Identification and management
By M. Mithal Jiskani, Assistant
Professor (Plant Pathology),
July 02 - 08 , 2001
Sindh Agriculture University, Tandojam.
Cotton is one of the most important fiber and cash
crops of Pakistan, which earns foreign exchange for the country. The
crop has maximum area in Punjab followed by Sindh and very negligible
in NWFP. The yield per hectare of seed cotton in Punjab is more to
that of Sindh province. On a whole, cotton is a major crop in parts of
African tropics, Australia, China, Egypt, India, Mexico, Pakistan,
Soviet Union, Sudan, United States, and warmer regions of central and
South America.
Archaeologists and historians believe that cotton
existed 5000 years ago. Mohanjo-Daro was nature place of cotton, where
the people were knowing the arts of spinning and weaving. Cotton lint
was separated from seed on charkha (a kind of hand cranked roller gin)
and the fibers processed in to fabrics with drop spindles and
primitive looms. The quality of the textile produced has been
excellent (Bhatti and Soomro, 1996 and Khoso, 1992). The history of
'cotton crisis' is also as old as its cultivation. Following poem of
Shah Abdul Latif, a saint poet of Sindh can be quoted as first example
(during 1689-1752 AD).
In the midst of the trees no cotton plants are:
So here are no spinners. The empty bazaar
Has ensalted my heart; Foolish girl, in your brain.
Translated by: H. T. Sorely (1938)
The second example regarding cotton diseases was
quoted in Taxas Agricultural Experiment Station Bulletin No.4 (1888).
Palmel studied and wrote about root rot of cotton (Anonymous, 1981).
The struggle against cotton diseases continued up to date. It had been
revealed that this crop was subjected to more than 60 diseases
(Anonymous, 1981). The diseases reduced the yield and brought about
heavy losses. The work carried out so far in Pakistan shows that
seedling rot or wilt, root rot, boll rot, anthracnose, different types
of leaf spot diseases, premature opening of bolls (Tirak), stunting
and reduction in size of leaves, some nematode species, bacterial
blight (angular leaf spot and boll rot), leaf curl and stenosis of
cotton, found causing damage to the crop (Kamal and Moghal, 1968;
Hafiz, 1986 and Jiskani, 1992 and 1999). Such diseases are injurious
in some areas, in some years and on some plant parts. The magnitude of
disease damage depends up on the environment and cultivar.
The crop record revealed that root and boll rot
diseases of cotton were considered as most severe and destructive, but
since last decade, cotton leaf curl virus (CLCV) found to be most
important disease. This disease was first time recorded in 1967 at
Multan on cotton plants. In Sindh, this disease was first reported
during 1996 at Ubauro, District Ghotki. Now it is reached up to New
Saedabad, District Hyderabad during 1999-2000. It was considered a
minor disease until 1987, but in 1991-92, it infested 35,000 acres and
294,000 acres during 1992-93 causing a huge production and monetary
loss to the nation (PARC, 1993).
However, it is quite difficult to present accurate
estimates of the losses due to diseases. The losses vary from year to
year and from one region to the other. The fields have been found to
show as much as 100 per cent damage in certain cases. Table present
area, production and yield per hectare of cotton crop in Pakistan. The
causes of fluctuations in production may be many more, but cotton
diseases could not be ignored, neglected and or regretted, because
they also cause variable loss time by time to the crop.
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Table:
Area, production and yield per hectare of cotton crop in
Pakistan.
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|
Year |
Area |
Production |
Yield/hectares |
| |
(000 hectares) |
(000 Bales) |
(Kg) |
|
1990-91 |
2,662 |
9,628 |
615 |
|
1991-92 |
2,836 |
12,822 |
769 |
|
1992-93 |
2,836 |
9,054 |
543 |
|
1993-94 |
2,805 |
8,041 |
488 |
|
1994-95 |
2,653 |
8,697 |
557 |
|
1995-96 |
2,997 |
10,595 |
601 |
|
1996-97 |
3,149 |
9,374 |
506 |
|
1997-98 |
2,960 |
9,184 |
528 |
|
1998-99 |
2,923 |
8,790 |
512 |
|
1999-2000 P* |
2,983 |
11,240 |
64l |
|
P:
Provisional, *: Jul.-Mar, Source: Economic Survey, 1999-2000,
Govt. of Pakistan.
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The aim to elaborate all above actual and potential
hazards, damages and losses were determine crop diseases. It is
becoming obvious that: now, it is up to the cotton growers and crop
protectionists, to design and formulate ways or mean to combat all
enemies of the crop, so that the losses may be minimized.
The causes, symptoms, preventive and curative
control measures of some important diseases of cotton, are being
summarized here under and based on the recommendations by Bhatti and
Jiskani (1995 and 1996); Hafiz (1986); Jagirdar and Jagirdar (1980),
Jiskani (1992), Kamal and Moghal (1968) and PARC (1993), for the
benefit of the cotton growers.
Cotton leaf curl virus
Cause: The disease causing virus belongs to
Gemini group.
Symptoms: Upward and downward curling of leaves
accompanied by small as well as main vein thickenings (SVT as well
as MVT) on leaves, pronounced on underside. If a diseased leaf is
viewed from beneath against the light, thickened vein found darker
green and opaque than the normal. In extreme but not in frequent
cases, formation of the cup shaped or leaf laminar (veins) out
growth called "enation" appears on the back or underside of
the leaf. The newly produced leaves are small, excessively crinkled
and curled at the edge. The primary stem often tends to grow taller
than normal. The enter-nodes being elongated and irregularly curved
but sometimes the whole plant is stunted. The flowers checked in
growth and become abortive. Bolls remained small in size and failed to
open. All parts of badly hit plants are very brittle and ready broken.
Transmission: The disease transmitted by
feeding of the white fly, Bemisia fabaci with in 6.5 hours. A
single female, carrying virus, can infest many plants. It may also be
kept in mind that white fly is known to survive on as many as 53 host
plant species, and is responsible for transmitting 23 crop diseases in
region. At global level, white fly infests 600 different plant
species.
Boll rot
Cause: Aspergillus niger, Fusarium
oxysporium, Rhizopus oryzae (belongs to fungi) and a bacterium Xanthomonas
malvacearum reported as predominant causes of boll rot.
Symptoms: The research studies revealed that
four different types of symptoms may occur, which can be distinguished
on the basis of their specific casual agent, as below:
Black boll or Aspergillus rot: Affected bolls
start losing green color altogether, become pinkish brown and finally
sooty black due to over growth of fungus.
Rhizopus rot: Infected portions become grayish
along with softening of internal tissues. The fungus grows abundantly
and covers many bolls under moist conditions.
Fusarium rot: The bolls become dried with color
assuming reddish and brownish tinge and showing dry and white fluffy
fungal growth inside the bolls on opening.
Bacterial or Xanthomonas rot: Water soaked
areas developed on the bolls giving out gummy substance and foul
smell.
Perpetuation: Diseased plant debris and seeds
carry over the disease causing organisms. Humid conditions after rain
and speedy wind favour the spread and severity of boll rot. Sometimes,
different boll worms also play a role, to transmit disease, from
infected to healthy bolls/ plants.
Angular leaf spot or bacterial blight
Cause: A bacterium Xanthomonas malvacearum
cause angular leaf spot or bacterial blight or boll rot of cotton.
Symptoms: The disease attacks all parts of the
plant above ground level, at all stages, causing seedling rot, angular
spots on leaves and stems (sometimes called black arm disease)
and boll rot (as already mentioned). In initial stages, water
soaked lesions (spots) appears on lower surface of the leaves.
Later on, these spots increase in size, turn brown to black, becoming
necrotic, angular and are visible on the upper surface. These spots
vary in size and then coalesce, forming irregular patches and giving
rise to gummy bacterial exudate. Heavily infected leaves turn yellow
and drop down. The disease produces elongated black lesions on the
stem, branches and petioles. Stems show cracking and gummosis (gummy
substance) and are easily broken, even by wind. Bolls are marked
by the appearance of water soaked lesions, which are dark brown to
black, invariably sunken, results in reduced boll size, poor
production of lint and loss in viability in seed.
Perpetuation: Infected seeds and plant debris
act as a source of infection, but can also spread through irrigation
water, rain splashes, wind, insects and contaminated field implements.
Root rot
Cause: The fungi Macrophomina phaseoli,
Rhizoctonia spp., Fusarium spp. etc. are predominantly
isolated from diseased roots.
Symptoms: The disease affects the roots
exclusively, causing pre-wilt shedding of leaves, yellowing of
foliage, disintegration of root tips, discoloration and shredding of
roots, exudation of drops of smelly liquid from the rotted plant
parts. Mostly, wilting of shoots occur in only few diseased plants,
which ultimately results in the death of entire plant. This disease
generally appears, when plants are about 4-6 weeks old and continue up
to boll formation. Diseased plants can be easily pulled out of the
soil, appears in patches. Roots and root-lets show rotting, yellowing,
disintegration and shredding.
Perpetuation: Disease causing fungi are soil
borne, hence it may be claimed that both (fungi and soil) factors are
responsible.
Minor diseases
Anthracnose, leaf spots (caused by different fungi), sooty
mold, stenosis, stunting and premature opening of bolls (Tirak) etc.
are also reported to cause disease in cotton and damage to the crop,
which may reduce the yield, sometimes very low and sometimes so much.
Management
Following disease management practices may help to
save the crop from all above major and minor diseases of cotton.
• Cultivation of disease resistant variety is
only safe measure of all different diseases.
• Eradication including collection and burning of plant debris may
help to control seedling root and boll rots as well as bacterial
blight, because disease inoculum may also survive through plant
debris.
• Deep plowing with short duration, at least two months before
sowing, help to control seedling and root rot.
• Proper land levelling is a preventive measure against seedling and
root rot.
• Use of healthy seed, acid delinting and chemical seed treatment
minimize the disease incidence of seedling, root and boll rots as well
as bacterial blight.
• Crop rotation with non-host i.e. sowing of sorghum for 3 to 4
years is useful for control of seedling and root rot.
• Mixed cropping with kidney bean or fodder and leguminous crops
saves the cotton crop from root rot.
• Proper use of irrigation and chemical fertilizers improves the
disease resistant power in cotton plants.
• Early sowing of crop is preventive measure for control of boll
rot.
• White fly transmits cotton leaf curl virus from diseased plant to
healthy one, whereas, different cotton boll worms may play a role to
transmit the boll rot diseases, hence white fly and boll worms must be
controlled.
• Lady's finger (okra), sun kukra, china rose, thorn apple (dhatura),
mint (podina), karund, cucurbits (especially water melon),
beans, tomatoes, tobacco, chilies, soy bean, sun flower, cow peas, egg
plant (brinjal), holly hock (gul-e-khera), zinnia,
sesame, Ak (Calotropis), shesham, citrus species etc. are
recorded as alternate host plants of cotton leaf curl virus as well as
white fly, and also some of them are alternate host of boll worms.
Therefore, they all must be eradicated before and during cotton
cropping season. Cotton growing zones may play a better role for this
purpose.
Meanwhile, use of proper cotton production
technology as per recommendations of agricultural experts/researchers
are economical and most effective for cotton disease management. It is
out look and responsibility of the cotton growers to adopt the modern
cotton production technology and play a role for the development and
prosperity of the country.
Reference
1. Anonymous. 1981. Compendium of cotton
diseases. Edited by: Q. M. Watkins. American Phytopathological
Society.
2. Bhatti, I. M. and A. H. Soomro.1996. Agricultural inputs and
field crop production in Sindh. Agricultural Research Sindh, Hyderabad.
3. Bhatti, I. M. and M. M. Jiskani. 1995. Cotton leaf curl
virus. Monthly "Modern Agricultural Research", Agricultural
Research Sindh, Hyderabad. 3(7): 1-3.
4. Bhatti, I. M. and M. M. Jiskani. 1996. Modern Agricultural
Guide. Agricultural Research Sindh, Hyderabad.
5. Hafiz, A. 1986. Plant diseases. PARC, Islamabad.
6. Jagirdar, S. A. P. and H. A. Jagirdar. 1980. Cotton diseases
in Sindh. Agricultural Research Institute, Tandojam.
7. Jiskani, M. M. 1992. Diseases of cotton and their control.
Monthly "Sindh Agriculture", Agricultural Extension Sindh,
Hyderabad: 2(8): 9-13.
8. Jiskani, M. M. 1999. A brief outline "THE FUNGI"
(Cultivation of mushrooms).
9. Kamal, M and S. M. Moghal. 1968. Studies on plant diseases
of South West Pakistan. Agricultural Research Institute, Tandojarn. 10.Khoso,
A. W. 1992. Crops of Sindh. 5th Edition. 11.Sorely, H. T. 1938. Shah
Abdul Latif of Bhitt. 12.PARC. 1993. A research compendium on cotton
leaf curl viral disease and its Vector-White fly.
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