Combining ability, heterosis and heritability of sweetpotato root protein, β-carotene, sugars and mineral composition

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, beta-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 x 2008-3-1' did not produce seeds, therefore, only 24 families were evaluated in the field using a 14 x 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, beta-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 x 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 x Khumo' had the highest specific combining ability for protein, beta-carotene zinc and iron at Jozini while family 'Bophelo x 1987-2-1' had the highest protein, iron and zinc content. Family '2012-8-4 x 2008-3-1' had over 95% heterosis for root beta-carotene content at Roodeplaat. Family 199,062.1 x Ndou x 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.