Symptoms, perpetuation and control strategies
By M. MITHAL
JISKANI
Assistant Professor (Plant Pathology)
Sindh Agriculture University, Tandojam
Nov 19 - 25, 2001
Human beings are cultivating different crops for
food, fiber as well as fodder for their animals. The land and
irrigation water resources available to them are limited and could not
be increased. However, there is a need to grow more from each piece of
land and from every drop of irrigation water available. Otherwise, it
is very difficult, but even impossible to meet the requirements of
ever increasing population. Hence, there is a need to preserve and
save the basic resources along with the environment, to face the
present as well as future challenges.
Edible oil is one of the basic food requirements.
The shortage of edible oils had started developing from 1970 due to
rapid increase in population, per capita consumption and local edible
ol production remained almost stagnant. Despite the fast increasing
demand of edible oil, the outflows for the last 5 years were 413.4 to
856 million US Dollar (Table 1). Cottonseed is the major domestic
source of edible oil with rapeseed mustard and canola occupying the
second place. Part production from sesame and entire production from
groundnut is comsumed as raw with no oil extracted. On over all, the
content vary from 10-50 per cent according to variety (Table 2).
Sunflower, soyabean, groundnut, sesame and caster belong to Kharif,
while canola, rapeseed and mustard, safflower and linseed are Rabi oil
seed crops, which are being used to fulfil local requirements.
Table 1:
The outflow (import) of edible oils (US Dollars in million)
for the last 5 years
|
|
Year 1996 |
1997 |
1998 |
1999 |
2000 |
|
Dollar 856 |
611.7 |
767.9 |
824.1 |
413.4 |
| Source:
State Bank of Pakistan, Annual Report, 1999-2000. |
Table 2:
Oil content percentage of various oil seed crops.
|
|
Name of crop |
Oil content (%) |
Remarks |
|
Kharif oil seed crops |
|
Sunflower |
Over 40 |
Good edible, free from toxic compounds |
|
Soyabean |
18-22 |
Used in ghee & industrial purposes |
|
Groundnut (Peanut) |
50 |
High edible quality |
|
Sesame |
50 |
Good quality edible oil |
|
Castor |
Over 50 |
Used for number of industrial purposes |
|
Rabi oil seed crops |
|
Rapeseed and mustard |
38-41 |
Several edible and non edible uses |
|
Safflower |
32-36 |
Excellent quality edible oil |
|
Linseed |
Over 40 |
Used for medicines, paints, printing ink etc. |
| Source:
Bhatti and Soomro. 1996. Agriculture inputs and field crop
priduction in Sindh. Directorate General, Agri. Res. Sindh, Hyderabad. |
Amongst the Kharif oilseeds, sunflower has gained
higher popularity and acreage among the new oilseed crops introduced
for boosting edible oil production. The important features of this
crop are short growing period, high yield potential and wide range of
growing season viz. autumn, spring and winter. It fits well in
different cropping patterns, low irrigation water requirements, wide
adaptability to soil and moisture conditions. Its seed contain high
oil (over 40%) of good edible quality and meal of good quality free
from toxic compounds. Three irrigations are necessary. The 1st
irrigation should be given 30-35 DAS. 2nd at start of flowering and
3rd just after petal fall. Soyabean requires 5-7 irrigations from
sowing to maturity. Irrigation at pod filling stage is very necessary,
drought at this stage will reduce yield drastically. Groundnut needs
30 acre inches during 5-7 irrigations. The first irrigation shold be
given 25-30 DAS and subsequent at 15-20 days intervals. The critical
stage is seed development. The sesame is cultivated throughout
Pakistan as irrigated as well as un-irrigated crop. It requires 3-4
(21 acre inches) irrigation at 30 days interval. Caster is grown,
under arid conditions, mostly as rainfed crop. Under irrigated
conditions, it needs 5-7 (20 acre inches) irrigation at days interval.
Canola, Rapeseed and Mustard, Safflower and Linseed
are Rabi crops. In case the cultivation of Canola, Rapeseed and
Mustard, 3-4 irrigations may be given to Toria and Sarsoon, 1-2
irrigations to Jambho or Taramira at 25-30 days intervals. Seed
development stage is critical for irrigation. No irrigation is
required for Dobari Bosi crop. Safflower is sensitive to heavy
irrigations, especially in later growth stage. However, 5-6
irrigations are required under irrigated conditions. Linseed needs 4-5
irrigations. First irrigation 30 DAS and subsequent doses at 20-25
days intervals should be given. No irrigation is required, when it is
grown as Dobari crop.
It must be kept in mind that only irrigation water
is not alone input for increasing per unit production, nor a land
alone or in combination with irrigation water is enough for the
purpose. Different diseases are aso responsible to damage the crops
and result sometimes negligible and sometimes 100 per cent loss in out
put. Oil seed crops are subject to various mechanical, physiologic and
biological stresses in all stages of growth and in all natural
enviroments, that interfere with their normal growth and development.
Weather, toxicants, pollutants, insects, viruses, fungi, nematodes,
bacteria and seeds are primary hazards to the production. Overall, all
diseases are injurious in some areas, in some years and on some plant
parts. All parts of plant are subject to diseases 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.
Crop wise brief account of the most important
diseases of oil seed crops in Pakistan being discussed for readers
(including agriculture research and extension workers, students and
teachers) as well as for the benefit of farmers or growers. This will
include the causes, symptoms, perpetuation, preventive and curative
control measures of very destructive diseases. All information is
based on personal experience and the recommendations by Hafiz (1986),
Chaudhry et al. (1988), Mirza (1988), Bhatti and Jiskani (1996),
Bhatti and Soomro (1996) and Khoso (1992).
Sunflower
Septoria leaf spots, Septoria helianthi
Symptoms: Small angular to more or less circular or
sometimes diamond shaped, brown to dark brown spots develop on upper
leaf surface and lighter gray brown on lower leaf surface. In these
spots many small black bodies (Pyenidia) are develop on both surfaces
of leaves under moist conditions. Spots coalesce and leaves wither and
dry first on lower and gradually spread to upper leaves.
Charcoal rot, Macrophomina phaseolina,
Rhizoctonia bataticola and Sclerotium bataticola
Symptoms: Brown to dark brown spots appear on stem.
The plants become weak, dry and show light gray or ashy black
discoloration of stem. Poorly filled heads can be seen and premature
ripening and drying of stalks occur, which also become normally
discolored. Pith distintegrates and vascular fibers apppear shredded,
covered with small bodies (Sclerotia) of disease causing fungi.
Perpetuation: The fungi perpetuate on the infected
host plant debris in dry soils for a long period., but in moist (wet)
soil it can not survive for longer.
Alternaria blight, Alternaria helianthi
Symtomps: Dark brown to black, circular to oval
spots appears on leaves. The spots are surrounded by necrotic zones
with gray white necrotic center marked with concentric rings. Spots
enlarge and coalesce resulting in leaf blight and sometimes cause
rotting of stem and heads.
Perpetuation: Infected seeds, plant debris, weed
host plants help the fungus to survive, while it is wind borne also.
Sclerotinia stalk and head rot, Sclerotinia
sclertiorum
Symptoms: The disease is characterized by sudden
wilting of leaves. Gray to brown colored portions encircling the
stems. The spots are covered partially or completely with white
cottony mold having large whitish gray to black bodies, irregular in
shape. Stems shred in to vascular strands and become straw colored on
drying. Heads disintegrate and stalk rot can occur at any part of
plant.
Rhizopus head rot, Rhizopus arrhizus and R.
stolonifer
Syptoms: Brown irregular water soaked spots at back
of head. These spots enlarge, turn brown, become soft and pulpy.
Perpetuation: The fungus is air borne but injury by
borers or birds are necessary for infection.
Rust, Puccinia helianthi
Symptoms: Small, chestnut brown or orange to black
powdery scattered pustules appears on lower leaves, may also found on
stem and floral bracts of capitulum. The leaves become dry prematurely
affecting yield and seed quality.
Perpetuation: The fungus survives on volunteer
seedlings in high altitude areas and carried through air currents.
Verticillium wilt, Verticillium dahliac
Symptoms: Prominent yellow, inter-veinal patches
appear on leaves, which are gradually enlarged and coalesce, while
leaf centers turn brown and necrotic having mottled appearence. Plants
show stunting, small flower heads and destruction of root system.
Perpetuation: The fungus survives in the soils.
Minor diseases
Root rot caused by Rhizoctonia and Macrophomina
species, Cercospora leaf spots caused by Cercospora helianthi
are also sometimes less as well more important fungal diseases.
Soyabean
Anthracnose, Colletotricum truncatum
Symptoms: Dark brown lesions on cotyledon, become
water soaked, quickly wither and fall off in seedling stage. Irregular
brown lesions appear on stem and petiole and round to elongate on
pods. Pin cushions like fruiting bodies with minute black spines can
be seen with hand lens.
Perpetuation: Infected crop residues and seeds help
the fungus to survive.
Charcoal Rot, Macrophomina phaseolina,
Rhizoctonia bataticola and Sclerotium bataticola
Symptoms: The disease characterized by sudden
wilting of plants. Brown to dark brown lesions appear on stem. Plants
become weak, mature early and when dry, show light gray or ashy black
discoloration of stem. Small minute black bodies are found in plant
tissue as well as in pithy area of stem after removing of epidermis.
Perpetuation: The fungi perpetuate on the infected
host plant debris in dry soils for a long period, but in moist (wet)
soil it can not survive for longer.
Pod and stem blight, Diaporthe Phaseolorum
Symptoms: Many black flasks shaped pycnidia
developed on the lower portion of the main stem, branches and pods as
plants reach maturity. Pycnidia also found scattered on dry poorly
developed pods. Seeds are badly cracked, shriveled and covered with
mycelium.
Perpetuation: Carry over through infected seeds and
host plants.
Purple seed stain, Cercospora kikuchii
Symptoms: Pink to pale or dark purple coloration of
seed coat. Seed are often dull, cracked and rough. Round, reddish
purple spots that later become purplish black also develop on pods.
Perpetuation: Carry over through infected seeds and
host plants.
Minor diseases
Leaf spot caused by Alternaria tenussine,
pod bligh cause by Alternaria species and yellow patches on
leaves turn chlorotic to brownish, remain stunted and do not flower in
early infection.
Groundnut (Peanuts)
Tikka disease, Cercospora personata
Mirza (1998) reported this disease as early leaf
spot (caused by Cercospora arachidicola) and late leaf spot
(caused by Cercosporidium personatum).
Symptoms: When the crop becomes two months old,
conspicuous dark brown circular to subcircular spots appears on
leaves. These spots spread to other plant parts also. Mature spots are
surrounded by light yellowish haloes, leaves started shedding and
development of nuts are badly affected.
Perpetuation: Carry over through diseased seeds and
plant debris.
Minor Diseases
Root rot and wilt (caused by Rhizoctonia
bataticola, Fusarium coeruleum and Botryodiplodia theobromac),
stem rot (Diplodia sp.), kernel rot in storage (Aspergillus
sp.), anthracnose (Colletotrichum arachis and C.demtium),
leaf spots (Alternaria arachidis and A. alternatia) and
crown rot (caused by Choancphora sp., Phyllosticta sp.
and Aspergillus sp.).
Sesame
Root and Stem Rot, Rhizoctonia phaseoli,
Macrophomina phaseoli and Botryosphaeria ribis)
Symptoms: The disease attacks roots and stems,
causing discoloration and rotting. As a result the leaves turn yellow
and wither. Brown blackish patches on stems and dot like structures on
diseased plant parts.
Perpetuation: The disease causing fungi may survive
due to mixed with seed and plant debris, while are reported as soil
borne in nature.
Phyllody
Symptoms: Floral parts are transformed in to green
leafy structures with abundant vegetative growth. Sepals become leaf
like and stunted . Veins are thickened and dark green in color.
Anthers do not contain viable pollen. Carpels also are transformed in
to leafy out growth . The leaves are formed small in heavy bunches at
top portions of the plants. Grains shriveled and not viable.
Castor
Root rot (caused by Rhizoctonia bataticola)
and powdery mildew is recorded but not distructive. The symptoms,
perpetuation and control measures are similar to that of caused by
same organisms on other oil seed crops.
Canola, Repeseed and Mustard
White Rust, Albugo candida
Symptoms: Initially white or cream colored pustules
of varying size develop on under surface of the infected leaves. The
pustules also appear on stem, pod and terminal parts of flower stalk.
The pustules increase in number and size, coalesce to form big
patches. These pustules raised up and ultimately rupture releasing
chalk like powdery mass of disease causing fungus. Infected leaves and
other plant parts looked thikened because of swelling.
Perpetuation: Carry over through plant debris and
seed, spread by wind.
Downy Mildew, Peronospora parasitica
Symptoms: The disease also appears on several Brassica
species as irregular spots. The spots are small light green or grayish
white on the lower and yellowish brown on the upper surface of the
leaves. The spots increase in size and number, covering large area of
foliage followed by defoliation and infection of stem also.
Perpetuation: Perpetuate through diseased plant
debris or seed.
Powdery Mildew, Erysiphe polygoni
Symptoms: Initially white talcum powdery spots
appear on leaves, stem and pods. These spots increase in number and
size, cover entire surface of the host plant like a talcum powder.
Severely affected leaves start dropping., stems rot, pod and seed
formation badly affected because chlorophyll of plant is checked.
Perpetuation: The diseased plant debris and
volunteer host plants help the fungus for its survival.
Blight, Alternaria brassicae, A. raphani and A.
brassicola
Symptoms: Initially light brown spots appear on
leaves including cotyledon, which rapidly turn black or range from
gray to black. The spots also develop on stem and pods and plants are
heavily damaged.
Perpetuation: Infected seeds, plants debris and
weed host plants help the fungi to survive and wind to spread.
Minor Diseases
Fusarium wilt, stem and root rot (caused by
Selerotinia selerotiorum), and storage rots (caused by Rhizoctonia
bataticola, Aspergillus, Penicillium and Fusarium
species) are also some times cause damage to the crop and produce.
Safflower
Alternaria Blight, Alternaria carthami
Symptoms: Small brown to dark spots with concetric
rings appears first on lower leaves and later spread on upper ones.
These spots increase in number and size, coalesce and form large
irregular lesions. The center of mature spots usually becomes lighter
in color. Infected seeds may show dark sunken lesions on the testa at
the floret end.
Perpetuation: The disease causing fungus may
perpetuate through seeds and plant debris, reported as wind borne
also.
Remularia Leaf Spot, Remularia carthami
Symptoms: Light brown circular spots with silvery
appearance due to fungus spores or conidia and conidiophores on
leaves. These spots coalesce and form large irregular withered areas
on leaves during rainy weather.
Perpetuation: Germinating conidia penetrate the
stomata
Rust, Puccinia carthami
Symptoms: Orange yellow or chestnut brown colored
pustules developed on leaves, flowers and capsules. When plants
mature, pustules turn in to dark brown color.
Perpetuation: Wild safflower species help the
fungus to survive.
Sclerotinia Wilt, Sclerotinia sclerotiorum
Symptoms: Infected plants become yellowish, light
brown, wilted and killed. White mycelial growth and large whitish gray
to black. Sclerotia are found on stem as well as inside stem.
Shredding of the affected tissue may also take place.
Perpetuation: The disease causing fungus is soil
and seed borne.
Linseed
Wilt, Fusarium lim
Symptoms: End points of brances begin to droop and
whole plants dry. Root bark becomes loose and shredded.
Perpetuation: The fungus is reported as soil borne.
Control strategies
1. Cultivation of disease resistant or tolerant
varieties are alone safe, economical and most easy way against all
diseases.
2. Healthy and un-damaged quality seeds should be
used, otherwise seed treatment with any suitable seed dressing
fungicide must be done.
3. Crop rotation with non host crops for 2-3 years
is also reported as beneficial.
4. Proper tillage operations can minimize the
diseases caused by seed borne pathogens.
5. Irrigation water and fertilizers must be applied
as per requirement of the crop with normal methods and proper dose.
6. Collection and burning of diseased plant parts
and debris may minimize disease intensity.
References
1. Bhatti, I. M. and A. T. Soomro. 1996.
Agricultural inputs and field crop production in Sindh. Agri. Res. Sindh, Hyderabad.
2. Bhatti, I. M. and M. M. Jiskani. 1996. Modern
Agricultural Guide. Agri. Res. Sindh, Hyderabad.
3. Chaudhry, A. H., B. R. Oad and K. Mehraj. 1988.
Highlights of improvement research on oilsed crops in Sindh. A. R. I., Tandojam.
4. Hafiz, A. 1986. Plant diseases. PARC, Islamabad.
5. Khoso, A. W. 1992. Crops of Sindh. 5th revised
edition.
6. Mirza. M. S. 1988, Major diseases of oilseed
crops in Pakistan. In 'Field crop diseases', CDRI, NARC, PARC,
Islamabad.
7. State Bank of Pakistan, Annual Report,
1999-2000.
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