origin of dwarfing genes in many wheat cultivars suitable for temperate countries.
The Norin 10 dwarfing genes are now present in [70 % of current commercial
wheat cultivars worldwide (Evans 1998; Hedden 2003).
1.3.1.1 High-Yield Varieties
Although the term Green Revolution originally described developments for rice
and wheat, high-yielding varieties (HYVs) have since been developed for other
major food crops important in developing countries, including sorghum, millet,
maize, cassava, and beans.
HYVs were characterized by (a) high-yield, improved varieties of crops that
give us more yields per hectare, (b) dwarfness, due to short height, and plants are
stronger and hence can withstand strong winds. The problem of lodging is less in
these improved varieties. (c) Better response to fertilizers, this means that when
fertilizers are supplied to HYV and their yield increases substantially but is not so
in case of traditional varieties, and (d) early maturation, it takes less time for
maturing; as a result, some additional crop can be raised in the spare time thus
saved. However, there are also disadvantages of using HYV. For example, the
dwarfing of HYVs produce yields less fodder than the tall, traditional varieties of
crops that require higher inputs such as more water and more fertilizers as compared to the traditional varieties of crops; weeding is more frequent, needs a
continuous use of pesticides, and is generally more susceptible to diseases than the
traditional varieties (Dalrymple 1974, 1986).
Even with its drawbacks, the HYVs were adopted quickly by the characteristics
they possessed. By 1970, about 20 % of the wheat area and 30 % of the rice area
in developing countries were planted to HYVs, and by 1990, the share had
increased to about 70 % for both crops. Yields of rice and wheat virtually doubled.
It is estimated that between one-third and one-half of the rice areas in the
developing world was grown with high-yielding varieties, in the decade of the
1980s varying from 9 % in Thailand to 78 % in the Philippines, the yield increases
due to these varieties is about 1 ton/ha in irrigated areas and 0.75 tons/ha on
favored upland rice areas (Pinstrup-Andersen and Hazell 1985). The impact was
estimated to be about 10 million tons in the Far East and less than one-half of a
million tons in Latin America for the year 1976/1977 (Pinstrup-Andersen and
Hazell 1985). In the same sense, 27 million tons from production of rice in eight
Asian countries produced 85 % of Asia’s rice in 1980. Another 29 million tons
was added by fertilizers, and irrigation contributed 34 million tons for modern rice
varieties. Higher yields and profitability were characteristics that led farmers to
increase the area of rice and wheat they grew at the expense of other crops. And
with faster growing varieties and irrigation, they grew more crops on their land
each year (Hazell 2002) HYVs play an important role in increasing crop yield due
to their resistance against pests. Ahmad et al. (2007) showed that the main constraints faced by farmers in adopting HYVs were unavailability of seed and lack of
1 Strategies for Sustainable Plant Food Production
5
The Norin 10 dwarfing genes are now present in [70 % of current commercial
wheat cultivars worldwide (Evans 1998; Hedden 2003).
1.3.1.1 High-Yield Varieties
Although the term Green Revolution originally described developments for rice
and wheat, high-yielding varieties (HYVs) have since been developed for other
major food crops important in developing countries, including sorghum, millet,
maize, cassava, and beans.
HYVs were characterized by (a) high-yield, improved varieties of crops that
give us more yields per hectare, (b) dwarfness, due to short height, and plants are
stronger and hence can withstand strong winds. The problem of lodging is less in
these improved varieties. (c) Better response to fertilizers, this means that when
fertilizers are supplied to HYV and their yield increases substantially but is not so
in case of traditional varieties, and (d) early maturation, it takes less time for
maturing; as a result, some additional crop can be raised in the spare time thus
saved. However, there are also disadvantages of using HYV. For example, the
dwarfing of HYVs produce yields less fodder than the tall, traditional varieties of
crops that require higher inputs such as more water and more fertilizers as compared to the traditional varieties of crops; weeding is more frequent, needs a
continuous use of pesticides, and is generally more susceptible to diseases than the
traditional varieties (Dalrymple 1974, 1986).
Even with its drawbacks, the HYVs were adopted quickly by the characteristics
they possessed. By 1970, about 20 % of the wheat area and 30 % of the rice area
in developing countries were planted to HYVs, and by 1990, the share had
increased to about 70 % for both crops. Yields of rice and wheat virtually doubled.
It is estimated that between one-third and one-half of the rice areas in the
developing world was grown with high-yielding varieties, in the decade of the
1980s varying from 9 % in Thailand to 78 % in the Philippines, the yield increases
due to these varieties is about 1 ton/ha in irrigated areas and 0.75 tons/ha on
favored upland rice areas (Pinstrup-Andersen and Hazell 1985). The impact was
estimated to be about 10 million tons in the Far East and less than one-half of a
million tons in Latin America for the year 1976/1977 (Pinstrup-Andersen and
Hazell 1985). In the same sense, 27 million tons from production of rice in eight
Asian countries produced 85 % of Asia’s rice in 1980. Another 29 million tons
was added by fertilizers, and irrigation contributed 34 million tons for modern rice
varieties. Higher yields and profitability were characteristics that led farmers to
increase the area of rice and wheat they grew at the expense of other crops. And
with faster growing varieties and irrigation, they grew more crops on their land
each year (Hazell 2002) HYVs play an important role in increasing crop yield due
to their resistance against pests. Ahmad et al. (2007) showed that the main constraints faced by farmers in adopting HYVs were unavailability of seed and lack of
1 Strategies for Sustainable Plant Food Production
5