The mango is known to suffer from a number of
diseases caused by different organisms, which affects different
parts of plants, at all stages of growth and development. Powdery
mildew (Oidium mangiferae), sooty mould (Capnodium romasum or Tripospermum
acorium), fruit rot (Aspergillus niger), leaf blight (Pestaloptiopsis
mangiferae), anthracnose (Glomerella cingulata-Colletotrichum gloeosporioides),
stem blight or die back (Diplodia spp.), root rot (Rhizoctinia and
Fusarium species) and tip die back (Fusarium equiseta, Alternaria
alternate, Aspergillus niger and Rhizopus nigricans) are recorded
as fungal diseases; bacterial leaf spot (Erwinia mangifera); and
malformation of mango inflorescence (the actual cause is still not
confirmed) are reported from Pakistan. No information regarding
the extent of damage to the plant is available, but some of these
are certainly responsible for causing considerable damage and become
a limiting factor in many mango-growing areas.
It is also pertinent to mention here that almost all commercial
mango varieties are old, released from 1949 to 1967 and are under
cultivation. Therefore, it is a question that how these varieties,
after long period, could be resistant to the diseases? More or less,
all varieties are reported to be susceptible, to most of the above
diseases. Mango growers also neglect their orchards and show interest
only at the time to decide contract rate and period. Contractors
pay their attention and or interest and try to recover their money
spent on contract and obtain high profit at low cost of production,
but do not think about health and life of mango trees. Even growers
avoid irrigating their orchards at requirement; interculturing and
manure applications are also not carried on timely. Now it is up
to the growers, to whom they may call responsible for present severe
and serious situation of diseases in mango orchards. What the researchers
would like to do for identification of actual problem. How the existing
disease or complicated disease's case occurred in mango orchards
could be controlled?
However the symptoms of all these possible factor diseases are summarized
hereunder just to guide mango growers and students, whereas, the
researchers are requested to plan their future strategies against
the diseases causing huge loss to tree as well as fruit, for the
benefit of nation and country.
Anthracnose (Fig 1) is prevalent
in almost all parts of the country. The leaves, petioles, twigs
and fruits are attacked. Appearances of oval and irregular blister
like brown spots develop on the tips, margins and centre of leaves
and twigs. Blackening of petioles, elongated necrotic streaks on
young twigs and branches are observed, and leaves drop down from
top to bottom. Drying and rupturing of affected tissues, drying
and falling of leaves, brightening of blossoms, staining and rotting
of fruits are also main symptoms of anthracnose.
Tip die back disease occurs on the branches/ trunk of infested
trees that start drying slowly at first and suddenly branches become
completely dried / killed resulting gummy substance oozes out or
remains hanging on the tree
Stem blight or die back become
evident by discoloration and darkening of the bark as well as exudation
of gum from infected portion (Fig 2). The withering of leaf tips
and shedding of leaves (Fig 3), the twigs dying back from top to
bottom is also one of the major evident of this disease. Brown streaks
are observed on vascular tissues by length wise splitting of diseased
twigs (Fig 3). Almost all mango varieties are reported as susceptible
to this disease.
Root rot is also prevalent
in almost all orchards; manifest itself as withering and drying
of the plant from top to bottom and whole plant die up (Fig 4).
Initially rootlets are affected and are rotten, later on the smaller,
tertiary roots and ultimately the bigger, secondary and primary-
main roots are infected which result in gradual decline of the plant
and the plant die (Fig 4). The uptake of nutrients and water is
blocked due to the rotting of the roots, which results in drying
of the plants.
Leaf blight; initially appear as minute yellowish
spots on the upper surface of the mature leaves. The spots become
more in number, bigger in size and often coalesce, forming big irregular
patches. The lower size of the spot is brown in colour, while upper
portion becomes white in centre with a brownish purple margin that
separate diseased and healthy portion. Some of the symptoms are
present in infected mango trees.
Bacterial leaf spot is noticed on the leaves as angular water soaked
spots or lesions, surrounded by clear holes. These become necrotic
and dark brown and viscous bacterial exudates deposit on these necrotic
portions that become corky and hard after drying. Sometimes, longitudinal
cracks also develop on the petioles. Some of the similar signs are
present in suffering mango orchards (Fig 5).
Fruit rot starts usually in
the ripe and over ripe fruits as spots of different colours, which
soon increase in number and size. Affected fruits may become soft,
pulpy and unfit for consumption. The present situation is so much
away from this problem (Fig 6).
Powdery mildew (Fig 7) is one of the worst diseases affecting almost
every variety and is common in all over Pakistan. It appears from
December to March, as superficial whitish or grey powdery growth
on the flowers and flower buds (inflorescence), tender leaves, thin
stem (shoots and trunk) and spreads to fruits. Infected flowers
fail to open and sometimes shed before being fertilised and results
in a substantial reduction of fruit set. If the fruit is already
set, it may drop off prematurely. The axis may begin to dry, showing
characteristic dieback symptoms, but dying of mango trees is not
due to this disease, but is another unknown havoc disease.
Malformation (Fig 7) is very common and widely
distributed in orchards (to a lesser or greater extent) in all over
country. Compact leaves formed at the apex of shoot or in the leaf
axil, to form the bunchy top seedlings and are usually shallow with
few tertiary roots. The tap root may be twisted and may show necrosis.
Sometimes, small leaves appear as shootlets, growth of which is
checked and several similar shootlets arise from the axil of the
scaly leaves and form bunches, which are thicker than the main stem.
Floral aggregation (malformation) may also appear on shortened primary
axil of the inflorescence, which is further branched to secondary
and tertiary branches, on which flowers are borne in clusters and
no fruit or very poor fruit setting is observed. Infected inflorescence
remains green for long time; no malformed heads dry up in black
masses but persist on trees. The symptoms are persistent in almost
all those gardens in which pruning have not yet been done.
Sooty mould (Fig 8) appears
as black velvety growth on the leaf surface. The entire leaf surface
or portion of the leaf may be covered with fungal growth and in
severe cases the whole plants are affected. The thin layer formed
on the leaf surface can be rubbed off easily. Under the dry conditions
this may be blown off as small fragments by the wind. The disease
causing fungi in true sense are non pathogenic, however, photosynthetic
activity of the plant is impaired due to covering of the leaves.
The symptoms occurring in diseased orchards are different to that
of this disease.
Sudden death of mango trees (Occurrence of new symptoms, especially
The present situation of mango orchards, with special reference
to the province of Sindh, needs special attention, where about all
mango orchards are suffering due to an unknown disease problem,
causing sudden death of mango trees. At present mostly 3 to 5 and
most likely 60 to 85 percent of trees are suffering from this type
disease, in various mango orchards of Sindh. There are different
opinion of plant disease specialists, but I think it is complicated
case emerged mostly due to combine attack of anthracnose, stem blight
or die back, root rot, tip die back, leaf blight, bacterial leaf
spot and malformation diseases, which are responsible for the decline
(dying of trees). That may also be proved through presence of the
symptoms of most of these diseases in a single plant at same time;
isolation of near about all the fungi causing these diseases from
diseased specimens collected from same single diseased plant; as
well as nature and behaviour of these diseases causing organisms.
High temperature, high relative humidity and weak plants are main
contributing factors in the spread of anthracnose and die back,
while root rot and tip die back caused by Fusarium species develop
more on weak plants, in high soil temperature and drought conditions.
It is also true that dying of trees or decline is generally observed
more in the neglected orchards, which is common factor. The shortage
of irrigation water may also be another main cause, which helps
to the disease causing organisms to grow, develop and spread more.
However, development of small saprophytic white mushrooms on dried
trunk (stem) of diseased trees (Fig 9), rotting of roots / trunks
having very bad smell and small holes on trunk (Fig 10) due to inset
pests (perhaps because of bark beetles) are the most common but
newly occurring symptoms, which are also present in almost all mango
orchards. The growers are going to cut-off / remove diseased trees
from their orchards because they feel no way except destruction
of diseased mango trees (Fig 11).
Possible control measures
The researchers had conducted various experiments on the
diseases of mango plants and fruits and evaluated various ways by
which the diseases can be controlled. Therefore, it is suggested
that integrated disease management practices must be applied by
using different fungicides in combination with suitable insecticides;
whereas different cultural practices may also help to check the
diseases. It must be kept in mind that use of fungicides is not
alone source. On the other hand, it is also pertinent to mention
here that the fungicides increase the cost of production. Their
use is risky for the health of worker. The fungicides decrease the
fruit quality because of their toxic substance residues that may
remain present so much time in the fruit. Therefore, following integrated
disease management principles should be applied.
1. Only healthy seeds, seedlings and plants should be used for planting
and budding or grafting.
2. Inter cropping, mix cropping, cover cropping
and or multiple cropping in or in the surrounding of mango orchards
must be avoided so that the similar possible pathogens of the sown
crop and mango (both) may not be multiplied and spread in orchards.
3. Irrigation must be applied as per requirement,
but not subject to the availability.
4. Avoid high doses of nitrogen fertilisers, but
apply proper and balanced fertilizers, on the basis of soil type,
age and need of the tree.
5. Proper sanitation of orchards and pruning of
trees (eradication of disease causing organisms through removing
and burning of diseased plants or plant parts) helps to reduce the
infection and growth, development and further spread of the disease
causing fungus or so.
6. Easily available broad spectrum fungicides should
be used, in combination with insecticides at proper dose. However,
encouraging results could be obtained with consulting pathologist