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The breeding stages of a clonally propagated crop entails several steps and can take more than five years from hybridisation till cultivar release. The Accelerated Breeding Scheme (ABS) in sweetpotato relies on the use of multiple locations at the early breeding stages to reduce the years required for field evaluation. The aim of the study was to select the best progenies based on the ABS in sweetpotato towards the development of genotypes that combine high protein content with other important agronomic traits. Botanical seeds were generated from crosses between two diverse sets of parents, crossed using a North Carolina II design. F1-progenies (n = 363) were planted in a lattice design at three distinct locations during the 2017/18 planting season. Parameters recorded included pest and disease infestation, storage root traits and yield components, root protein content and nutrient related traits. Nutrient content was determined by near-infrared spectrometry. Analysis of variance and multiple t-distribution test and best test grouping were performed. There were significant differences (p < 0.001) among the genotypes for total number of roots, total root yield, marketable number of roots and marketable yield. The severity of Alternaria blight was significantly higher at Jozini. Forty progenies were selected (12.8% selection pressure) based on agronomic performance. Using the nutrient content results, four promising orange-fleshed clones (NC12-9, NC53-11, NC55-8, NC55-2) and one cream-fleshed clone (NC51-1) were identified with high storage root protein, iron and zinc contents. NC51-1 and NC55-2 produce promising storage root yields. The ABS approach is resource-demanding in the first phase but advances progenies rapidly to the subsequent breeding phases for cultivar release. [ABSTRACT FROM AUTHOR]

Sweetpotato improvement is influenced by selection of superior and best combiner parents with desirable traits. This study determined the genetic control of root nutrients: protein, β-carotene, starch, simple sugars and selected minerals. Two heterotic groups of five parents were crossed using a North Carolina II mating design to generate 25 full-sib families. Family 'Bophelo × 2008-3-1' did not produce seeds, therefore, only 24 families were evaluated in the field using a 14 × 26 simple lattice design with three replications at two sites. Root yield-related traits were recorded at harvest and nutrient content determined using Near-Infrared Spectroscopy. Genetic control parameters (general and specific combining ability and mid-parent heterosis) were calculated for the two sites. Significant interactions (p < 0.05) between female, male and/or families with sites were found in most nutrient and yield components. The highest overall mean values for protein, β-carotene, iron, zinc, fructose and glucose were recorded at the Jozini site whereas calcium, magnesium, sucrose and starch were higher at the Roodeplaat site. Significant (p < 0.01) interactions between female or male general combining ability and specific combining ability of family effects with sites were also found for most nutrient quality traits. The female parents '199,062.1 × Ndou' and '2012-8-4' were the best general combiners for most of the nutrient traits at the two sites while male parents '2003-8-1' and 'Khumo' were the two best general combiners. Several families had the highest specific combining ability for different nutrients in the two sites. 'Bophelo × Khumo' had the highest specific combining ability for protein, β-carotene zinc and iron at Jozini while family 'Bophelo × 1987-2-1' had the highest protein, iron and zinc content. Family '2012-8-4 × 2008-3-1' had over 95% heterosis for root β-carotene content at Roodeplaat. Family 199,062.1 × Ndou × 2005-5-5 had 35% for MRY. Understanding the genetic control of root nutritional quality traits is key to design suitable breeding strategies to improve these nutrients which are vital in combating malnutrition particularly in sub-Saharan Africa. [ABSTRACT FROM AUTHOR]