OKLAHOMA
OKLAHOMA STATE UNIVERSITY
Department of Plant and Soil Sciences, 368 Ag Hall, Stillwater, OK 74078-6028, USA.
Jeff T. Edwards.
Drought was a major hindrance to Oklahoma wheat research and production in 2006. Our research efforts are frequently hampered by drought but to have a large portion of our wheat plots emerge and then die due to moisture limitations was a new experience and was hopefully a one-time event.
A major thrust of our research and extension efforts centered on sensor-based nitrogen recommendations (see www.nue.okstate.edu for more information). We were successful in creating over 600 nitrogen-rich strips in farmer's fields in the autumn of 2006. These strips will be sensed by county educators in the spring of 2007 and nitrogen recommendations will be given to producers. We will record grower adoption of sensor recommendations and use these data to retool extension efforts where appropriate.
Our work evaluating early-season radiation use efficiency (RUE) and canopy closure of wheat cultivars continued in 2006. We found that RUE of our most popular wheat cultivars ranged from 2.0 to 2.8 g/MJ. Our data also revealed a 150 Cd difference in thermal time until canopy closure among wheat cultivars, which resulted in a 114 g/m2 difference in wheat forage production by 1 November. We will continue this research in 2007 and 2008 to further evaluate how early-season wheat physiology affects wheat forage production.
Finally, we established no-till versus conventional till wheat cultivar comparisons in the autumn of 2006.
This research will evaluate the effect of no-till systems on wheat forage and grain yield of approximately 20 wheat
cultivars and investigate insect predator/prey relationships in no-till systems. Although commonplace in many areas, no-till
wheat production is still a relatively new practice in the southern Great Plains, so research and demonstration efforts are
needed by producers.
Brett F. Carver.
The Oklahoma Wheat Improvement Team, the Oklahoma Agricultural Experiment Station, and the USDAARS announced the release of Duster and Centerfield HRWW cultivars in late 2006.
Centerfield has the pedigree 'TXGH12588-105*4 / FS4 // 2*2174'. The germ plasm indicated by FS4 originated with BASF Corporation (formerly American Cyanmid) and provides tolerance to imazamox herbicide. Centerfield is moderately resistant to WSSMV and WSBMV and should exhibit insignificant losses to these viral diseases. Though susceptible in the seedling stage, Centerfield shows moderate to high adult-plant resistance to wheat leaf rust caused by races of P. triticina present in Oklahoma and Texas from 2004 to 2006. Centerfield appears to be at least moderately resistant to P. striiformis f. sp. tritici in the field. Seedling tests in the greenhouse indicate a susceptible reaction to tan spot and to S. tritici leaf blotch and a moderately susceptible reaction to powdery mildew. Centerfield shows a heterogeneous reaction (46 % resistant : 54 % susceptible) to biotype-E greenbug. Field ratings in Oklahoma indicate a tolerant reaction to Hessian fly, similar to those of Chisholm, 2174, and Ok102, although its seedling reaction in the greenhouse is heterogeneous. Early seeding of Centerfield is not recommended because of its heat-sensitive germination response. Milling and baking characteristics are an improvement over those of Okfield and AP502CL, current imazamox-tolerant cultivars grown in Oklahoma, with above-average kernel size and grain-volume weight, good dough strength, and moderately high wheat protein content of (13.0 %, 12 % m.b.).
Wheat producers in the southern Plains who are shifting to conservation-tillage practices while planting early for forage production in a graze-plus-grain (dual-purpose) management system are increasingly challenged by Hessian fly infestations. The majority of cultvars grown in this area possess no Hessian fly-resistance genes. A driving force in the release of Duster was its resistance to the Great Plains biotype of Hessian fly. As a high-tillering cultivar, it also exhibits excellent biomass accumulation prior to autumn grazing and canopy regeneration during grazing, and exceptional recovery from grazing. These are characteristics we continue to emphasize in our GRAZEnGRAIN breeding system. Hence, it is positioned for all areas inclusive of and immediately adjacent to Oklahoma, particularly those featuring a dual-purpose management system. Duster originated from the cross 'W0405 / NE78488 // W7469C / TX81V6187', which was produced in the HRWW-breeding program of Pioneer Hi-Bred International, Inc. Duster is resistant to WSSMV and to WSBMV. Although susceptible to leaf rust in the seedling stage, Duster exhibited a resistant adult-plant reaction in the field in Oklahoma and Texas during the three crop seasons of 200406. Reaction to stripe rust has varied from intermediate to moderately susceptible in the Great Plains. Thus, reaction to stripe rust may be highly dependent on the environment and/or races of the pathogen present. Based on combined greenhouse and field observations, Duster is moderately susceptible to tan spot but shows an intermediate reaction to Septoria leaf blotch and an intermediate to moderately resistant reaction to powdery mildew. Aside from kernel size being intermediate (kernel diameter of 2.2 mm), Duster shows excellent mixing tolerance at a intermediate protein level (wheat protein, 12.4 %, 12 % m.b.), and it exhibits a unique but desirable farinograph pattern of short peak time (<5 min) and long stability time (>15 min). Duster contains alleles which encode HMW-glutenin subunits 2* at the Glu-A1 locus, 7+8 at Glu-B1, and 5+10 at Glu-D1.
Two experimental HWWW lines are under breeder-seed production in the 200607 crop season, OK00514W and OK00611W. The former is a reselection of OK Bullet (HRWW cultivar) with agronomic and quality characteristics almost identical to OK Bullet. OK00611W was a sister selection to OK Bullet and features a moderately high level of preharvest sprouting tolerance and postharvest seed dormancy that is accentuated by high soil temperature. With their foliar disease resistance and ability to tolerate acid soils, both lines may be positioned for the Central Plains, offering a HWWW alternative in an area dominated heavily by HRWW cultivars. A release decision for one of these will be made in June 2007. Currently, we allocate 80 % of our resources in the latter stages of selection to HRWW line development, although 50 % of the crosses made each year involve HWWW parentage to varying degrees. About 20 % of the crosses made each year involve strictly HWWW parentage.
Marker-assisted selection is playing an increasing role in our wheat improvement program, primarily for
the purpose of gene enrichment in early segregating generations. This activity is tied directly to participation in the
multi-institutional CAP project funded by USDACSREES (award no. 2006-55606-16629), in conjunction with the
Hard Winter Wheat Genotyping Laboratory (USDAARS, Manhattan, KS) supervised by Dr. Guihua Bai and in
coöperation with Dr. Liuling Yan (Oklahoma State University molecular geneticist). Target traits currently under watch are
Hessian fly resistance, acid-soil tolerance, preharvest sprouting tolerance, resistance to leaf rust, WSMV, and BYDV.
The Wheat Improvement Team at OSU currently has ten members: Brett Carver (team leader), Liuling Yan (molecular genetics), Bob Hunger (pathology), David Porter (USDAARS; aphid resistance), Tom Royer and Kris Giles (Hessian fly resistance), Art Klatt (prebreeding and germ plasm development), Jeff Edwards (extension, management), Patricia Rayas-Duarte (cereal chemistry), and Bjorn Martin (physiology). Dr. Yan is our newest addition to the team, having recently moved from a postdoctoral position in wheat molecular genetics at the University of CaliforniaDavis. His research will focus on identification and cloning of genes responsible for agronomically and economically important traits in wheat and other cereal crops. Projects already in progress include genetic analysis of variation in vernalization requirement and duration among winter wheat cultivars and establishment of a genome-scale gene network for flowering time in wheat and barley. Molecular markers will be developed to assist breeding programs to select gene combinations that maximize plant adaptation to different environments.
USDA-ARS-SPA WHEAT, PEANUT AND OTHER FIELD CROPS RESEARCH UNIT
1301 N. Western Road, Stillwater, OK 74075.
Cheryl A. Baker, John D. Burd, Norman C. Elliott, Yinghua Huang, Dolores W. Mornhinweg, David R. Porter, Gary J. Puterka, and Kevin A. Shufran.
In conjunction with collaborators from Oklahoma State University, we continued research to develop a predictive
model for the predatory impact of Coccinellidae on the greenbug. During the previous year, we conducted field and
laboratory studies to quantify the spatially explicit population dynamics of the greenbug in relation to parasitism by L. testaceipes and predation by Coccinellidae and other predators and initiated development of a preliminary spatially explicit
simulation model. The research has potential to improve pest management practices for the greenbug in wheat. If
successful, treatment decisions will be more accurate and based on improved knowledge of the potential for biological control.
In conjunction with collaborators from the Texas Agricultural Experiment Station and SST Development Group Inc., we are developing remote sensing technology to detect and monitor greenbug infestations in winter wheat. During the previous year we documented that multi-spectral remote sensing differentiated stressed areas in production winter wheat fields caused by greenbug infestation from nonstressed areas. Remote sensing technology has the potential to markedly improve pest management practices for the greenbug in winter wheat because infestations in fields will be efficientlydetected and delineated at an early stage, which could result in more economically and environmentally sound management.
Approximately 370 RWA clones we collected from 70 sites in Texas, Oklahoma, New Mexico, Colorado, Nebraska,
and Wyoming in 2005. The collections were made primarily from wheat with the exception of a few from wild grasses and
a majority collected from barley in northern Wyoming. The clones were evaluated on Dn4 and Dn7 resistance in wheat in replicated trials. A subsample of 30% of the collections were evaluated on Dn1Dn9 RWA resistance in wheat
and STARS 9301B and 9577B RWA resistance in barley for a complete biotype determination. Colorado, Texas,
Oklahoma, Kansas and Nebraska had equal proportions of RWA clones virulent and avirulent to Dn4. New Mexico had 76% of the samples avirulent to Dn4 (RWA1) while Wyoming had 70% of the samples virulent to Dn4. No clones were found to be virulent to Dn7 or the two sources of RWA resistance in barley. The subsamples tested were found to be either RWA1
or RWA2, based on chlorosis ratings. Therefore, our survey indicates the RWA2 is now present in significant levels in
the wheat and barley growing regions RWA infests.
Diuraphis noxia biotypes RWA1 and RWA2 (10 clones each) were subjected to RAPD and COI mtDNA sequence analysis. No variation was found within or between biotypes. Zero nucleotide variation in the COI was found in an additional 40+ field collected individuals of unknown biotype (collected from 2003 to 2005 in TX, CO, NM, KS, NE, OK, and WY). COI sequences from the USA were identical to those from Canada, Ethiopia, Turkey, Syria, and the Czech Republic as reported in GenBank by Belay and Stauffer (AY241697AY241705). Microsatellite analysis revealed US populations were made up of multiple clones. Clonal variation was found within and between RWA1 and RWA2, however no biotype specific loci or alleles were found. Microsatellite markers are being used to study gene flow in US populations.
Biotypic diversity of the greenbug, was assessed among populations collected from cultivated wheat and sorghum, and their associated noncultivated grass hosts. Greenbugs were collected during May through August from 30 counties of Kansas, Nebraska, Oklahoma, and Texas. Discounting the presumptive biotype A, five of the remaining nine letter-designated greenbug biotypes were collected; however biotypes C, F, J, and K were not detected. Biotypes E and I exhibited the greatest host range and were the only biotypes collected in all four states. Sixteen greenbug clones, collected from eight plant species, exhibited unique biotype profiles. Eleven were collected from noncultivated grasses, three from wheat, and two from sorghum. The most virulent biotypes were collected from noncultivated hosts. The great degree of biotypic diversity among noncultivated grasses supports the contention that the greenbug species complex is composed of host-adapted races that diverged on grass species independent of, and well before the advent of modern agriculture.
Greenbug was first discovered damaging seashore paspalum (Paspalum vaginatum) turfgrass in November 2003 at Belle Glade, Florida. Several golf courses with seashore pasplaum in central and southern Florida were subsequently infested by April 2004. Damage symptoms progress from water soaked lesions surrounding feeding sites within 24 hours to chlorosis and necrosis of leaves within 96 hours. Problems caused by greenbug feeding were initially misdiagnosed as fertilizer, disease or water management problems because aphids previously were not found on warm season turfgrasses in Florida. The Florida greenbug isolate exhibited a unique biotypic profile, which was most similar to the profiles of biotypes F, G, and H. These biotypes are typically not abundant on cultivated crops, but are commonly found on Kentucky bluegrass lawns and/or noncultivated grass hosts. Moreover, the Florida isolate was virulent to all currently available resistant sorghums and GRS1201, which is resistant to the principal agricultural biotypes that attack small grains.
At the 2005 WERA-066 meeting, it was determined that there was a pressing need for specific guidelines to be set and followed when screening for resistance to Russian wheat aphid. These guidelines were published in the 2005 WERA-066 Annual Meeting Minutes, which are available at the following link:
http://www.oznet.ksu.edu/entomology/wera-066/WERA-066report.pdf.
Included in the guidelines were recommendations for establishing set plant differentials for use as screening tools, thereby eliminating one of the obvious sources of variability in our screening techniques. In order to standardize the seed source, we determined that these plant differentials would be available to RWA researchers via Stillwater USDA-ARS, as soon as sufficient seed is available. We hope that enough seed will be available for small screening tests, and if larger amounts of seed are required for an individual program, then starter seed can be obtained from Stillwater, and seed can then be increased as needed at the various locations. In order to establish this uniform set of differentials, the suggested differential lines were screened for homogeneity for RWA1 resistance, and plants were then grown and harvested with an eye for uniform maturity, height, and other observable characteristics. Off-types were discarded. Progeny screening will be done prior to further increases.
In addition, it was determined that Stillwater ARS would be the official source for the RWA1 biotype and Colorado State University would be the official source for RWA2. When research is to be done with either of these biotypes, it would be advantageous to know that we are all working with the same aphids and not relying on new field collections of aphids. For example, if a new RWA collection is virulent on Dn4 wheat, it must be noted that it does not logically follow that the new aphid is RWA2- it merely confirms that it is not RWA1. Other additional biotypes have been collected that are also virulent on Dn4, so the use of a small number of differentials may not successfully distinguish between biotypes.
We have continued with the development of our breeding lines that are resistant to RWA1. Even though they may not be useful as germ plasm or cultivar releases in the near future with the current prevalence of RWA2, different sources of RWA1 resistance that are due to different genes may provide additional differentials for screening against new RWA biotypes that may develop.
In addition, screening current breeding lines for resistance to RWA2 also is underway, as space and
conditions allow. Several of our winter breeding lines containing Dn7 appear to be resistant to all of the RWA biotypes
against which they have been tested. A germ plasm release is planned for this autumn.