By Zeeshan Sattar M.Sc. (Hons.), Muhammad Mohsin Raza, Sabir Hussain Khan, Muhammad Aslam Khan and Iqra Ashfaq
MANGO, MANGIFERA indica L. is one of the most important overseas cash earning fruit crop of Pakistan, through exporting to all over the world. It is known as the “King of fruits”, because the mango fruit is nutritionally rich in vitamin A and C and carbohydrates. It is savoured and liked by every one for its dietetic value and flavour and is also claimed to be of medicinal value. A wide choice of near about 200 mango varieties Pakistan offers and the most famous varieties are Sindhri, Dusheri, Anwar Ratole, Langra Summer Behist and Chaunsa. These varieties were released from 1949 to 1967, with yield potential of 8000 to 21600 kg/ha. All varieties are divergent in fruit charms, viz., color, tinges, shape taste flavor, and size, traits that determine the quality of the fruit and hence its market value at home and foreign.
Diseases are summarized here under just to guide mango growers
l Anthracnose: It is one of the most severe diseases of mangoes in many areas where rains during the mango flowering and fruit set stages. On leaves, tan to dark brown spots normally with a darker border infection of young leaf flushes may arise when their development accords with rainy weather. When newly formed fruits appear large, sunken, black lesions are formed and pre-harvest anthracnose show large lesions which are glossy, black and sunken. With these fruit, splits and oozing often occurs and the grey-black areas in the skin on ripening fruit.
l Powdery mildew: It is one of the worst diseases affecting almost every variety and is common in all over Pakistan. It appears from December to March, This disease spreads rapidly with heavy rains and high temperature 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 fertilized and results in a substantial reduction of fruit set.
l Dieback: In affected mango plants dieback is observed on trees, twigs die from the tips back into old wood; giving a scorched look to the limb the young green twigs start withering first at the base and then extending outwards along the veins of leaf edges. The affected leaf turns brown and its margins roll upwards. Leaves scorch and drop, leaving a departed branch. In severe conditions, branches start drying one after another in an arrangement resulting in death of the whole tree. Almost all mango varieties are testified as susceptible to this disease.
l Quick decline/Collar rot: Rotting of bark at collar portion, attachment of flaccid leaves partial or complete drying of the tree
l Gummosis: The infected plants show profuse gum ooze from branches, stem, and main trunk. Initially the gum seems as a small bead. However, as the disease growths, it increases and covers most of the branch and trunk. Under stark conditions, the outer wood of a branch crashes and splits which shows a yellow to brown, gum-like substance
l Root rot: It is also dominant disease of mangoes in almost all orchards; visible itself as withering and drying of the tree from top to bottom and whole tree die up. Primarily rootlets are affected and are rotten, later on the smaller, tertiary roots and finally the bigger, primary and secondary main roots are infected which result in gradual decline of the tree. The uptake of nutrients and water is blocked due to the rotting of the roots which results in drying of the whole part of mango plants.
l Leaf blight: Primarily it ap pears as tiny yellowish spots on the superior surface of the mature leaves. The spots develop more in number, bigger in size and often merge, making big irregular patches.
l Bacterial leaf spot: It 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.
l Fruit rot: It starts usually in the ripe and over ripe fruits as spots of different colors which soon increase in number and size. Affected fruits may become soft, pulpy and unfit for consumption.
l Mango Malformation: Compact leaves formed at the apex of shoot bunchy top seedlings and are usually shallow with few tertiary roots show necrosis. Sometimes 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
l Mango sudden death syndromes: This is the most dramatic form of the decline syndrome. The tree looks or appears normal and suddenly starts to wilt and within a couple of days is completely wilted and dies observance of tree trunk and main branches reveal gummosis of different colors, forms and intensities coming out at different positions on the tree. Infection in this case is often not limited only to the bark of the tree but observed on the inner wood tissue of the xylem as striated brownish streaks within the woody tissue. In some cases, further scraping of the infected wood tissue releases stinking liquids of milky and sometimes brownish or blackish appearance. At this stage there is often little the grower can do to save the tree
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 fertilizers, 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 arena fungicides should be used, in combination with insecticides at proper dose. However, inspiring results could be obtained with referring pathologist and entomologist.
7. Regularly use of spray programmed 3 sprays in year first spray at the end of February, 2nd spray in June and 3rd in start of rainy season.
8. Use gypsum rendering to the soil analysis
9. Eliminate the soil around the stem and notice root infection
10. To reduce the diseases and improve fruit quality it is essential to improve the integrated orchard management packages and reduce periodic bearing and improve mango supply
The writer is writers are associated with the Department of Plant Pathology, University of Agriculture Faisalabad, Pakistan. They can be reached at <firstname.lastname@example.org>