Mg is a component of chlorophyll, hence essential for photosynthesis. It is an activator of many enzyme systems involved in carbohydrate metabolism and synthesis of nucleic acids. It also promotes uptake and translocation of P and movement of sugars within the plant.

The characteristic symptom is the interveinal chlorosis of the lower leaves beginning from the tip and the edges of the foliar lobes and extending inward between the central and secondary veins. The chlorotic tissue is generally yellow and some times pale green. When deficiency of Mg becomes severe, chlorotic areas can become necrotic and turn brown to whitish. The symptoms usually appear from 3rd month of planting continues till harvest and there are some cultivars/ varieties more susceptible to Mg deficiency (cassava variety, H-1687 popularly known as Sree Visakham). Moreover, when cassava is cultivated continuously in the same field, the occurrence of Mg deficiency is very common as evidenced from the long term manurial trial  being carried out at CTCRI since 1977.