Arendt und Zannini - 2013 - Cereal grains for the food and beverage industries

Rice 119
annual species, under favourable environmental conditions, O. sativa may
grow more than once per year. Similarly to other taxa belonging to the tribe
Oryzeae, rice may be classified as semi-aquatic plants, although extreme
variants are grown not only in deep water (up to 5 m) but also on dry land
(Chang, 1985). In Africa, the rice cultivated belongs to the species O. glaberrima
Steud. that differs from O. sativa mainly in its lack of secondary
branching on the primary branches of the panicle. It is also a strictly annual
plant (Chang, 1965).
The majority of commercial rice varieties range from 1 to 2 m in
height; however, the rice plant varies in size from dwarf mutants (only
0.3-0.4 m tall) to floating varieties (more than 7 m tall). The vegetative
structures consist of fibrous roots, culms (made up of series of nodes and
internodes) and leaves that consist of a leaf sheath and leaf blade (lamina).
The leaf sheath is continuous with the blade. It envelops the culm
above the node in varying length, form and tightness (Chang, 1965). It
supports the plant during the vegetative growth, being photosynthetically
active and acting as a storage site for starch and sugar before heading
(Chang, 1964). The panicle is composed of a panicle neck node (base),
rachis (axis), primary and secondary branches, pedicles, rudimentary
glumes and spikelets (or flower). Panicle shapes range from compact to
intermediate to open. Compact shape is preferred in the modern cultivation
because this type has generally been associated with higher yields
(IBPGR-IRRI, 1980).
The duration of growth for cultivated rice varies from 80 to 280 days and
can be generally divided into early (80-130 days), intermediate (130-160
days) and late (160-t- days) maturing cultivars (Yoshida, 1981). In the rice
plant, three growth phases can be distinguished: the vegetative phase -
when the plant begins to partition assimilation to the developing panicle;
the reproductive phases with panicle (flowering) development; and the
ripening or grain-filling phase which begins after anthesis and ends at maturation
(Tanaka, 1965).
Different environmental factors influence the development of the rice
plant, such as temperature, day length, nutrition, planting density and
humidity (Nemoto et ai, 1995). Although normally a cereal of the wetland,
rice can be grown either on dry land or under water. The common practice
of flooding the paddy fields has been adopted as a means of irrigation and
also to control weeds (Kent and Evers, 1994). The Malayan word padi
means ‘of rice straw’, but the anglicized form of the vtord,paddy, is used to
refer both to the water-covered fields in which rice is grown and also to the
harvested rice, with attached husk or hull. Rice can be cultivated in temperate
and tropical areas, and in cool and warm regions. It is grown, for
example, in hot, wet climates, as well as in the foothills of the Alps, up to
1220 m in the Andes of Peru, 1830 m in the Philippines and 3050 m in India.
This wide adaptability of the rice plant partially explains its importance as
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