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Cotton reddening: A red signal to Pakistan Economy
Cotton crop is
the main stay of Pakistan economy. It occupies a pivotal
position in the national economy and plays important
role in the economic progress of the country. It is not
only a sole source of the survival of a millions of
farmers’ families in Pakistan but it also contributes a
major share of approximately 65% in foreign exchange
earnings. Therefore, cotton is known as ‘white gold’ of
Pakistan economy.
The growers of Pakistan are suffering huge losses in
yield and quality of cotton crop due to various diseases
and unaccepted maladies every year. During the previous
decade, cotton production experienced many ups and
downs. It was at its lowest during the period when it
passed through its most serious crisis in the form of
cotton leaf curl virus (CLCuV). Recently, a new
mysterious malady, commonly known as ‘reddening’ or
‘red-leaf-disease’ is now emerging very speedily and
become a serious problem in various cotton growing belts
of Pakistan especially in Sindh. The PCCC also observed
the new emerging problems like stunning of cotton
growth, wilting of the plants and reddening of cotton
leaves endangering the cotton production in Sindh.
Thousand acres of cotton crop were found to be affected
by this complex in major cotton growing belts of Sanghar,
Mirpurkhas Nawabshah, Khairpur, Naushero Feroze and
other districts of Sindh.
This mysterious cotton disorder is known as bronze wilt
and was first appeared in the USA, Brazil, Argentina,
and Bolivia during the hot summers of 1995, 1996, and
1998. Similar disease symptoms were seen in peanuts and
soybeans.
Because of its symptoms, it has called ‘reddening’ or
‘red-leaf-disease’ in Pakistan, “copper top,” “early
foliar decline,” “sudden wilt” and “phloem wilt” in the
U.S. and “red leaf,” “red wilt” and “anthocyanosis” in
other countries.
The disease, which causes death of feeder roots and
deficiencies of phosphorus and potassium in tissues,
took its toll on cotton grown in Arkansas, Georgia,
Louisiana, Mississippi, South Carolina, and Texas.
In 1998, cotton losses in Georgia were valued at nearly
$25 million. Even Pima varieties of cotton grown in
Arizona and California showed yield losses that year.
SYMPTOMS AND CAUSES
The common symptoms have included wilting, reddening of
stems and leaves, leaf and fruit shed, and a higher
temperature of the leaf tissues and the plants grow
poorly and may produce no bolls. Bronze wilt is related
to restricted water transport in the plant and manifests
itself with numerous symptoms.
One of the first and prominent symptoms to appear is the
bronze or red color on the first fully expanded leaves
near the top of the plant. In the upper part of the
plant, there will be some rugate leaves, which means the
area between the veins, will be raised, giving the leaf
a rough appearance. The stems turn red all the way to
the top of the plant, giving an appearance similar to
that following an application of the herbicides. Another
very noticeable characteristic symptom was the absence
of flowers or squares. However, the affected plants can
have bolls. Bronze wilt plants will be stunted. Usually
plants devoid of fruit due to lygus damage will be tall
due to not having a sink for the photosynthate produced.
This is just opposite the effect shown on bronze wilt
plants. The diseased plants will wilt and may eventually
die.
The exact cause of the disorder has yet to be unknown.
Both biotic andabiotic factors have been proposed as
possible causative agents. Generally it has been
believed that plausible cause of bronze wilt is high
concentrations of certain strains of Agrobacterium spp.
(Agrobacterium tumefaciens), a soil and seed bacterium,
that cause damage to the secondary roots. Differences in
resistance to bronze wilt are influenced by cultivar,
environment (temperature, light intensity, and
photoperiod), production practices and abiotic stresses
(high temperature and water stress), soil type and
fertility, relative nitrogen content of fertilizer and
fertilizer ratio of phosphorous and potassium. Potassium
deficiency frequently has been mentioned as a primary
suspect. Plant age, fruit set and load, earliness in
fruiting and maturity, and high yield potential also
effect symptom severity.
Bronze wilt flourishes when daytime temperatures are
above 95 °F for 2 to 3 weeks, which enhances foliar
bronze wilt symptoms, and necrosis and browning of fine
roots. Necrosis of fine roots reduces the ability of the
plant to actively take up water and nutrients, such as
potassium and iron. Water availability to the plant is
very critical, bronze wilt is more severe under drought
conditions and heat stress.
MANAGEMENT OPTIONS
No doubt, the complete and reliable solution to this
problem is resistant cotton varieties. Though our
agricultural research institutes have evolved more than
50 registered cotton varieties up to 2003, but
unfortunately most of them are susceptible to this
malady. Consequently the government has allocated Rs24.1
million for managing reddening malaise of cotton leaves,
but a period of some twelve long years is required to
evolve a new cotton variety. Currently, there seems to
be no variety fully resistant to this disease, therefore
government needs to be heedful and careful for the
preventive measures against this disease for the next
crop.
There is basically no cure. If any of the varieties
known to show the symptoms are planted, they must never
be allowed to stress. It appears that the incidence of
this problem is worse when the plants have a boll load
and are put under a hot-dry stress or just a heat
stress. Perhaps low potash can influence this as well.
Only the variety selection is the best means of
prevention.
Avoid planting the susceptible varieties. Planting
varieties that have no known history of bronze wilt is
the easiest way to reduce losses from this disease.
In the absence of disease resistant varieties, the
immediate solution for reducing the severity of disease
lies in the adoption of modern agricultural techniques
and management practices. Deep plowing, clean
cultivation, sowing at recommended time, seed treatment
with proper fungicide, adequate manuring, proper plant
spacing, judicious irrigation, and balanced and timely
use of fertilizer can reduce the risks of disease.
Bronze wilt severity is directly proportional to
nitrogen fertilizer rate and inversely related to
phosphorus rate, hence application of balanced
fertilizer of nitrogen, phosphorus, potassium and
sulfur, are important to reduce bronze wilt severity.
Use of potassic fertilizers and foliar application of
micronutrients, especially zinc, boron and copper at
recommended rate and at specific growth stages, as
practically experienced by the writer during several
field experiments, have proved quite beneficial for
reducing the malady.
If susceptible varieties are planted, the following
cultural practices may make the disease less severe:
Plant at recommended time to avoid high soil
temperatures during fruiting.
Balanced and timely use of fertilizers, especially use
no more nitrogen fertilizer than is appropriate to
achieve desired yields.
When soil tests indicate deficiencies, fertilize with
phosphorus, potassium and sulfur before planting.
Prevent water stress by irrigating sufficiently.
Susceptible cultivars can still suffer considerable
losses in spite of good cultural practices if climatic
conditions favour the disease.
Diseases are an annual problem that reduces yields,
quality and economic returns to producers. Research is
needed to provide a better understanding of factors that
influence cotton diseases and to develop management
strategies that reduce economic losses. Our cotton
scientists are aware of the problem and are working on
it. However it must be remembered that there is nothing
to do to control the problem once observed.
By
Mohammad ali
khaskheli |
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Pakissan.com;
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