Agriculture Reference
In-Depth Information
in serious lodging (Figure 1.20b). A solution to both problems is to lower the panicle height in the
canopy (Figure 1.20c). Such adaptations may be relevant to other rice ecosystems as well as to other
cereals (Khush, 1995).
Peng et al. (2000) reported that during the past three decades, rice production in Asia more than
doubled as a result of the adoption of modern cultivars, increased investments in irrigation, greater
use of fertilizer, and some expansion in cultivated area. Peng et al. (2000) also studied the trend
in the yield of rice cultivars/lines developed since 1966 by the IRRI in the Philippines. Regression
analysis of yield versus year of release indicated an annual gain in rice yield of 75-81 kg ha
−1
,
equivalent to 1% per year. The highest yield obtained with the most recently released cultivars was
9-10 Mg ha
−1
, which is equivalent to reported yields of IR8 and other IRRI cultivars obtained in
the late 1960s and early 1970s at these sites (Peng et al., 2000). Peng et al. (2000) further reported
that the increasing trend in yield of cultivars released before 1980 was mainly due to the improve-
ment in GHI, while an increase in total biomass was associated with yield trends for cultivars/lines
developed after 1980. These authors further reported that further increases in rice yield potential
will likely occur through increasing biomass production rather than increasing GHI.
Rice panicle architecture is one of the most important agronomic traits affecting grain yield (Zhu
et al., 2009; Li et al., 2013). The diversity of rice panicle architecture has long been the interest of
many breeders (Zhu et al., 2009). Since the 1980s, many high-yielding
Japonica
rice cultivars with
greater spikelet density than traditional cultivars were bred in northeastern China (Yang, 1984).
Because the vertical angle of the panicle stems of these cultivars is generally <40° at maturity,
they are known as high-yielding potential cultivars or erect panicle cultivars. In comparison, tra-
ditional cultivars have a panicle stem angle that is typically >40° (Xu et al., 2005). These cultivars
are known as curved panicle type. Erect panicle rice cultivars have about 45% more spikelets per
panicle than curved panicle-type cultivars (Zhou et al., 2006).
Wu (2009) reported that there were two breakthroughs in rice breeding in the last century. The
first one was the development of the dwarf rice in the 1960s, which raised over 20% of rice yield per
unit urea. The second one was the development of hybrid rice using three-line or cytoplasmic male
sterile (CMS) system in the 1970s, which added another 20% increment in the average yield (Yuan,
1997). Yuan (1998) reported that rice yield remained almost stagnant between 1970s and 1990s
since the introduction of the three-line system. According to plant physiologists, it is feasible to
increase the rice yield potential to as high as 21.6 Mg ha
−1
if the solar energy is efficiently harvested
and converted (Cao and Wu, 1984; Wu, 2009).
1.2.4.2.1.2 Wheat
The global wheat production in 2009 stood at 685 million metric tons har-
vested from 225 million ha, with an average yield of 3.04 Mg ha
−1
(FAO, 2011). To meet global
demand, wheat production needs to increase to about 900 million metric tons by the year 2020,
with an average yield of 4 Mg ha
−1
(Ortiz et al., 2007). Because there is little scope of increasing
the land area, a major yield increase should come from increased productivity. Wheat production is
constrained worldwide by many biotic and abiotic stresses (Singh et al., 2008; Sharma et al., 2012).
Breeding had played a significant role in the wheat yield improvement in the past and will con-
tinue to be a powerful tool to improve wheat yield in the future. However, genetic yield potential
of a cultivar can be achieved when improved management practices are adopted. Among the crop
management practices, the use of essential plant nutrients, especially N, is fundamental (Fageria,
2009, 2014).
The modification of wheat plant architecture through breeding is another example of ideal
plant type for improving the yield of an important cereal (Byerlee and Curtis, 1988). Wheat yield
has increased in a most noteworthy way during the twentieth century, with an average global
increase of 250% during the past 50 years (from 1 to 2.5 Mg ha
−1
). This is remarkable when one
considers that wheat yields remained practically unchanged during the first half of the century
(Slafer et al., 1994, 1996). Better plant architecture through plant breeding and better manage-
ment practices are responsible for this accomplishment (Calderini and Slafer, 1998).
