Variability of high dry matter orange-fleshed sweetpotato [Ipomoea batatas (L.) Lam.] in later breeding stages and allocation of breeding resources in the humid tropics of Peru

Orange-fleshed sweetpotato (OFSP) [Ipomoea batatas (L.) Lam] often lacks high dry matter (DM) in elite breeding material. The objectives were to examine the potential to combine yield with high root DM and high root beta-carotene (BC) content by variance-covariance analysis and optimization of breeding scenarios for "OFSP dry and starchy," which was exemplarily shown for the humid tropics of Peru. The trial series across seasons suggested a good chance to combine yield and quality (high DM and high BC). The unique data were used to estimate variance components and correlations among four yield traits and four quality traits. For the optimization of selections in our breeding program, we used the selection response by Cochran's approach and developed a small R script. Responses to selection were predicted for storage root yield and a modified Elston index aggregating eight traits. The differences between two- and three-stage selection scenarios were small. For storage root yield, the recommended optimized two-stage selection increased the response relative to the standard (one-stage selection 100%) to 141.6% for 2268 plots and to 189.1% for 540 plots; the corresponding optimized three-stage selection increased the response to 144.3% for 2268 plots and to 190.5% for 540 plots. A two-stage selection is recommended with two to three locations at the first stage and 6-12 locations at the second stage, according to low- or high-test capacity, respectively. Optimization of breeding schemes is much more important for smaller breeding programs than those with larger test capacity, and this allows testing even larger numbers of genotypes in a small breeding program.