From a single seed - Tracing the Marquis wheat success story in Canada to its roots in Ukraine (3 of 11)
In terms of area under cultivation, wheat is the most widely cultivated plant on Earth. In 1935, about 155 million hectares (ha) of the world's land area were wheat fields -- about 1% of the world's land area or 1/6 of the total area under cultivation at that time. If the world's total land area is 130.52 million square kilometres (km2) (13,052 million hectares (ha)), the total area under cultivation in 1935 was about 950 million ha. (4, page 19) Wheat cultivation worldwide is distributed very unevenly. However, it can grow from as far North as the Arctic Circle to the southernmost ends of the continents in the Southern Hemisphere.
The 1935 world harvest of wheat totalled 1,500 million centners. If all this wheat had been loaded into railway boxcars, the freight train would have circled the earth twice.
Almost the entire population of our planet eats wheat because of its good taste, good assimilation by the human body, and high nutritive value, with a protein content of 8-20% and up.
Classification of Wheat
Wheat belongs to the cereal family. To distinguish one variety or genus from another, it was necessary to establish a wheat classification based on its observed characteristics. Such observation began in earliest times: descriptions of different varieties are found in the works of the Greek and Roman historians. For example, Theophrastus, a student of Plato, wrote in his book The Needs of the Plant in about 300 B.C.: "... There are many kinds of wheat named after the areas where they grow -- Libyan, Pontian, Frankish, Assyrian, Egyptian, and Sicilian. They differ in colour, size, shape, and individual characteristics, as well as their general attributes and particularly their value as food." Theophrastus catalogues numerous other differences. During the first century B.C. writers like Varo, Pliny, and Columellus cited, reviewed, and expanded on the writings of Theophrastus.
No one can say how people determined the quality of wheat in prehistoric times; however these Greek and Roman descriptions show that many of the primary wheat characteristics were already known by those cultures. The wheat characteristics recorded by eighteenth-century botanists are similar to those found today. Most prominent among them was Tournefort, who recorded 14 varieties of wheat in 1719. The practical classification of wheat began with Linnaeus's work in 1753. In his Species Plantarum he describes seven varieties of wheat. Before 1922, wheat had been classified by some 37 authors, although their works seldom agreed: for example, only a few distinguished between winter and spring wheat.
Structure of the Wheat Kernel
The wheat kernel (caryopsis) has a dorsal (back) and ventral (front) side as well as a top and bottom. The ventral side has a deep crease extending from top to bottom. A brush structure is formed at the top of the caryopsis and the embryo exists at the lower dorsal surface.
The kernel consists of four parts: the seed coat (pericarp), the fruit coat (aleurone layer), the endosperm, and the germ, or embryo. The embryo consists of a scutellum (or cotyledon), which secretes enzymes to dissolve the endosperm starch to nourish the embryo during germination; a coleoptile, which becomes the first leaf at germination and shields subsequent leaves; and a coleorhiza, which encloses the primary root or radicle. The endosperm occupies about 76% of the whole kernel and consists of an arrangement of large and small starch granules deposited in a protein matrix. The proportions and arrangements of the components determine the hardness or softness of the kernel.
Wheat belongs to the family Gramineae, subfamily Hordeae, tribe Triticeae, genus Triticum. This genus is very diverse. In Ukraine it is divided into two main groups: winter and spring wheat. In Western Europe there is a third (the so-called alternative) intermediate group, which has minor, local significance and can be planted either in the fall or very early in the spring. The wheat stalk may be either awned or awnless: this is true of both winter and spring wheat.
From a morphological point of view, wheat has a fibrous root system. At seed germination, both the radicle or primary roots, and a subcrown internode emerge: the latter gives rise to a crown near the soil surface. This structure gives rise to four to six tillers for each plant, with each tiller supported by secondary roots. The secondary root system can be quite extensive, reaching depths of up to two metres. It is responsible for supplying nutrients to the plant.
The stalks, or tillers of the plant, consist of five or six internodes. These are separated by dense structures called nodes, which give rise to the leaves. The stalks can be hollow or filled with pith. Wheat with pith-filled stalks is known as solid-stemmed. It offers resistance to insects such as the wheat stem sawfly. The leaves consist of two sections, the blades and the sheaths. The sheaths effectively strengthen the stalk and protect the growing apical meristem. Growth and development of the tillers occur by means of a telescopic action so that all leaves are fully expanded before the spike emerges from within the structure.
The spike of the wheat plant (Figure 1) consists of a central axis called a rachis. Each node of the rachis gives rise to a spikelet consisting of a pair of outer glumes that enclose three to four florets. Each floret consists of two outer integuments, called a lemma and a palea, that enclose the reproductive organs. The female reproductive structure is the feathery stigma that is attached to the ovary by a style. Each floret (Figure 2) contains three anthers, or male reproductive organs, supported by filaments. The stigmatic and anther structures mature simultaneously and mature pollen is shed onto the stigma. The pollen germinates on the stigma, which sends a pollen tube containing two male gametes down the style to fertilize the egg cell and polar nuclei. This gives rise to the embryo and endosperm, respectively, of the new seed.
This process is called self-pollination. Wheat is thus a typical self-pollinating plant, although up to 5% outcrossing can occur when stray pollen is present. The awns on all durum wheats and some bread wheats grow at the tips of the lemmas and to a lesser extent on the top of the outer glumes.
There are about 25 different species of wheat at the diploid, tetraploid, and hexaploid levels -- that is, their genetic structure contains 14, 28, and 42 chromosomes respectively. The two main groups of commercial wheats are the durums (Triticum durum) and bread wheats (Triticum aestivium) with 28 and 42 chromosomes respectively. These originated and evolved naturally through a series of intercrosses among the diploid species. It is estimated that the commercial wheats were isolated about 10,000 years ago. The wild species are still a valuable source of useful agronomic traits for the continued improvement of cultivated wheats.
The durum wheats are grown commercially in drier regions of the country, for example, the brown soil zone of the central Prairies in Canada. They are characterized by having large, ovate-shaped, amber-coloured kernels that are very hard, almost flinty in texture. This class of wheats is used exclusively for pasta products throughout the world, as well as for other specialty products, such as cous-cous, in some countries.
The bread wheats encompass a wide range of different types classified largely by their growth habit and functionality. The various classes are combinations of winter or spring growth habit with white or red kernels and hard- or soft-textured kernels. For example, both spring and winter wheats include types with hard or soft and red or white kernels.
Bread is baked from the flour of varieties with hard kernels, predominantly the red type. They have a high protein content and high levels of predominantly two protein fractions, gliadins and glutenins. These impart elasticity to the dough during baking so that large loaves of bread can be produced.
The soft wheats typically have lower protein contents and lower levels of the two critical protein fractions. They are used in unleavened bakery products like pastries and breakfast cereals: indeed, white soft wheat flour is preferred for breakfast cereal processing.
Within any class of wheat there are numerous varieties that represent the efforts of plant breeders, who regularly produce new strains with improvements in yield, disease resistance, and seed quality. It is estimated that 25,000 different varieties of wheat have been produced worldwide.
Slavonic Terms in Wheat Nomenclature
Botanists use Greek and Latin terms to describe plant anatomy. In Latin the glume of the wheat floret is called palea; later, certain botanists replaced this term by the Greek word lemma. What is the origin of these two words?
I believe it is the ancient Slavonic language. Let me explain why. Early grain growers learned the anatomy of wheat and its floret from the terminology used in the area where it originated. Figure 3 shows the wheat floret with its reproductive organs, the stigma and anthers, surrounded by two strong glumes that form a coat to protect it. The glume has two "halves" which fall away from the ripe grain and are eliminated as chaff at threshing time. The old Slavonic term for each of the glume halves was polova, meaning "half." This word may well have been changed into paleva or palea and adopted by the ancient Greeks and later the Romans.
Similarly the Greek word for chaff, achiron, may be adapted from the Slavonic word okhorona, meaning protection, which is what the chaff is for the wheat spikelet. Finally there is another kind of chaff which sticks to the grain, known in Ukraine as prylipka. Here the old Slavonic word liplyu, or leplyu (to stick or adhere), may well have come into the Greek language in the form of lepo, which transforms the adverb lepo into lema, or lemma.
These three terms may well represent evidence of the antiquity and importance of the development of wheat cultivation on the territory of modern Ukraine. One of the great wheat historians of the former Soviet Union, M. M. Yakubintser, writes, "The territory of Ukraine was one of the world's major areas for both spring and winter wheat as early as the fourth century B.C."(6, p.17) He claims that traces of wheat were also found in the Northern Caucasus and Kazakhstan in the second century, as well as the upper Volga Valley at the end of the first century A.D. Ukrainian wheat thus may have spread to both neighbouring and distant countries. According toYakubintser both soft and hard wheat have been grown in the area since antiquity. He reports finds of hard wheat samples dating from the fourth century B.C. in Ukraine, others from the third century B.C. in the Transcaucasus (in Azerbaijan) and the tenth to twelfth centuries A.D. near the Don River in Bila Vezha. Samples of the hard wheat Triticum spelta excavated in Ukraine date from the fourth century B.C. (6, page 18)
About Ukrainian wheat Yakubintser writes, "Ancient Ukrainian wheats, especially winter ones, were famous throughout the world -- and not just as food grain. They played a very important role in world agriculture as seed grain, mainly because of their high quality and resistance to cold." (6, page 31) This key quality of Ukrainian wheat -- resistance to cold -- can serve to introduce its contribution to the New World country first to use it: Canada.
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