Initially the disease was attributed to various factors such as nutritional deficiency, hormonal imbalance, virus or mycoplasma and mites. The hypotheses and logic that put forward in their support and various discrepancies in these hypotheses have been critically reviewed. The role of the above mentioned factors in light of the experimental evidence generated in recent years has been delineated. The reasons that doubted the pathogenicity of Fusarium moniliforme var. subglutinans (F. mangiferae) and the subsequent plethora of experimental evidence clearing the ambiguities and confusion as the inducer of the disease have been presented in the fifth chapter. The chapter also contains a detail account of morphological and cultural characters, systemic position and nutritional requirement of the fungus, the stepwise description of the infection process by the fungus and physiology of pathogenesis. Some other fungi have also been reported to be associated with the malformed tissues. Their status in causation of malformation has been discussed.