VIRGINIA
VIRGINIA POLYTECHNIC INSTITUTE AND STATE UNIVERSITY
Department of Crop and Soil Environmental Sciences 1 and Department of Plant Pathology, Physiology and Weed Science 2; Blacksburg, VA 240610404, USA.
Carl A. Griffey, Daniel E. Brann, Wendy L. Rohrer, Jianli Chen,
Matthew Chappell, Thomas H. Pridgen, and Jane Shaw.
W. L. Rohrer, C.A. Griffey, and D.E. Brann.
Growing conditions. The unusual weather patterns during the 1997-98 growing season continued into 1998-99. However, the most significant factor this year was lack of moisture, whereas moisture was excessive in the spring of 1998. Higher than normal temperatures and lack of snowfall made for another mild winter. The absence of any significant winter snow or spring rain resulted in relatively light disease pressure (particularly welcome considering last year's disease-ridden crop). Lodging was kept to a minimum by the absence of heavy rain and high winds near harvest (1.3 on a scale from 0.2-10, 10 being complete lodging). Such dry conditions also helped to keep test weights at or slightly below 60 lbs/bu (772.2 kg/m^3^) across the state. However, a 10-day period of heavy rainfall occurred immediately prior to harvest at two of the state's research stations, so test weights at those sites were noticeably lower. Unexpected sprouting, possibly caused by early breaking of dormancy, was observed at these sites and may have been a significant cause of the lower test weights.
Disease incidence and severity. As mentioned previously, the dry winter and spring of 1999 helped alleviate disease proliferation. Leaf rust, powdery mildew, Septoria, and BYDV were present but not significant across the state.
Production. According to the Virginia Agricultural Statistics Service, Virginia producers harvested 240,000 acres (97,200 ha) of SRWW for grain in 1999. Grain yields across the state averaged 58.0 bu/acre (3897.0 kg/ha). This figure is 9.0 bu/acre (604.7 kg/ha) lower than the state yield record set in 1997 but is 14.0 bu/acre (940.7 kg /ha) higher than yield in 1998. Total grain production for the Commonwealth in 1999 was 13.9 million bushels (378,296.0 metric tons).
Virginia wheat yield contests. Participation in the
1999 Wheat Yield Contest was excellent with 18 producers representing
11 Virginia counties. Actual yields ranged from 72.59 bu/acre
(4,877.3 kg/ha) to 117.74 bu/acre (7,911.0 kg/ha) over a minimum
area of 3 acres (1.2 ha). Participants' yields were evaluated
with consideration of their respective county's average yield.
Among participants, Jay Justice of Fluvanna County had the highest
yield score (9,127.2; actual yield of 115.9 bu/acre (7,787.3 kg/ha)
compared with a county average of 47.3 bu/acre (3,178.1 kg/ha)).
Ten producers representing eight counties participated in the
No-till Wheat Contest. Actual yields ranged from 64.52 bu/acre
(4,335.1 kg/ha) to 136.2 bu/acre (9,151.3 kg/ha) over a minimum
area of 3 acres (1.2 ha). Ted Haberland of Orange County had the
highest yield score (144.7; actual yield of 136.2 bu/acre (9,151.3
kg/ha) compared with a county average of 53.0 bu/acre (35,61.1
kg/ha). In 1999, a rookie category was added to the yield contest
to encourage entries from new participants. Charles D. Tankard
of Northampton County won the Rookie Wheat Contest with an actual
yield of 93.6 bu/acre (6,289.0 kg/ha), and John Petik of Prince
George County won the Rookie No-Till Wheat Contest with an actual
yield of 101.8 bu/acre (6,839.9 kg/ha).
State cultivar tests. A total of 74 entries was evaluated
at six locations across Virginia in 1999. Included in the tests
were 36 experimental lines (including one white-seeded line and
one hybrid line), 33 released cultivars, three released wheat
hybrids, and two triticale cultivars. Test averages for yield
ranged from 63.0 to 89.0 bu/acre (4,233.0-5,979.9 kg/ha) with
an overall test average of 75.0 bu/acre (,5039.3 kg/ha). Wheat
genotypes with yields significantly above the test average included
USG 3209, USG 3408, FFR518, Roberts, Century II, and Roane; 10
experimental lines; Baytan-treated Jackson and Pioneer 26R46;
one Baytan-treated experimental line; three wheat hybrids (Raxiltreated
Quantum 7123, 7203, and 706); and Trical 498. Yields among members
of this group ranged from 79.0 to 89.0 bu/acre (5,308.0-5,979.9
kg/ha). Tests conducted in the Coastal Plain Region yielded an
average of 76.0 bu/acre (5,106.4 kg/ha), whereas tests conducted
in the Piedmont and Blue Ridge Region yielded an average of 75.0
bu/acre (5,039.3 kg/ha). Test weights obtained across the seven
test sites reflect the dry growing conditions and low disease/pest
pressure present throughout the growing season. Averages ranged
from 54.2 lbs/bu (697.6 kg/m3) to 60.1 lb/bu (773.5 kg/m3), and
the test average was 58.1 lb/bu (747.7 kg/m3). Sprouting, particularly
at two of the six locations, did have an adverse effect on average
test weights. Of the 26 entries with test weights significantly
higher than the test average, seven were experimental lines, two
were wheat hybrids, and 17 were released cultivars. Virginia experimental
lines and released cultivars made up 23 % of this group. Entries
exhibiting significantly higher than average yield and test weight
included USG 3408, Century II, and Roane; three experimental lines;
Baytan-treated Jackson and Pioneer 26R46; one Baytan-treated experimental
line; and two wheat Hybrids (Raxiltreated Quantum 7123 and 7203).
C.A. Griffey, J. Chen, T. Pridgen, M. Chappell, J. Shaw, and
W. Xie*
* University of Minnesota, St. Paul, MN 55108, U.S.A.
Assessment and rational utilization of scab resistant sources. Optimal techniques of disease establishment and host resistance assessment have been established. We have identified and/or confirmed a high level of type II resistance in six wheat lines from China (Sumai3, Shaan85, W14, Fan 1, Wuhan 1, Futai 8944, and Futai 9002); three from Canada (H821, HC374, and H192); one from France (VR95B717); and two from Japan (Shinchunaga and Saikai 165). We also have identified or confirmed the presence of tolerance resistance to kernel infection, yield loss, and DON production in SRWW cultivars such as Roane (Virginia), Freedom (Ohio), and Ernie (Missouri). Through correlation analysis, scab severity (as a preharvest parameter) and percentage of scabby seeds as a (postharvest parameter) were found to be critical parameters for evaluation of scab resistance. Type II resistance can be assessed by severity, and type III (DON resistance), type IV (kernel resistance) and type V (yield loss) can be predicted and assessed by the percentage of scabby seeds and severity under both greenhouse and field tests. Highly resistant type II sources or individuals (1-4 infected spikelets) were found to also possess type III and type IV resistance, showing lower severity (< 20 %), lower scabby seeds (< 20 %), and lower than 10 PPM of DON accumulation, whereas highly susceptible sources or individuals were found to have variable or constantly high ratings. Therefore, resistant individuals should have no more than 20 % of disease severity and scabby seeds. Resistance from type II sources is being incorporated into SRWW via traditional breeding methods and also is being backcrossed into several diverse SRWW cultivars.
Inheritance of wheat scab resistance to disease spread, seed colonization, and DON accumulation in identified type II resistance sources W14 and Shaan85 and in the tolerant source Ernie. W14 was crossed with the susceptible SRWW cultivars Madison and Pioneer 2684, and Shaan 85 and Ernie were crossed with Pioneer 2684. Parents and F2 populations were assessed to discern the relationship among type II, type III, and type IV resistance using a floret inoculation method. Individual plants were evaluated for type II resistance based on the number of infected spikelets and severity at 21 days after inoculation. Type III deoxynivalenol levels were analyzed by a SIM Shimadzu QP5000 GC/MS system. Type IV, kernel resistance, was evaluated by determining the percentage of infected scabby seeds after hand threshing the inoculated spikes. Genetic analysis suggests that two major genes with complementary effects confer resistance in the sources W14 and Shaan 85. This result is based on similar segregation patterns of progeny characterized for infected spikelets, severity, and percentage of scabby seeds in the three F2 populations 'W14/Madison', 'W14/Pioneer2684', and 'Shaan 85/Pioneer 2684'. Two genes with additive effects conferred resistance in the cultivar Ernie. Improved levels of scab resistance could be achieved best by pyramiding genes conferring different types of resistance from diverse sources, such as Chinese type II sources and SRWW Ernie. Mapping and allelism studies of genes in W14, Shaan 85, and Ernie have been initiated.
Application of doubled haploid technique using wheat by maize hybridization. 'Wheat x maize' hybridization has proven to be efficient for haploid production in wheat. The F1 plants from 12 crosses between six scab-resistant sources and two susceptible SRWW cultivars were pollinated with pollen of maize F1 hybrid Seneca 60. Mean frequencies of fertilization, embryo formation, embryo germination, and haploid green plant regeneration were 83, 20, 45, and 8 %, respectively. Significant differences were found between two SRWW parents in F1 crosses for the efficiency of haploid production, based on the percentage of embryo germination and the percentage of haploid green plants regenerated. A total of 1,024 haploids was regenerated from 2,254 embryos derived from 13,527 florets pollinated.
Compared to anther culture and the H. bulbosum method, 'wheat x maize' hybridization has higher efficacy, less genotype-dependent response, less variation, and is less time consuming. The high efficiency of haploid production obtained by the 'wheat x maize' hybridization system likely will make it very useful for research on wheat scab resistance. Conventional methods of selection have given only incremental improvements to date. The reason for limited success may be due to the complex inheritance of resistance and to limited sources of unique resistance. Three people (2,400 hours) working over a 6-month period obtained the results and data presented. The doubled haploid plants produced in spring 1999 already have been planted in the 1999-2000 field trails at two locations to evaluate scab resistance and agronomic traits. Type II resistance will be evaluated in the winter of 2000 in greenhouse tests. This method theoretically will save about 3-5 years compared with the conventional breeding process. Pyramiding resistance genes by conventional selection likely would take a long time and have limited success and precision. Producing doubled haploid populations will shorten the time to cultivar release, improve efficacy and efficiency in screening for resistance, and greatly facilitate genetic and mapping studies.
In order to use the 'wheat x maize' system routinely in breeding programs, further enhancement of embryo formation, germination, and green-plant regeneration is needed. Some green plants will die during colchicine-induced chromosome doubling and during transfer. Therefore, the final population size may be too small to represent a sufficient number of possible genotypes to make selection effective. In the current study, an average of 20 % of the green plants died during chromosome doubling, and an additional 20 % of the surviving plants died during transfer stages. Approximately 80 % of the surviving green plants had normal seed set after the doubling and transferring stages.