Agriculture Reference
In-Depth Information
in population density, water consumption is expected to increase 35-60%
over the next several decades [20] and the agricultural demand for water
will be competing with the increased demands of the industry and domes-
tic sectors [6]. At present, 8% of the population, primarily in West Asia
and North Africa (Libya, Egypt, Saudi Arabia, Iran, Iraq, Pakistan, and
Afghanistan), and in South Africa are under intense drought conditions
where water is the major constraint in food production [39]. Several coun-
tries are entering water shortages including populated regions like India
and China, as well as Ghana, Ethiopia, Somalia, Kenya, and Zaire, which
accounts for approximately 7% of the world population that must improve
water access and utilization efficiency to meet future water requirements.
Analyses have shown that the water demand for agricultural purposes can
be improved by increasing the effi ciency and expansion of irrigation sys-
tems [40]. In addition, breeding for characteristics that limit water loss and
improve water use effi ciency in crop plants will also signifi cantly improve
the ability of the water-deprived societies to provide food for their grow-
ing populations.
To provide varieties that are better suited for drought conditions, a host
of molecular and physiological adaptations that improve water use effi -
ciency can be selected for, such as superior hormonal physiology, increase
in stomatal conductance, osmotic adjustment, as well as improved root
architecture, to achieve higher yields under dry conditions. One of the
simplest ways to improve yield in water-deprived systems is to gain ac-
cess to water reserves in deep soil by breeding for increased root depth
and distribution. It has also been noticed that selecting varieties that put a
greater portion of energy into reproductive organs over vegetative produc-
tion increases the harvest index of grains [41]. Unfortunately, identifying
genetic targets in respect to drought resistance has been diffi cult. Better
estimates for yield under stress can be reached by identifying varieties in
water stress environments that are free of undesirable traits. This method
of selection will likely involve a genetic shift toward dehydration avoid-
ance, resulting in advantageous physiological changes such as early fl ow-
ering, decreased plant height, and leaf area [42]. In general, these cultivars
may have a lowered yield potential, compared to modern well-watered
varieties, but are better able to adapt given water stress, allowing for yield
improvements in dry regions or where dry spells occur.
