2 Botanical Aspects of Cereals Gras Cereals are cultivated grasses that grow througl out the temperate and tropical regions of the orld. As members of the gramineae (or grass amily) they share the following characteristics but these are developed to different degrees in the various members Vegetative features of grasses 1. Conspicuous nodes in the stem Branching 2. A single leaf at each node. 3. Leaves in two opposite ranks. 4. Leaves consist of sheath and blade 5. Tendency to form branches at nodes and adventitious roots at the bases of node 6. Lower branches may take root and develop into stems as tillers Variation in vegetative features among species may be illustrated by reference to maize and wheat In wheat branches occur only at the base of the main stem or culm, to produce tillers(fig FIG 2. 1 The pattern of branching 2.1)(Percival, 1921). While all tillers have the in the wheat plant ttern of capacity to bear ears, the later formed ones may branching not actually do so; this habit is characteristic of most cereal In maize branches occur higher on the main among cereals in that, on the branches, only the tems and they are much shorter as the internodes female organs develop in the forets and on the do not extend(Fig. 2.2) main culm only male organs develop. The advent Leaf bases are very close together and the leaves itious roots that develop at the base of the main consist almost entirely of blades which surround stem provide support for the aerial parts of the the inflorescence, and the shortness of its stalk plant (Ennos, 1991); in maize they are called leads to branches that are almost entirely infore prop-roots and they are particularly well develope cence.At the tip of the main culm there is also as is appropriate to the large and heavy nature of an inflorescence as in wheat, but maize is unique the aerial parts
2 Botanical Aspects of Cereals Grasses Cereals are cultivated grasses that grow throughout the temperate and tropical regions of the world. As members of the Gramineae (or grass family) they share the following characteristics, but these are developed to different degrees in the various members: Vegetative features of grasses 1. Conspicuous nodes in the stem. 2. A single leaf at each node. 3. Leaves in two opposite ranks. 4. Leaves consist of sheath and blade. 5. Tendency to form branches at nodes and adventitious roots at the bases of nodes. 6. Lower branches may take root and develop into stems as tillers. Variation in vegetative features among species may be illustrated by reference to maize and wheat. In wheat branches occur only at the base of the main stem or culm, to produce tillers (Fig. 2.1) (Percival, 1921). While all tillers have the capacity to bear ears, the later formed ones may not actually do so; this habit is characteristic of most cereals. In maize branches occur higher on the main stems and they are much shorter as the internodes do not extend (Fig. 2.2). Leaf bases are very close together and the leaves consist almost entirely of blades which surround the inflorescence, and the shortness of its stalk leads to branches that are almost entirely inflorescence. At the tip of the main culm there is also an inflorescence as in wheat, but maize is unique FIG 2.1 The pattern of branching in the wheat plant. FIG 2.2 The pattern of branching in the maize plant among cereals in that, on the branches, only the female organs develop in the florets and on the main culm only male organs develop. The adventitious roots that develop at the base of the main stem provide support for the aerial parts of the plant (Ennos, 1991); in maize they are called prop-roots and they are particularly well developed as is appropriate to the large and heavy nature of the aerial parts. 29
TECHNOLOGY OF CEREALS Reproductive features of grasses 1. All stems and branches normally form terminal inforescences 2. Flowers are produced in spikelets 3. Each flower is enclosed between two bracts the lemma and palea (pales or flowering 4. At the base of each spikelet are two glumes (empty or sterile glumes) All cereal inflorescences are branched structures but the type of branching varies. The loose spreading structure found in oats is known as a panicle(Fig. 2.3) The main axis of the panicle, the peduncle bears several extended branches on which the spikelets are attached through short stalks or edicels. Within the spikelet forets alternate (Fig. 2. 4); the two closest to the base are similar in size but forets become progressively smaller towards the Each floret(Fig. 2.5)contains the female organs, a carpel containing a single ovule, with its stigma; and the male parts three stamens each consisting of filament and anther pollen released from the anthers, which split when ripe, FlG 2.3 The oat panicle Reproduced from Poehlman(1987) another plant. The elaborate feathery style has an extensive sticky surface well suited to intercept ing wind-borne pollen. Before the anthers mature udimentary tertiary floret the time of fowering or'anthesis'the pales are foret g corday pened primary floret forced open by the expansion of organs called Palea Lemmo lodicules at their base (lodicules swell as a result of an influx of water). The filaments of the stamens rapidly extend, projecting the opening others outside the pales, allowing the pollen to be shed onto the wind lets contain only one floret. Glumes are mostly insignificant small scales. Rice florets are unlike those of other cereals in having six stamens. Fig 26) In sorghum the situation is complex: infore- scences are panicles but they may be compact or Glume open(Hulse et aL., 1980). Spikelets occur in pairs one is sessile and the other borne on a short FIG 2.4 Spikelet of oat Reproduced from Poehlman(1987) pedicel. The sessile spikelet contains two florets, by courtesy of Avi Publishers, New York
30 TECHNOLOGY OF CEREALS Reproductive features of grasses 1. All stems and branches normally form terminal 2. Flowers are produced in spikelets. 3. Each flower is enclosed between two bracts, the lemma and palea (pales or flowering glumes). 4. At the base of each spikelet are two glumes (empty or sterile glumes). All cereal inflorescences are branched structures but the type of branching varies. The loose spreading structure found in oats is known as a panicle (Fig. 2.3). The main axis of the panicle, the peduncle, bears several extended branches on which the spikelets are attached through short stalks or pedicels. Within the spikelet florets alternate (Fig. 2.4); the two closest to the base are similar in size but florets become progressively smaller towards the tip. Each floret (Fig. 2.5) contains the female organs, a carpel containing a single ovule, with its stigma; and the male parts, three stamens, each consisting of filament and anther. Pollen released from the anthers, which split when ripe, is transferred by wind to the receptive stigma on another plant. The elaborate feathery style has an extensive sticky surface well suited to intercepting wind-borne pollen. Before the anthers mature, the time of flowering or ‘anthesis’ the pales are forced open by the expansion of organs called lodicules at their base (lodicules swell as a result of an influx of water). The filaments of the stamens rapidly extend, projecting the opening anthers outside the pales, allowing the pollen to be shed onto the wind. Rice inflorescences are also panicles but spikelets contain only one floret. Glumes are mostly insignificant small scales. Rice florets are unlike those of other cereals in having six stamens. (Fig. 2.6) In sorghum the situation is complex: inflorescences are panicles but they may be compact or open (Hulse et al., 1980). Spikelets occur in pairs, One is sessi1e and the Other borne On a short pedicel. The sessile spikelet contains two florets, inflorescences. FIG 2.3 The oat panicle. Reproduced from Poehlman (1987) by courtesy of Avi publishers, New yo&. Rudimentary tertiary floret they remain enclosed between the pales but at ned primary floret f‘oret FIG 2.4 Spikelet of oat. Reproduced from Poehlman (1987) by courtesy of Avi Publishers, New York
BOTANICAL ASPECTS OF CEREALS Carpel FIG 2.5 Reproductive organs in an oat floret. Repro Poehlman(1987)by courtesy of Avi Publishers Fertile spikelet Poehlman (1987) by courtesy of Avi Publishers, New York FIG 2.6 Reproducti of a rice floret. Note the six of Avi Publishers d from Pochlman(1987)courtesy one perfect and fertile and the other sterile. The pedicelled spikelet is either sterile or develops male organs only(Fig. 2.7) In barley the type of inflorescence is a spike (Fig.28) It is more compact than a panicle, the spikelets being attached to the main axis or rachis by much shorter rachilla. The rachis is fattened and adopts a zigzag form, spikelets occur in groups of three alternately on the rachis. In six-rowed types all spikelets develop to maturity and each bears a grain in its single foret. In two-rowed pes only the central spikelet in each three develops in this way; the others are sterile. The glumes are very small but the pales fully surround the grain and remain closely adherent to it even fter threshing. The lemma tapers to a long awn which does break off during threshing. Many variants of the barley spike are illustrated by Briggs (1978) FIG 2.8 Spikes of barley, showing: a. the le two- rowed and b The inforescences of wheat, rye and triticale the six-rowed form
BOTANICAL ASPECTS OF CEREALS 31 Poehlman (1987) by courtesy of Avi Publishers, New York. Sterile spikelet Fertile spikelet FIG 2.7 A pair of spikelets of sorghum. Reproduced from Poehlman (1987) by courtesy of Avi Publishers, New York. FIG 2.6 Reproductive organs of a rice floret. Note the six stamens present. Reproduced from Poehlman (1987) courtesy of Avi Publishers, New York. one perfect and fertile and the other sterile. The pedicelled spikelet is either sterile or develops male organs only (Fig. 2.7). In barley the type of inflorescence is a spike (Fig. 2.8). It is more compact than a panicle, the spikelets being attached to the main axis or rachis by much shorter rachillas. The rachis is flattened and adopts a zigzag form, spikelets occur in groups of three alternately on the rachis. In six-rowed types all spikelets develop to maturity and each bears a grain in its single floret. In two-rowed types only the central spikelet in each three develops in this way; the others are sterile. The glumes are very small but the pales fully surround the grain and remain closely adherent to it even after threshing. The lemma tapers to a long awn which does break off during threshing. Many variants of the barley spike are illustrated by Briggs (1978). The inflorescences of wheat, rye and triticale FIG 2.8 Spikes of barley, showing: a. the two-rowed and b. the six-rowed forms
TECHNOLOGY OF CEREALS FIG 2.9 Spikes of A. wheat and B rye. Wheat may be awned(bearded)(ii)or awnless (i) are also spikes with spikelets alternating on a are many different species belonging to several rachis, each spikelet however contains up to six different tribes(see Fig. 2. 25) and no generaliza forets(Fig. 2. 9). tions about their inforescences are possible( details It is unusual for all six forets in a spikelet to of most are given in hulse et al., 1980 ) Pearl be fertile and those at the extremes of the millet has a spike which may be anything between inflorescence may bear only one or even no fertile a few centimeters to a metre long. It is densely forets. Variants of wheat spikes are illustrated packed with groups of 2-5 spikelets, surrounded by Peterson(1965). As in oats the grains in the by 30-40 bristles(Fig. 2. 11). Florets may be wo basal forets are the largest. Those in the bisexual or male only centre of the spike are larger than those at In maize the male spikes occurring at the top the extremes(Bremner and rawson, 1978). The of the culm bear spikelets in pairs, one being variation in size occurs as a function of the ability sessile, and the other pedicellate. Both types of each grain to compete for nutrients but also contain two forets, each with three anthers. The of the period of development, the earliest to entire male inflorescence is known as the tassel flower being those in the basal forets of the (Fig. 2. 2). On the female inflorescences the central spikelets(Fig. 2.10) spikelets again carry two florets but only one is Millets are an extremely diverse group there fertile, the upper functions while the lower one
32 TECHNOLOGY OF CEREALS FIG 2.9 Spikes of A. wheat and B. rye. Wheat may be awned (bearded) (ii) or awnless (i). are also spikes with spikelets alternating on a are many different species belonging to several rachis, each spikelet however contains up to six different tribes (see Fig. 2.25) and no generalizaflorets (Fig. 2.9). tions about their inflorescences are possible (details It is unusual for all six florets in a spikelet to of most are given in Hulse et al., 1980.) Pearl be fertile and those at the extremes of the millet has a spike which may be anything between inflorescence may bear only one or even no fertile a few centimeters to a metre long. It is densely florets. Variants of wheat spikes are illustrated packed with groups of 2-5 spikelets, surrounded by Peterson (1965). As in oats the grains in the by 30-40 bristles (Fig. 2.11). Florets may be two basal florets are the largest. Those in the bisexual or male only. centre of the spike are larger than those at In maize the male spikes occurring at the top the extremes (Bremner and Rawson, 1978). The of the culm bear spikelets in pairs, one being variation in size occurs as a function of the ability sessile, and the other pedicellate. Both types of each grain to compete for nutrients but also contain two florets, each with three anthers. The of the period of development, the earliest to entire male inflorescence is known as the tassel flower being those in the basal florets of the (Fig. 2.2). On the female inflorescences the central spikelets (Fig. 2.10). spikelets again carry two florets but only one is Millets are an extremely diverse group, there fertile, the upper functions while the lower one
BOTANICAL ASPECTS OF CEREALS FIG 2 10 Typical profiles of wheat grain weights within a towards the tip of the spikelet, and represented by o, A,t O.( Bremner and Rawson, 1978) aborts(Fig. 2. 12). Each fertile floret contains a single ovary; its style is not of the feathery type typical of most cereals but a long threadlike structure covered in fine hairs which entrap wind-borne pollen. A single ear may contain 800 fertile florets so the same number of stigmas or silks'is present The ear or cob is wrapped by modified leaf sheaths forming husks or shucks and the silks emerge together from the distal open end of the Perhaps the protection afforded by the husk spikelet. earl millet: a spike, b. part of spike enlarged, c protective husk(Fig. 2. 13) FIG 2.11 obviates the need for enclosure of the reproduc tive structures by bracts and pales. these are outbreeding habit fits it admirably for Fl hybrid insignificant in maize and as a result grains are production, whereby yields have been increased not separated one from another on the cob In dramatically through the heterosis or hybrid some cases their mutual pressure imposes an vigour which results angular form on them. While most cereals are dependent to some degree on cultivation for their Life cycle of cereals survival, maize has the ultimate dependence on man since there is no mechanism for dispersal of Although other parts of cereal plants have ts seeds remaining The concentration of the value, particularly in providing feed and bedding sexual organs on separate spikes encourages cross- for livestock, the ripe fruit or grains are economic pollination, which is the norm for maize. Its ally by far the most valuable parts of the plant
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