आम का गुच्छा-मुच्छा रोग: आम उत्पादन में एक गम्भीर समस्या
The disorder was first reported by Maries (Watt, 1891) in Darbhanga, Bihar (India). In the last three decades or so it has assumed an alarming situation in the Northern India where it is threatening for the mango growers because all the commercial cultivars are highly susceptible to malformation.
It widely occurs in Punjab, Delhi, Uttar Pradesh and less prevailing in Gujarat and Maharashtra. However, it is negligible in West Bengal and Bihar. The southern mango growing regions like Tamil Nadu, Andhra Pradesh, Karnataka and Kerala almost free from this disorder.
Symptoms of malformation:
The incidence of malformation varies from year to year, cultivar to cultivar and also with age of the trees. Generally it is occur in two forms; vegetative and floral malformation.
i. The vegetative malformation is observed at seedling stage in nursery. On, seedling over three month old, swelling appears in the axil of leaves. The affected plant shows bunching of terminal portion of leaf, shortening of the size of leaf lamina, shortening of internodal length and reduced length of petiole.
ii. Flora malformation directly affects the tree productivity. In the case of bearing trees the panicles are affected. The peduncles become thick and fleshy with profuse branching. The floral branches are crowded and enlarged flowers pedicels, calices and petals. Fertile flowers are rarely formed and fruits are seldom formed.
A profuse development of numerous small, leafy, structures occurs in place of flowers resulting in a witch’s bloom appearance. A few or all the inflorescence produced by a tree may be malformed and attachment of panicle even during off season.
Causes of malformation :
This malady has attracted the attention of many workers and various causes have been attributed to this from time to time. The probable causes of malformation have been reported as;
1. Varietal Factor -
The cultivars Bombay Green, Dashehari, Lucknow Safeda and chousa Showed a higher percentage of malformed panicles with Baramasi being the least affected. Average percentage of malformation was higher in the older trees than younger ones.
2. Environmental factor -
Malformation occurs frequently in sub tropical climate but tropical areas almost free from it. Moreover the panicles which appear early in the season even under subtropical climate tends to be malformed. It can be concluded that environmental temp. appear to be most closely related with cause of malformation. When flowering takes place at a temp. less than 25°C in the month of December-January at flower bud differentiation stage under North Indian conditions the tree tends to produce more malformed panicles.
3. Pathological factors
- Fungi - Fusarium moniliformae, oxysporum and F. solani found cause of malformation.
- Mites - Role of mites (Aceria mangiferae, Cheletogenas ornatus and Tyrophagus casleleannii) is a carrier of fungal pathogen as a cause of malformation.
4. Nutritional factors
Malformed tissue had lower level of nitrogen than the healthy tissue but the other records found higher nitrogen and potassium and low zinc in malformed tissues. However, enhanced application of nitrogen curtailed malformation whereas, addition of phosphorus and potassium significantly increase the malformation.
5. Physiological factors -
- Chlorophyll content - Higher amount of chlorophyll a, b and total in the leaves from malformed shoot and vice-versa by the others.
- Phytohormones - A low level of auxins, high level of gibberellic acid, cytokinins, ethylene and abscissic acid in the malformed seedling cause inhibition in their apical growth which affect the orientation and development of lateral organs resulting in the numerous small shoots. The cumulative evidence suggested that mango malformation since to be linked with the imbalance between growth promoters and inhibitors.
- Enzymes - The activities of IAA oxidase and poly phenol oxidase enzymes were reported to be higher in malformed panicles than the healthy panicles. In contrast the activities of amylase and catalase higher in healthy panicles.
- Nucleic acid - healthy panicles contains higher level of RNA and DNA than the malformed panicles.
- Carbohydrates - The carbohydrate level (reducing, non- reducing, polysaccharides & total carbohydrates) to be higher in the shoots bearing malformed panicles than the healthy one.
- Protein & amino acid - The malformed seedlings had higher protein and total amino acids than healthy seedlings.
6. bio-chemical factors -
- Carbon: Nitrogen ratio - Malformed panicles failure to fruit set is caused by improper C:N ratio which was considered to be an important factor responsible for differential growth and sex ratio in panicles.
- Malformin - The accumulation of malformin like substances from malformed panicles results an excessive vegetative growth which helps in continuous emergence of rudimentary leaves, inflorescence bearing florets in the intermingled leaflets probably due to hormonal imbalance.
- Mangiferine - It is a non-toxic poly phenols isolated from the malformed tissues, establishing the fact that higher content of phenols and steroids have strong co-relation with the intensity of malformation.
- Fussicoccin - A phyto-toxin produced either by the insect injury and fungi have been reported to be one of the cause of malformation.
Mango Malformation Management:
1. Removal of panicles
Panicles which appear early in the season (December-January) when the temp. is low tends to malformed and unproductive. Hence it is advisable that such panicles should be removed as when they appear.
2. Mulching
Use of black polythene as mulch or covering the whole plant with it rise the temp. to some extent, malformation does not appear.
3. De-blossoming
At bud burst stage along or in combination with NAA @ 200 ppm during flower bud differentiation is proven most effective treatment to reduce malformation of panicles. For de-blossoming ethrel @ 200-500 ppm, cyclo-hexamide @ 200 ppm should be sprayed at panicle emergence stage.
4. Nutrient application
The application of nitrogen @ 200 g per plant reduce it for some extent but addition of phosphorus and potassium enhance malformation.
5. Selective pruning
Pruning of the malformed parts helps in reducing the malformation in subsequent years.
6. Raising seedling in polyhouse -
Vegetative malformation is a serious problem in seedling mango plants. It is advisable to raise mango nursery in low cost polyhouses.
7. Use of malformin antagonist
- For taking fruitful yield from the malformed panicles 3 spray of Glutathione @ 2250 ppm, Ascorbic acid @ 2110 ppm and Silver nitrate @ 600 ppm when the panicles are 4-6 cm long.
8. Use of chemicals
- Application of pesticides viz, Diezinon @ 0.04% or Bavistin @ 0.01% or Phosphomidon @ 0.04% or Methyl Dematon @ 0.1% or Phytolon @ 0.2% or sulphur @ 0.25% minimize the incidence of malformation.
- Spray of fungicide like Topsin M and Captan were applied during panicle pruning in April and after harvesting during the month of July produces less malformed panicles.
- Application of NAA or Planofix @ 200 ppm in October (prior to FBD) is most effective to minimize the incidence of floral malformation in almost all the cultivars. In addition to this, spray of Ethrel @ 400 ppm at bud inception stage during February.
- Use of Gibberellic acid @ 30 ppm or NAA @ 150 ppm and Paclobutrazol @ 1000 ppm at post harvest stages proved better to check panicle malformation.
9. Growing resistant varieties
At present none of commercial varieties are free from mango malformation. Although Bhaduran, Alib and Illaichi are resistant varieties. Lal Sindhuri has been used as one of the parent in hybridization programme to develop varieties free from malformation.
Authors:
Raj Bala Choudhary¹* and Virendra kumar²
¹Ph.D. Scholar, Sri Karan Narendra Agriculture University, Jobner, Jaipur, (Raj.)
²Agriculture Officer, Oriental Bank of Commerce
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