ITEMS FROM THE UNITED STATES

OKLAHOMA

OKLAHOMA STATE UNIVERSITY
Department of Plant and Soil Sciences, 368 Ag Hall, Stillwater, OK 74078-6028, USA.

E.G. Krenzer and B.F. Carver.

Outstanding wheat yields and test weight were routine in the 1998 Oklahoma harvest. Oklahoma Agricultural Statistics reported production of 198.9 million bushels of wheat from 5.1 million acres with an average yield of 39 bu/acre. This average yield exceeds the previous all-time high of 38 bu/acre set in 1979. Variety trial yields were the highest in more than 10 years, averaging 49.1 bu/acre. Test weights were also the highest since 1982, averaging 60.3 lb/bu across all varieties and locations.

Excellent wheat planting conditions occurred in very late August 1997. However, temperatures were above 95·F in early September, and soils dried quickly. By mid-September, most fields were too dry to obtain stands. Rains occurred statewide beginning on 22 September, and planting resumed by 1 October. Only 28 % of the wheat was planted by 28 September, compared to the 5-year average of 43 %. The somewhat later planting date may be one of the reasons for the higher yields.

Most locations received ample to excessive soil moisture from November through January. Temperaturesin November were lower than normal and slowed the development of wheat planted in late October but appeared to be ideal for September-planted wheat. A few cold nights occurred in early December, but temperatures were warmer than normal for the remainder of December through February. Each wheat stem produced a full new leaf between 14 December and 20 January, which was very unusual.

Wheat development was well ahead of normal by 1 March, 1998. Varieties that respond to heat reached the first-hollow-stem stage of development earlier than in any of the past 5 years of monitoring. However, cold temperatures in early March delayed later starting varieties, so first-hollow-stem was reached at a more normal time. Because of wet soils, many producers had difficulty applying top-dress nitrogen. Some fields were never top-dressed, and nitrogen deficiency may have limited yields. Excellent growing conditions existed at most locations for the spring growth period. Excessive moisture may have reduced yields on locations where drainage is poor. High temperatures in late May and early June hastened maturity and resulted in a very early harvest.

The only general pest problem in the autumn of 1997 and spring of 1998 was cheat. Many fields had vert high cheat infestations. Because wheat test weight was exceptionally high, producers were very effective in separating the cheat from the wheat with the combine, and relatively little dockage occurred. Some leaf rust developed in the autumn, but not enough to be of concern. Insect problems were few. In the spring, high numbers of aphids (primarily bird-cherry oat aphids) may have limited yields and/or caused very late infection of BYDV at some locations. Leaf rust also developed just before maturity.


Wheat breeding and genetics research.

B.F. Carver.

The formation of the Wheat Improvement Team ushered in a new era of wheat cultivar development at Oklahoma State University, following a productive 30-year history of wheat breeding under Dr. Ed Smith's leadership. Forming the team are nine research faculty from the Department of Plant and Soil Sciences (Brett Carver, Art Klatt, Gene Krenzer, Bjorn Martin, and Arron Guenzi); Department of Entomology and Plant Pathology (Bob Hunger and Jeanmarie Verchot), Department of Biochemistry and Molecular Biology (Patricia Rayas-Duarte); and the USDAARS Plant Science Research Laboratory in Stillwater (David Porter). A website describing the team's mission and activities in wheat breeding research was established in 1998 at http://clay.agr.okstate.edu/wheat/wit.html.

Beginning with the current crop season, future cultivar development will follow a modified selection protocol as diagramed on the website. Central to this protocol is a greater emphasis on adaptation to dual-purpose management systems, characteristic of wheat production in the southern Great Plains. The Wheat Pasture Center near Marshall, OK, will provide a principal selection site under early-planted, grazing conditions, beginning with early segregating generations (bulk populations) and proceeding through the advanced generations (breeder lines). Agronomic traits that will be considered under this regime are rapid stand establishment under hot soil conditions, forage production and regrowth, timely dormancy release based on appearance of first-hollow-stem, tolerance to bird- cherry oat aphid and greenbug, spring recovery from grazing, and tolerance to several diseases including root rots and BYDV.

Approximately 25 % of the breeding program is dedicated to hard white wheat cultivar development, with the remainder devoted to HRWW. Emphasis on end-use quality for both classes was strengthened by expansion of the Wheat Quality Laboratory. The lab is now housed in the new Food and Agricultural Products Research and Technology Center. Several pieces of equipment were purchased in the past year to provide greater capacity for starch and protein analysis, with applications to both bread and noodle production.

Technical assistance in the wheat breeding program is provided by Wayne Whitmore, senior agriculturalist in charge of field operations, and Wayne Wood, senior agriculturalist in charge of greenhouse and laboratory operations. Mr. George Morgan retired as senior agriculturalist on 31 March, 1999, after 26 years of dedicated service to wheat breeding research in Oklahoma.

Assistance is also provided by two graduate students. Joy Martin, M.S. candidate, will investigate the combined effects of awn production and leaf rust resistance on wheat productivity and grain quality. Iftikhar Khalil, a Ph.D. candidate from Pakistan, will conduct a series of studies designed to estimate past and to predict future genetic gains in grain-only and dual-purpose systems.

Dr. Art Klatt, Professor, has joined the Wheat Improvement Team and the Department of Plant and Soil Sciences, after serving as director of international programs at Oklahoma State University. Dr. Klatt's research will focus on germ plasm enhancement, with special attention given to improvement of nitrogen-use efficiency.


Wheat cultivar testing.

E.G. Krenzer

Wheat forage data were collected from several trials conducted in 1997-98. Autumn forage data can be found in publication PT 98-13 "Fall Forage Yield Wheat Variety Trials 1997" or in PT 98-17 "Wheat Forage Management in Low pH Soils 1997". Full-season forage data may be found in PT 98-21 "Full Season Forage From Wheat Varieties 1997-98". Grain yield results were published in PT 98-22 "Wheat Grain Yield from Variety Trials 1997-98". Variety trial data can also be found on the internet at http://clay.agr.okstate.edu/wheat/wit.html.


Publications.

Carver BF and Bona L. 1998. Reciprocal performance of winter wheat in Hungary and Oklahoma. J Plant Breed 117:113-118.

Bona L and Carver BF. 1998. A proposed scale for quantifying aluminum tolerance levels in wheat and barley detected by hematoxylin staining. Cereal Res Commun 26:97-99.

Epplin FM, True RR, and Krenzer EG. 1998. Practices used by Oklahoma wheat growers by region. Oklahoma Curr Farm Econ 71:14-24.

Wu J, Carver BF, and Goad CL. 1999. Kernel color variability of hard white and hard red winter wheat. Crop Sci 39:(in press).

Wu J and Carver BF. 1999. Sprout damage and preharvest sprouting resistance in hard white winter wheat. Crop Sci 39:(in press).

Zhang H, Johnson GV, Krenzer EG, and Gribble RD. 1998. Soil testing for economcally and environmentally sound wheat production. Commun Soil Sci Plant Anal 29:1707-1717.

Entomology & Plant Pathology Department, 127 Noble Research Center, Stillwater, OK 74078, USA.

Bob Hunger, Kris L Giles, Larry J. Littlefield, Tom A. Royer, Larry L. Singleton, Jeanmarie Verchot, and Mark E. Payton (Department of Statistics).

Barley yellow dwarf virus.

Bob Hunger and Janmarie Verchot.

Although BYDV was present in many fields in Oklahoma during 1998, significant yield losses generally were not observed because the the disease resulted from infection by aphids arriving late in the season. Thus, symptoms were observed on flag leaves but affect on yield was minimal.

Field plots planted to investigate losses associated with BYDV and the optimization of the use of imidacloprid (Gaucho, Gustafson Corp) to limit aphid infestations and BYDV incidence yielded minimal information because of the late infestation by aphids.

We developed a method to mechanically inoculate BYDV into plants. Purified virus has been inoculated using a hand-held 'gun' that injects the virus into leaves using helium pressure. We have seen the progress of infection to systemic leaves after inoculation using the biolistic method. This new method may be useful for analyzing virus infection in wheat varieties that have been bred for BYDV resistance.

Second, we have developed a PCR assav to detect BYDV in aphids. This assay will he useful for assessing the proportion of aphids transmitting BYDV and for idenfifyirlg specific strains of BYDV in the field.

Wheat entomology.

Kris L. Giles and Tom A. Royer.

The following research projects were initiated in 1998:

- Interaction of imidacloprid insecticide dosage and planting date for control of greenbug and bird cherry oat aphid in winter wheat. Preliminary results suggest that the economic returns from aphid control are variable and dependent upon planting date, but certain combinations of reduced levels of insecticide and planting date can provide economic benefits and effective control of aphids.

- Refinement of injury thresholds for greenbug. This project was initiated in 1998, and it will be ongoing for the next 3 years.

- Development of decision thresholds and presenceabsence sampling plans for natural enemies of aphids. This project was initiated in 1998 and will continue for 2 years.

- Development of presenceabsence protocols for greenbug in winter wheat. Data is currently being collected and will be analyzed following the 1998-99 growing season. This information will be used along with the information from the previous two projects to develop new recommendations for aphid management in winter wheat in Oklahoma.

- Evaluation of tri-trophic interactions among varieties of resistant and susceptible winter wheat, cereal aphids, and natural enemies of cereal aphids. The goal of this research is to understand these interactions in order to develop an effective, integrated management program for cereal aphids in winter wheat.


Wheat rust.

Bob Hunger.

Wheat leaf rust was present in the autumn, but an extended period of dry weather from late winter through spring inhibited spread and develoment of leaf rust until late in the spring. Consequently, although leaf rust was severe on susceptible varieties in Oklahoma in 1998, losses were minimal because of the late timing of the infection. Reactions to leaf rust at Perkins, OK, are as indicated in Table 1.

Wheat soilborne mosaic virus.

Bob Hunger and Jeanmarie Verchot.

The incidence and severity of WSBM in Oklahoma for the 1998-99 season was the lowest observed in the last 16 years. Symptoms of WSBM never were strongly pronounced in susceptible varieties growing in areas with a history of severe WSBM, although an occasional plant would have mild symptoms and test positive for WSBM using ELISA. The winter of 1998-99 was one of the mildest winters on record in Oklahoma and may be the reason for the lack of WSBM.

We have modified the ELISA assay for WSBMV making it 10-fold more sensitive than the previous assay. This will allow us to detect minimal quantities of virus accumulating in plants earlier in either field or greenhouse experiments.

Experiments have been initiated to compare the effectiveness of host resistance in Tonkawa, Newton, and Hawk HRWWs against different concentrations of virus inoculum. Virus resistance in any of these three varieties is not effective against high concentrations of virus (5 mg/ml). Further analysis will be conducted using more dilute inoculum to determine if the three resistant varieties respond differently to different virus concentrations.

These three varieties are being crossed to the susceptible varieties Vona and Custer to analyze segregation of resistance in the F1 progeny. Segregation analysis will be conducted to determine if the resistance in these varieties is due to a single or multiple genes.

Because WSBMV is inoculated through the roots of susceptible wheat in the field, experiments are being conducted to compare virus accumulation in the roots of resistant and susceptible varieties. These experiments will allow us to determine if virus can accumulate in the roots of resistant wheat varieties.


Ultrastructure of Polymyxa graminis.

Larry Littlefield.

Current research includes preliminary work to localize the WSBM virus in the vector.


Breeding for disease resistance.

Bob Hunger.

Incorporation of resistance to leaf rust and WSBMV from emmer wheats collected in Israel and Turkey is continuing. Crosses were made several years ago between emmers resistant to these diseases and HRWWs such as Chisholm and Tonkawa. BC3 lines are being tested in the field this season in a WSBM nursery. Other lines involving crosses with various sources of resistance to leaf rust (e.g., South African germ plasm (Lr19) and Eastern European wheats) are at various stages of testing in the field.


Wheat root rots.

Larry Singleton and Bob Hunger.

The 1998-99 crop season. Isolates of Rhizoctonia cerealis (sharp eyespot) and R. solani are being field tested for their influence on stand establishment, forage production, and yield in microplot tests at Stillwater. These tests are being conducted for wheat planted early in September and mid-October and will provide information about the relative importance of these pathogens in our wheat production systems. In another field test, the efficacy of nine seed treatments for controlling these pathogens and Fusarium spp. is being evaluated.

The 1997-98 crop season. Thirty biocontrol and chemical seed treatments were evaluated for control of sharp eyespot and Fusarium root rot at Stillwater. These trials were planted on 15 September, 1997, and were harvested on 3 June, 1998. Disease incidence and seventy data for sharp eyespot, Fusarium root rot, and yield were effective in increasing yields over their respective checks.

At two locations (Chickasha and Lahonia), six varieties (Chisholm, Custer, Triumph 64, TAM 101, TAM 107, and TAM 202) were evaluated in a planting date study. Plots were planted in 1997 on 22 September, 6 October, 20 October, and 3 November. Disease incidence and severity data for sharp eyespot and Fusarium root rot were taken along with standard yield. Results suggest that Triumph had a lower incidence and severitv of sharp eye spot and Fusarium root rot. There was a significant effect from planting date, with incidence and seveiity values for both diseases being higher with early planting. In this trial, Fusarium root rot was the major diseatse at both locations.

Continued recommendations. In areas of chronic root rot disease pressure, cultural control by delayed planting (15 October) is an effective altemative to early planting, espcially in root rot-prone fields. Because these are management decisions, these methods are cost effective because they do not require major dollar investments for the producer. Planting in mid-October, when the soil temperature at planting depth is lower than 77·F offers a mechanism for escaping seedling infection by this group of root rot pathogens. By contrast, with early planting (1 September), we know that soil temperatives can be 87·F or greater, which has a greater potential for root rot infection and damage. For a more detailed discussion of control measures, see OSU Extension Fact Sheet No. 7622.

Departmental and personnel changes.

Barbara Driskel is a new senior agriculturalist working in the laboratory of Jeanmarie Verchot and is conducting growth chamber experiments to compare WSBMV accumulation in resistant and susceptible wheat cultivars. Aigen Fu is a new graduate student in the laboratory of Jeanmarie Verchot and is conducting analyses to detect WSBMV accumulation in the roots of inoculated susceptible and resistant wheat varieties. Aswathy Sreedharam is an M.S. student working with Bob Hunger and Larry Singleton. Ms. Sreedharam is a native of India and is defining the pathogenicity of R. soilani from wheat and peanuts and R. cerealis from wheat on wheat.

Publications.

Evans CK, Hunger RM, andSiegerist WC.- 1999. Comparison of greenhouse and field testing to identify wheat resistant to tan spot. Plant Dis 83:In press.

Hunger RM and Siegerist WC. 1998. Seedling reaction of the 1998 Regional Germplasm Observation Nursery to wheat leaf rust. Proc 2lst Hard Winter Wheat Workers Conf, 2730 January, 1998, Denver, CO.

Hunger RM, Sherwood JL, Siegerist WC, Myers L, and Payton M. 1998. Reaction of wheat genotypes to wheat soilborne mosaic (WSBM), 1997. Biol Cul Test Control Plant Dis 13:130.

Hunger RM, Siegerist WC, Smith EL, Morgan G, and Payton NE. 1998. Reaction of wheat genotypes to wheat leaf rust, 1997. Biol Cul Tests Control Plant Dis 13:127.

Hunger RM, Verchot J, Siegerist WC, Myers L, and Payton M. 1998. Effect of wheat soilbome mosaic on yield and quality of grain from wheat. Phytopathology 88:In press (abstract).

Littlefield LJ, Whallon JH, Doss PJ, and Hassan ZM. 1998. Postinfection development of Polymyxa graminis in roots of Triticum aestivum. Mycologia 90:869-882.

PLANT SCIENCE RESEARCH LABORATORY, USDA-ARS

1301 N. Western St., Stillwater, OK 74075, USA.

http://www.csrl.ars.usda.gov/pswcrl/pswcrl.htm

C.A. Baker, J.D. Burd, M.H. Greenstone, S.D. Kindler, D.R. Porter, K.A. Shufran, and J.A. Webster.


Host plant resistance and germ plasm enhancement.

Efforts are ongoing to develop RWA, greenbug, and BCO-resistant wheat germ plasm. Our development of a new technique for screening for resistance to BCO has stimulated much interest in the damage caused by this pest of small grains. In the past, the importance of BCO was underestimated, because it wa