Plant 343

Manihot esculenta Crantz (Euphorbiaceae)


Manihot esculenta is widely grown in sub-Saharan Africa providing food security and a source of income for subsistence farmers, many of whom are women. Cassava is an adaptable tropical crop capable of growing in poor soils with low rainfall. Its root-tubers are rich in carbohydrate and a good source of calories, but are low in protein and vitamins A and E. The leaves have a higher nutrient content and are widely used as a leaf vegetable. However, without preparation, all parts of the plant are toxic; the levels of cyanogenic glucosides in the leaves making it almost immune to locust attack.

Sixty percent of global cassava production is in Africa, where up to 300 million people rely on this starchy root as their staple diet. With up to 800 million people reliant on cassava worldwide, the human consequences of any threat to the health of this plant could be dire.

The United Nations has designated 2020 International Year of Plant Health. This is an opportunity to increase global awareness of how protecting plant health positively impacts economic development, reduces poverty and hunger, and safeguards the environment.

Cassava is susceptible to a broad range of diseases caused by viruses and bacteria. The most severe is Cassava Mosaic Disease (CMD), caused by African Cassava Mosaic Virus (ACMV); just one of many mosaic viruses responsible for morphological and cytological modifications in cassava. Viral infections can account for up to 82% yield loss in cassava harvests.

The primary route of viral infection in cassava is through vegetative propagation. Once in the field, the whitefly vector, Bemisia tabaci, is responsible for transmission from infected to uninfected plants. Cassava, originally from South America, was introduced to Africa in the 1500s, where ACMV is understood to have jumped species from wild host plants.

A dual approach of research and innovation is likely to be the most effective means of managing ACMV and CMD. Moreover, understanding the roles wild plants have in hosting and transmitting ACMV is crucial. Completion of the cassava genome sequence will help accelerate the development of cultivars tolerant or resistant to CMD. The Next Generation Cassava Breeding Project is using genetic sequencing to identify traits that are resilient to a warming climate, whilst improving the crop’s nutritional quality and yields. The International Institute for Tropical Agriculture is working to increase the impact of cassava breeding programmes, making the process socially inclusive and demand led.

Further reading

International Institute of Tropical Agriculture

Lin ZJD et al. 2019. Engineering disease-resistant cassava. Cold Spring Harbor Perspectives in Biology 11: a034595.

NextGen Cassava

Kate Pritchard