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PRODUCTION PAPERS

Adaptation and Performance of Winter Durum Wheat in Virginia

^a Dep. of Crop and Soil Environ. Sci., Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061
^b Naval Surface Warfare Cent. Dahlgren Div., Dahlgren, VA 22448

^* Corresponding author (cotton{at}vt.edu)

Received for publication February 25, 2002.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Durum wheat (Triticum durum Desf.) produced in the northern Great Plains and the Pacific Southwest of the United States is primarily of spring growth habit. The objective of this research was to determine the feasibility of winter durum production in Virginia, typically a soft red winter wheat (T. aestivum L.) production area. Adaptation and yield potential of 19 winter durum lines were evaluated at locations in different regions of Virginia: the northern piedmont plateau (1995–1998), the northern ridge and valley (1995–1998), the southern ridge and valley (1995–1998), and the northern coastal plain (1996–1998). Durum lines were planted in replicated trials along with soft red winter wheat in late September to early October and harvested in late June to early July, depending on location. Durum yields were highest and the yield advantage of soft red winter wheat lowest in the 1996–1997 growing season, which was drier than the 1995–1996 and 1997–1998 growing seasons. The highest yields and test weights of durum wheat were obtained at the northern piedmont plateau location. Winter durum lines from the Ukraine were best adapted to the Virginia climate. Winter durum yields averaged 30 to 40% less than soft red winter wheat. Test weights of most durum lines met the required minimum for grade U.S. no. 2 or better only in 1997. The results demonstrate that durum production in Virginia is possible, but inconsistencies in yield and test weight indicate that durum may be a relatively high-risk alternative to soft red winter wheat production.

Abbreviations: CIMMYT, Center for Maize and Wheat Improvement

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
DURUM WHEAT in the United States is primarily grown in the northern Great Plains (Montana, North Dakota, and South Dakota) and in the Pacific Southwest (Arizona and California) (Wrigley, 1995). The northern Great Plains accounts for at least 75% of the durum production in the United States. Fall-planted spring durum genotypes may be more productive in winter wheat locations because of the available moisture and favorable temperatures during the spring (Entz and Fowler, 1991). Wheat planted in the spring will develop later and thus may encounter poorer environmental conditions than fall-planted wheat. Furthermore, higher grain yields, test weights, and kernel mass were associated with fall- and early spring–planted durum (Pearson, 1994). For these reasons, spring durums are planted in December or January in the Pacific Southwest. However, fall-planted spring types are usually not winter hardy enough to survive winters in the northern part of the country; hence, spring durum wheat is typically planted in April or May at those locations (Quick and Ball, 1981).

Durum wheat production is best in well-drained clay or clay loam soils that are at least 0.5 m deep and not compacted. Durum wheat is most successful in soils of pH 6 (in CaCl₂), but it may also grow well where the surface pH is 5 and the subsoil is pH 7 or greater (Impiglia and Anderson, 1998). In addition to soil type and pH, soil fertilization is an important consideration in durum production. Nitrogen is often necessary to raise both yields and quality.

A premium price is paid for durum wheat with high grain protein. Some cultivars inherently produce more grain protein; however, grain protein content is also influenced by environment. Additional N may help to increase the grain protein levels. Nitrogen applied up to and at the tillering stage increases yields while later N applications increase grain protein content. However, it is important to consider the environmental conditions before fertilizing as there may be little response under dry conditions or too much leaching under wet conditions. Protein synthesis requires twice as much energy as that required for starch synthesis (Làsztity, 1996); therefore, a negative correlation exists between grain yield and protein concentration.

Interest in producing durum wheat in Virginia, typically a soft red winter wheat area, began in 1993. A milling company in Winchester, VA, prompted extension agents in Shenandoah, Frederick, Clarke, and Page Counties to request an investigation into the possibility of growing durum wheat in Virginia. At the time, the milling company was importing approximately 27 000 to 28 000 Mg yr^-1 durum wheat by rail from North Dakota. Speculation has been that if durum wheat could be successfully produced in Virginia, the reduction in transportation costs and generally higher price for durum would translate into increased income for Virginia wheat producers. To be considered successful, the durum produced in Virginia must produce sufficient yields and be of adequate quality to be an economically feasible alternative to soft red winter wheat production. The objective of this research was to determine the feasibility of winter durum production in Virginia. This information is needed to estimate the profitability of durum production in comparison to soft red winter wheat production.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field studies were conducted from 1995 to 1998 at different locations in three regions of Virginia. In the 1995–1996, 1996–1997, and 1997–1998 growing seasons, one location in the northern piedmont plateau, one in the northern ridge and valley, and one in the southern ridge and valley were selected. An additional location in the northern coastal plain was added in the 1996–1997 and 1997–1998 growing seasons.

Soil at the northern piedmont plateau site was Starr–Dyke silty clay loam (fine-loamy, mixed thermic Fluvenitic Dystrochrepts) in the 1997–1998 growing season and Davidson–Rabun silty clay loam (fine, kaolinitic, thermic Rhodic Kandiudults) in the 1995–1996 and 1996–1997 growing seasons. In the northern ridge and valley, soil type for the 1995–1996 and 1997–1998 growing seasons was Frederick–Poplimento silt loam (fine, mixed, semiactive, mesic Typic Paleudults) while Nicholson–Duffield silt loam (fine-silty, mixed, active, mesic Oxyaquic Fragiudalfs) was the soil type for the 1996–1997 field trials. Plots in the southern ridge and valley were planted in Hayter fine loam (fine-loamy, mixed, mesic Ultic Hapludalfs). Soil in the northern coastal plain consisted of Kempsville sandy loam (fine-loamy, siliceous, thermic Typic, Hapludults) from 1996 to 1998.

Our initial field study initiated in 1993 included 55 durum wheat lines and five soft red winter wheat cultivars. The soft red winter cultivars were selected based on their yield potential, agronomic performance, and adaptation to Virginia. Based on observations during the 1993–1994 growing season, it was determined that several of the original 55 durum lines did not possess sufficient winter hardiness to be grown in Virginia (Abaye et al., 1997). These and other lines with poor yield performance were dropped from subsequent field trials.

Data presented in this paper cover the 1995–1996, 1996–1997, and 1997–1998 growing seasons, in which 19 winter durum wheat lines (Table 1) and one soft red winter wheat check cultivar (FFR 555W) were selected based on the results of earlier field trials (Abaye et al., 1997). The inherent cold hardiness and potentially greater grain yields made winter durum lines preferable to spring-type durums. The soft red winter cultivar was selected based on its yield potential, agronomic performance, and adaptation to Virginia. While other check cultivars were used in earlier tests (Bullard, 1999), FFR 555W was selected because it is a later-maturing cultivar that was closer in maturity range to the durum lines. With fungicide treatment, it is also representative of the high-yielding soft red winter wheat cultivars. Lines that matured much later than FFR 555W likely would not have been highly adapted to Virginia and would not fit well into the double-cropping system in the state. Durum wheat lines originated in Romania, Ukraine, France, Mexico at the International Center for Maize and Wheat Improvement (CIMMYT), and several states in the USA. The three Hungarian winter durum wheat cultivars—Basa, Minaret, and Pannondur—were obtained from Ohio where similar field trials were performed (Berzonsky and Lafever, 1993). Additionally, Western Plant Breeders of Phoenix, AZ, contributed five experimental winter durum wheat lines, identified in the Virginia field trials by the prefix BZ. The breeding program at Oregon State University also supplied several durum lines. The CIMMYT lines were previously tested in Oregon and are referred to here under an experimental number with the prefix OR. Four lines from the Ukraine (obtained from the International Winter Wheat Performance Nursery) were referred to as the Odessa lines in the Virginia field trials; however, the actual line designation for these lines is given in Table 1.

Plots at each location were fertilized according to soil test recommendations. Typically, about 672 kg ha^-1 10–10–10 (N–P–K) fertilizer was applied in the fall before planting. In addition to the fall fertilization, approximately 44.8 kg ha^-1 25–0–0–3 (N–P–K–S), depending on location, was applied just after green up, at Zadoks growth stage 25 (Zadoks, 1974). During the 1995–1996 growing season, a second N application of approximately 56 kg ha^-1 25–0–0–3 (N–P–K–S) was applied at Zadoks growth stage 30.

Seeds were treated with triadimenol [ß-(4-chlorophenoxy)--(1,1-dimethylethyl)-lH-1,2,4-triazole-1-ethanol] (30 g a.i. per 100 kg seed) and captan (n-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) (78 g a.i. per 100 kg seed) to control powdery mildew [caused by Erysiphe graminis DC. f. sp. tritici Em. Marchal; synonym: Blumeria graminis (DC) E.O. Speer] and other seedling and foliar diseases. Seeds were also treated with imidacloprid {[1-(6-chloro-3-pyridinyl)methyl]-n-nitro-2-imidazolidinimine} (32 g a.i. per 100 kg seed) to control insects, especially aphids, which vector Barley Yellow Dwarf Virus. Beginning at Zadoks growth stage 25, in early spring, plots were scouted for diseases, especially powdery mildew. Usually an application of a fungicide, such as propiconazole {1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole}, was needed to control powdery mildew (5% upper leaf area infected), leaf rust (caused by Puccinia triticina Eriks.) (three to nine pustules visible on upper leaves), and glume blotch [caused by Stagonospora nodorum (Berk.) Castellani & E. G. Germano] (one out of four leaves has one lesion) before Zadoks growth stage 37. Another fungicide, such as triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H- 1,2,4-trizol-1-yl)-2-butanone], was applied if needed, either before or after the application of propiconazole, depending on location and disease pressure.

Plots were visually assessed for powdery mildew severity, heading date, plant height, lodging, and winter survival. The crop was permitted to completely dry down, according to the latest-maturing durum line in the study, before harvest. Depending on location, crop maturity, and weather conditions, plots were harvested using a small-plot combine in late June to early July. Yield, grain moisture, and test weight for each plot were measured after harvest.

Data Analysis
Data from all locations and years were analyzed by analysis of variance using SAS software (SAS Inst., 1991). Effect of replication, location, line, and all interactions were tested. Because the data were not homogenous, we analyzed each location and year separately. Mean separations were performed by Fisher's LSD if the ANOVA F statistic indicated significant effect at the 0.05 level (SAS Inst., 1991). Correlation analysis between test weight and yield was performed using SAS software package (SAS Inst., 1991) to determine the relationship between yield and test weight.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Location, line, and the interaction between location and line in all years had a significant effect (P < 0.05) on yield each year. With one exception (in 1996–1997), test weights of the durum lines were also affected (P < 0.05) by location, line, and the interaction between location and line during all years. In the 1996–1997 growing season, line did not have a significant effect (P > 0.05) on the test weights at the northern ridge and valley location. It is not surprising that the geographic location of the field trials was an important factor in determining the amount of grain each line produced, considering differences in soil type, environment, precipitation, and disease pressure. Because the durum lines originated in and thus were adapted to several different locations around the world, the adaptation of each line to different locations within Virginia was expected to vary.

Cold, wet weather marked the 1995–1996 growing season (Fig. 1) . Combined with some fusarium head blight (Fusarium graminearum Schwabe), these conditions were probably partly responsible for the reduced yields and low test weights observed in the 1995–1996 growing season. Durum wheat is well adapted to locations with hot, dry days and cool nights with winter rains and dry summers (Bozzini, 1988). At all locations, durum yields were less (P < 0.05) than those of the soft red winter wheat cultivar FFR 555W (Table 2). Mean durum yields for the locations in the northern piedmont plateau, northern ridge and valley, and southern ridge and valley were 40, 39, and 42% less than the soft red winter wheat check. N1013/84 was the highest-yielding durum line at both the northern piedmont plateau and the southern ridge and valley locations, producing 24 and 26% less grain yield than FFR 555W, respectively. DF 222-95 was the top-producing durum line at the northern ridge and valley location, producing 20% less grain yield than FFR 555W.

View larger version (35K): [in this window] [in a new window]   Fig. 1. Precipitation and temperature in the regional areas of the locations of the winter durum wheat field trials (1995–1998) (U.S. Dep. of Commerce Weather Bureau, 1993–1998).

The 1996–1997 growing season conditions were excellent for both soft red winter and durum wheat production (Fig. 1). Averaged across locations each year, durum yields were highest and the yield advantage of soft red winter wheat lowest in the 1996–1997 growing season. Heading date and height of the durum lines were determined at both the northern piedmont plateau and southern ridge and valley locations. Both heading date and height of the genotypes varied slightly by location, with lines tending to head later in the wet, cool spring of the southern ridge and valley. Most of the durum lines headed later, 3 to 9 d, and were shorter than the late-heading FFR 555W. Plant height of all of the durum lines was under 108 cm, with the exception of the Colorado cultivar Korall.

The more favorable, drier conditions in 1996 to 1997 compared with 1995 to 1996 were reflected in the higher yields and test weights of the durum lines (Tables 2 and 3). Mean durum yields in the northern piedmont plateau, southern ridge and valley, northern ridge and valley, and the northern coastal plain locations were 14, 25, 43, and 11% less than FFR 555W, respectively (Table 3). As in 1995 to 1996, durum wheat yields were the highest at the northern piedmont plateau location for the 1996–1997 growing season. Yields of 10 durum lines at the northern piedmont plateau location were not significantly different (P > 0.05) from FFR 555W (Table 3). The yield of FFR 555W was greater than all of the durum lines (P < 0.05) at the northern ridge and valley location. The mean durum yield was low at the northern ridge and valley location where the highest-yielding line, N1013/84, produced 26% less than FFR 555W. At the southern ridge and valley location, two durum lines, N1291/86 and N736/89, produced yields that were not different (P > 0.05) from FFR 555W. While the mean durum yield at the northern coastal plain location was not as high as at the northern piedmont plateau location, several durum lines at the northern coastal plain location produced grain yields comparable (P > 0.05) to the soft red winter wheat line, FFR 555W. Overall, only 6 of the 19 durum lines yielded significantly less (P < 0.05) than FFR 555W at this location.

In contrast to the favorable conditions of 1996 to 1997, the 1997–1998 growing season had excessive rainfall from planting until almost June (Fig. 1). For all locations, the yield of FFR 555W was consistently higher (P < 0.05) than the mean durum yields. Heading date and height data were collected from the southern ridge and valley and the northern coastal plain locations. As in 1996 to 1997, both heading date and height of the genotypes varied slightly by location, with lines tending to head later in the typically wet, cool spring of the southern ridge and valley. Most of the durum lines headed 3 to 9 d later and were shorter than FFR 555W.

In 1997 to 1998, the severity of powdery mildew was scored at the northern coastal plain location, 20 d after the first fungicide application. Despite the wet growing conditions, little powdery mildew was evident in the 19 durum lines, and all had a lower (P < 0.05) severity of powdery mildew than FFR 555W, which is susceptible to powdery mildew (data not shown). The excessive rain during this growing season, combined with elevated temperatures, created a humid environment, which was ideal for the development of several fungal head diseases that were observed (but not rated) on the durum crop, such as fusarium head blight and glume blotch and leaf diseases, such as leaf rust. The widespread incidence of such diseases, especially fusarium head blight, were a probable factor in the reduced grain yields and test weights in the 1997–1998 study, but the absence of disease data prevents establishment of a more definitive relationship.

For all locations, the yield of the soft red winter wheat cultivar FFR 555W was consistently higher (P < 0.05) than the mean durum yields (Table 4). The highest mean durum wheat yields were observed at the northern piedmont plateau and the northern ridge and valley locations. N1439/83 produced the highest durum yields at all locations, except for the northern ridge and valley location, yielding 27 to 39% less grain than FFR 555W. At the northern ridge and valley location, Korall was the highest-yielding durum line, producing 32% less yield than FFR 555W. For the 1997–1998 growing season, the correlation coefficients (r) between yield and test weight were significant, and the values were 0.68, 0.84, 0.69, and 0.76 for the northern piedmont plateau, northern ridge and valley, southern ridge and valley, and northern coastal plain locations, respectively (Table 4).

Suitability to Virginia
To be an acceptable alternative to soft red winter wheat, both the yield and test weight of durum must be considered. Durum yields must be high enough that the price premium paid for durum would compensate for any difference in yield from that of soft red winter wheat. Unlike soft red winter wheat, a premium is paid for durum with an acceptable test weight, making a durum test weight that is at least 77.2 kg hL^-1, the minimum test weight for grade U.S. no. 1, very desirable. The lower the durum test weight, the more important it is that the durum yields are high compared with soft red winter wheat.

Results of our field study indicate that the most successful Virginia durum crop, in terms of both yield and test weight, was grown at the northern piedmont plateau location (Tables 2– 4). The climate may have contributed in part to the performance of the durum at the northern piedmont plateau. Like the northern coastal plain, temperatures at this location tended to be warmer each month compared with temperatures at the northern ridge and valley and southern ridge and valley locations (Fig. 1). With the exception of the 1995–1996 growing season, the precipitation at the northern piedmont plateau location was generally lower than that at the other locations during grain maturation (Fig. 1). The overall better performance of durum at the northern piedmont plateau location compared with the other test locations was also probably partly influenced by the favorable soil type in this location. The soil at the northern piedmont plateau location was silty clay loam, whereas soil types at the other locations were either silt loam, fine loam, or sandy loam. The yield data further indicate that most of the high-yielding durum lines in the Virginia field trials originated from the Ukraine. The Ukrainian line, N1013/84, consistently produced relatively high durum yields across Virginia. Other Ukrainian lines, such as N736/89 and N1439/89, were also among the top-yielding lines at each location.

Considering test weight results, it appears that some winter durum wheat lines, grown at specific locations within the northern coastal plain and northern piedmont plateau of Virginia, have the potential to meet the minimum test weight requirements for grade U.S. no.2 in most years and U.S. no. 1 in a few years. Pannondur (Hungary), N1439/83 (Ukraine), and Korall (Colorado) generally produced higher test weights than the other durums, and often there was no difference (P > 0.05), within years and location, between the test weights of these three lines. Pannondur was among the top-performing winter durum wheat lines in a similar study in Ohio, also in the soft red winter wheat region (Berzonsky and Lafever, 1993). Pannondur, however, tended to produce yields below the mean durum yield at each location, suggesting that a price premium is not likely to compensate for its lower yields compared with soft red winter wheat. N1439/83 produced yields greater than the mean durum yield in the southern ridge and valley (1995–1996) and in the northern piedmont plateau (1996–1997). Additionally, N1439/83 was the top-yielding durum line at all locations in the 1997–1998 growing season, with the exception of the northern ridge and valley location where it was among the top-yielding durum lines. Korall tended to be a top-yielding durum line in the northern ridge and valley location although it did not yield consistently well at other locations. In 1995 to 1996, several durum lines produced test weights comparable (P > 0.05) to Pannondur at the northern piedmont plateau location. N1291/86, N1013/84, N736/89, and DF 222-95 were among the durum lines that produced yields in the upper half of the field trials, at all locations.

The greatest hindrance to durum yield and test weight in Virginia is probably the wet, humid climate. Years such as 1996 to 1997 proved that it is possible for durum yields to be competitive with soft red winter wheat, but such favorable, relatively dry, growing conditions are the exception rather than the rule in Virginia. Over all years of the field trials, temperatures in each location tended to be milder than the average minimum and maximum temperatures for each location (U.S. Dep. of Commerce Weather Bureau, 1993–1998). The best durum production occurs under an annual rainfall of 50 to 70 cm (500–700 mm) (Bozzini, 1988). Virginia receives an annual average precipitation of 109 cm (U.S. Dep. of Commerce Weather Bureau, 1993–1998). Average rainfall at each location during the durum growing season was >70 cm (October to July) (Fig. 1). These wet climatic conditions may adversely affect durum yield and test weight potential by reducing photosynthesis and N availability and increasing diseases.

The high amount of precipitation in Virginia and warm temperatures create a humid climate during grain ripening, which likely had a strong influence on the yields and test weights of durum lines grown in the Virginia field trials (Fig. 1). Previous field trials of durum lines in another area of the soft red winter wheat region, Ohio, suggested that successful winter durum wheat production depended on overcoming such problems as winterkill, preharvest sprouting, lodging, and susceptibility to disease (Berzonsky and Lafever, 1993). Although the high amount of rainfall in Virginia may create a situation favorable for preharvest sprouting, this was not a problem in the 1995–1998 field trials, as indicated by acceptable falling number data ranging from 374 to 501 (Bullard, 1999). Winter durum lines grown in this study had already been screened for winter survivability in previous field trials (Bullard, 1999); thus, minimal to no winterkill was present in the plots across Virginia (data not shown). Therefore, winterkill likely did not affect the yield or test weight of the durum lines in this study. Observed amount of lodging varied by location, weather, and extent of disease damage (Bullard, 1999). Generally, lodging was minimal in the winter durum wheat plots although some lodging was observed in the 1997–1998 growing season. As in Ohio (Berzonsky and Lafever, 1993), it is apparent that not only good cultivars and management practices, but also drier weather, especially during grain maturation, are keys to a successful durum crop. Producing stable, high durum yields in Virginia will probably require durum lines with a higher tolerance to wet conditions and increased levels of disease resistance.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The lack of consistently acceptable durum production over the years makes durum a somewhat high-risk alternative to soft red winter wheat. Lines such as N1439/83, which tended to produce above the mean durum yields and higher test weights, may help to mitigate this risk until durum lines are developed with greater tolerance for wet, humid conditions and resistance to fusarium head blight. Korall would be the best selection currently available in the northern ridge and valley location as this line not only tended to produce higher test weights, but was also a top-yielding durum line at this location. N1291/86, N1013/84, N736/89, and DF 222-95 tended to be among the top-yielding durum lines at all locations. While the test weights of such lines often did not meet test weight requirements numerically, the test weights of these lines often were not significantly different from the highest durum test weight at each location. The test weights of these lines may be improved through crossing with lines such as N1439/83. Test weights were generally positively correlated with yields. Furthermore, the performance of N1439/83 during the wet 1997–1998 growing season suggests that this line may also offer some greater level of tolerance to disease compared with many of the other durum lines. However, further disease data will have to be taken to provide more definitive evidence of the disease tolerance of each durum line. By improving test weight of higher-yielding durum lines, it is possible that durum would be a more competitive alternate to soft red winter wheat. However, before durum can be considered a consistently low-risk alternative to soft red winter wheat in Virginia, new durum lines will have to be developed with resistance to fusarium head blight and tolerance for wet conditions.

	ACKNOWLEDGMENTS

 
The durum field trials would not have been possible without the care and management of the farm staff at each location. Special thanks to Mr. David Starner and Mr. Denton Dixon (Orange, VA) who cared for the durum plots from planting to harvest. Thanks are also extended to Mr. Bobby Ashburn (Suffolk, VA), Mr. Mark Vaughn, Mr. Bill Sisson, and Mr. Lin Barrack (Warsaw, VA); Mr. Bill Wilkinson III and Mr. Bud Wilmouth (Blackstone, VA); and Mr. Bobby Clark, Mr. Tom Stanley, and the Mathias Brothers (Shenandoah County, Virginia).

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Abaye, A.O., D.E. Brann, M.M. Alley, and C.A. Griffey. 1997. Durum wheat: Do we have all the answers? Ext. Publ. 424-802. Virginia Coop. Ext., Blacksburg.
• Berzonsky, W.A., and H.N. Lafever. 1993. Comparison of Hungarian winter durum wheat to Ohio soft red winter wheat. J. Prod. Agric. 6:276–279.
• Bozzini, A. 1988. Origin, distribution and production of durum wheat in the world. p. 1–6. In G. Fabriani and C. Lintas (ed.) Durum chemistry and technology. AACC, St. Paul, MN.
• Bullard, A. 1999. Protein indicators, quality and yield of winter durum wheat gown in Virginia. M.S. thesis. Virginia Polytechnic Inst. and State Univ., Blacksburg.
• Entz, M.H., and D.B. Fowler. 1991. Agronomic performance of winter versus spring wheat. Agron. J. 83:527–532.[Abstract/Free Full Text]
• Impiglia, A., and G. Adam. 1998. Durum variety wheats in farmer's fields [Online]. 1998 Crop Updates. Available at http://www.agric.wa.gov.au/cropupdates/crop_varietytest/demodurm.htm (verified 9 Jan. 2003). Dep. of Agric.–Western Australia.
• Làsztity, R. 1996. The chemistry of cereal proteins. 2nd ed. CRC Press, Boca Raton, FL.
• Pearson, C.H. 1994. Performance of fall- and spring-planted durum wheat in western Colorado. Agron. J. 86:1054–1059.[Abstract/Free Full Text]
• Quick, J.S., and W.S. Ball. 1981. Durum: A North Dakota specialty. Revised ed. Circ. A-381. North Dakota State Univ. Coop. Ext. Serv., Fargo.
• SAS Institute. 1991. SAS/STAT user's guide: Version 6. 4th ed. Vol. 1 and 2. SAS Inst., Cary, NC.
• U.S. Department of Commerce Weather Bureau. 1993–1998. Climatological data. Virginia. Vol. 103–108, no. 1–7, 10–12. Washington, DC.
• Wrigley, C.W. 1995. Identification of food-grain varieties. AACC, St. Paul, MN.
• Zadoks, J.C. 1974. A decimal code for the growth stages of cereals. Weed Res. 14:415–421.

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