Agriculture Reference
In-Depth Information
leveled lands; water accumulate in the fields or plots during most of the crop-growing cycle and
most of the cases have controlled irrigation (Fageria et al., 2011a). Soils of the lowland rice are
saturated during most of the growth cycle.
Increasing rice yield is the perpetual goal of rice breeding programs in most rice-growing
regions or countries because of the growing food demand caused by population growth and reduc-
tion of areas devoted to rice production. Rice breeding has significantly increased in the past few
decades. Breeding for both types of rice (upland and lowland) has been successful in improving the
yield and grain quality (Peng et al., 2008). A typical example of breeding semidwarf high-yielding
cultivars comes from IRRI. The tall tropical cultivar “peta” from Indonesia and the subtropical
semidwarf cultivar “De-geo-woo-gen” from Taiwan were crossed to produce the semidwarf IR 8,
which produced a record yield of 11 t ha
−1
and responded well to N rates up to 150 kg ha
−1
at several
locations in tropical Asia (Chang, 1976). Dissemination of this improved plant type throughout
Latin America was initiated in 1968 by the Colombian-based program of the International Center
of Tropical Agriculture together with National Research Institutes in the region (Cuevas-Perez et al.,
1995). Scientists at IRRI and several national breeding programs combined most of the desired fea-
tures in the improved plant type, including reduced height (about 100 cm), leaf erectness, short, dark
green leaves, stiff culms, early maturity, photoperiod insensitivity, N responsiveness, and high har-
vest index (Yoshida, 1981). The wide adoption of IR 8 and other high-yielding cultivars, such as IR
20 and IR 22, made it possible for the semidwarf cultivars to become important cultivars in Brazil,
Colombia, Peru, Ecuador, Cuba, Mexico, Indonesia, Malaysia, the Philippines, India, Pakistan,
Bangladesh, and South Vietnam. By 1972-1973, semidwarf cultivars occupied a large part of the
area planted to high-yielding rice cultivars, including about 10% of the world's total area and 15%
of the area in tropical Asia (Chang, 1976). Today, high-yielding semidwarf cultivars predominate in
most lowland rice-producing areas.
Work is in progress at IRRI and many other international and national research centers to fur-
ther improve plant type, grain quality, and pest resistance (Khush, 1995). Figure 1.20a-c shows the
development of modern high-yielding rice cultivars from formerly prevalent traditional cultivars,
and ideotype rice plants of the future. As shown in Figure 1.20b, the new plant type for irrigated
rice was designed to attain yields of 12-13 t ha
−1
. Yield improvement beyond 12 t ha
−1
will require
new plant architectures because of two major problems: the leaves responsible for grain filling
will be shaded beneath a dense cover of panicles, and the immense weight of panicles will result
FIGURE 1.20
Traditional old (a), modern high-yielding (b), future ideotype (c), and plants of lowland rice.
(Adapted from Fageria, N. K., V. C. Baligar, and R. B. Clark. 2006.
Physiology of Crop Production
. New
York: The Haworth Press. With permission.)
