Winter Durum Wheat Yield Evaluations at Various Virginia Physiographic Locations 

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Chapter II Literature Review

Origin of Durum Wheat

The development of agriculture and civilization has been closely linked with the production and utilization of wheat as early as 16 300 -15 000 BC (Harlan, 1981). Wheat cultivation is thought to have originated in the Fertile Crescent of the Middle East (Inglett, 1974). Durum wheat (Triticum durum Desf.) is derived from a tetraploid hybrid of the diploid T. monococcum (einkorn) and a diploid wild grass of unknown origin (Schmidt, 1974). During the Roman empire, wheat was primarily of the Triticum durum-turgidum-dicoccum group. Both T. durum and T. turgidum were once utilized for several foods, including breads, couscous, bulger, chapatis, etc. (Bozzini, 1988). After thousands of years of natural and human selection, T. durum is now primarily used for high quality pasta products, couscous and some flat breads.

Geographical Distribution of Durum Wheat

According to 1991/1992 USDA official statistics, 33.5 million metric tons of durum wheat were produced worldwide, making up six percent of the total world wheat production (NDSU, 1992). Durum wheat production covers approximately eight percent of the world’s total wheat cultivated land area (Porceddu and Srivastava, 1990). It is grown in the Mediterranean countries, Eastern Europe, North Africa, West Asia, North Central and Southwestern United States, Mexico, and Canada (Gooding and Davies, 1997), with Canada being the world’s largest producer of durum wheat (Wheat Yearbook, 1998). The United States, Canada and the European Countries (mainly France) account for 95% of all durum wheat exports, and Algeria is the primary world durum wheat importer (NDSU, 1992).
Durum wheat was first introduced to the United States in the 1850’s (Joppa and Williams, 1988). Durum wheat in the United States is primarily grown in the Northern Great Plains (Montana, North Dakota, 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 (U.S. Wheat Associates, 1997). Although the U.S. is one of the primary centers of durum production, the history of higher prices of U.S. durum has prompted many U.S. millers to buy Canadian durum. Additionally, the increased incidence of scab (Fusarium graminearum) has caused U.S. millers to turn to Canadian durum. Even still, in 1998, the U.S. remained a net exporter of durum grain and products mainly to the European Union, Morocco and Tunisia (Wheat Yearbook, 1998).

Introduction of Durum to the United States

The first durum wheat cultivars introduced to the United States originated from Algeria, Turkey and Palestine. The hard kernels were difficult for flour millers to mill, so at first, most of the durum produced was used for livestock feed. More adapted durum wheat cultivars were collected in the 1890’s and tested at agricultural experiment stations across the United States (Joppa and Williams, 1988). Studies in the early 1900’s clearly indicated that durum wheat grown in North Dakota, South Dakota and Central Nebraska produced higher yields and was more resistant to leaf rust than hexaploid spring wheat (Salmon and Clark, 1913, as cited in Joppa and Williams, 1988). Cultivars introduced from other countries, especially the Russian cultivar Kubanka, were grown from 1850-1920. In 1929, the first durum breeding program was started in Langdon, ND. The focus of durum breeding in the United States was necessarily on stem rust resistance until the release of the cultivars Wells and Lakota in 1960 (Joppa and Williams, 1988). Since both cultivars possessed stem rust resistance, the focus of breeding was able to shift to yield and quality improvement.

Climatic Adaptation

Durum wheat is adapted to many of the same areas as common bread wheat, but it is not as inherently tolerant to long, cold winters. However, durum wheat is often more productive in marginal areas and soils than common bread wheat. Durum wheat is well adapted to the steppes or semi-arid regions, which typically have hot, dry days and cool nights with winter rains and dry summers (Bozzini, 1988). The highest durum wheat yields are associated with a long, moist and cool grain-fill period (Gebeyehou et al., 1982). Most of the world durum wheat production is under rainfed conditions, with a significant portion being produced in areas with less than 350 rainfall annually (Bozzini, 1988). It is especially well adapted to droughty areas such as the Mediterranean region of the Syrian wheat belt, which receives only about 300-400 mm of rainfall annually (Pecetti and Annicchiarico, 1993). Forty-five percent of the world durum wheat is grown in North Africa and West Asia due to the tolerance of durum wheat to hot and dry conditions (Porceddu and Srivastava, 1990). Durum wheat landraces, rather than cultivated pure lines, are still grown in these marginal regions because of their innate adaptation to drought, minimum fertilizer inputs, and area specific stresses. In addition, the landraces produce high grain yields with good quality (Srivastava and Damania, 1989).
Although irrigation may improve durum yields, there is a potential of reducing protein content with the use of too much water. Unfortunately, moisture related problems may also arise in rainfed regions. Humid weather or weather that is excessively wet before harvest can greatly reduce the quality of durum wheat. Too much moisture may result in preharvest sprouting, leading to reduced kernel vitreousness, reduced market quality and increased cooking loss (Clarke et al., 1994). The best quality durum wheat is produced in regions with rainfall during the vegetative growth stage and dry periods during later grain maturation (Berzonsky and Lafever, 1993).

Management and Environmental Factors Affecting Durum Yield and Yield Components

Cultural Practices

Currently, the United States primarily grows spring type durum, but some spring durum is fall sown in the Pacific Southwest (Ottman et al., 1990). Entz and Fowler (1991) suggested the fall planted spring type durums were more productive in winter wheat regions because of the available moisture and favorable temperatures during the spring. Wheat planted in the spring will develop later, and thus may encounter poorer environmental conditions. Additionally, a study performed at the Colorado State University Fruita Research Center near Grand Junction, Colorado, found that 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 cold hardy enough to survive winters in the northern part of the country. So, spring durum wheat is typically planted in April or May in those regions (Quick and Ball, 1981).
High durum wheat yields result from the combination of high yielding cultivars, good management practices, and sufficient rainfall (500-700 mm) (Bozzini, 1988). Yields may simply be improved by using certified seed due to the high level of germination and purity. In fact, a North Dakota study estimates that by using certified seed as opposed to bin-run seed, the 1988 durum wheat production could have been increased by $6.0 million (Spilde and Hafdahl, 1994). Spilde and Hafdahl (1994) also found that large durum seeds tended to have better viability and performance.
Yield increases have been indirectly achieved by breeding for certain traits, such as drought resistance. Yield increases have been successfully achieved by selecting for drought tolerance particularly during the grain filling stage (McCaig and Clarke, 1994). The lower the rate of water loss from the plant, the higher the yield. Low rate of water loss is associated with tall plants that are able to withstand environments of low moisture and low input. An experiment conducted to investigate drought responsive characteristics in Syria found most plants with low rates of water loss to also be late flowering, late maturing and tall, with glaucous and nonchlorotic leaves (Yang et al., 1991). In India, plant height, grains per spike, spikelets per spike and grain weight were all positively correlated with durum grain yields (Hanson et al., 1982). A study in Canada, spanning a test period from 1964 to 1992, determined that most yield increases in the durum cultivars have been due to increases in the number of kernels produced (McCaig and Clarke, 1994). Similarly, Gebeyehou et al. (1982) reported that grain yield is positively correlated with the number of kernels per spike and kernel mass. Furthermore, these traits are affected by the length of developmental periods. Kernel weight and kernels per spike are both positively affected by longer vegetative periods, and higher yields are associated with longer grain fill periods. Environmental effects must be taken into consideration when indirectly breeding for improved yields by altering traits associated with a particular growth stage. For example, lengthening the grain filling period to increase yields is not reasonable in areas where frost or summer rains, and thus, preharvest sprouting, are a danger.

Soil Characteristics and Fertilization

Soil type is an important consideration in the production of durum wheat. Well-drained clay or clay loam soils, at least 0.5 m deep, that are not too compacted are ideal for durum wheat. Soil pH is also an important consideration. Durum wheat is most successful in soils of pH 6 (in CaCl₂), but it may also grow 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, in particular, is often necessary to raise both yields and quality. Crop rotations with legumes may be used to build up the soil nitrogen, to provide a disease break and to control weeds (Gooding and Davies, 1997). Nitrogen deficiency is a common problem in cool, wet areas, or places where the soil is waterlogged, such as in highland Vertisols (Geleto et al., 1996). Split nitrogen applications are often employed to reduce nitrogen losses due to leaching, denitrification, volatilization, and erosion run-off. Specific fertilization requirements will vary by location, so durum wheat fertilization should be based on soil test recommendations.
A premium price is paid for durum wheat containing a high amount of protein. The demand for high protein durum wheat (in excess of 13%) stems primarily from pasta manufacturers in Europe, Japan and North America (ESSO Farm-Tek, 1997). Some cultivars inherently produce more protein; however, protein content is actually influenced more by environment than genotype. Proper fertilization may help to increase the protein levels. For example, both grain and total nitrogen uptake increased with split nitrogen applications in Ethiopia, where continuous cropping has depleted the soil (Geleto et al., 1996). Nitrogen applied up to and at the tillering stage increases yields, while later nitrogen 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. One way to determine the need for extra nitrogen to increase grain protein is to test the flag leaf. If the nitrogen content is less than 4%, the crop may need more nitrogen to increase the protein content. A foliar application of nitrogen between heading and flowering stages may increase protein by 0.5%. The additional nitrogen should not be applied when the plant is under stress, between 11 am and the evening, or before a rainfall (ESSO Farm-Tek, 1997). Protein synthesis requires two times the energy required for starch synthesis (Lásztity, 1996), and, therefore, a negative correlation exists between grain yield and protein concentration.

Diseases of Durum Wheat

Durum wheat is susceptible to numerous diseases at all stages of development. Leaf spots, rusts, scab (Fusarium head blight), black point, root and crown rots, powdery mildew and smuts are all diseases of economic importance in durum wheat (Miller et al., 1988). Every year, about 20% of the wheat crop is lost due to disease either in the field or storage (Wiese, 1987). Disease control in durum wheat generally includes the use of resistant cultivars, if available, seed and foliar fungicides, foliar sprays and crop rotations. Specific control measures depend upon the pathogen and the expense to the producer. The use of foliar sprays, resistant or tolerant cultivars, disease free seed, wheat stubble removal, and crop rotations all aid in the control of leaf spots (Miller et al., 1988). Leaf (Puccinia recondita) and stem (Puccinia graminis) rust are best controlled by the selection of resistant cultivars, however; the development of new pathogen races through mutation or hybridization necessitates the use of cultivars with more than one resistance gene (Statler et al., 1982; Miller et al., 1988). Fungicides also help to reduce the incidence and severity of rust. Scab (Fusarium graminearum) may be reduced by burying crop debris, rotating to a non-host crop, and not planting wheat near corn fields; however, this is not always practical. Currently, there are no scab resistant durum cultivars (North Dakota Extension Service, 1998). Black point of wheat (Cochliobolus sativus) may be controlled by using resistant cultivars (Statler et al., 1975). Root and crown rots (Cochliobolus sativus and Gaeumannomyces graminis) are best reduced through use of fungicide seed treatments, such as triademenol, imazalil, and difenoconazole, and crop rotations. Smuts (Tilletia spp.) may be reduced with the use of seed treatment fungicides (NDES, 1998), but some types, such as karnal bunt (Tilletia indica), are extremely difficult to control and no cultivars are known to be immune (Wiese, 1987).
Viruses have not been extensively studied in durum wheat. Wheat streak mosaic and wheat striate do occur in North Dakota, but have rarely created a serious problem (Joppa and Williams, 1988). Wheat streak mosiac virus may be controlled by destroying volunteer wheat, not planting near corn fields, and adjusting the planting date for winter wheat to later in the fall and for spring wheat to earlier in the spring (NDES, 1998)

Insect Control in Durum Wheat

Hessian fly (Mayetiola Destructor Say), aphids, especially greenbug (Schizaphis Graminum Rondani), and cereal leaf beetle (Oulema Melanopus L.) are the three most troublesome insects for wheat. Damage by the Hessian fly results in dwarfed plants, reduced tillering, increased winter injury in winter types, and straw breaking. Burying stubble and rotating crops with non-susceptible plants such as oats may control hessian fly. Both the greenbug and the cereal leaf beetle feed on the wheat leaves, with the cereal leaf beetle often responsible for yield losses up to 25% (Poehlman and Sleper, 1995). Cereal leaf beetle damage may be reduced by planting winter wheat early and by insecticides (Youngman et al., 1994). Aphid lions, Syriphid fly, lady beetles and parasitic wasps all provide natural controls for aphids (NDES, 1998). Depending on the location, there are other possible pest problems, such as wheat stem sawfly damage in North Dakota, so it is helpful to familiarize oneself with the environment and potential pests before growing durum wheat. For example, powdery mildew will likely be the most important disease of durum in the eastern United States, while it is not a problem elsewhere in the United States.

Title Page 
Abstract
Acknowledgments 
Chapter I. Introduction
Chapter II. Literature Review 
Origin of Durum Wheat
Geographical Distribution of Durum Wheat
Introduction of Durum to the United States
Climatic Adaptation
Management and Environmental Factors Affecting Durum Yield and Yield Components
Cultural Practices
Physical Characteristics
Pasta Quality
Wheat Pigment Content
Dough Rheology
Chapter III. Winter Durum Wheat Yield Evaluations at Various Virginia Physiographic Locations 
Abstract
Introduction
Materials and Methods
Data Analysis
Results
Discussion and Conclusions
Best Yielding Durum Lines
Conclusions
Chapter IV. Physical and Chemical Quality Aspects of Winter Durum Wheat Grown in Virginia 
Abstract
Introduction
Physical Quality Characteristics and Protein Content
Aluminum Lactate – Polyacrylamide Gel Electrophoresis (A-PAGE)
Semolina Yield and Milling
Spaghetti Cooking Loss and Firmness
Results and Discussion
Kernel Vitreousness
Gel Electrophoresis (SDS-PAGE)
Conclusions
Chapter V. Conclusions 
Appendices
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Protein Indicators, Quality, and Yield of Winter Durum Wheat Grown in Virginia