation. Plant breeders report that some of these entries have greater yield potential than their respective highest yielding check varieties, lodging resistance superior to M-202 and/or improved grain quality. Medium grain entry 94-Y-237 is being advanced in Hawaii for retesting in 1995. It has very good straw strength, blanking resistance, and M-201 level of stem rot resistance. Progress is being made to improve seedling vigor in superior experimental lines using M-16 and Italico livorno seedling vigor sources. Increased effort in breeding for seedling vigor has resulted in these materials occupying a significant part of the, medium-grain program. The greatest challenge facing plant breeders has been to combine strong seedling vigor it with improved stem rot resistance. Short Grains The main focus of the short-grain breeding effort is improved yield potential, resistance to lodging, and improved grain and milling characteristics. Plant breeders are aiming Ito improve on S-201, the primary commercial short grain. It has a number of undesirable characteristics, including intermediate maturity and variable heading. 91-Y-171 is a very early maturing short grain first reported in 1992. It was the highest yielding entry, producing over 10,000 pounds/acre. in the very early group of the Statewide Yield Tests in both 1993 and 1994. It also has shown high head and total milled rice yields in four years of milling tests. Quality evaluations by marketing organizations have been positive. This line is pubescent, although not heavily awned, and is susceptible to stem rot. The high milling yield, large translucent kernels, very early maturity and high yield potential make 91-Y-171 of particular interest for further testing and seed increase. Premium Quality Premium quality short and medium grains have unique cooking characteristics that are in strong demand by certain ethnic groups, especially Japanese and Korean consumers. These rices are very glossy after cooking, sticky with a smooth texture and remain soft after cooling. Aroma and taste are also cited as important features. RES has placed a high priority on developing agronomically improved medium and short grains with these characteristics. The premium quality breeding program is focused on developing earlier maturing, high yielding lines with lodging resistance and high milling yields. Plant breeders will be taking a harder look at some premium quality short grains like 94-Y-022, a very early maturing experimental line. Although its grain yield was comparatively low in 1994 tests, it showed a 2,000 pound/acre yield advantage over the Japanese premium quality short grain Akitakomachi. Milling yield and kernel appearance were very good but results of cooking quality evaluations have been somewhat variable. A number of other premium quality lines that hold promise for further improvements in cooking quality are being advanced in the Hawaii winter nursery. Special Purpose Types Work continues on a number of special varieties with unique characteristics. Among them are long grains distinguished as aromatic, soft cooking and waxy types. Plant breeders have emphasized Basmati types, aromatic rices with extreme kernel elongation. As a group the aromatic experimental lines yielded and milled poorly. However, 91-Y-631 yielded comparably to L-202 and A-301. The earliness of this experimental along with its superior seedling vigor would make it easier to grow than A-301. Although it performed well in taste tests, it lacks the degree of kernel elongation shown by traditional Basmati rice. Another shortcoming is its low head rice yield. Breeder seed of 91-Y-631 was produced in 1994. It will be advanced further if desired by aromatic long-grain rice growers. Several promising new experimental lines with the desired cooked kernel elongation of Basmati rice will be advanced to statewide yield trials in 1995. 92-Y-521, an early waxy long-grain rice with smooth leaves and hulls and superior seedling vigor is being evaluated for suitability as a waxy long grain. Work on other specialty types of rice include short-grain waxy (mochi) varieties like Calmochi-101. Plant breeders are focusing on improved agronomic and quality characteristics. Crosses have also been made to a number of new waxy germplasm introductions. Breeding for the large-seeded "Arborio" types continues at the RES. Grain Quality RES scientists screen for the factors that determine grain quality - kernel size, shape, breakage and translucency - at every step of the breeding process until an experimental line is ready for release as a new variety. Milling yield is a particularly important yet difficult rice quality component to improve. Detailed milling studies continue to be conducted on advanced breeding materials. In 1994 researchers conducted 37 harvest moisture milling tests on advanced experimental lines and commercial varieties. Samples are harvested twice a week for seven to 11 harvests, enabling scientists to determine optimum harvest moisture for maximum head rice yield. The USDA-ARS Rice Quality Research Laboratory in Beaumont, Texas performs a variety of physiochemical tests to help public breeding programs assess cooking and processing qualities. In 1994 more than 2,000 long-grain milled samples from the RES were evaluated for amylose content and alkali spreading values. Additionally, the RES is now using a Rapid Visco Analyzer (RVA) to determine starch pasting properties of samples. RVA viscograms, apparent amylose content and alkali spreading values are used to screen for Southern long grain and Newrex cooking qualities. More than 1,500 samples were tested with the RVA last year and another 4,000 long grain samples will be evaluated in 1995. The RES screening capabilities were further advanced last year with the acquisition of a near-infrared (NIR) scanning spectrophotometer, which permits rapid chemical analysis in minutes. They are currently in use in rice quality labs in Japan and Australia to measure protein and cooking quality. RES scientists are working with USDA laboratories to develop new methods for analyzing apparent amylose and protein content of rice flour and milled rice. Disease Resistance Breeding for disease resistance, a cooperative effort among the breeders and the plant pathologist, has been a slow, difficult process. Because of its importance, however, efforts are intensifying in this area. One hundred sixteen new crosses were made to transfer stem rot resistance from Oryza rufipogon to adapted California varieties. Three years of water-seeded rate tests were concluded to improve disease screening techniques. Only a very small percentage of the lines screened showed better levels, of stem rot resistance than M-201. A new supplementary selection scheme emphasizing rapid generation advance of the agronomically best second generation populations was initiated this year. A cooperative study with the International Rice Research Institute (IRRI) is making backcrosses of the highly stem rot-resistant Oryza officinalis and M-202. Seed of resistant lines will be returned to RES for quarantine introduction and screening. Scientists at the IRRI have found that certain other wild species are highly resistant to stem rot. These materials were processed through quarantine in 1994 and will be evaluated for disease resistance in 1995 under California conditions. Forty-two new crosses were made in 1994 to transfer aggregate sheath spot resistance. However, the frequency of selections with resistance was less than 4 percent. IRRI researchers found that certain wild species are also highly resistant to sheath blight. These materials were processed through quarantine in 1994 and will be evaluated for disease resistance under California conditions in 1995. A cooperative project with USDA geneticist Dr. David J. Mackill is using advanced techniques in molecular genetics to identify and map stem rot resistant genes from the resistant long grain 87-Y-550. In related work to improve stem rot resistance, other crosses of medium and long grain lines are being advanced and evaluated in the field and greenhouse for future genetic analysis. These molecular genetics studies, coupled with rapid generation advance at RES, may hasten development of stem rot resistance for California. In a study of how nitrogen and potassium interact with disease severity, researchers found that disease incidence was generally affected more by nitrogen than by potassium. Stem rot was pronounced at the highest nitrogen rate (180 lb.N/acre) but nitrogen had less effect on aggregate sheath spot. Potassium level had no effect on stem rot or aggregate sheath spot severity. Last year's research also showed that stem rot incidence in M-201, M-202, M-204, L-202, L-203 and S-201 generally increased with nitrogen levels. Correlations between nitrogen level and stem rot severity were much lower for short and long grain varieties than they were for medium grains. Aggregate sheath spot incidence was only slightly affected by nitrogen rate. Nitrogen appears to have a larger influence on stem rot severity than variety. In contrast, variety played a more significant role in aggregate sheath spot incidence than nitrogen levels. Seedling Vigor Forty-four crosses of the Hungarian varieties Italica livorno and M-16 were made to transfer improved seedling vigor into California varieties. Incubator tests were used to screen 76,000 backcrossed seedlings. Approximately 1,200 seedlings were selected and transplanted to the field for further screening for maturity, short stature and stem rot resistance. Advanced generation selections from backcrossed populations that derive their high seedling vigor from M-16 have been recovered and appeared to have high vigor, short stature, improved grain quality and yield potential, as well as better stem rot resistance. A few were entered this year in the preliminary yield trials. Seven Russian plant introductions were brought through quarantine in 1994 and will be evaluated for seedling vigor in 1995. Rice Water Weevil Tolerance The donor parent for tolerance to the rice water weevil is PI 506230 developed at RES. Researchers are trying to improve some of the agronomic deficiencies, such as blanking, in this line through crossing, selection and screening in cold tolerance nurseries. Several experimental lines in the preliminary yield tests gave high yields comparable to M-201 in the Furadan� treated yield nursery. The more promising entries are being purified and will be further evaluated and tested in 1995 to test their performance and RWW tolerance.

Rice Breeding Program-94

Project Leaders

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

Bolstered by rising domestic consumption and new markets overseas, California rice acreage remains at levels not seen in recent years - 485,000 acres in 1994. The vast majority of this acreage was medium grain (94 percent), followed by short grain (5 percent) and long grain (1 percent). Yields crept up another notch to 8,500 pounds per acre, due in large part to improvements made in public rice varieties developed at the Rice Experiment Station, coupled with integrated management by growers.

Breeding Nurseries

Plant breeders made more than 900 new crosses for varietal improvement during 1994, bringing the total since the program began in 1961 to 20,500. Approximately 100,000 progeny rows were grown in nurseries at the RES, UC Davis, San Joaquin County and Hawaii. Progeny rows included selected lines in the third through seventh generation after crosses were made. From these rows breeders select, purify, advance and evaluate promising lines for seedling vigor, cold tolerance, disease reaction, and grain quality and yield. Additionally, several thousand pots of plants were grown in the greenhouse to screen for disease resistance and cold tolerance, and for use in crossing and generation advance.

The University of Hawaii nursery on Kauai - the "Paddy Crop Farm" - plays a critical role in accelerating the variety development process by enabling plant breeders to grow an additional generation of select lines each year. In 1993 research facilities were severely damaged from a hurricane but the University of Hawaii transplanted a full nursery of 5,300 rows on schedule for breeding and genetic research. Seed from this nursery was harvested, inspected, processed and grown in the mainland nurseries last summer. Another 5,300 selections from the RES nursery were transplanted in December 1994 and harvested in early April 1995.

The 1994 RES nursery comprised about 60 acres. Second generation (F₂) populations were drill-seeded on 12 acres. The nursery contained 70,000 progeny rows, 4,000 small plots and 2,600 large plots in various water-seeded yield tests. In addition 40 experimental lines were headrowed for seed increase and purification, and three advanced lines were grown in small breeder increases. Headrow seed of all public California varieties and advanced lines to maintain pure seed will be stored in a cold storage facility enlarged and retrofitted in 1993.

The cold tolerance nursery at UC Davis contained two acres of precision-drilled F₂ populations and 5,000 dry-seeded progeny rows. At the 11-acre cold tolerance nursery on Staten Island in San Joaquin County breeders planted more than 20,000 dry-seeded progeny rows and precision drill-seeded F₂ populations.

An estimated 300,000 panicles were selected from the various F₂ populations in these different nurseries for further screening and advancement. An additional 25,000 to 30,000 panicles were harvested for selection and purification from progeny rows. Some of this material is being advanced in the Hawaii nursery; the remainder to be screened and processed for planting in 1995.

Germplasm

Germplasm is a broad term that refers to rice varieties, breeding lines, plant introductions, mutants and wild species of rice. From these diverse sources plant breeders can tap into genetic diversity to improve California rice.

In 1994 RES researchers grew and evaluated the Cooperative Regional Uniform Rice nursery consisting of 200 entries from Southern U.S. public rice breeding programs.

Induced mutation has been a successful breeding tool in the past - both M-401 and M-203 were developed this way. Selections were made from M₂ populations at RES, UC Davis and San Joaquin County nurseries.

Seed from foreign sources started becoming more readily available with the advent of a plant introduction permit in 1988. Many new varieties and germplasm lines have been received from Japan, Russia and the Philippines. As required by quarantine procedures, materials are grown in the winter greenhouse when rice is not growing in the field and insect activity is minimal. Thirty-five new lines were successfully introduced for enhancement of grain quality and disease resistance.

Yield Tests

Rice Experiment Station and UC Cooperative Extension scientists annually conduct statewide yield tests to evaluate the agronomic performance and adaptation of advanced experimental lines and commercial varieties. Please see the section Variety Trials elsewhere in this report for the results of these tests. Preliminary yield tests, the initial step of replicated large plot testing for experimental lines are performed at the RES. These tests included 552 entries and check or standard varieties in 1994.

Long Grains

Improved milling and cooking characteristics remain the focus of long-grain rice breeding. Current long grains grown in California, L-202 and L-203, have good yield potential but are low in whole kernel (head) milling yield. In addition, the starch characteristics are different from Southern long grains.

Plant breeders are trying to incorporate some of the cooking characteristics of Southern long grains into California long grains. They have identified an early experimental line, 91-Y-093, as a promising entry with similar traits. It also has yield potential above L-203 and promising head rice yield based on milling tests. Evaluation will continue in 1995.

Another goal in the long grain program is to develop a variety with "Newrex type" cooking characteristics. Newrex rice cooks drier and fluffier than other Southern long grains and is considered superior for processing purposes. Plant breeders are looking closely at 93-Y-092, an early maturing experimental line, that yields similar to L-203. Milling yields tended to be on the low side for 93-Y-092 during preliminary evaluations.

Researchers are also continuing studies of five stem rot-resistant long grains. Tests in 1994 showed a wide range of disease incidence. The nature of this variability will be studied again in 1995 to determine whether further selection can narrow the range to that of 87-Y-550, a stem rot resistant long grain germplasm line developed at RES.

Medium Grains

Some of the multiple goals of the medium-grain rice breeding program include higher yield potential, resistance to lodging and disease, seedling vigor, improved milling yields and resistance to blanking.

Selection for grain quality factors continues to be an integral part of the RES breeding effort. Increased emphasis is being placed on identifying advanced experimentals with improved head and total milled rice yields.

Early and very early experimental entries occupied 95 percent of the medium-grain program. Harvest moisture values at cooler locations, along with evaluations of heading uniformity and green kernels at harvest were used to identify superior early maturing experimental entries. Two of those entries that will be retested in 1995 are of particular interest because they have improved lodging resistance, seedling vigor and milling yields.

91-Y-381 is a very early to early maturing smooth medium grain that has shown very high yield potential and high head rice yield. It has ranked first overall in three years of testing in the early group of the Statewide Yield Tests. It heads three days earlier than M-202, has and seedling vigor equal to M-202. Its strengths are good lodging and blanking resistance equal to M-204, early maturity, adequate straw strength and very high grain and milling yields. Breeder seed will be produced in 1995.

The second advanced medium grain experimental is 92-Y-624, an early maturing smooth medium grain. It has a larger seed size and seed weight that averages 3.5 percent heavier than M-204. Results from tests in 1993 and 1994 show that it is a "very acceptable" candidate for rice cake production.

Twenty-four different medium grains are being grown in the Hawaiian nursery for purification, seed increase and additional agronomic evaluation. Plant breeders report that some of these entries have greater yield potential than their respective highest yielding check varieties, lodging resistance superior to M-202 and/or improved grain quality. Medium grain entry 94-Y-237 is being advanced in Hawaii for retesting in 1995. It has very good straw strength, blanking resistance, and M-201 level of stem rot resistance.

Progress is being made to improve seedling vigor in superior experimental lines using M-16 and Italico livorno seedling vigor sources. Increased effort in breeding for seedling vigor has resulted in these materials occupying a significant part of the, medium-grain program. The greatest challenge facing plant breeders has been to combine strong seedling vigor it with improved stem rot resistance.

Short Grains

The main focus of the short-grain breeding effort is improved yield potential, resistance to lodging, and improved grain and milling characteristics. Plant breeders are aiming Ito improve on S-201, the primary commercial short grain. It has a number of undesirable characteristics, including intermediate maturity and variable heading.

91-Y-171 is a very early maturing short grain first reported in 1992. It was the highest yielding entry, producing over 10,000 pounds/acre. in the very early group of the Statewide Yield Tests in both 1993 and 1994. It also has shown high head and total milled rice yields in four years of milling tests. Quality evaluations by marketing organizations have been positive. This line is pubescent, although not heavily awned, and is susceptible to stem rot. The high milling yield, large translucent kernels, very early maturity and high yield potential make 91-Y-171 of particular interest for further testing and seed increase.

Premium Quality

Premium quality short and medium grains have unique cooking characteristics that are in strong demand by certain ethnic groups, especially Japanese and Korean consumers. These rices are very glossy after cooking, sticky with a smooth texture and remain soft after cooling. Aroma and taste are also cited as important features. RES has placed a high priority on developing agronomically improved medium and short grains with these characteristics.

The premium quality breeding program is focused on developing earlier maturing, high yielding lines with lodging resistance and high milling yields. Plant breeders will be taking a harder look at some premium quality short grains like 94-Y-022, a very early maturing experimental line. Although its grain yield was comparatively low in 1994 tests, it showed a 2,000 pound/acre yield advantage over the Japanese premium quality short grain Akitakomachi. Milling yield and kernel appearance were very good but results of cooking quality evaluations have been somewhat variable. A number of other premium quality lines that hold promise for further improvements in cooking quality are being advanced in the Hawaii winter nursery.

Special Purpose Types

Work continues on a number of special varieties with unique characteristics. Among them are long grains distinguished as aromatic, soft cooking and waxy types. Plant breeders have emphasized Basmati types, aromatic rices with extreme kernel elongation.

As a group the aromatic experimental lines yielded and milled poorly. However, 91-Y-631 yielded comparably to L-202 and A-301. The earliness of this experimental along with its superior seedling vigor would make it easier to grow than A-301. Although it performed well in taste tests, it lacks the degree of kernel elongation shown by traditional Basmati rice. Another shortcoming is its low head rice yield. Breeder seed of 91-Y-631 was produced in 1994. It will be advanced further if desired by aromatic long-grain rice growers.

Several promising new experimental lines with the desired cooked kernel elongation of Basmati rice will be advanced to statewide yield trials in 1995. 92-Y-521, an early waxy long-grain rice with smooth leaves and hulls and superior seedling vigor is being evaluated for suitability as a waxy long grain.

Work on other specialty types of rice include short-grain waxy (mochi) varieties like Calmochi-101. Plant breeders are focusing on improved agronomic and quality characteristics. Crosses have also been made to a number of new waxy germplasm introductions. Breeding for the large-seeded "Arborio" types continues at the RES.

Grain Quality

RES scientists screen for the factors that determine grain quality - kernel size, shape, breakage and translucency - at every step of the breeding process until an experimental line is ready for release as a new variety.

Milling yield is a particularly important yet difficult rice quality component to improve. Detailed milling studies continue to be conducted on advanced breeding materials. In 1994 researchers conducted 37 harvest moisture milling tests on advanced experimental lines and commercial varieties. Samples are harvested twice a week for seven to 11 harvests, enabling scientists to determine optimum harvest moisture for maximum head rice yield.

The USDA-ARS Rice Quality Research Laboratory in Beaumont, Texas performs a variety of physiochemical tests to help public breeding programs assess cooking and processing qualities. In 1994 more than 2,000 long-grain milled samples from the RES were evaluated for amylose content and alkali spreading values. Additionally, the RES is now using a Rapid Visco Analyzer (RVA) to determine starch pasting properties of samples. RVA viscograms, apparent amylose content and alkali spreading values are used to screen for Southern long grain and Newrex cooking qualities. More than 1,500 samples were tested with the RVA last year and another 4,000 long grain samples will be evaluated in 1995.

The RES screening capabilities were further advanced last year with the acquisition of a near-infrared (NIR) scanning spectrophotometer, which permits rapid chemical analysis in minutes. They are currently in use in rice quality labs in Japan and Australia to measure protein and cooking quality. RES scientists are working with USDA laboratories to develop new methods for analyzing apparent amylose and protein content of rice flour and milled rice.

Disease Resistance

Breeding for disease resistance, a cooperative effort among the breeders and the plant pathologist, has been a slow, difficult process. Because of its importance, however, efforts are intensifying in this area.

One hundred sixteen new crosses were made to transfer stem rot resistance from Oryza rufipogon to adapted California varieties. Three years of water-seeded rate tests were concluded to improve disease screening techniques.

Only a very small percentage of the lines screened showed better levels, of stem rot resistance than M-201. A new supplementary selection scheme emphasizing rapid generation advance of the agronomically best second generation populations was initiated this year.

A cooperative study with the International Rice Research Institute (IRRI) is making backcrosses of the highly stem rot-resistant Oryza officinalis and M-202. Seed of resistant lines will be returned to RES for quarantine introduction and screening. Scientists at the IRRI have found that certain other wild species are highly resistant to stem rot. These materials were processed through quarantine in 1994 and will be evaluated for disease resistance in 1995 under California conditions.

Forty-two new crosses were made in 1994 to transfer aggregate sheath spot resistance. However, the frequency of selections with resistance was less than 4 percent. IRRI researchers found that certain wild species are also highly resistant to sheath blight. These materials were processed through quarantine in 1994 and will be evaluated for disease resistance under California conditions in 1995.

A cooperative project with USDA geneticist Dr. David J. Mackill is using advanced techniques in molecular genetics to identify and map stem rot resistant genes from the resistant long grain 87-Y-550. In related work to improve stem rot resistance, other crosses of medium and long grain lines are being advanced and evaluated in the field and greenhouse for future genetic analysis. These molecular genetics studies, coupled with rapid generation advance at RES, may hasten development of stem rot resistance for California.

In a study of how nitrogen and potassium interact with disease severity, researchers found that disease incidence was generally affected more by nitrogen than by potassium. Stem rot was pronounced at the highest nitrogen rate (180 lb.N/acre) but nitrogen had less effect on aggregate sheath spot. Potassium level had no effect on stem rot or aggregate sheath spot severity.

Last year's research also showed that stem rot incidence in M-201, M-202, M-204, L-202, L-203 and S-201 generally increased with nitrogen levels. Correlations between nitrogen level and stem rot severity were much lower for short and long grain varieties than they were for medium grains. Aggregate sheath spot incidence was only slightly affected by nitrogen rate. Nitrogen appears to have a larger influence on stem rot severity than variety. In contrast, variety played a more significant role in aggregate sheath spot incidence than nitrogen levels.

Seedling Vigor

Forty-four crosses of the Hungarian varieties Italica livorno and M-16 were made to transfer improved seedling vigor into California varieties. Incubator tests were used to screen 76,000 backcrossed seedlings. Approximately 1,200 seedlings were selected and transplanted to the field for further screening for maturity, short stature and stem rot resistance. Advanced generation selections from backcrossed populations that derive their high seedling vigor from M-16 have been recovered and appeared to have high vigor, short stature, improved grain quality and yield potential, as well as better stem rot resistance. A few were entered this year in the preliminary yield trials. Seven Russian plant introductions were brought through quarantine in 1994 and will be evaluated for seedling vigor in 1995.

Rice Water Weevil Tolerance

The donor parent for tolerance to the rice water weevil is PI 506230 developed at RES. Researchers are trying to improve some of the agronomic deficiencies, such as blanking, in this line through crossing, selection and screening in cold tolerance nurseries. Several experimental lines in the preliminary yield tests gave high yields comparable to M-201 in the Furadan� treated yield nursery. The more promising entries are being purified and will be further evaluated and tested in 1995 to test their performance and RWW tolerance.