The wheat species of the genus Triticum are characterized by spikelets placed flatwise at each rachis joint. The plant is a midtall annual or winter annual grass with flat blades and terminal spike. The spikelets are solitary with 1-5 flowers, sessile and arranged on the nodes of a zig-zag, channelled or articulate rachis. The glumes are keeled, with three or more nerves and obtuse acute or acuminate. The lemmas are keeled or rounded on the back, many-nerved and terminated in a single tooth or awn.
The stem of the mature wheat plant is a hollow, joint cylinder that comprises 3-6 nodes and internodes. The length of the internodes increases from the lowest one. The upper internode of the stem, the peduncle, bears the spike. The stems of most varieties are solid at the nodes, but the internodes are hollow.
Stems are white to yellow or, in some varieties mostly purple in colour. The purple colour in such varieties may not be apparent under all environments. It usually is most distinct on the peduncle, but often runs down to the sheaths of the lower leaves.
Total plant height, with spike included, may vary from 60,96 cm to 152,4 cm, but it may be even shorten in dryland areas. Wheats have been classified as short, midtall and tall. Under good growing conditions, wheats from 30,48 - 91,44 cm in height would be classed as short; wheats from 60,96 - 121,92 cm midtall; wheats from 91,44 - 152,4 cm tall.
Tillers of lateral branches develop from buds in the axils of the lower leaves attached to the basal or crown nodes below the soil surface. In field - sown wheat the second and third buds usually develop into tillers (which make three stems per plant) but the fourth, fifth and sometimes later buds may also develop tillers. Secondary tillers may develop from later buds on tillers, so that a single plant with ample space may bear from 30 -100 or more stems. Although varieties differ in tendency, thin seeding, abundant moisture and fertile soil favour increased tillering.
Wheat varieties with weak or slender stems may lodge or fall over under conditions of excessive moisture, high winds or high nitrate content of soil.
The wheat foliage leaf consists of the sheath, blade, ligule and auricle. The leaf-sheaths normally enclose the lower two-thirds of the stem. The sheaths may be white or purple in color. The leaf blades of white varieties vary considerably in dimension, shade of green color, and angle of projection from the stem. As the plant matures, the blades dry and frequently break off. The blade may be pubescent or glabrous. Blade color varies with the condition of the plant as affected by temperature, soil moisture and soil solution. In general, the hard red winter wheats have dark green blades, whereas all durum wheat varieties have light green blades. The ligule, which arises at the junction of the blade and sheath, encircles the stem. It is a thin, colorless, membranous structure with an irregular edge fringed with minute hairs.
A maximum of 5-7 seminal roots may function throughout the life of the wheat plant. Normal coronal roots develop from the nodes of the main axis or its branches near the soil surface. Tillers develop a similar series of coronal roots.
The mature root system ordinarily reaches a maximum dept of 15,40 - 23,36 cm. Winter wheat usually has a more extensive root system than does spring wheat. The extent of the root system also is markedly affected by texture, fertility and moisture content of the soil.
Morphology of the inflorescence:
The wheat inflorescence is a terminal spike which is usually 76,20 - 101,6 mm in length, but it may vary from 50,8 to 127 mm. Spikes may be flattened parallel or at right angles to the plane of the face of the spikelets. They may be fusiform, oblong, clavate or elliptical in shape. Spikes also may be lax, mid-dense or dense. The spike bears 10-30 spikelets which are borne singly at nodes on alternate sides of a zig-zag rachis. Each short internode of the rachis is narrow at the base and broader at the apex. One side of the internode is convex; the side that faces the spikelet is flattened or concave. Spikes may be awnless, awnleted, or awned. An awn terminates the lemma on all spikelets of awned varieties.
The spikelet consist of 1-5 flowers or florets attached alternately to opposite sides of a central axis of rachilla. One or more of the upper florets usually are sterile, with the result that only two or three kernels mature. The spikelet is subtended by two empty glumes, which are keeled, rigid and obtuse, acute or acumate. The glume tip may be extended into a beak that resemples a short awn. The glumes may be glabrous or pubescent and be white, yellow, brown or black according to the variety.
The wheat floret consist of a lemma and palea which enclose the sexual organs - three stames and a single ovary. The lemmas, keeled or rounded on the back, often are awned. The palea which occurs opposite to the lemma is membranous awnless, two-keeled and with infolded margins.
Kernel or Caryopsis:
The wheat is a dry, one-seeded, indehiscent fruit or caryopsis. Kernels differ in shape, size, color texture and numerous other characteristics.
The kernel, which is roughly egg-shaped (ovate), ranges from 4-10 mm in length, depending on variety, location in the spike and position in the spikelet during development. A well-filled kernel of most common varieties is smoothly curved on its dorsal surface, except at the base where the fruit coat (pericarp) is wrinkled over the underlying germ or embryo. On its ventral surface the kernel has a furrow or crease between two cheeks, which extends inward nearly to the center in commonly grow varieties. At the apex or tip of the kernel is a brush composed of many hairs. The color of the kernel usually is classified as white or red. Those of the white class may be white or may vary from cream to yellow, while those of the red class vary from light brown to the darken shades of red. The dark color of red wheat arises primarily from materials present in the seedcoat, but it also is influenced by the texture of the endosperm as well as by the nature of the pericarp. Wheat kernels vary in texture - soft, semihard and hard. A normally developed soft kernel has a soft, meanly or starchy endosperm.
The tissues of the
pericarp form a thin protective layer over the entire kernel. The endosperm
fills the interior of the grain, except for the embryo.