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.
W.L. Rohrer, C.A. Griffey, and D.E. Brann.
Growing conditions. The 2000-01 growing season was relatively dry with temperatures fluctuating but generally cooler, especially during December, as compared to the exceptionally warm winters of 1999 and 2000. Little precipitation fell during the winter months. A late cold spell in April resulted in significant freeze injury to wheat nurseries at Blacksburg. Subsequently, warm temperatures and dry conditions prevailed through most of the season. Both the Blacksburg and Warsaw areas remained very dry throughout most of the spring. Because of the relatively dry conditions, disease prevalence and severity, with the exception of powdery mildew, generally remained low in most areas. Crop lodging also was generally low due to lack of heavy precipitation late in the growing season.
Disease incidence and severity. Leaf rust and powdery mildew were the most prevalent diseases of wheat in Virginia in 2001. Powdery mildew was prevalent in most wheat-production areas of the state and was most severe in the coastal plain and eastern shore regions. Although leaf rust was observed in several regions of the state, it generally developed late in the season and disease severity was low. However, significant leaf rust infection of wheat was observed on the eastern shore of Virginia. The incidence of FHB generally was low or nil; although isolated foci were observed. Stripe rust was found in Virginia for the first time in 2000 near Blacksburg in the western part of the Commonwealth. In 2001, a stripe rust foci was found in the coastal plain region near Warsaw, Virginia.
Production. According to Virginia Agricultural Statistics Service 200,000 acres (81,000 ha) of winter wheat were planted in the Commonwealth in the autumn of 2000. This figure is down from 240,000 acres (97,200 ha) planted in the autumn of 1999 and 280,000 acres (113,400 ha) planted in the autumn of 1998. Of the 200,000 acres seeded in the autumn, Virginia producers harvested 175,000 acres (70,875 ha) of SRWW for grain in spring 2001. Grain yields across the state averaged 57.0 bu/acre (3,830 kg/ha). This figure is 10 bu/acre (672 kg/ha) lower than the state yield-record set in 1997 and is 6 bu/acre (403 kg/ha) lower than in 2000. Total grain production for the Commonwealth in 2001 was 10 million bushels (272,109 metric tons).
Virginia Wheat Yield Contests. Participation in the both the conventional-till and no-till wheat yield contests was down in 2001 though yields were characteristically high. Richard Sanford of Westmoreland County was the sole entrant in the 2001 Virginia Conventional-Till Wheat Yield Contest. Mr. Sanford entered two different cultivars and took first place with a yield of 100.7 bu/acre (6,766 kg/ha) over a minimum area of 3 acres (1.2 ha). Two producers representing two counties participated in the No-till Wheat Yield Contest. In first place was the team of Louis and Randolph Aigner of Henrico County with a yield of 108.5 bu/acre (7,290 kg/ha) over a minimum area of 3 acres (1.2 ha). Second place went to William C. Crossman of Westmoreland County with a yield of 79.1 bu/acre (5,315 kg/ha).
State cultivar tests. A total of 71 entries were evaluated
at seven locations across Virginia in 2001. Included in the tests
were 46 experimental lines (including two white-seeded lines and
four lines of triticale), 23 released cultivars, and one triticale
cultivar. Average grain yields ranged from 63-94 bu/acre (4,233-6,316
kg/ha) with an overall test average of 77 bu/acre (5,174 kg/ha).
Wheat genotypes with yields significantly above the test average
included Trical 498, three experimental triticale lines, Raxil-Thiram-treated
USG 3209 and Sisson, Baytan-treated Pioneer 26R24, Dividend-treated
Century II; untreated SS 550, SS 520, and an experimental Pioneer
line. In addition, 11 experimental Virginia lines (including one
white-seeded line) had yields significantly higher than the test
average. Yields among genotypes in this group ranged from 81-94
bu/acre (5,442-6,316 kg/ha). Tests conducted in the Coastal Plain
Region yielded an average of 76 bu/acre (5,106 kg/ha), whereas
tests conducted in the Piedmont and Blue Ridge Region yielded
an average of 79 bu/acre (5,308 kg/ha). Test weights for wheat
(excluding triticale) obtained across the seven test sites ranged
from 55.8 lbs/bu (718.1 kg/m3) to 60.3 lbs/bu (776.1 kg/m^3^)
with a test average of 57.3 lbs/bu (737.5 kg/m^3^). Of the 15
entries with test weights significantly higher than the test average,
11 were experimental lines (seven from Virginia) and four were
released cultivars. Six entries (a Pioneer experimental line and
five Virginia experimental lines) had both grain yields and test
weights that were significantly higher than the test average.
C.A. Griffey and W.L. Rohrer (Virginia Tech), and Lynda Whitcher (USDA-ARS, Raleigh, NC).
Virulence spectra of 38 isolates of Blumeria graminis f. sp. tritici was determined by Lynda Whitcher, USDA-ARS, Department of Plant Pathology, NCSU. Single-pustule isolates were derived from cleistothecia collected in Warsaw, VA, in 2001. The 38 powdery mildew isolates were screened for virulence/avirulence on 13 wheat differentials with known genes for mildew resistance and the susceptible cultivar Chancellor (Table 1). Among the 38 isolates, virulence was found for all resistant genes except for Pm1, Pm4b, and Pm17. The 38 isolates possessed virulence for 1 to 10 resistance genes; however, 27 isolates (71 %) possessed virulence for 7-10 genes. Among the 38 isolates, 24 had different virulence spectra. Among the 38 isolates, 26 to 37 had virulence for genes Pm3a, Pm3c, Pm5, Pm6, Pm7, Pm8, and Michigan Amber. Virulence for genes Pm2, Pm3b, and Pm4a was observed in 17, 9, and 20 isolates, respectively.
Among the 13 resistance genes, Pm1, Pm2, Pm3a, Pm3b, Pm4a, Pm4b, Pm5, Pm6, Pm8, and Pm17 have been commonly deployed in commercial SRWW cultivars, so it is not surprising that virulence for most of these genes was observed. Virulence for gene Pm17 was not found, which is not surprising since this gene has been deployed only recently and only a few commercial cultivars are known to possess this gene. Surprisingly, virulence for genes Pm1 and Pm4b was not identified in the mildew population. Upon evaluation of powdery mildew data from field tests conducted in Virginia from 1990 to 2001 (Table 2), it is apparent that virulence for gene Pm4a increased following release of the cultivar Roane in 1998, which possesses this gene. However, it is not clear why virulence for gene Pm4b, which the cultivar Pocahontas is proposed to possess, was not identified in the mildew population since susceptibility of Pocahontas to powdery mildew increased after its release in 1997. Verification of the presence of gene Pm4b in Pocahontas is needed in order to understand this phenomenon. On the contrary Wakefield, possessing gene Pm1, was susceptible to powdery mildew throughout most of Virginia at the time of its release in 1990, and was not widely grown commercially in Virginia. In 1991, Wakefield had a powdery mildew rating of 2.8. In subsequent years (1992-97), its mildew ratings declined dramatically to a low of 0.0 in 1995 and 1997, after which Wakefield was no longer tested in Virginia's official variety trials. Although virulence to gene Pm1 occurred at a high frequency when cultivars such as Wakefield and Coker 9733 were in commercial production, it was soon eliminated from the pathogen population once these cultivars became obsolete. Resistance conferred by gene Pm1 is easily overcome apparently, yet virulence to this gene must be disadvantageous to the pathogen population as it is quickly eliminated once it is no longer needed by the pathogen population. Therefore, we doubt that recycling of this gene alone would give durable resistance.
| Line | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 | 2001 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Wakefield | 2.8 | 2.5 | 2.0 | 2.0 | 0.0 | 1.0 | 0.0 | ||||
| Pocahontas | 0.0 | 0.0 | 0.5 | 0.0 | 0.0 | 2.7 | 3.3 | 8.3 | |||
| Roane | 0.3 | 0.0 | 1.5 | 0.3 | 1.8 | 0.0 | 3.0 | 6.3 |
J. Chen, C.A. Griffey, M.A. Saghai Maroof, W. Zhao, J. Wilson and D. Nabati.
The overall goal of the current research is to accelerate development of scab resistant wheat varieties and germ plasm using MAS. A population of 82 F2 individuals derived from the cross 'Pioneer 2684 (susceptible)/W14 (resistant)' was used as the initial mapping population. Percentages of infected spikelets (severity), scab-colonized seeds, and DON content (ppm) were characterized in greenhouse tests using floret inoculation method. SSR markers were used to identify QTLs associated with scab resistance. DNA polymorphism between parents was significant and was observed for 76 % of SSR primers (152 out of 200). Among 36 pairs of primers used, a total of 45 loci have been mapped to five chromosomal regions in this population. A major QTL, in addition to the 3BS QTL, has been identified on chromosome 2BS. Fifteen markers from these chromosome regions were significantly (p < 0.05) associated with scab resistance and explained 23 %, 28 %, 21 %, and 36 % of the total variation in percentage of scabby seeds, DON content, severity in 82 F2 individuals, and severity in 82 corresponding F2:3 families, respectively. Additional markers are being identified to saturate these chromosome regions in F2 and a DH populations of 'Pioneer2684/W14'. SSR markers Xgwm533/493 (on 3BS) and Xgwm410/BARC18 (on 2BS) are being used to tag resistance gene(s) in the development of near-isogenic backcross lines and in the evaluation of advanced breeding lines in our program.
Eight DNA markers from the five chromosome regions were used to genotype six putatively diverse resistance sources (Funo, Sumai 3, Shaan 85, W14, Ernie, and VR95B717). DNA polymorphism was found among these resistance sources for marker loci associated with postulated resistance genes. Differences observed among some of these sources for marker loci indicate that some lines may possess different resistance genes that could be useful in pyramiding resistance and, thereby, improve the level of scab resistance. W14 may possess a gene or allele different from that of Sumai 3 in the 2BS-QTL region, and Ernie may possess resistance genes different from other type-II resistance sources in both the 2BS and 3BS QTLs regions.
C.A. Griffey, J. Wilson, D. Nabati, J. Chen, T. Pridgen, W. Rohrer, and B. Robinson.
A major objective of our breeding program is to transfer type-II resistance from unadapted sources, primarily of spring habit, into SRWW backgrounds to develop scab-resistant germ plasm and varieties with high yield potential and resistance to other prevalent diseases including powdery mildew, leaf rust, and glume blotch. Strategies being used to accelerate development of scab-resistant wheat genotypes include 1) incorporating and pyramiding of type-II and other types of resistance into adapted SRWW backgrounds via selection of progeny from topcross, backcross, and DH populations; 2) screening and selecting for type-II and other types of resistance in inoculated mist-irrigated greenhouse and field tests and; 3) simultaneously evaluating progeny for resistance to other diseases and agronomic traits.
Thirty-six scab-resistant sources (21 Chinese, two French, one Japanese, two Canadian, and 10 SRWWs) have been used as parents in the breeding program, and over 500 populations have been developed. In 2001, 68 of 234 (29 %) populations were advanced on the basis of scab incidence and severity. In headrow tests, 2,960 F5 lines, derived from populations previously screened for scab resistance, were evaluated for agronomic traits and resistance to diseases other than FHB at Warsaw, VA. From these headrows, 47 topcross derived lines and three DH lines were selected for further testing in our scab nursery at Blacksburg, VA, and in Observation Yield Tests at two locations. Twenty-three advanced F6 lines and 13 DH lines were evaluated simultaneously for scab resistance in a mist-irrigated nursery at Blacksburg, VA, and for other agronomic traits in a noninoculated observation yield test at Warsaw, VA. Nine of the F6 lines and two of the DH lines were advanced for testing in Preliminary Wheat Trials. Three elite lines were evaluated in Preliminary Yield Trials; one of these lines was selected for further testing in our Advanced Yield Trial and another will be evaluated in Virginia's Official Variety Trial. Seven lines were tested in the Uniform Winter Wheat FHB Nurseries, and two adapted lines, VA98W-591 and VA98W-593, slated for release were shown to possess moderate resistance to FHB.
Progress in transferring type-II resistance into SRWW genotypes has been accelerated via use of the wheat by maize DH system. To date, 165 DH lines have been derived from three-way crosses, comprised of diverse scab-resistant parents, and will be evaluated for FHB resistance in an inoculated, mist-irrigated greenhouse test in spring 2002. Type-II resistance derived from six different sources has been backcrossed into seven SRWW backgrounds, of which two (Ernie and Roane) are adapted sources with other types of resistance. Ninety backcrosses between resistant progeny, derived from 5 BC4F1 and 83 BC3F1 populations, and their recurrent parents will be screened for FHB resistance and evaluated for similarity to the recurrent parent in a greenhouse test in spring 2002. Molecular markers (Xgwm533 and Xgwm493) have been implemented in selection of backcross progeny possessing the 3BS QTL. Of 12 BC3F1 lines evaluated thus far, one possessed both marker loci, and five possessed a single marker locus (Xgwm533 in all cases). The relatively low frequency of 3BS markers identified among the resistant progeny indicates putative presence of resistance genes derived from other chromosomal regions yet to be identified. Ultimately, adapted SRWW NILs with type-II resistance will be developed and will facilitate pyramiding of different types of resistance.