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Effects and heat stress tolerance studies in Cotton
By;
Shehzad Ahmad Kang, Department of Plant Breeding and
Genetics, University of Agriculture, Faisalabad, Pakistan.
Corresponding author’s email; shehzadpbg@gmail.com.
Cotton is a major and cash crop of Pakistan because of
source of economy boost up, totally textile industry based
on cotton that improve Pakistan economy and provided maximum
job to human. hirsutum is tetraploid specie which belong to
family Malvaceae and contain 2n=52 chromosomes. This specie
also known by American cotton.
Global warming is the major a biotic stress that occur due
to increase in temperature that severely effecting the plant
germination, vegetative and reproductive growth. Heat stress
often is defined as where temperatures are hot enough for
sufficient time that they cause irreversible damage to plant
function or development. In addition, high temperatures can
increase the rate of reproductive development, which
shortens the time for photosynthesis to contribute to fruit
or seed production. I also will consider this as a
heat-stress effect even though it may not cause permanent
(irreversible) damage to development because the
acceleration does substantially reduce total fruit or grain
yield.
The extent to which heat stress occurs in specific climatic
zones is a complex issue. Plants can be damaged in different
ways by either high day or high night temperatures and by
either high air or high soil temperatures. Also, crop
species and cultivars differ in their sensitivity to high
temperatures.
At higher temperature, when seed sown in soil, the soil heat
up which cause seed injury, rapture the cell membrane,
stored food in seed is loss and embryo will be die. Usually
the delinted cotton seed show negative response to higher
temperature tolerance. Of the different low molecular weight
organic osmotica determined in this study, leaf soluble
proteins, soluble sugars and proline were significantly
tolerance higher temperature stress in cotton crop.
The reduction in maximal emergence of annual crops due to
hot soils can be so pronounced that yield of the economic
product is reduced substantially. This can be a major
problem for cotton crop. Heat stress at emergence is a major
problem in cotton crop if that are sown in the hot
temperature and Plant growth efficiency, photosynthesis
activity reduced due to increase in temperature.
The acceleration of reproductive development by high
temperatures may effect and create problem in flower droping,
boll dropping and boll bursting but not opening. These
problems severely reduced the yield higher temperature
during the vegetative and reproductive stage significantly
reduces crop vigor and yield. The cellular membrane
thermostability (CMT) show indirectly measures integrity of
cellular membranes through quantifying electrolyte leakage.
This also implied that in upland cotton these two traits
were independent of each other, the presence or absence of
heat stress determined their relationship. The differential
ability of cotton cultivars and Hybrids to adjust to CMT
under heat-stressed conditions points towards physiological
adaptation to heat stress or heat Dark respiration is a
continuous process in which mitochondria within a plant's
cells oxidize carbohydrates to create energy. Cotton plants
make more starch during the day than they require for
growth. The excess starch is stored in plant cells'
chloroplasts, where photosynthesis occurs. At night, that
starch is broken down via respiration and other metabolic
processes and used to support new growth, such as cotton
bolls.
The cultivars with the greatest heat tolerance generally
have lower rates of dark respiration and more efficient use
of carbohydrates. If ongoing studies support these
observations, the scientists may be able to use these traits
to improve the cotton breeding program.
The extent of heat stress that can occur in a specific
climatic zone depends on the probability of high
temperatures occurring and their duration during the day or
night. Where global climate change is occurring these
probabilities may not be predicted well based only on
historical records for specific locations. Heat stress is a
complex function of intensity (temperature degrees),
duration and rate of increase in temperature. The magnitude
of heat stress rapidly increases as temperature increases
above a threshold level and complex acclimation effects can
occur that depend on temperature and other environmental
factors.
During the vegetative stage, high day temperatures can cause
damage to components of leaf photosynthesis, reducing carbon
dioxide assimilation rates compared with environments having
more optimal temperatures. Sensitivity of photosynthesis to
heat mainly may be due to damage to components of
photosystem II located in the thylakoid membranes of the
chloroplast and membrane properties (Al-Khatib and Paulsen
1999). More stable membranes exhibit slower electrolyte
leakage. Floral bud development also can be damaged by heat
such that plants do not produce flowers. For cotton, two
weeks or more of consecutive or interrupted hot nights
during the first month after germination caused complete
suppression of floral bud development. In extreme cases the
floral buds become necrotic and die.
Surface and internal tissues of cotton fruit can be damaged
by the combination of high temperatures and intense solar
radiation. High tissue temperatures also can damage cambium
layers in exposed trunks and branches.
It is concluded that degree of heat tolerance in cotton at
germination and later growth stage does not vary. Membrane
thermo stability is a successful measure of heat tolerance
in cotton. Leaf soluble proteins, Heat shock gene influence
when temperature exceed from 30 ˚C and produces heat shock
protein that influences embryogenesis, germination, plant
growth, flowering, pollen development, pollination, fruiting
setting, fruit maturation in heat stress condition. General
response to heat stress involves signaling via redox system;
Ca+2 and plant hormone activate the genomic re-programming
via signal cascade. Proline and soluble sugars are important
adaptive components of heat tolerance of this crop.
Physiological genetic investigation indicates that heat
tolerance traits are polygenic and they are highly
influenced by environmental variation. Heat stress problem
can also be minimizing by cultural practices.
There some morphological traits which tolerant heat stress.
Linted cotton seed because fibrous material present on seed
surface that resist high temperature. Good Plant growth -
plant complete vegetative growth in less time because of
minimum heat stress. Short life span-short duration variety
complete life cycle in less time because less heat stress
effect. Long root length which has good ability to uptake
water and nutrients from the soil service. Hairiness on stem
and leaf that provide partially shade to cell wall, cell
membrane and repel high energy sun rays. Crown red color.
Small leaf area--that resist evaporation due to shortening
of stomata. Leaf orientation enhances the photosynthetic
efficiency and develops tolerance against heat stress.
Yellow pollen color, good pollen viability and
fertilization. Balance macro and micro nutrients in soil.
In 2003 to onward in Pakistan, mostly cotton research
institute actively busy for the development of heat stress
tolerant by using conventional and modern breeding
techniques , there is positively result shown by scientist
i.e.CIM-506,FH-114,BT-886,BT-456,BT-222 And SK-280. as a
result of their collaboration Cotton Breeders released seven
upland cotton lines with superior fiber quality and heat
stress tolerance. Those lines have been picked up by
commercial seed companies and breeders for further
development and majorlly play role to boost up Pakistani
economy.
.
Corresponding author’s email:
shehzadpbg@gmail.com
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