MANGO is a very difficult tree and it is always confusing to understand its pattern of vegetative and reproductive growth and its various disorders. Malformation is an intricate disorder of mango which was first reported by Watt in 1891 in Darbhanga, Bihar, India. Now it is widely reported in mango-growing countries India, Egypt, South Africa, Brazil, Sudan, USA, Israel, Mexico, Bangladesh and Pakistan.
The frequency of infestation is, however, variable being very heavy to slight. Although it first appeared in a tropical region it is comparatively less reported in this region. In Pakistan there is no region and no variety which is free from this disorder.
The intensity of infestation is however, different being less in `Langra’ and more in Chaunsa and Dusehri. The prevalence of this disorder for a long time is causing heavy losses in yield (about 10 per cent). This problem has attracted many agencies and governments of mango-growing countries to find out the causes and method to control this disease.
SYMPTOMS: The malformation of mango has two distinct types i.e. vegetative and floral. Vegetative malformation is also called as bunchy top. It is characterised by disrupting of apical growth resulting in several small flushes with quite short internodes at the apical ends of various branches. It may appear even in nursery stages on the main stem of the plants. These shoots bear small leafy structures appearing as if a crowded unhealthy and ugly looking mass.
Malformation of inflorescence manifests as deformed, suppressed and clustered inflorescence, thickened rachis, shortened primary and secondary axis. The panicles bear males with seldom a hermaphrodite flower. The manifestation is intricate in respect that from the same terminal, few buds are normal others malformed. On the same panicle, a part may be normal and the rest malformed. And on the same healthy panicle only one lateral is malformed while on a completely malformed inflorescence only one lateral is healthy. It indicates the intricacy of the problem or that there is some disorder in the internal system which either stops proper functioning or promotes abnormal functions at a certain site and from there the normal growth of the panicle is disrupted. This abnormality hence could be only localised.
CAUSES: Floral malformation, in view of the intricate symptoms, is quite tedious to explain, which seems to be localized. However, there are several workers/researchers who attributed it in the past to be due to viruses, having hopper as a vector, but failed to transmit the disease through grafting fungi (Fusarium subglutanens, F. moniliform etc.) but could not be treated with fungicides.
After experiments, it is proved that there is no difference in C/N ratio of healthy and malformed shoots of mango seedlings. High levels of carbohydrates in malformed shoots and panicle have been reported as well as contradicted. The malformed panicles and shoots possessed malformin-like substances, whereas healthy panicles and shoots do not. The uses of antimalformins have resulted in substantial reduction in the number of malformed panicles on the tree, but have failed to eradicate the malady. This is a sum up of efforts of over 100 years which still stand almost controversial.
On the other hand, observations over the years indicate that the infestation is more dominant and significant in the ignored and neglected orchards and a tree once infested maintains its level of infestation. It is also noted that the disorder is more prevalent in panicles appearing on the late flushes i.e. June and afterward, during the last year or the panicles appearing late in the season i.e. after mid March.
CONTROL MEASURES: The summary of results of the above experiments to control the disease is as under:
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 minimise 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.
The studies regarding malformation of inflorescence are under way with us and almost in the whole mango-growing region. Thus efforts are being made continuously to solve the problem. There are on the other hand claims to identify the casual organism and its control from different sources.
From the same places/countries the counter claims are also reported. This sort of controversy is prevalent everywhere. It is therefore, only a partial solution is available so far. It needs much intensive and systematic effort to find out the causes and method to control serious malady.
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