Identification and management
By M. Mithal Jiskani
July 16 - 22 , 2001
Rice is one of the leading food crops of the world,
an important staple food and cash crop of Pakistan. It contributes 15
percent to the foreign exchange earnings. Its area under cultivation,
production and yield per hectare (Table) also indicates its
importance. This crop is very suitable, where other crops are not
possible to grow or where Kharif (summer) irrigation water supply is
abundant. According to Cheema et al. (1991) rice prefers 5.0-6.5 soil
pH, and is moderately tolerant to exchangeable sodium percentage (ESP)
in the level of 20-40%. This crop may also tolerate up to 0.40-0.60
percent of white alkali and 0.10-0.20 percent of black alkali in soil
(WAPDA report, 1961). The rice is frequently grown on heavy clay soils
that have an impervious, subsoil layer (hard pan) that limits
drainage, because it requires a constant and plentiful supply of
water. The rice production can be used to reclaim saline soils,
because flooding leaches salts from the soils (Bhatti and Soomro,
1996).
The rice crop is subjected to more than forty
diseases, which are one of the factors, for low yields of rice in the
world (including Pakistan). The diseases may appear at any stage of
the growth and development of plant, attacking the seed sown, root
system, foliage, stalk, leaf sheath, inflorescence and even the
developing grain. The fungi, bacteria, nematode and virus cause
different infectious diseases. Non-infectious diseases may be caused
because of low or high temperature, decrease or increase in different
nutritional elements essential for the crop. Overall, Table present
area, production and yield per hectare of rice crop in Pakistan. The
causes of fluctuations in production may be many more, but the
diseases could not be ignored, neglected and or regretted, because
they also cause variable loss time by time to the crop. These all
diseases are injurious in some areas, in some years and on some plant
parts. All parts of plant are subject to disease and one or more
diseases can occur on virtually every plant and in every field. All
draw attention because of symptoms or signs and generate great concern
because of their effects on the quality and/or quantity of plants,
straw or grain.
According to Kamal and Moghal (1968), Hafiz (1986),
Nyvall (1979), Bhatti and Soomro (1996) and Jiskani (1999), brown
spot, blast, stem rot, bunt, bacterial blight, false smut, ufra and
khaira (zinc deficiency) are sometimes considered important diseases
at various parts of rice growing areas of Pakistan. Therefore
identification, management practices and some other relevant knowledge
of the most important diseases of rice are being summarized, so that
the growers may protect their crop from these diseases, research
workers may decide their future strategies, extension workers may also
to be alert.
Blight or brown spots (Helminthosporium oryzue)
Symptoms: This disease has been recorded all
over Pakistan. Initially small dots or circular eye shaped or oval
spots appear light in colour on leaves. These spots coalesce and
result in linear spots brown in colour. Later on withering and
yellowing of leaves occur. Seed setting also affected and causes
sterility, shrivelling and show rotting and poor germination.
Perpetuation: Diseased seeds, plant debris and
soils help the fungus to survive, while air and irrigation water help
to the fungus for transmitting from diseased to healthy plants.
Control: 1) Use of resistant varieties or
disease free seed in healthy soils, 2) Sanitation and crop rotation,
3) Hot water seed treatment at 54 °C for 10 minutes or with seed
dressing fungicides, 4) Collection and destruction of stubble and
spraying with copper fungicides at right time and 5) Application of
suitable foliar fungicides may help to minimise further dissemination
of the disease.
Bunt of rice (Tilletia barclayana)
Symptoms: This disease also called black or
kernel smut, is generally distributed wherever rice is grown. Diseased
grains are filled with black powder, which can be detected by breaking
them. Only a few grains may be affected wholly or partially in an ear.
If not severely infected, seeds may germinate but seedlings are
stunted.
Perpetuation: The disease causing organism is
soil borne.
Control: 1) Cultivation of resistant varieties,
2) Use of healthy seed, 3) Sowing early maturing varieties, 4) Avoid
high rates of nitrogen fertilizer, 5) Avoid winnowing and threshing of
diseased crop in field, 6) Treat the seed with suitable chemicals
easily available in the market and 7) Collect and burn diseased ear
heads.
Rice blast (Pyricularia oryzae)
Symptoms: Some times this disease refers as
Pyrricularia blight or rotten neck, generally distributed where ever
rice is grown. Small spots appear on leaves, nodes, panicles and
grains and some times on leaf sheaths. The spots begin as small,
water-soaked, whitish, greyish or bluish dots. These spots rapidly
increase and become grey in centre. Brown to black spots also develop
on inflorescence and glumes. In later stages, diseased heads appear
blasted and whitish in colour. Grain development is affected and the
panicles droop.
Perpetuation: The disease perpetuates through
diseased plant debris lying in the field, seed and wild grasses.
Control: 1) Burn and destroy diseased plant
debris and stubble, 2) Early planting, 3) Cultivation of resistant
varieties, 4) Use of healthy seed, 5) Dusting the seed with any one of
the organic mercurial seed dressing fungicides, 6) Spray the crop with
organo-mercurials, 7) Avoid excessive depth application of irrigation
water, 8) Avoid excessive plant population and 9) Control grasses and
other weeds.
Bakanae disease (Fusarium moniliforme)
Symptoms: This disease is also called white
stalk, generally distributed where ever rice is grown. Infected
seedlings are thin, chlorotic, may die before or after transplanting.
In the field, infected plants have few tillers and leaves die in short
time. Live plants have empty panicles. Some infected plants may be
stunted instead of elongated, while the abnormal elongation of these
(infected) plants in seed bed or field is most common symptom of this
disease.
Perpetuation: The disease causing fungus is
seed and soil borne, through which it can survive for a long period. :
Control: 1) Cultivation of resistant varieties
and 2) Seed treatment.
Ufra of rice (Ditylenchus angustus)
Symptoms: The disease has been reported from
Bangladesh, Egypt, India and South Asia. The leaves become yellow and
wither, seedlings die. Brown spots appear on leaves and leaf sheaths.
Stems may also bear spots. These spots become darker brown along with
upper inter-nodes of the stem. Ears may not emerge or may show
swellings and become twisted and distorted. Grains are not formed
usually.
Perpetuation: Diseased plant debris carrying
disease causing nematodes.
Control: 1) Burn the stubble, 2) Grow early
maturing varieties, 3) Use healthy seed and 4) Plough the field
thoroughly after harvest so as to expose the soil to sun-heat.
Bacterial blight (Xanthomonas oryzae)
Symptoms: Water soaked stripes appear along the
margin of leaf blades, which later on enlarge and turn yellow. These
lesions may cover the entire blade, may extend to the lower end of
leaf sheath. Similar symptoms may occur on glumes of green grains.
Perpetuation: Survive in rhizophere of weed
hosts, infected straw and root stubble. Disseminate by wind and water.
Control: Cultivation of resistant varieties is
alone easy and safe way to prevent the crop against diseases including
this disease also.
Stem rot (Sclerotium oryzae)
Symptoms: Two to three months old plants begin
to wither and ultimately dry up, the sheaths soon turn somewhat dark
and start rotting. Black dots (fruiting bodies of sclerotia) occur at
the base of dried leaves and leaf sheaths. Stem begins to rot and
become soft, plant falls down.
Perpetuation: Infested soil helps the organism
for its survival.
Control: 1) Use of resistant varieties, 2)
Burning of diseased rice stubble, 3) Crop rotation and 4) Antagonistic
organisms.
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Table: Area (000 hectares), production (000 tonnes) and yield (kg
per hectare) of rice in Pakistan.
|
|
Year |
Area |
Production |
Yield |
|
1990-91 |
2,113 |
3,261 |
1,543 |
|
1991-92 |
2,097 |
3,243 |
1,546 |
|
1992-93 |
1,973 |
2,116 |
1,579 |
|
1993-94 |
2,187 |
3,995 |
1,826 |
|
1994-95 |
2,175 |
3,447 |
1,622 |
|
1995-96 |
2,162 |
3,966 |
1,835 |
|
1996-97 |
2,251 |
4,305 |
1,912 |
|
1997-98 |
2,317 |
4,333 |
1,870 |
|
1998-99 |
2,424 |
4,674 |
1,928 |
|
1999-2000P* |
2,515 |
5,156 |
2,050 |
|
P= Provisional; * = Jul.-Mar; Source: Economic survey 1999-2000;
Govt. of Pakistan.
|
References:
1. Bhatti, I. M. and A. H. Soomro. 1996.
Agricultural inputs and field crop production in Sindh. Agricultural
Research Sindh, Hyderabad.
2. Cheema, S. S., B. K. Dhaliwal and T. S. Sahota. 1991. Theory
and digest of agronomy. Kalyani Pub., New Delhi.
3. Hafiz, A. 1986. Plant diseases. PARC, Islamabad.
4. Jiskani, M. M. 1999. A brief outline "THE FUNGI"
(Cultivation of mushrooms).
5. Kamal, M and S. M. Moghal. 1968. Studies on plant diseases
of South West Pakistan. Agricultural Research Institute, Tandojam.
6. Nyvall, R. F. 1979. Field crop diseases handbook. AVI Pub.
Co. Inc. Westport.
7. WAPDA Report, 1961.
The author is Assistant Professor (Plant Pathology)
Sindh Agriculture University, Tandojam
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