About 70 million people obtain more than 500 cal per day from cassava roots. The crop is fundamental as food security of poor rural communities, but little is known about variability of root nutritional and quality traits. Roots from 2457 genotypes comprising landraces and improved clones, were screened for their nutritional (cyanogenic potential, carotene, minerals, and sugars contents) and agronomic (dry matter content, color intensity, and postharvest physiological deterioration) traits. The objective was to assess the range of variation for the traits evaluated to define future research strategies. Results are mostly based on unreplicated measurements. Carotene contents in the roots ranged from 0.102 to 1.040 mg/100 g fresh tissue and correlated positively with color intensity (ρ = 0.860) and cyanogenic potential (ρ = 0.305). Average levels of Fe and Zn were 17.1 and 7.5 mg/kg, respectively. Many clones derived from Meso-America showed high protein levels in the roots, probably as a result of the introgression from wild relatives only found in that region. The observed values for carotene, proteins and minerals contents suggest the potential for improving the nutritive value of cassava.

Cassava (Manihot esculenta Crantz) roots spoil 2 to 3 d after harvest because of postharvest physiological deterioration (PPD), which has remained an unsolved problem. Roots from different sources of germplasm were evaluated 5, 10, 20, and 40 d after harvest and some were found to be tolerant to PPD. Three genotypes showed zero levels of PPD even 40 d after harvest. Tolerance to PPD in roots with high carotenoid levels may be explained by their antioxidant properties. Irradiation of seeds in mutagenized populations may have silenced one of the genes involved in the expression of PPD. The tolerance to PPD found in other sources cannot be properly explained. The identification of several sources of resistance (and at least two different modes of action) suggests that now there are alternatives available for solving this problem, benefiting millions of resource‐limited farmers worldwide.

Improving total carotenoids content (TCC) in cassava roots is an important strategy to reduce vitamin A deficiency in human populations that rely on cassava as a source of energy in their diets. The high heritability for TCC in the roots allowed the International Center for Tropical Agriculture to implement a rapid cycling recurrent selection approach that reduced the standard length of each cycle from the ordinary 8 yr to 3. Data from successive evaluation nurseries suggested that gains have been made through time. However, no comparison of different cycles of selection has been made when representatives of each cycle were grown together. This study compares 4 to 5 clones representative of cycles of selection from 2004 to 2009. Results demonstrated significant gains for TCC as well as for total β‐carotene (TBC) expressed both in a fresh and dry weight basis. Although dry matter content (DMC) was not a selection criterion during the selection process, it increased with the successive cycles of selection. This suggests that indeed, simultaneous gains for TCC, TBC, and DMC are feasible. This finding is relevant for the important ongoing efforts at the International Institute of Tropical Agriculture and African National Programs to release biofortified cassava clones in Africa with adequate levels of dry matter content.

The cassava core collection (601 genotypes)

No abstract