Agriculture Reference
In-Depth Information
seed yield and year of cultivar release was indicated with a 0.58% average annual increase. The seed
number per plant was the most important contributor to yield gain, with a 0.41% increase per year.
A 33% increase in the photosynthetic rate, 10.6% increase in plant dry weight and 19.0% increase
in harvest index were found, while LAI decreased by 17.3%. Jin et al. (2010) also reported that in
modern cultivars, plant height was reduced, which gave resistance to lodging, with the lodging score
dropping from 3.2 in 1951 to 1.0 in 2006. Plant resistance to disease and pest infestation were also
improved. Furthermore, yield stability was increased over years, which could be attributed to the
stable pod production across different environments.
1.2.4.2.1.5 Peanut
Peanuts also known as groundnuts (
Arachis hypogaea
L.) are grown in the
temperate and tropical climates. It is one of the world's most important oilseeds crops, along with
soybean, cottonseed, rapeseed, and sunflower. Although originating in South America, the vast
majority of peanut is produced in Asia and Africa. Approximately 94% of the peanut is produced
in the developing countries, mostly under rainfed conditions (Dwivedi et al., 2003). There are many
biotic and abiotic stresses to peanut production; these include drought, low and high temperatures,
low fertility, diseases, and insects (Wynne and Gregory, 1981; Knauft and Wynne, 1995; Dwivedi
et al., 2003). Genetic improvement and adopting adequate management practices have contributed
significantly in peanut yield increase. However, there is a big gap in yield among developed and
developing countries (Dwivedi et al., 2003).
Over 276 peanut cultivars were released between 1920 and 2000 for cultivation in various coun-
tries in Asia, Africa, and the Americas. Each has a specific adaptation to its respective region of
production and cropping system (Dwivedi et al., 2003). A yearly genetic gain of nearly 15 kg per
hectare has been reported for large-seeded Virginia type cultivars released from the 1950s to the
1970s in the United States (Mozingo et al., 1987). The higher-yielding cultivars developed during the
1950s, 1960s, and 1970s had an average yield increase of 3.4%, 10.2%, and 18.55, respectively, over
the standard NC 4. However, since the 1970s, there has been increased emphasis on improving the
pest resistance and quality traits so that the yield potential of cultivars released since that time has
not surpassed those of the highest-yielding cultivars released during the 1970s (Dwivedi et al., 2003).
1.2.4.2.1.6 Cotton
Alteration of plant architecture in narrow-row cotton using management
and genetic strategies to improve light penetration into the canopy and increase crop yields (Reta-
Sanchez and Fowler, 2002) and N use efficiency. The modification of plant architecture such as
reduced plant height, short branches, and modified leaf shape increased light penetration into the
canopy. However, certain characteristics were more efficient in modifying light distribution into the
canopy. Kerby et al. (1980) proposed that cotton plants with a combination of normal-type leaves
near developing bolls and erect mutant-type leaves at the top of the canopy could be more efficient
in increasing production and use of assimilates in narrow row cotton. Reta-Sanchez and Fowler
(2002) reported that plants with modified leaf shape at the upper part of the canopy and normal
leaves at the medium and lower part of the canopy increased light availability only at node 16. This
behavior suggests the necessity of an earlier and greater canopy modification using other plant char-
acteristics such as short branches (Kerby and Buxton, 1981) and modified leaf shape (Kerby et al.,
1980; Wells et al., 1986; Peng and Krieg, 1991). Reta-Sanchez and Fowler (2002) also reported that
the combination of leaf shape, reduced plant height, and short branches gave a greater light penetra-
tion through the canopy than the control. These authors further reported that plant with reduced
plant height, short branches, and modified leaves grown at 97,000 plants ha
−1
reached high values of
light interception (90-97%), with LAI ranging from 3.7 to 5.2.
Bridge et al. (1971) and Bridge and Meredith (1983) reported that yield gains due to the genetic
improvement of cotton averaged 10.2 and 9.5 kg ha
−1
year
−1
since about 1910 in the United States.
These yield advances have been accompanied by higher lint percentages, smaller seed bolls, and
higher micromere values (Fageria et al., 2006). Wells and Meredith (1984) indicated that the major
