Tapioca(kappa) followed by wheat became popular in' rice only ' kerala due to famine condition around 1940 to 1960

It was the Portuguese and the Dutch who introduced plants like the pineapple, tapioca, papaya, peanut ,potatoes, tomatoes, and chili peppers and rubber to Kerala ;from americas
 Tapioca became popular in kerala due to near famine conditions of 1930's to 1960's;followed by the introduction of wheat in kerala later in 1960's

Cassava

The cassava plant belongs to the spurge family. Native to South America, it is now widely grown throughout the tropics for its starch-containing roots, from which tapioca and bread are made. (Manihot utilissima, family Euphorbiaceae.) Cassava is grown as a staple crop in rural India, especially in the southern states like, Kerala and Tamil Nadu. Cassava is the food of the common class people of Kerala. Altogether, it provides a staple crop for approximately 200 million people. The root cells contain the poison cyanoglucoside (converted to hydrogen cyanide in the body) but the plant's latex (milky fluid) contains enzymes that break down the poison. During the processing of cassava the two must mix; the commonest method is by fermentation, although some poison may remain. Tapioca is basically a root starch derived from the cassava, or yuca plant. It's often used to thicken soups and sweeten the flavour of baked goods, and it makes a dandy pudding.