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Among mango growing countries, Pakistan offers a wide choice of more than 100 mango varieties

By M. MITHAL JISKANI
Asstt. Prof. (Plant Pathology) 
Sindh Agriculture University, Tandojam
 Mar 18 - 24, 2002

Mango, Mangifera indica L. is one of the most important foreign currency earning fruit crop of Pakistan. It is known as the "King of fruits". The mango is nutritionally rich in carbohydrates and vitamin A and C. It is relished and liked by every one for its flavour and dietetic value and is also claimed to be of medicinal value. For instance, a chutney made from the green (unripe) fruit is considered to be an effective antidote for mild forms of sunstroke. Apart from this, unique mango recipe such as mango ice cream, mango milk shakes, mango squashes etc. are favourite desserts. Mango juice, jelly, marmalade, pickles etc. are also commonly consumed.

In Pakistan, the mango is grown over an area of 94.1 (000) ha, while its production is 916.8 (000) tonnes. Its area in Sindh is about 43.5 (000) ha, with 320.7 (000) tonnes production, which is about 46.2 and 34.9 per cent of total area and production respectively (Pakistan Statistics Year Book, 2001). According to Export Promotion Bureau, Pakistan has exported 47,601,678 and 31,000 kg of fresh and dried (amchoor) mangoes with a value of 11,589.6 and 21.3 (000 dollars) respectively during July-June 1999-2000, to many countries, mainly to Dubai, Saudi Arabia, UK, Germany, France, Holland, Switzerland, Italy, Singapore and Malaysia.

Among mango growing countries, Pakistan offers a wide choice of more than 100 mango varieties. Some of the most famous varieties are Sindhri, Dusheri, Summer Behist, Chaunsa, Anwar Ratole and Langra. These are differing in fruit characters, viz.: taste, flavour, colour, tinges shape and size, traits that determine the quality of the fruit and hence its market value at home and overseas. At present, one late season, five mid seasons and six early seasons (total 12) mango varieties are cultivated commercially in Sindh. These varieties were released from 1949 to 1967, with yield potential of 8000 to 21600 kg/ha (Table). After that, no any popular variety has been released of if is released, most of us are unaware to that!

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 dying of trees. It is really very difficult for me to comment on what I see daily that many trucks running on road, loaded with not a mango fruit but loaded with cutted mango weed logs! I can neither define nor explain standard mango growers and contractors. What I want to say about the despond labour involved in planting and managing mango orchards, picking, packing, loading and transporting mango fruits. Even I could not answer to question arose by worried for mangoes!!

I do not know about entire situation (!?) , but have personally visited many mango orchards and viewed badly declined mango trees, because of an unknown problem, to which we may call "disease". Because the disease can be defined as any disturbance or deviation of a plant that interfere with its normal structure, function or economic value. The diseases are usually caused by living organisms, called pathogen, such as fungus, bacterium, nematode and insect pest, regarded as infectious diseases. The diseases may also be caused by other factors like physiological disorders or due to changes in environmental conditions, and are termed as non infectious. These diseases are caused due to low or high temperature, unfavorable oxygen and soil moisture relations, injurious atmospheric gases of chemical injury, lightening injury and deficiencies or excesses of nutrients. The viruses are sometimes considered living and sometimes as non living though are taken up independent existence of their own. Therefore, plant diseases caused by viruses are sometimes regarded as infectious and sometimes as non-infectious. On the other hand, changes in environmental conditions, due to global warming and the green house effect, resulting in low rainfall, high Co2, air and water pollution, soil degradation by drought, land erosion, salinity, waterlogging and desertification also directly hit the crop as well as help to disease causing organisms, so that they may develop more and could cause abnormality (disease) in normal function, structure or economic value of plants.

Any injury or abnormality brought about by insects belong to the field of entomology. The remaining causes of all disturbance and deviations are taken place in the field of plant pathology. The plant pathology constitutes a big sector of plant protection, is a study of nature, cause and prevention of plant diseases. Crop protection is mother discipline of entomology and plant pathology, is concerned with the health and productivity of growing plants. The disease losses are hazards, can be minimized only by a continuous process of research and education. To evaluate and solve new disease problems, is the responsibility of the crop protection. To work out practicable procedures, which growers can adapt to their needs and in a result, the farmers must be benefited, is the aim of crop protection.

Mango diseases recorded in Pakistan

However, 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 gloesporioides), stem blight or die back (Diplodia spp.) and root rot (Rhizoctinia and Fusarium species) are recorded as fungal diseases; bacterial leaf spot (Erwinia mangiferae); 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.

Symptoms of the diseases

Powdery mildew is one of the worst disease affecting almost every variety and is common in all over Pakistan. It appears from December to March, as superficial whitish or gray 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. 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, it is an other unknown havoc disease.

Sooty mould 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 affected. The thin layer formed on the leaf surface can 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.

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.

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.

Malformation 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 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 has not yet been done.

Anthracnose is prevalent in almost all parts of the country. The leaves, petioles, twigs and fruits are attacked. Appearance of oval and irregular blisters likes 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.

Stem blight or die back become evident by discoloration and darkening of the bark, withering of leaf tips and shedding of leaves, the twigs dying back from top to bottom. The exudation of gum from infected portion is also one of the major evident of this disease. Brown streaks are observed on vascular tissues by length wise splitting of diseased twigs. 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. 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. The uptake of nutrients and water is blocked due to the rotting of the roots, which results in drying of the plants.

Present situation?

This is on the disposal of individuals, who have visited and are well aware to various problematic mango orchards, can decide that what is the problem? I think it is clear from the symptoms of anthracnose, stem blight or die back and root rot that present problem is not because of any one disease. Perhaps, it is complicated case emerged mostly due to combine attack of anthracnose, stem blight of die back, root rot, leaf blight, bacterial leaf spot and malformation diseases, which are responsible for the decline (dying of trees). That may also be proved through the 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 caused by Fusarium species may 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. Present shortage of irrigation water is another main cause, that also help to the disease causing organisms to grow, develop and spread more.

It is also pertinent to mention here that almost all commercial mango varieties are old, which were released from 1949 to 1967. However, such old mango varieties are under cultivation. It is question that how such 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 discussed diseases. Now it is up to the researchers what they would like to do for identification of actual problem, how they control the existing disease or complicated disease's case.

Research work on identification of disease problems

The following research achievements by several research workers, has been reviewed, so that the mango growers or contractors may easily decide to adopt preventive and curative measures. Whereas, the researchers may also plan their future strategies against this most destructive problem, for the benefit of nation and country.

Florence (1989) reported that the fungi such as Botrydiplodia theobromae, Alternaria, Acremonium, Scytalidium, Fusarium and Ceratocystis stained both the surface and the deeper wood of mango. Sharma (1991) observed that out of 219 isolates obtained from 225 diseased samples from mango orchards, Botrydiplodia theobromae, Colletotrichum gloeosporiodies [Glomerella cingulata], Pestalotia mangiferae, Phoma sp., Scleratium [Corticium] rolfsii, Rhizoctonia solani, Diplodia sp. and Fusarium solani were establishedas pathogenic. Mixed infections were common. B. theobromae was the most frequent isolate and appear to be the primary cause of die back in this region, though other pathogens causing necrosis may facilitate invasion by B. Theobromae. According to Kore and mane (1992) Fusarium solani infects mango and disease development increased with decreasing soil moisture, with maximum development at 22% soil moisture. While in same year Narasimhudu and Reddy (1992) found that trees of the mango were severely affected by gummosis. Botryodipladia theobromae was isolated from diseased trees and pathogenicity was confirmed. Colyn and Schaffer (1993) stated that Powdery mildew, floral malformation, blossom blight [Dothiorella dominicana?] and bacterial black spot (Xanthomonas campestris pv. Mangiferaeindicae) are most important pre-harvest diseases/ disorders of mango. Whereas, Darvas (1993) reported that Dothiorella dominicana has been identified as an important pathogen of mango in South Africa. It was associated with blossom blight, branch die-back, fruit stem-end rot and fruit rot. Disease symptoms on the flowers are referred to as blossom blight. The pathogen may continue to grow into the wood behind the killed flower axis and cause branch die-back. It can also directly infect branch tips causing die-back. The pathogen overwinter in pycnidia formed in dead wood. No sexual stage of the fungus was found in this study. Tsao et al. (1994) isolated Phytophthora palmivora from infected crown and root tissues of mango showing crown and/or root rot and wilt symptoms in the Philippines. Ploetz et al. (1996a) sampled mangoes with decline symptoms from Florida, USA, and reported that during artificial inoculation A. alternata, G. cingulata, D. dominicana, B. theobromae and Phomopsis spp. caused all or some decline symptoms that included bud necrosis, tip dieback, gummosis and vascular discoloration. Ploetz et al. (1996b) isolated Fusarium decemcellulare as a pathogen associated with large galls of mango in the United States. On the basis of the work done by above researchers it is concluded that mango decline is a disease complex involving several different fungi.

Research work on control of diseases

Ahmed (1991) evaluated 8 different fungicides and reported that, Dithane M-45 (mancozeb) gave the best control of anthhracnose [Colletotrichum golelsporiodes (Glomerella cingulata]) followed by Bordeauux mixture. Sooty mold (Capnodium ramosum) was best controlled by Bordeaux mixture and Thiovit [sulfur]. According to Narasimhudu and Reddy (1992), the disease gummosis, Botryodiplodia theobromae could be controlled using a paste of Bordeaux mixture or carbendazim. Darvas (1993) well controlled the blossom blight, caused by D. dominicana with benomyl (0.025% a.i.) sprays. Sharma and Gupta (1994) evaluated the efficacy of 8 different fungicides agianst Botrydiplodia theobromae Pat., casual organism of canker and dieback of mango. Maximum disease control was achieved by 1% Bordeaux mixture followed by 0.8% Bordeaux mixture and carbendazim. The addition of borax, urea and NPK was not effective. Sharma et al. (1993) controlled wilt of mango caused by Fusarium solani (Mart.) Sacc. with carbendazim (0.1%) or captafol (0.25%), when symptoms appeared was highly effective. Ahmed et al. (1995) evaluated various fungicides against die-back disease caused by diplodia natalensis in mango at their recommended doses and reported that three foliar sprays of each of thiophanate-methyl (as Topsin-M) and benomyl (as Benlate), at 1.5 g/liter and 0.5 g/liter, respectively, were effective in controlling disease.

Conclusion and suggestions

It is concluded on the basis of personal expereince and work reviewed that the present problem is not becasue of any one disease, but mango decline is the combine attack of anthracnose, stem blight or die back, root rot, leaf blight, bacterial leaf spot and malformation diseases, involving several different fungi, which are responsible for the dying of mango orchards. Therefore, it is suggested that integrated disease management principles should be applied by using different fungicides in combination with suitable insecticides. Whereas, various cultural practices may also be helpful 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 residue, that may remain present so much time in the fruit. Therefore, following integrated disease management principles should be applied. The researchers are requested to plan their future strategies against this most destructive problem, for the benefit of nation and country.

Only healthy seeds, seedlings and plants should be used for planting and budding or grafting.

Irrigation must be applied as per requirement, but not subject to the availability.

Avoid high doses of nitrogen fertilisers, but apply proper and balanced fertilizers, on the basis of soil type, age and need of the tree.

Proper sanitation of orchards and pruning of trees (diseased plants or plant parts should be removed and burnt) may help to reduce the infection and growth, development and further spread of the disease causing fungus or so.

Easily available broad spectrum fungicides should be used, in combination with insecticides at proper dose.

However, modern mango production technology must be adopted as per recommendations of researchers. The encouraging results could be obtained with consulting pathologist and entomolgist.

Mango varieties, year of release and yield potential (kg/ha)

Name of variety

Year of release

Yield potential (kg/ha)

Late season

    

Neelum

1965

11070

Mid Season

    

Swarnarika

1953

11070

Summer Behisht Chaunsa

1959

9000

Benganpali

1953

20430

Saleh Bhai

1965

9450

Anwar Ratole

1867

9900

Early Seaon

    

Sindhri

1949

21600

Zafran

1958

12600

Siroli

1953

8000

Langara

1952

10000

Dusheri

1951

12870

Gulab Khasa

1959

9900

Source: Introduction to Agriculture Research in Sindh. Directorate General, Agricultural Research Sindh, Hyderabad, June, 1990.