Major Physiological Disorders in Mango (Mangifera indica)
Introduction: Mango (Mangifera indica) is the leading fruit crop of India and considered to be the king of fruits. Besides delicious taste, excellent flavor and attractive fragrance, it is rich in vitamin A&C. Mango fruit is utilized both in its immature and mature state. Raw fruits are used for making chutney, pickles and juices. The ripe fruits besides being used for desert are also utilized for preparing several products like squashes, syrups, nectars, jams and jellies. Fresh mangoes and mango pulp are the important items of Agri-exports from India. India’s main export destinations for mango are UAE, Kuwait and other Middle East countries with a limited quantity being shipped to European market. Although, India is the largest mango producing country, accounting about 60% of world production, the export of fresh fruit is limited to Alphonso and Dashehari varieties. India’s share in the world mango market is about 15 percent. Mango accounts for 40 percent of the total fruit exports from the country. There is good scope for increasing the area and productivity of mango in the country but there are few physiological disorder which are major constrain in mango production, here we have discussed about their causes and symptoms and treatment in brief.
It is a major problem in Alphonso, where a pulp patch fails to ripen. This malady is caused due to inactivity of ripening enzymes due to high temperature, convective heat and post harvest exposure to sunlight.
Control: Use of mulching and post harvest exposure to low temperatures between 10-15 C for 10-18 hours has been useful in reducing the malady.
Malformation is widely prevalent in northern India, particularly in the states of Punjab, Delhi and Western U.P. where more than 50% of the trees suffer from this problem.
Symptoms: The malformed panicles remain unproductive and are characterized by a compact mass of male flowers, greenish in colour and Stunted in growth. The main and secondary rachis is thick and short and bears flowers with relatively larger bracts, sepals and petals as compared to normal flowers. The malformed panicles remain intact on the trees for a considerable long period.
Cause: The complexity of the disorder is attributed to cultural, Nutritional and factors like, mites, fungal, viral, hormonal imbalance etc. The exact cause and control of the malady is yet to be established.
- Pruning of malformed panicles: The shoots carrying malformed panicles were removed from March 15 to May 15. The treatment proved useful to reduce the intensity of malformation of inflorescence during the subsequent years. There was significantly less number of malformed panicles in cv. Langra during the succeeding year if the malformed panicles were removed by 15th of April, the previous year.
Nutrition: The experimental trees were applied with recommended doses of NPK according to traditional method and in split applications on bio-monthly and quarterly basis. The trees were also sprayed with trace element solution of zinc, boron, and copper before bloom and after fruit harvesting. Treatments proved effective to control or minimize the incidence of malformation. However, urea spray after fruit harvest in early July proved to reduce the incidence of malformation of inflorescence in the treated trees.
- Application of plant growth regulators: The experimental trees cv. Langra and Chaunsa were sprayed with GA (20, 30, 40 and 50ppm), NAA (100 to 250ppm), Paclabutrazol (1000 and 1500 ppm) and ethrel (500-1000ppm) at prebloom and post harvest stage. GA @ 30ppm reduced incidence of malformation when sprayed prebloom, NAA @ 150ppm and paclabutrazol @ 1000ppm at post harvest stage proved significantly effective to control the incidence. Ethrel however, could not affect to control the incidence. Spray of fungicides:
- Spray of fungicides like Topson-M and Captan were applied during panicle pruning in April and after harvesting during the month of July. The trees sprayed with Topson-M particularly during July produced less malformed panicles as compared to the control trees.
Symptoms: The term biennial, alternate or irregular bearing generally signifies the tendency of mango trees to bear a heavy crop in one year (On year) and very little or no crop in the next year (Off year). Most of the commercial varieties of north India, namely, Dashehari, Langra and Chausa are biennial bearers, while south Indian varieties like Totapuri Red Small, Bangalora, and Neelum are known to be regular Bearers.
Causes: When a tree produces heavy crop in one season, it gets exhausted nutritionally and is unable to put forth new flush thereby failing to yield in the following season. The problem has been attributed to the causes like genetical, physiological, environmental and nutritional factors.
Control: For overcoming biennial bearing, deblossoming is recommended to reduce the crop load in the ‘On’ year so that it is balanced in the ‘Off year. Proper maintenance of orchard by way of effective control of pests and diseases and regular cultural operations may also result in better performance of the tree every year. Soil application of Paclobutrazol (PP) or Cultar @ 4 g/tree in the month of September resulted in early flowering with higher fruit set and yield. It may be applied every year for regular fruiting, particularly in young trees. Ringing of branches is recommended as means of inducing flowering in the ‘Off’ year. However, Weak, stunted, unhealthy trees should not be ringed to force flowering. It involves removal of 1 cm wide ring of bark on a branch of about 15 cm thicknesses. Ringing stops vegetative growth and results in accumulation of carbohydrates and other metabolites in the portion of the branch above the ring, thereby creating physiological condition for flowering. Ringing should be done in August or early September, well before the time of fruit-bud differentiation.
The intensity of fruit drop varies from variety to variety. Among the commercially grown varieties, Langra is more susceptible to drop, while Dasheri is the least. The fruit drop is more or less a continuous process and can be classified into three phases, viz. (i) pinhead drop, (ii) post-setting drop and (iii) May-month drop. The fruit drop in first two phases is insignificant compared to the third phase which affects the final yield significantly and needs more attention.
Causes: Embryo abortion, climatic factors, disturbed water relation, lack of nutrition, attack of disease and pest and hormonal imbalances are the major factors that lead to fruit drop.
Control: The foliar application of Alar (B-nine) @ 100 ppm or NAA 20 ppm at pea stage of fruit was found effective in controlling fruit drop in mango.
Black tip is a serious disorder, particularly in the cultivar Dasheri.
Symptoms: The affected fruits become unmarketable and reduce the yield to a considerable extent. The damage to the fruit gets initiated right at marble stage with a characteristic yellowing of tissues at distal end. Gradually, the colour intensifies into brown and finally black. At this stage, further growth and development of the fruit is retarded and black ring at the tip extends towards the upper part of the fruit.
Causes: Black tip disorder has generally been detected in orchards located in the vicinity of brick kilns. It has been reported that the gases like carbon monoxide, sulphur dioxide and ethylene constituting the fumes of brick kiln are known to damage growing tip of fruits and give rise to the symptoms of black tip. Apart from these factors, irrigation, condition of the tree and management practices also play important role in deciding the severity of the disorder.
Control: Planting of mango orchards in North-South direction and 5-6 km away from the brick kilns may reduce incidence of black tip to a greater extent. The incidence of black tip can also be minimized by spraying Borax (1%) or other alkaline solutions like caustic soda (0.8%) or washing soda (0.5%). The first spray of Borax should be done positively at pea stage followed by two more sprays at 15 days interval.
Clustering in Mango (‘Jhumka’):
A fruiting disorder, locally known as ‘Jhumka’, is characterised by the development of fruit lets in clusters at the tip of panicles. Such fruits cease to grow beyond pea or marble stage and drop down after a month of fruit set.
Causes: Absence of sufficient population of pollinators in the orchards is the major reason. The other reasons causing the disorder are old and overcrowding of trees, indiscriminate spraying against pests and diseases, use of synthetic pyrethroids, monoculture of Dashehari and bad weather during flowering.
Control: Introduction of beehives in the orchards during flowering season for increasing the number of pollinators and restrict insecticidal sprays at full bloom to avoid killing of pollinators. Pests and diseases should be controlled in time by spraying the recommended pesticides and concentrations. Spraying of NAA (300 ppm) during October-November is recommended. The practice of monoculture of a particular variety may be avoided. Particularly in case of Dashehari, 5- 6% of other varieties should be planted in new plantations.