OKLAHOMA
OKLAHOMA STATE UNIVERSITY
Department of Plant and Soil Sciences, 368 Ag Hall, Stillwater, OK 74078-6028, USA.
The 2000-01 crop season
marked the first year in which the parent bulk populations of
all head rows (F4:5) were shuttled through a 3-yr selection system
that can best be pictured as a pinwheel (see Fig. 1 at the right).
At the center of the pinwheel is the process of plant selection
and seed production of breeding populations for 3 consecutive
years under a dual-purpose (DP) grazing system at Marshall, OK.
Simultaneously, these breeding populations are evaluated (and
eliminated, if inferior) under a grain-only (GO) system in north
central Oklahoma in the F2 generation, in southwest Oklahoma in
the F3, and in central Oklahoma in the F4. Each year, a new set
of about 30,000 breeder lines are extracted from 200-250 breeding
populations, after having cycled through this 'pinwheel' for 3
years. This selection and testing program leads to breeder lines
with improved adaptation to a dual-purpose production system,
but only from those populations with highest yield potential in
a grain-only production system. There is one caveat, however.
We learned for the first time in 2001 that selection strictly
for adaptation to grazing may lead to a plant type that, ironically,
is less conducive to high forage production. That may be the plant's
way of conserving its energy for reproductive development and
grain production. Consequently, selection in succeeding generations
is needed to restore forage growth patterns to which wheat producers
in the southern Great Plains are accustomed.
The Oklahoma Agricultural Experiment Station and USDAARS will jointly announce in May 2002 the release of Ok102 HRWW. Tested under the experimental name, OK97508, its pedigree is '2174/Cimarron'. Ok102 is widely adapted to Oklahoma and should mimic the adaptation range of one its parents, 2174. This cultivar should be most competitive in areas with i) a history of WSBMV, ii) the likelihood of leaf rust infection in adult-plant stages, or iii) moderate soil acidity and aluminum toxicity. Severe soil acidity (pH near 4.0) and/or soils with high aluminum saturation (near 30 %) will restrict its forage and grain performance. Ok102 also is adapted for the High Plains, with or without irrigation. Ok102 has no known defects in physical grain quality or in milling and baking quality, regardless of production site. Moreover, it has consistently demonstrated moderately high protein levels and good protein strength and, therefore, constitutes a desirable grain source for leavened bread products. The test weight of Ok102 is very good, with moderately high kernel size.
With regard to grain yield and quality, Ok102 may be used in dual-purpose and grain-only management systems, but its temperature-sensitive seed dormancy will cause it to be a 'slow starter' if planted extremely early under hot soil conditions. Thus, Ok102 is not recommended for a forage-only management system where planting date is earliest and emphasis on fall forage production is highest. An avoidance for premature plant dormancy release should allow extended grazing without sacrificing grain yield, provided grazing termination precedes first-hollow-stem stage. A more erect vegetative growth habit makes it potentially less likely to fully recover from intensive grazing than prostrate genotypes, though yield depression in a dual-purpose management system has not been extensively quantified.
Ok102 is highly resistant reaction to WSBMV, and it shows a susceptible seedling reaction (Lr3 and Lr24) but a resistant adult-plant reaction to leaf rust. The reaction to stripe rust is intermediate. An intermediate reaction to BYDV places Ok102 in a class unlike most HRWW varieties that tend to be more susceptible.
Identification of Ok102 as a candidate cultivar was accomplished
through OSUs Wheat Improvement Team, which includes Brett Carver
(lead scientist), Gene Krenzer, Art Klatt, Arron Guenzi, Guihua
Bai, and Bjorn Martin, Department of Plant and Soil Sciences;
Bob Hunger and Jeanmarie Verchot, Department of Entomology and
Plant Pathology; Patricia Rayas-Duarte, Department of Biochemistry
and Molecular Biology; and David Porter, USDAARS Plant Science
Research Laboratory, Stillwater.
G. Bai and B.F. Carver.
Leaf rust is an important disease in the southern Great Plains. Molecular markers linked to genes for rust resistance can facilitate pyramiding of those genes with resistance to different races of the pathogen. Two series of NILs contrasting in Lr41 and Lr42 from Ae. tauschii in a Century background were screened with AFLP markers. PstI and MseI enzymes and matching adapters and primers were used for DNA preparation and PCR amplifications. Bulked resistant and susceptible NILs and the three parents were screened with 400 sets of primers. Nine markers closely linked to the two genes were identified. Among them, five markers were linked to Lr42 and three to Lr41. Conversion of the AFLP markers into STS markers is underway.
Wheat scab is a destructive disease of wheat. Conversion of AFLP markers into STS markers can generate breeder-friendly markers for MAS and make full use of AFLP markers developed for the major scab-resistance QTL on 3BS. We used PstI-AFLP markers to further saturate the original AFLP map on the 3BS QTL region and identified five markers that were significantly associated with the QTL. One of the markers explained up to 50 % of the phenotypic variation for scab resistance. Successful conversion of the 222-bp fragment yielded a codominant STS marker that explained about 50 % of the phenotypic variation for scab resistance in an F7 recombinant population derived from 'Ning 7840/Clark'. The STS was validated in 14 other cultivars and the banding pattern perfectly matched their pedigrees. This is the first STS marker for a scab resistance QTL converted from an AFLP marker. Application of this marker in breeding programs may accelerate breeding procedures to enhance wheat scab resistance in wheat.
Genome-wide analysis of gene expression patterns in response to scab infection may lead to gene discovery and provide insight into further understanding genetic mechanisms of resistance. To enrich differentially ESTs for scab resistance, cDNA subtraction libraries were generated from F. graminearum-infected spikes of two bulked RILs differing in scab resistance using the suppression-subtractive hybridization (SSH) method. The bulked RILs were formed by pooling infected spikes from five F8:12 scab-resistant and five susceptible RILs based on their type-II resistance from four greenhouse tests. The RILs were derived from the cross between the resistant cultivar Ning 7840 and the susceptible cultivar Clark. The selected RILs were grown in the growth chamber and inoculated with a conidiospore suspension of F. graminearum by single-floret inoculation at the early flowering stage. The infected spikes were harvested for mRNA extraction at 6, 36, and 72 hours after inoculation. About 1,000 cDNA clones were isolated from the three libraries. Eighty-six clones were randomly selected from the libraries and sequenced; most of them (92 %) were singletons. Sequence homology search using the BLAST program from NCBI showed some of them were similar to those genes involved in stress or defense responses and signal regulation. The clones from the libraries will be used for temporal gene expression analysis with microarrays.
Aluminum toxicity is a major constraint for wheat production in the southern Great Plains. To enrich differentially ESTs for Al tolerance, cDNA subtraction libraries were generated from Al-stressed roots of two wheat NILs differing in an Al-tolerance gene from Atlas 66, using SSH. Expression patterns of the ESTs were investigated with macroarrays of 1,311 cDNA clones from the subtraction libraries. Gene-expression profiles exhibited about one-fourth of ESTs with significantly altered levels of expression in both tolerant and susceptible lines in response to different durations of Al stress. Furthermore, several ESTs showed consistently increased expression only in the tolerant NIL after Al treatment, indicating that those ESTs may play a significant role in enhancing wheat Al tolerance. Those highly expressed clones were sequenced, and some of them showed high similarity with genes involved in signal transduction, membrane transport, oxidative stress, and cell defense and rescue processes. Therefore, wheat response to Al stress may involve complicated defense-related signaling and metabolic pathways.
To identify molecular markers linked to aluminum-tolerance
genes, an F2 mapping population was derived from the cross 'Atlas
66/Century'. The F2 population was evaluated for Al tolerance
by hematoxylin staining and measuring lengths of roots after two
days Al treatment. This population will be further phenotyped
in F3 families and putative markers previously derived from NILs
will be further verified.
A.K. Klatt.
The variability enhancement/germ plasm development program at Oklahoma State University continued to give priority to transferring durable leaf rust resistance from CIMMYT spring wheats to winter wheats adapted to the southern and central Great Plains. An extensive crossing program with new synthetics and synthetic derivatives developed by CIMMYT is also in progress. These crosses have multiple objectives including new sources of leaf rust resistance, improved kernel size, enhanced stay green characteristics, and improved biomass and yield potential.
During the 2000-01 cycle, more than 1,800 additional winter and spring wheat materials were introduced (primarily from CIMMYT) and cleared through quarantine procedures. These materials are currently being evaluated for multiple disease resistance and agronomic performance. The best materials will be utilized as parents to introduce new genetic variability into the program. For information regarding this program, contact Art Klatt, Department of Plant & Soil Sciences, 274 Ag Hall, Stillwater, OK 74078.
Entomology & Plant Pathology Department, 127 Noble Research Center, Stillwater, OK 74078, USA.
Bob Hunger, Brian Olson, and Mark Payton.
Aphids, and subsequent BYDV infections were not a major disease in Oklahoma for the 2000-01 wheat crop. Although trials were conducted in several locations to evaluate the effectiveness of insecticide seed treatments to control aphids and subsequent BYDV, limited results were obtained because of the low incidence of aphids during the crop season. This low incidence most likely resulted from an extremely dry autumn, which resulted in later planting of wheat over much of the state. This was followed by a severe period of abnormally cold weather during late November through early January, which not only slowed wheat development, but also was unfavorable for insect and disease development.
In growth chamber studies, the effects of aviruliferous bird
cherry-oat (BCO) aphids (Rhopalosiphum padi) on HRWW seedlings
were investigated. Caged wheat seedlings were grown hydroponically
at 16.5 C with a 16:8 photoperiod. Ten-day-old seedlings were
infested with 0, 10, 20, or 30 aviruliferous BCO aphids for 2,
4, 6, 8, or 10 days. Nymphs were removed daily. At 20 days after
planting, length of roots and shoots was quantified using Rootedge
software. Seedlings were transplanted into clay pots, vernalized,
and grown to maturity in a greenhouse. Results indicated that
low population levels of aviruliferous BCO aphids adversely affected
root and shoot length of seedling wheat. Increasing aphid density
decreased number of heads, number of seeds, and grain weight.
Bob Hunger and Larry Singleton, Gene Krenzer and Ray Sidwell (Department of Plant & Soil Sciences), and Mark Payton.
Eyespot causes sporadic losses in Oklahoma, but was severe in many fields during the 1998-99 and 1999-2000 seasons. Severe lodging caused by eyespot was observed in a wheat field located at the North Central Experiment Station near Lahoma, OK, so a replicated trial was conducted in this field during the 1999-2000 season. This study examined the affect of planting date (early = 20 September, 2000; late = 22 November, 2000), tillage (disking or moldboard plowing after harvest), and burning or not burning the residue. Results indicated that only planting date affected the severity of eyespot, with early planted wheat showing significantly more severe eyespot and more severe lodging (Table 1). Later planted wheat was less severely affected by eyespot and showed no lodging. However, the reduced disease in the later planted wheat did not translate into increased yields because of the lateness of the late planting date (1-15 October is optimum) and because of the extremely cold weather that occurred after the late planting date that prevented normal development in these plots. Results do confirm conclusions from studies on this disease in the Pacific Northwest that indicate an effect of planting date, but not of burning or tillage, on the incidence and severity of eyespot.
| Agronomic practice | Eyespot severity (1-5) ** | Lodging (1-5) *** | Yield (Lb) |
|---|---|---|---|
| Early planted | 4.43* | 1.92* | 40.2* |
| Late planted | 2.55 | 1.00 | 29.3 |
| Disked | 3.53 | 1.63 | 35.2 |
| Moldboarded | 3.45 | 1.29 | 34.2 |
| Burned | 3.28 | 1.25 | 35.0 |
| Not burned | 3.70 | 1.67 | 34.4 |
| 1 Eyespot severity is the mean of the rating
given to 15 lowest internodes of 15 stems collected at random
from each plot. Internodes were rated on a scale of 15,
where 1 = 025 % discoloration; 2 > 2550 % discoloration;
3 > 5075 % discoloration; 4 > 75100 % discoloration;
and 5 = dead or eyespot lesions present. 2 Lodging was rated in each plot in the field on a scale of 15, where 1 = no lodging; 2 < 10 % of tillers in the plot were lodged; 3 = 1025 % of tillers in the plot were lodged. * Indicates significant difference between the pair of values at P = 0.05. |
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Bob Hunger and Jeanmarie Verchot.
Many regional nurseries, including the Southern Regional Performance Nursery, the Northern Regional Performance Nursery, and the Regional Germplasm Observation Nursery, were tested for reaction to WSBMV (field) and leaf rust (seedling and greenhouse). Results from these and other trials conducted on winter wheats are summarized at http://www.ianr.unl.edu/arslincoln/wheat/default.htm. For a description of releases from the wheat breeding program at Oklahoma State University, see the annual summary in this newsletter from the Plant & Soil Science Department at Oklahoma State University.
A new technique was developed that allows for uniform inoculation of wheat plants with WSBMV. In this technique, an artist's tool called a NIB is employed. Use of the NIB to inoculate WSBMV eliminates the wound-induced necrosis normally associated with rub inoculating virus to wheat leaves. This new inoculation technique was used along with inoculation by growing seedlings hydroponically and in Polymyxa graminis-infested soil to analyze the resistance of one WSBMV-susceptible and three WSBMV-resistant cultivars to WSBMV. Results indicate that resistance to WSBMV likely functions in the roots to block virus infection.
In other studies, experiments were conducted to determine the path for WSBMV transport from roots to leaves. Results of immunogold labeling suggest that WSBMV enters and moves long distances through the xylem. WSBMV may enter primary xylem elements before cell death occurs, and then move upward in the plant after the xylem has matured into hollow vessels. There is also evidence for lateral movement between adjacent xylem vessels.
As in 2000, wheat stripe rust was the most common foliar disease observed in Oklahoma in 2001. The areas most affected were southwestern Oklahoma northward to Kansas. Although stripe rust was severe in some fields and on certain varieties, yield reductions were not severely affected. As in 2000, this higher incidence of stripe rust was attributed to a mild and moist winter followed by a cool and moist spring, which provided conditions favorable for stripe rust from Texas to become established in Oklahoma. Losses due to stripe rust were significantly higher in Kansas, where the cool moist the cool moist conditions in the spring provided a longer optimum environment to facilitate the spread and development of stripe rust.
Other foliar diseases observed in Oklahoma included leaf and
glume blotch, tan spot, and powdery mildew. No significant losses
from these diseases were observed.
Bob Hunger and Larry Singleton.
Commercial wheat produced in Oklahoma in 2001 was examined for the presence of teliospores of T. indica. Testing was conducted using methods and following protocols approved by the Animal and Plant Health Inspection Service (APHIS). In 2001, 70 samples collected from elevators representing 39 counties were tested, which satisfied APHIS's National Karnal Bunt Testing Program. Testing has been conducted every year since 1996 in Oklahoma, with no positive samples being found.
Mr. Brian Olson completed a Master of Science degree in May, 2001, under the direction of Dr. Bob Hunger. The title of Brian's thesis was 'Effect of the bird cherry-oat aphid (Rhopalosiphum padi) on wheat and control of the aphid/barley yellow dwarf complex with Gaucho (Imidacloprid) insecticide.' Brian currently is working at Oklahoma State University as the Plant Disease Diagnostician in the Department of Entomology & Plant Pathology.