Thirty years of cassava breeding for productivity - Biological and social factors for success

The Centro Internacional de Agricultura Tropical (CIAT, head-quartered in Colombia) established a cassava (Manihot esculenta Crantz) breeding program in the beginning of the 1970s with the aim of extending the Green Revolution success to less privileged sectors of the tropical populations. The initial decade was mainly dedicated to the collection of germplasm and generation of basic breeding materials. The later decades were devoted to applied breeding in collaboration with international and national programs in Latin America, Asia, and Africa. This paper focuses on the basic breeding at CIAT/Colombia (CIAT/HQ), applied breeding at CIAT/Thailand (CIAT/Thai), and distribution and selection of improved materials with many collaborators in Asia. Fresh root yield of populations was improved by >100% and root dry matter content by >20%. The national program collaborators used these populations to develop many improved cultivars in many countries. The biological factors considered as critical for this successful breeding effort were as follows: inclusion of a broad base of genetic variability obtained in the center of crop origin and diversification; evaluation of breeding materials under diverse environmental conditions including high stress environments; and a clear understanding of the different operational principles at different stages of breeding advancement, as illustrated by the emphasis on harvest index in selection within populations and on biomass in population building. The understanding of crop germplasm being a common heritage and the determination of agricultural scientists to use this for the welfare of the neediest people were the social factors for the overall success.