Rapid Cycling Recurrent Selection for Increased Carotenoids Content in Cassava Roots

Abstract

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.

Progress update: Crop development of biofortified staple food crops under HarvestPlus

“…Studies on GxE interaction for carotenoid content did not find significant changes in the relative ranking of genotypes, and found high (>0.6) heritability of carotenoid content in cassava roots [35,36,37,38]. Rapid-cycling recurrent selection was used to shorten the normal breeding cycle from eight years to two to three years for high carotenoid content [39].…”

Vitamin A cassava in Nigeria: Crop development and delivery

“…In Phase II (2009-2013), HarvestPlus and its partners developed analytical methods for cassava screening, demonstrating that spectrophotometric screening overestimated high-performance liquid chromatography (HPLC) values in yellow-fleshed cassava [17]. Rapid-cycling recurrent selection was used to shorten the normal breeding cycle from eight to 2-3 years for high carotenoid content [18]. Three first-wave vitamin A cassava varieties with 6-8 ppm total carotenoid content were released in 2011 (see Table 9.3).…”

The analysis of candidate genes and loci involved with carotenoid metabolism in cassava (Manihot esculenta Crantz) using SLAF-seq

“…Both proteins probably participated in the downstream pathways of carotenoid metabolism. There are many previous reports that focus on root-nutrient improvement and selection for high carotenoid content for cassava (Ceballos et al 2013;Carvalho et al 2016), while there are few reports involved in the relative genes and loci associated with carotenoid metabolism. XanDH and AAO in a flacca Tomato Mutant with Deficient Abscisic Acid and Wilty Phenotype, which suggests that XanDH and AAO are key enzyme genes in ABA synthesis (Sagi et al 1999).…”

“…Interestingly, there was no correlation between root color and expression of major carotenoid biosynthesis genes . Conventional breeding and genetic modification are the common strategy to improve total carotenoid content in cassava roots (Carvalho et al 2016;Ceballos et al 2013;Welsch et al 2010). It was showed that fibrillin and Or proteins may induce carotenoid accumulation by initiating the synthesis of a carotenoid deposition sink in the form of the large carotenoid-sequestering sheets (Li et al 2001;Carvalho et al 2012).…”