The Intractable Cassava Problem

The FAO estimates that 600 million persons use cassava as a staple food. [FAO Newsroom, Partnership formed to improve cassava, staple food of 600 million people] In 2010, the cassava harvest worldwide covered 18,568,788 hectares of land, and produced 230,265,639 metric tonnes of cassava root, for a yield of 12.4 t/ha. [FOASTAT 2010 world data]

Why is cassava a problem? Two reasons. First, the protein is low quality, so the food mainly provides carbs. The hungry of the world lack protein and fat; cassava provides no fat and little protein. This results in protein deficiency and illness in any population dependent on cassava, unless they have a second staple food with high quality protein. A population can survive in good health with rice or wheat or quality protein maize as their sole carb and protein staple food. But a population cannot survive in good health with cassava as their carb and protein staple.

A second problem is the “cyanogenic glucosides of cassava (linamarin and lotaustralin). These, on hydrolysis, release hydrocyanic acid (HCN).” [Wikipedia, Cassava] HCN is highly poisonous; it is liquid at or below room temperature but it evaporates easily. Cassava contains HCN bonded to a sugar molecule (similar to glucose). When the cells of the root are damaged, an enzyme is released that breaks the bond between the sugar molecule and the HCN, releasing the cyanide poison. This makes untreated cassava highly poisonous.

Why is cassava an intractable problem? Two reasons. First, the crop is exceedingly drought tolerate. It can survive for months without any rain. The plant drops its leaves and simply waits for rainfall to regrow its leaves. The root crop can remain in the ground for months in dry conditions without spoilage. There is simply no staple crop, anywhere in the world, that is more drought-tolerant than cassava.

Second, the cyanogenic glucosides function as a highly effective pesticide. If any insects or animals attempt to eat the root, hydrogen cyanide is released by the plant cells to kill the pest. In the developing world, many farmers cannot afford pesticides, and they cannot survive if their staple crop is devastated by pests.

These two factors, drought-tolerance and pest control, make cassava a very attractive crop to grow, despite its problems. There exist cultivars of cassava, called “sweet” cassava, that have far lower levels of cyanogenic glucosides. But this version of cassava does not resist pests anywhere near as well as tradition cassava varieties.

If we are going to defeat hunger in populations dependent on cassava, we must break the hold that cassava has on agriculture. We need to develop more drought tolerant crops, and also expand the area of land that is irrigated. Fertilizer will make the marginal land on which cassava is usually grown more amenable to better staple foods. Fertilizer also helps alleviate pest and plant disease problems, because a healthier plant resists pests and diseases more easily. A transition from subsistence farming to commercial farming will make money available to growers for irrigation, fertilizer, pesticides, and workers. So the solution to the cassava problem is complex, and will require much time and effort.

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