The disease spreads on a tree very slowly, but if left unchecked, can reduce yields in orchards.
The main spread of MMD to new areas is by infected pruning equipment or vegetative planting material.Mango is the only known host of the disease.
It may be associated with the bud mite, Aceria mangiferae but the mites have been shown to
spread the disease within a tree and not between trees.
Tree with the disease developed galls in the leaf axils of flush tissue that had been produced at least six months earlier. The galls were roughly circular, 20–50 mm in diameter and consisted of a proliferation of shoots which grew to a length of 10–30 mm,before dying and promoting the growth of new shoots.
The MMD symptoms are a result ofa hormonal imbalance in the trees, induced by theFusarium infections, and associated with bud mite infestations.
Abnormal, compact development of shoots and flowers are common signs of mango malformation disease. Both normal growth and mango malformation disease-affected growth may be present on a plant at the same time.
Growing points such as leaf and stem buds produce misshapen shoots with short internodes and brittle leaves. The leaves are significantly smaller than those of healthy plants and re-curve towards the stem giving a squat, bunchy-top appearance.
Shoot damage occurs in mature trees but symptoms are particularly serious for young plants, which become severely stunted.
Affected flower stems or panicles are thickened and highly branched, producing up to three times the normal number of flowers.
The flowers are enlarged, sterile and do not bear fruit. There are often high numbers of male flowers compared with perfect flowers. Panicles may also form dwarfed and distorted leaves.
The severity of the disease varies from variety to variety and tree to tree in the same variety. Seasonal variations in the occurrence and severity of problem correlate with ambient temperature at flowering
Protecting your Mango Treesproperty from Mango malformation disease( MMD)
Good orchard management occupies paramount importance in this context and plays a vital role in checking the disorder.
To avoid introducing mango malformation disease on to your trees, establish new plantings with pest-free nursery stock. Grafting or marcot material should never be taken from an infected orchard. Nurseries should not be established in orchards affected by mango malformation disease.
Thorough cleaning of pruning equipment between trees reduces the spread of pests and disease.
Make sure that you and your farm workers are familiar with mango malformation disease symptoms and other mango pests.
Ensure that workers, visitors, vehicles and equipment are decontaminated before they enter and leave your farm.
Different measures like application of growth regulators, urea, nutrients, acaricides and fungicides are suggested to control it. Of these the most simple, effective, economically viable and eco-friendly approach that has been tested at IARI to control this malady is the use of the leaf extracts of common weeds namely Datura stramonium, Calotropis gigantean, and neem tree (Azadirachta indica).
The biological constituents of these weeds possessing medicinal properties are alkaloids from datura, azadirachtin in neem and sugars, flavonoids, flavonol glycosides, oxypregnane-oligoglycosides, terpenes, terpene derivatives, pentacyclic triterpenoids and triterpenoids from C.gigantea.
Control of Malformation
Since there are different schools of thoughts regarding the causes of this malady. attempts have been made by various workers to control it by application of plant growth regulators, nutrients, pesticides, phenolics, anti-malformins and malformin-antagonists. deblossoming with or without growth regulators and pruning without or in combination with pesticides.
* Application of Plant Growth Regulators and Phenolic Compounds
Spray of NAA (100 to 200 ppm) during the first week of October has been worked out to reduce floral malformation.
Later, four sprays of 250 ppm NAA at weekly intervals from 20th October onwards have been suggested to reduce the intensity of malformation to the maximum possible.
Hence. spray of 100 ppm NAA has been suggested instead of 200 ppm NAA.
They also observed that spraying 200 ppm NAA in first week of October followed by spraying of 500 ppm of ethrel at bud inception stage during February was highly effective in reducing floral malformation.
Spray of 400 ppm of Ethephon at bud inception stage reduced the floral malformation significantly.
Increase in floral branches and yield was observed by the spraying of ethrel (250 or 500 ppm). or uniconazole 500 ppm in the month of December.
The gibberellic acid at 50 ppm causes delayed panicle emergence, increased number of perfect flowers and increased pollen viability.
Sprays in the months of October and November cause 50% reduction in malformation.
Spraying of 1000 ppm Paclobutrazol (10-60 gm/tree), prior to FBD, during the first week of October reduced malformation, increased number of healthy flowers and increased the yield.
Deblossoming at the bud burst stage alone and in combination with the spraying of 200 ppm NAA was reported very effective.
Deblossoming alone at bud burst stage gives substantial reduction in malformation; and alleviate panicle malformation however there is no effect of deblossoming in reducing the intensity of malformation.
Malformed and healthy buds prior to deblossoming and found that only those buds which are free from malformation produced normal panicles and those having malformation produced diseased inflorescences and reported that there is no effect of deblossoming.
The process of deblossoming is very cumbersome and hence it is advisable to develop a chemical for deblossoming purpose.
The effect of abscission promoting chemicals e.g. ethephon (500 and 1000 ppm). M and B 25105 (250. 500. 1000 and 2000 ppm) and carbaryl (5000 and 10.000 ppm) on chemical deblossoming was studied in Dashehari and Chausa cvs. of mango.
Ethephon affected almost a total kill of panicles irrespective of initial size at both the concentrations In Dashehari and panicles were completely shed within seven days of the treatment.
M and B 25105 was slightly effective at lower concentrations while carbaryl was ineffective.
In case of Chausa various treatments were found to be ineffective in inducing deblossoming.
However, ethephon caused deblossoming of only smaller panicles.
Different chemicals were also found to exert profound inhibitory effect on the growth of mango panicles as compared to the control to deblossom chemically.
The application of 200 and 500 ppm ethrel to get complete control.
The panicle can be deblossomied by applying 250 ppm of cycloheximide.
Application of Nutrients
Soil application of N:P2O5:K2O (9:3:3) causes high N and low P and K reduced floral malformation.
Soil application of NPK + FeSO4 and is noticed a reduction in malformation and increase in yield.
The N reduced the floral malformation whereas high P and K had similar effect.
By the spraying of mangiferin Zn2+ and Cu2+, the partial control is achieved and good control by injecting phosetyl-Al+Zn+B in the tree trunk.
Reduction in floral malformation is achieved by cobalt sulphate ( 1000 ppm) when sprayed in first week of October
Application of Pesticides
The application of 0.04% diazinon controls malformation.
Two sprays of 0.32% diazinon minimize the malformation.
99% control of the disease is attained by excising the desired shoots 300-600 mm below the inflorescence and burning them and spraying trees with 0.1% parathion.
0.1% thiometon after every three weeks.
The simple removal of shoots In July and August had given 98% control with no disease for next two years.
Fumigating of the grafted plants with methyl bromide (30-40 mg/litre) for 1-3 hour kills the adults and nymphs of mite.
The recovery from malformation saplings is possible after pruning the seedling shoots except a terminal bud and few axillary buds and sprayed with 0.1% diazinon.
Aphidon chlordane. diazinon. fenitrothion. mecarbam and disulfoton gave 100% kill at 0.03 and fenthion. phosphamidon.
Phenthoate, azinphos-ethyl, methyl demeton and aldrin at 0.1% were equally effective against mite.
The percentage of malformed panicles is recorded with lowest (12.9) in swabbing treatment of the out ends with diazinon and highest (40.38) with the pruning alone.
Aldicarb. apocarb. dImethoate and phorate were most effec- tive against mite at 0.05 9 per plant.
Pruning is coupled with sprays of an acaricide and a fungicide have shown some promise in reducing the malformation.
It was found that 0.1% of diazinon, monocrotophos and phosphamidon were comparatively better in checking the infestation of bud mite, Acelia mangiferae.
It was found that diazinoll was the best followed closely by 0.1% monocrotophos and chlorophenamidine, 0.3% phosphamldon, 0.1% parathion and methyl parathion and 0.25% WP sulphur in reducing the malformation, if sprayed from July to December at 21 days of interval.
The complete control of the malady is achieved with the spraying of Fytolan (0.2%) once before inoculation followed by two sprays at 5 and 8 days intervals.
The mango malformation is incited by the eriophyid mites.
It is the feeding of these mites that leads to physiological disturbances in cell sap resulting in the abnormal growth.
In addition the injury caused by these mites and also provides entry for the fungus which is often found associated with this malady.
It has been further observed that the temperature plays a major role and is responsible for the low incidence of malformation in South India.
In North India, during winter season the bud development remains in diapause and it is during this period that the mites cause severe damage, resulting in malformed growth.
In South India there is no such diapausing period hence mites though present they are not in a position to cause sufficient damage to result in malformation.
It has also been established that mites carry spores of the fungus and act as carriers.
The over all effect of the mite and the fungus may be causing nutritional disbalance in the plant parts.
The real disbalance of phenolic compounds enzymatic activity. phytohormones and malformin like substances needs to be examined systematically and to arrive at some conclusion.
The control measures reported are impractical and controversial.
It is therefore concluded that the orchards may be kept in good hygienic conditions and disease free planting material be used for planting.
The orchards may be inspected quite frequently and any malady noticed may be removed from time to time.
Pruning of malformed panicles and parts along with affected shoots (at least 30 cm) may be done regularly.
It is observed by the author that systematic eradication of affected shoots and inflorescence resulted in gradual decrease in incidence of the disease.
The Spraying of insecticides and fungicides may be done after pruning operation is over.
The deblossoming at bud-burst stage alone or in combination with spray of 200 ppm NM prior to bud differentiation has been suggested and met with success, but manual deblossoming in a tree is rather impossible, hence a serious effort towards chemical deblossoming needs immediate attention.
Compiled by Harsh Saxena