Cultivar Development and Selection
There is a large amount of genetic variability in the wheat gene pool. It has been estimated that this variability has been exploited to produce in excess of 17,000 wheat varieties that are adapted to environments which range from higher elevations in the tropics and subtropics to regions near the arctic circle. This pool of genetic variability provides plant breeders with raw materials that can be re-combined to produce new improved varieties with more specific adaptation.
Western Canada and Siberia have the coldest climates for crop production of any large agricultural region in the world. The frost free period for much of the Canadian prairie region is less than 120 days and in some areas the growing season is so short that only very early maturing varieties of summer annual species are reliable as commercial crops. Extreme winter temperatures, which often fall below -35o C, have limited winter annual and perennial crop production to only the most cold hardy species unless some means of cold avoidance can be provided. Moisture availability during the growing season is also a major factor limiting crop productivity on the Canadian prairies, especially in the southwest. In spite of these limitations, a large crop based industry that makes a significant contribution to Canada's trade balance has been developed in western Canada. The cornerstone of this industry has been the production of spring wheat under extensive management systems.
While spring wheat dominates on the Canadian prairies, winter wheat has captured approximately 75 percent of the world's wheat acreage. Where it can be successfully overwintered, winter wheat has an advantage of a longer growing season than spring wheat because it establishes in the fall and starts growth early in the spring. The competitive advantage and higher yield potential associated with the winter growth habit has prompted a continued interest in the possibilities for winter wheat production in western Canada. Early settlers made the first attempts to grow winter wheat in this region around 1800. Since then, farmers and researchers throughout the prairie region have toyed with the idea of winter wheat production.
Winter wheat was grown extensively in the Chinook belt of southern Alberta before spring wheat became popular. Winter wheat production has persisted in this region and peaked at nearly 450,000 acres harvested in 1978. A high frequency of winterkill prevented the establishment of winter wheat as a viable crop option outside of southern Alberta until the practice of stubbling-in became widely accepted starting in the early 1980's. Snow trapping by the standing stubble essentially eliminates the risk of winterkill with the result that winter wheat can now be successfully overwintered throughout the Canadian prairie region.
Wheat belongs to the Gramineae family. This family includes cultivated wheats, ryes, barleys, oats, and important forage grass species. Within the Gramineae family, the genus Triticum includes a number of species that form a series based on multiples of seven related chromosomes (diploids = 7, tetraploids = 14, hexaploids = 21). Common wheat (Triticum aestivum) is a hexaploid (ABD) derived from three diploid species (Figure 1): Triticum monococcum (A), a modified diploid (B), and Triticum tauschii (D). Durum wheat (Triticum turgidum var. durum) is a tetraploid (AB) derived from the two diploid species that it has in common with hexaploid wheat. The diploid Triticum species presumably also have a common seven chromosome ancestor. The close relationships among Triticum species allows for the exchange of genetic material with the result the wheat relatives have provided plant breeders with a valuable source of exploitable genetic variability, especially for disease and insect resistance.
Figure 1. Evolution of common spring and winter wheat (Triticum aestivum).
The need for a vernalization period of several weeks growth at temperatures approaching freezing before normal heading will occur in winter wheat is the major difference between spring and winter wheat. The vernalization requirement can be controlled by a single gene. Consequently, there are essentially no restrictions on the plant breeder's ability to move genes between spring and winter wheat classes within species.
Wheat was domesticated from its wild relatives nearly 10,000 years ago in what is now the Mesopotamian region of the Near East. Man has continued to select for adapted varieties of wheat since these early attempts at farming. The Swiss of the Neolithic Period cultivated varieties of wheat and, in ancient Greece, kinds of wheat that had been selected for productivity and value as food were described by one of Plato's pupils in writings completed about 300 B.C.
The development and application of plant breeding methods has allowed man to further exploit the evolutionary variability that nature provided in wheat. Prior to 1900, plants with desirable characters were being selected, intermated, and their superior progeny selected for cultivation. The understanding of genetics that arose out of the work set forth by Mendel in 1865 provided for more rapid, controlled manipulation of desirable genetic traits. With this knowledge, modern plant breeding was born at the start of the 20th century. The basic principles of wheat breeding now include: 1) the search for and identification of plants or varieties possessing desired traits such as rust resistance, 2) the development of suitable practical methods of reliably measuring these traits such as greenhouse screening for rust, and 3) the exploitation of the methods of transfer of superior genes for these traits into adapted cultivars like Norstar, which have the remaining necessary favorable economic traits.
Crimean varieties introduced from eastern Europe into Kansas by Russian Mennonites in 1872 and by the United States Department of Agriculture scientists in 1900 provided the basic germplasm for successful production of hard red winter wheat in the Great Plains of North America. Although most of the early introductions and selections are no longer of commercial importance, most of the strains of hard red winter wheat grown on the Great Plains prior to 1969 were developed from hybrids involving selected Crimean cultivars. It is noteworthy that this same material still ranks with the most winter hardy cultivars grown on the Canadian prairies today.
The early winter wheat introductions into the Great Plains region were landrace mixtures rather than pure line cultivars. Subsequent reselection yielded a number of cultivars, including Kharkov 22MC that was released from Macdonald College in Quebec in 1912. Kharkov 22MC, Jones Fife, and Yogo were the main cultivars grown in southern Alberta in the first half of this century ( Table 1
). These cultivars all had poor milling and baking quality, especially compared to the spring wheat cultivars grown at that time.
In 1949, winter wheat development in western Canada moved beyond the testing and selection of introductions when a winter wheat breeding program was initiated at Lethbridge. In 1961 this program released Winalta, which had superior breadmaking quality but poorer winter hardiness than Kharkov 22MC. The Lethbridge program also released Sundance in 1971 and Norstar in 1977. Norstar represented the successful combination of good yield potential and baking quality of an adapted parent (Winalta) with superior winterhardiness of an introduced parent (Alabaskaja) and it soon replaced all other winter wheat cultivars on the Canadian prairies.
Recent cultivar releases in western Canada include an introduction from Montana (Norwin), a selection from the Montana cultivar Redwin (AC Readymade), and CDC Kestrel, which was developed from a cross between a cultivar from Colorado (Vona) and Norstar. These releases demonstrate the continued strong reliance of western Canadian breeding programs on cultivars developed for the USA Great Plains region.
Plant breeding involves the management of a cultivar development program that integrates the knowledge and priorities of a large number of disciplines so that lines with the potential to be superior cultivars can be identified from among thousands of progeny originating from the intermating of selected parents. Plant breeding programs have long term objectives. They must be organized with the understanding that cultivars originating from crosses among parents selected today will not enter the commercial market for 10 to 15 years.
To be successful, wheat breeders should be part of a team made up of pathologists, cereal chemists, plant physiologists, agronomists, biotechnologists, market analysts, etc., and supporting technicians. However, in today's administrative climate of short term objectives (up to 5 years) and contract research, this "team" concept has little basis in reality. In Canada, many of today's plant breeders have been left with the dilemma of priorizing the purchases of expertise from support disciplines (where they continue to exist) using funds from budgets that are rapidly ceasing to exist.
Steps in cultivar development
a) Selection of superior strains
The purpose of a breeding program is to generate genetic variability from which desirable individuals can be selected to produce improved cultivars. Most breeding programs are based on the premise that large populations must be assessed to provide an acceptable probability that individuals with the desired combinations of parental characteristics will exist in the population. Consequently, as many individuals and lines as resources will permit pass through programs each year. However, little is gained by carrying inferior types from year to year, so they are discarded as soon as effective selection pressure can be applied for important characters.
Selection of parents is the initial step in a breeding program ( Figure 2
). This is also the most important step because it establishes limits on the genetic variability among the progeny available for selection in subsequent generations. Normally one of the parents in a cross will be an adapted cultivar, such as Norstar, while the other parent will possess an important trait that the adapted cultivar is
Steps in the development of a high yielding, winter hardy winter wheat cultivar.
missing, such as rust resistance. Winter hardiness, drought tolerance, disease resistance, insect tolerance, straw strength, plant height, resistance to shattering, harvestability, seed size, seed shape, seed color, test weight, and grain quality are among the many traits that winter wheat breeders must consider when selecting parents in a breeding program.
Plant breeders make as many as 100 new crosses each year. Consequently, considerable effort is spent on the evaluation of potential parents. A high winter survival requirement places a large restriction on a breeder's ability to objectively evaluate most potential winter wheat parents under western Canadian conditions, especially outside of southern Alberta. Because of this restriction, nonhardy parental lines used in western Canadian winter wheat breeding programs are often selected without the benefit of local performance data. In these instances the breeder will rely on performance data from trials grown in regions with milder winter climates.
A cross between two parents produces hybrid (F1
) seed ( Figure 2
). Normally each F1
seed is the result of a cross that is made by hand. This is a labor intensive process and, because the F1
generation is genetically uniform, fewer than 50 F1
seeds are usually produced for each cross. Biological male sterility and fertility restoration systems and chemical gameticides permit the production of larger amounts of F1
seed. If the yield potential of the F1
produced by these methods is high enough to offset increased seed costs and the need to purchase seed each year, then F1
seed may be sold as hybrid seed. Hybrid winter wheat cultivars have been developed for commercial production on the USA Great Plains. However, the production of hybrid winter wheat has not yet been given serious consideration in western Canada.
In contrast to the genetic uniformity of the F1
generation, the genetic differences between the parents are expressed in a multitude of combinations that appear in the next (F2
) generation ( Figure 2
). It is at this stage that the plant breeder may resume the selection process. However, the progeny from selected individuals does not breed true in early generations (F2
) and the plant breeder normally reselects within each generation. The progeny of selected individuals becomes genetically more uniform with each succeeding generation and selection for more complex traits, such as yield, normally begins by the F6
. Increased genetic uniformity and the availability of performance data from small plot trials, as opposed to individual plants or single rows, permits the rapid culling of selected strains as they pass from the F6
to the F8
The breeding procedures that have been outlined to this point represent a simplified version of most programs. Depending on the circumstances, wheat breeders may superimpose any of a number of options on this main theme.
Spring crop breeders normally have approximately eight months between harvest and the start of seeding in the spring for data analyses, quality evaluation, decision making, etc. In contrast, winter wheat is harvested in August and seeded before mid-September in most of western Canada. Unless they wait and advance their breeding material one generation every second year, winter wheat breeders have one to six weeks to complete the tasks that spring crop breeders perform in eight months. This time factor means that different approaches must be used in spring and winter wheat breeding programs.
Spring crop breeders may grow more than one generation each year by making use of winter increases in the southern U.S.A., Mexico, New Zealand, or other regions with production seasons that
are opposite to that of western Canada. Increases in regions with shorter winters would allow for the seeding of winter wheat as late as November while advancing harvest to June. This change would increase the efficiency of Canadian winter wheat programs by allowing more time for processing of breeding material between harvest and seeding. However, even with increases in southern U.S.A., winter wheat breeders would still only be able to advance their programs one generation each year. While they are more expensive to use, greenhouses and growth chambers provide the only real option for accelerating a winter wheat breeding program, especially in early generations when population sizes are small.
b) Cooperative testing and registration
or later generation strains are advanced to cooperative, or pre- registration trials where they undergo final evaluation for a minimum of three years at 10 to 20 locations scattered throughout western Canada ( Figure 2
). The Prairie Registration Recommending Committee for Grain (PRRCG) is responsible for coordination of cooperative trials established to evaluate potential winter wheat cultivars for the Wheat Board area of western Canada ( Figure 3
). The data from cooperative trials is used by PRRCG evaluation teams to determine the merit of strains that plant breeders propose for registration. Once a line under evaluation receives the necessary support from the PRRCG, the plant breeder applies to the Variety Registration Office of Agriculture Canada for registration.
When a superior winter wheat strain has been identified, the plant breeder will begin a strain purification process to ensure that acceptable breeder seed stocks are available for distribution to seed growers should the strain be successfully registered as a cultivar. This process usually starts no later than after the first year of evaluation in cooperative trials. Breeders seed is distributed to seed growers once a cultivar registration is approved. It then takes at least two more years of increase before seed of the cultivar is available in sufficient quantities for commercial production ( Figure 2
Winter wheat overwinters as a seedling. During the overwintering period the seedling must cope with extremes in winter weather. Many factors can influence winter survival. However, under western Canadian conditions, the main cause of winterkill is simply low temperature damage to critical parts of the plant during periods of cold (see Chapter 12
Considerable genetic variability for winter hardiness exists in the winter wheat gene pool. It is this variability that breeders must exploit in efforts to maintain and improve the winter hardiness of winter wheat cultivars developed for western Canada. Hardy winter wheat cultivars are a reality, but whether or not the existing genetic variability can be re-worked to produce super-hardy winter wheats is another question.
In 1929, the American researchers Quisenberry and Clarke observed that "the possibility of developing hardier varieties has been recognized for years." While this general optimism still prevails today, the record shows that since 1929, the total world breeding effort has achieved little or no increase in the winter hardiness of available cultivars ( Table 1
). Early wheat breeders/farmers, using trial and error methods, were very effective in selecting the most winter hardy strains, and new major advances have proven difficult to achieve. Minhardi and Kharkov 22MC were released for commercial production in 1902 and 1912, respectively. They were both reselections from Crimean introductions that arrived in North America in the late 1800's. These two cultivars still rank with the hardiest cultivars available today.
Table 1. Winter hardiness of selected winter cereal cultivars and strains.
*Field Survival Index (FSI) - Differences in cultivar FSI reflect average percent differences expected in field survival, e.g., Norstar versus Winalta = 514 - 463 = 51% difference in expected winter survival potential.
|Triticale (Puma plus Norstar)
Alabaskaja and Ulianovkia, two more recent introductions from Russia, have winter hardiness levels superior to Minhardi and Kharkov 22MC ( Table 1
). Part of this winter hardiness advantage has been captured in the cultivar Norstar, which originated from a cross between Alabaskaja and Winalta. However, both Alabaskaja and Ulianovkia have been available in Russia for many years and, while they have provided North American wheat breeders with additional genetic variability, they do not represent new sources of major genes for winter hardiness.
Related species (see section on Relatives) provide another potential source of genetic variability that may be exploited to improve the winter hardiness of winter wheat. The superior winter hardiness of rye provides proof that the potential to survive winter stresses is much greater than is presently available in wheat ( Table 1
). However, transfer of this potential from rye to wheat has proven to be a difficult task. For example, the winter hardiness advantage of rye is completely suppressed when winter wheat and rye are combined to produce triticales ( Table 1
). Attempts at interspecific transfers of winter hardiness genes to wheat from its close relatives have also been unsuccessful.
Advances in biotechnology provide an opportunity for wheat breeders to expand their attack on the winter hardiness barrier that has frustrated them for so long. Exploitation of this new technology to produce adapted, super-hardy winter wheat cultivars will require close cooperation between wheat breeders and biotechnologists. This interdisciplinary effort will be expensive and immediate break-throughs should not be expected.
In western Canada, there are a large number of diseases and insects that have the potential to cause economic losses in winter wheat ( Table 2
). Plant resistance is the most environmentally safe, reliable, and cost effective means available for controlling these diseases and insects. However, existing winter wheat cultivars have poor resistance to most of the diseases and insects prevalent in this region ( Table 2
). The poor resistance of western Canadian winter wheat cultivars has not been due to the absence of satisfactory sources of genetic resistance. Rather, the problem has been the lack of resources to mount sustained breeding programs that give the production of disease and insect resistant cultivars a high priority.
The high level of cultivar disease and insect resistance that is an accepted part of spring wheat production in western Canada was achieved only after many years of intensive, coordinated efforts among wheat breeders and pathologists. Similar levels of resistance could be incorporated into winter wheat. However, as was the case with spring wheat, the development of cultivars with a broad spectrum of disease and insect resistance can be expected to proceed slowly and often in small increments. The efforts to develop rust resistant winter wheat cultivars provides an example of the difficulties winter wheat breeders have encountered in living up to the high standards of insect and disease resistance maintained by spring wheat breeders.
The expansion of winter wheat out of its traditional production area in Alberta has focused considerable attention on the need for rust resistant cultivars. Rust does not overwinter on the Canadian prairies and each year must be reintroduced from the southern USA. For most of western Canada, winter wheat reaches maturity before the rust inoculum has a chance to build up to significant levels. Since rust usually enters the southeast corner of the Canadian prairies first, the highest risk of damage exists in southern Manitoba and southeastern Saskatchewan.
In the northern part of the USA Great Plains region, all the major winter wheat cultivars are susceptible to leaf rust and most have poor levels of stem rust resistance. Consequently, rust resistant cultivars adapted to this region are not available for use as parents in Canadian breeding programs. So far efforts to transfer rust resistance from Canadian spring wheat cultivars to winter wheat have not been successful. In western Canada, Norwin and CDC Kestrel winter wheat cultivars have a slow rusting characteristic that delays the development of stem rust epidemics by a week to ten days. CDC Kestrel and breeding lines with this slow rusting reaction have had an average 40 percent yield advantage over Norstar in trials grown under favorable moisture and heavy, late rust epidemics in Saskatchewan and Manitoba. However, even with a yield advantage of this magnitude in the presence of a rust epidemic, the requirement for a resistant rust rating has prevented the disease evaluation team of the Prairie Registration Recommending Committee for Grain ( Figure 3
) from "supporting" slow rusting winter wheat lines for registration as cultivars for production in western Canada.
A farmers' income per acre (hectare) is determined by grain yield and price per bushel (tonne). The price that the farmer has received for No. 1 and 2 Canada Western Red Winter wheat has been similar to that of No. 3 Canada Western Red Spring wheat. Therefore, the top two premium wheat grades have been conceded to the Canada Western Red Spring wheat class and the price premium paid for these grades must be compensated for by higher yields if the Canada Western Red Winter wheat class is to ean economic option for the farmer (see Chapter 25 ).
The price of Canada Western Red Winter wheat has been closer to that of the high yielding Canada Prairie Spring than the Canada Western Red Spring wheat class. Therefore, unless there is new evidence that price per bushel (tonne) can be increased to reflect superior quality, winter wheat breeders must comply with long term breeding objectives that will allow Canada Western Red Winter wheat to remain competitive in markets that are priced similarly to that of Canada Prairie Spring wheat. This can only be interpreted to mean that winter wheat breeding objectives must reflect the lower protein and higher yield targets of the Canada Prairie Spring class
As a class, Canada Prairie Spring wheat cultivars have a protein concentration that is two percent lower and a grain yield that is 20 percent higher than Canada Western Red Spring wheat cultivars. This reflects a trade off of 10 percent gain in grain yield for each percentage point sacrificed in grain protein concentration of spring wheat.
Norstar winter wheat has had a 25 to 36 percent yield advantage over cultivars from the Canada Western Red Spring wheat class. Release of the winter wheat cultivar CDC Kestrel in 1991 established that the high yield potential of semi-dwarf wheat can be combined with good winter hardiness to further raise the yield advantage held by winter wheat in western Canada. CDC Kestrel has maintained a yield similar to Norstar under high drought stress conditions. Under more favorable moisture conditions, CDC Kestrel has yielded 22 percent higher than Norstar. Given the realities of the marketplace, winter wheat breeders must place continued emphasis on consolidating and improving this yield advantage while maintaining their efforts to improve other important agronomic and quality traits.
Assessment of quality has always been important to the wheat industry. The first wheat quality evaluation tests were extremely simple by today's standards. The chew test for gluten development was considered a valuable measurement in the selection for bread quality by early breeders in this country. While use of this test has fallen by the wayside, visual assessments of characteristics like the physical appearance of the grain have remained important quality indicators. Plump, sound, bright kernels are desired by millers for their high flour extraction rates and samples of dark vitreous kernels free of "piebald" or "yellowberry" are associated with high protein concentration. Minimum specific (bushel or hectolitre) weights are also still required in most wheat markets.
Developments in the area of cereal chemistry soon established that wheat quality was much more complex than the early simple tests indicated. However, identification of the basic components determining quality and an explanation of their mode of function and interrelationships have not proven to be an easy task. This absence of a clear definition of quality has resulted in a proliferation of tests, each of which is professed to measure some important quality property.
To be useful in the screening of breeding material, a quality prediction test should be simple, inexpensive, rapid and require only a small sample size. Measurements that can be made directly on the seed, such as kernel physical appearance, hectolitre weight, 1,000-kernel weight, kernel hardness, and grain protein concentration, fulfill these criteria best. Micro-milling and cooking tests (Table 3) have been developed. However, as one moves from measurements of the physical appearance of the grain to milling and baking, the tests become more complex, expensive, time consuming, and larger samples are required.
High milling quality is important for cultivar acceptance in the marketplace and, because complete milling evaluation requires large samples of grain and is very time consuming, a number of prediction tests have been developed to allow for the screening of lines from breeding programs ( Table 3
). Millers require wheat with high flour extraction rate because sale of flour realizes a much greater profit than does bran. Flour extraction rate can be modified by mill adjustment. However, increasing the extraction rate increases the flour contamination with bran, which in turn affects the flour color and ash content. White flour color is important in many products. Therefore, measures of flour color and ash content are used to establish the upper limits for flour extraction in screening tests for milling quality.
Table 3. Characters that may be evaluated in the assessment of hard wheat quality.
||Mixing, dough development,
and baking characteristics
Bushel or hectolitre weight
20 min. drop
Amylograph peak viscosity
Remix loaf volume
Remix baking strength
Remix crumb color
Remix loaf appearance
Canadian short process loaf volume
Canadian short process absortion
Sponge-and-dough loaf volume
AACC loaf volume
|Kernel hardness (soft vs hard)
|Grain protein concentration
|Flour yield (%)
|Flour ash (%)
|Mixing, dough development,
and baking characteristics
|Flour protein (%)
Height @ 5 min.
Loaf volume, cookie (or cake), and noodle measurements are usually considered the final quality measures of hard, soft, and durum wheat, respectively. For each of these quality tests there are a number of procedural modifications that have been developed to accentuate certain quality characters. For example, different flour blends, bromate levels and mixing times are used in the loaf volume test. These tests are valuable in the final stages of cultivar evaluation, when a complete description of quality is required. However, they require large samples of grain and the procedures are time consuming and costly. Therefore, as was the case for milling quality, a number of prediction tests have been developed to permit the screening of lines from breeding programs ( Table 3
Bread and pastry products are two of the major end uses of wheat. Hard wheat is used in the production of bread and soft wheat in the production of pastry products. There are a number of simple kernel hardness tests that can be used to quickly segregate lines in wheat breeding programs into hard and soft wheat classes. Kernel hardness is also under simple genetic control making it one of the easiest quality characters to select for in a wheat breeding program.
Cooking tests have traditionally been the final measures of quality. However, the multitude of cooked products produced and the variations in commercial production methods make it impractical to use only cooking tests to evaluate the quality potential of lines from wheat breeding programs.
A large battery of tests has been developed to measure wheat cooking quality (Table 3). In many instances, commercial procedures have been scaled down to laboratory size. Unfortunately, most of the equipment for these tests is expensive and must be operated under closely regulated conditions. The tests are also time consuming and require large amounts of seed. These restrictions greatly limit the number of samples that can be evaluated. In addition, complex procedures, such as baking tests, are particularly prone to high experimental errors and the empirical nature of the data generated is often difficult to interpret. In spite of these limits, cereal chemists have been able to demonstrate that differences among quality classes can be measured. However, the absence of a clear, simple definition of the factors primarily responsible for baking quality has greatly restricted advances in the wheat industry. This limitation is especially important to the plant breeder, for it is only through a simple, accurate, widely accepted definition of wheat quality in terms of its biochemical and physical components that the optimum manipulation of genetic and environmental factors can be realized to fulfill the quality requirements of the consumer.
Alpha-amylase is an enzyme that degrades starch to sugars. High levels of this enzyme reduce the baking quality of wheat and, for this reason, many importing countries have set maximum allowable alpha-amylase levels. All grain contains some alpha-amylase, but its level quickly increases in mature grain that has been exposed to conditions favorable for sprouting. Weather conditions at harvest are a matter of chance; however, alpha-amylase levels in the seed can be kept to a minimum by the development of cultivars that have good sprouting resistance and are genetically low in this enzyme.
Most hard red spring wheat cultivars have been selected for a high level of sprouting resistance or post-harvest dormancy. High levels of seed dormancy are a mixed blessing in winter wheat because it is planted in the fall immediately after harvest. Consequently, a high level of post-harvest seed dormancy would require that winter wheat seed be held over for planting one year after harvest to ensure rapid, vigorous germination and plant establishment.
Wheat is used primarily as an energy source by livestock feeders. Digestibility (obtained from feeding trials) and gross energy content determine the digestible energy of a grain. Significant genetic variability has not been found for digestibility of wheat grain. Therefore, variability in the digestible energy of wheat is dependent upon differences in gross energy content. However, only limited variability has been reported in the gross energy content of wheat. Consequently, it is doubtful that meaningful increases in digestible energy of wheat could be achieved by breeding for improved gross energy content. In addition, the kind and amount of variability in chemical constituents, such as crude fiber, ash, crude protein, and oil suggest that altering levels of these factors would not likely increase the gross energy content of wheat.
Crude protein concentration and specific weight are factors in some feed wheat markets. Therefore, if large quantities of winter wheat were grown for feed, it is possible that low fiber, high protein feed cultivars would have a market advantage.
Grain protein concentration (percent)
Protein is a primary quality component that influences most wheat grain quality measurements. Its importance to wheat quality is recognized in the marketplace and most exporting countries have some segregation of commercial grain lots on the basis of protein concentration. In hard wheats, the majority of the variation in loaf volume of bread can be attributed directly to differences in protein concentration.
Protein concentration can be measured quickly on small samples of grain. It is one of the least expensive quality tests to perform and, with modern technology, its determination need not be overly complex. However, where absolute measurements of protein concentration are required, care must be taken to insure accuracy of results.
When differences in grain yield are corrected for, genetic variation in protein concentration is a maximum of two percentage points in wheat. The protein concentration of the winter wheat cultivar Norstar is in the middle of this range. Consequently, cultivars with a one percent increase or a one percent decrease in protein concentration, relative to Norstar, represent the maximum influence that winter wheat breeders can expect to have on this important quality character (Figure 4). This compares to a potential 12 percentage point range attributable to environmental effects. As a result, protein concentration is the quality character least accessible to the plant breeder.
The direct impact that a winter wheat breeder can have in influencing protein concentration is restricted to the manipulation of the genetic factors that regulate the efficiency of nitrogen extraction from the soil, its translocation to the grain, and its use for the synthesis of protein. The complexity of nitrogen metabolism in the wheat plant suggests that many genes will have at least a small effect on protein concentration. A large number of genes with small effects and a large environmental influence makes the development of high yielding cultivars with high protein concentration a difficult breeding objective ( Figure 4
In the marketplace, grain protein concentration is considered independently of grain protein and grain yield. However, if viewed from the standpoint of the wheat plant, grain protein concentration is determined by the ratio of grain protein yield to total grain yield (grain protein concentration % = grain protein yield total grain yield X 100). For this reason, grain protein concentration is very dependent upon both grain yield and grain protein yield. This difference in viewpoint helps to explain some of the difficulties wheat breeders have to deal with when selecting for both high grain yield and high protein concentration.
Relationship between total plant available soil nitrogen (N) and winter wheat grain protein concentration for environmental conditions that produce a maximum grain yield of 52 bu/acre for Norstar and 65 (Norstar yield + 25%) bu/acre for CDC Kestrel. Breeding objective - a cultivar with a grain yield potential equal to CDC Kestrel and a maximum protein concentration 1% higher than Norstar.
Maximum grain yield - indicates rate of total available N required to produce maximum grain yield.
Wheat protein contains approximately 17.5 percent nitrogen. This nitrogen is obtained from the soil. Therefore, available soil nitrogen has a direct influence on grain protein yield. Nitrogen uptake by the plant is determined by an unstable enzyme, nitrate reductase, that is regulated by the level of available soil nitrogen. Level of available soil nitrogen is controlled by environmental factors such as moisture, temperature, soil ion concentration, soil pH, and by the rate of nitrogen fertilizer applied by the farmer. Therefore, the significant effect that environment has on wheat protein yield should not be a surprise.
An evaluation of spring and winter wheat cultivars with a wide range of quality has shown that cultivar grain protein yield is closely related to total grain yield. In other words, one of the most effective ways of selecting for high grain protein yield in a winter wheat breeding program is to select for high grain yield. However, in most instances, the increase in total grain yield is greater than the increase in grain protein yield resulting in lower protein concentrations for higher yielding cultivars ( Figure 4
The negative relationship between grain protein concentration and grain yield has
aggravated one of the deficiencies in the winter wheat cultivar CDC Kestrel. CDC
kestrel has a protein concentration that averages 0.4 percent lower than Norstar when
the available soil nitrogen requirements for maximum grain yield have been satisfied ( Figure 4
However, this difference is magnified for N levels below those that produce maximum grain yield.
In our example (Figure 4), the grain protein concentration of CDC Kestrel was only 10.2 percent for total
available soil N levels that produced a grain protein concentration of 11 percent in Norstar. This presents a
problem because hard red winter wheat with a protein concentration less than 11 percent usually suffers a price
discount in the marketplace and is often sold as feed wheat. Consequently, even though they offer a huge
potential yield advantage over Norstar, the quality evaluation team of the Prairie Registration Recommending
Committee for Grain ( Figure 3
). has consistently "objected to" the registration of high yielding winter wheat
cultivars like CDC Kestrel. If we return to our example of the relationship between total available soil nitrogen
and winter wheat grain protein concentration (Figure 4), we find that there is a simple solution to the low
grain protein problem associated with high yielding cultivars like CDC Kestrel. The addition of 22 lb/acre
(25 kg/ha) nitrogen as fertilizer increased the grain protein concentration of CDC Kestrel from 10.2 percent
to 11 percent in our example. Not only was the market demand for 11 percent protein satisfied with this
fertilizer addition, but the farmer also profited from a significant grain yield increase (see Chapter 17
, Nitrogen Fertilization).
The control of available soil nitrogen levels is beyond the influence of winter wheat breeders.
Unless their winter wheat is degraded to feed wheat, there is little monetary incentive for farmers
to increase fertilizer rates to maintain quality standards because premiums are not paid for high
protein concentration in the winter wheat class. Consequently, because wheat breeders can only
manipulate protein concentration with great difficulty and within narrow limits, the Canadian cultivar
development and marketing system has exerted continuing pressure on wheat breeders to sacrifice
yield potential in breeding programs in order to maintain quality standards for grain protein concentration.
REGISTERED CULTIVARS (VARIETIES)
Norstar - Developed by Agriculture Canada, Lethbridge. Norstar was released in 1977 and soon
became the dominant winter wheat cultivar in western Canada. It is the most winter hardy cultivar
available and it is particularly well adapted to conditions of drought stress.
Norwin - A Montana cultivar that was released through the Crop Development Centre,
University of Saskatchewan in 1986. Norwin is a semi-dwarf cultivar with very short straw.
Its winter hardiness is inferior to Norstar. Norwin is sensitive to drought stress and should only
be grown under high moisture conditions where lodging and excessive straw production are problems.
Norwin has stem rust tolerance that is superior to Norstar.
AC Readymade - A selection from the Montana cultivar Redwin that was released by Agriculture Canada,
Lethbridge in 1991. AC Readymade is a medium tall cultivar with fair straw strength and excellent grain
protein concentration. It has performed best under favorable moisture conditions in southern Alberta. Poor
winter hardiness and a very susceptible stem rust reaction will restrict production of this cultivar to
CDC Kestrel - Developed by the Crop Development Centre, University of Saskatchewan.
CDC Kestrel is a tall semi-dwarf cultivar that was released in 1991. Its yield has been similar to
Norstar under drought conditions. Shorter, stronger straw makes CDC Kestrel better adapted than
Norstar to high moisture environments and irrigation. CDC Kestrel has stem rust tolerance that is
superior to Norstar.
Page revised in 1995
CDC Clair - Developed by the Crop Development Centre, University of Saskatchewan.
CDC Clair is a tall semi-dwarf cultivar that was released in 1995. Its agronomic performance
has been similar to CDC Kestrel. CDC Clair has a higher grain protein concentration than CDC Kestrel.
CDC Osprey - Developed by the Crop Development Centre, University of Saskatchewan.
CDC Osprey is a tall semi-dwarf cultivar that was released in 1995. Its agronomic performance
has been similar to CDC Kestrel. CDC Osprey is susceptible to leaf rust. CDC Osprey has a
higher grain protein concentration than CDC Kestrel.
Regional winter wheat cultivar recommendations can be obtained from the following provincial publications:
These publications are revised each year to provide producers with the most up-to-date information
available on winter wheat varieties registered for production in western Canada.
Winter wheat strains have been identified with superior winter hardiness, greater yield potential,
more diverse grain quality, and improved resistance to diseases and insects compared to the
registered cultivars listed previously. Successful selection for these traits has established that the
necessary genetic resources are available for the creation of better adapted, more productive
cultivars for a wide variety of wheat quality classes. The opportunity for rapid winter wheat cultivar
improvement has never been greater. However, before we make the investment that will be necessary to
seize this opportunity, funding agencies and farmers must be convinced that winter wheat has a
significant role to play in the future of western Canadian agriculture.