Sweetpotato, with a global annual planting area of approximately 9 million ha, is the second most important tropical root crop. It is widely adapted, being grown in more than 110 countries. Early maturing varieties grow in 3-4 months. It is hardy and has multiple uses. Both roots and foliage are edible and provide energy and nutrients in diets. Distinct quality types have different uses, with orange-fleshed sweetpotato being valued for its extremely high provitamin A content, and other types used in varied fresh and processed forms. Sweetpotato is easily bred, as true seed is easily obtained and generation cycles are short. There are five objectives of this review. The first objective is to briefly describe recent production and utilization trends by region; the second is to review knowledge about the origin and genetic nature of sweetpotato; the third is to review selected breeding objectives. The fourth objective is to review advances in understanding of breeding methods, including: (i) generation of seed through polycross nurseries and controlled cross breeding; (ii) a description of a new accelerated breeding approach; (iii) recent efforts to systematically exploit heterosis; and (iv) new approaches of genomic selection. The fifth objective is to provide information about variety releases during the past 20 years in West, East and Southern Africa, South Asia, East and South-east Asia, China and the Pacific.

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Orange-Fleshed Sweet Potato (OFSP) varieties have high pro-vitamin A and medium amounts of iron and zinc. Drought susceptibility is perceived as one of the major drawbacks of this crop type and currently available varieties do not allow sustainable and enduring production in drought affected regions. Screening and selection for OFSP for drought tolerance could have a positive impact on the livelihood and health of vitamin A deficient people in Sub-Saharan Afica (SSA). In this study 18 OFSP genotypes from Lima, Peru and two Kenyan check cultivars, Marooko (drought tolerant) and K566632 (susceptible) were screened for drought tolerance at Kiboko (Latitude 010 15' S; Longitude 360 44' E; Altitude 975 masl) and Marigat (Latitude 0° 38, 0" N; Longitude 36° 5, 0" E; Altitude 970 masl) during the years 2008-2009. A split-plot design was used with two levels of treatment, non-irrigated and irrigated as the main factor and the genotypes as the sub-factor. All the treatments were laid out in a randomized complete block design. Stress tolerance index was used to identify genotypes with high stress tolerance and high yield potential. In both site genotypes 194573.9, 420014, 440286, 189135.9, 187017.1 and 441725 showed high stress tolerance and yield potential compared with the check by registering higher stress index that ranged between 0.37-0.96 and very low susceptibility index. The multidimensional preference analysis of the bi-plot distinguished the same genotypes as high yielding in both treatments imposed. Correlation analysis revealed that Yield potential (Yp) and Stress yield (Ys) had highly significant positive correlation coefficients with Stress Tolerance Index (STI), Mean Productivity (MP) and Geometric Mean Productivity (GMP) and they can be used as the most desirable indices for screening drought tolerance genotypes.

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In vitro techniques have been shown to be useful in identifying relatively drought-tolerant genotypes at early stages of development. In this study, drought-induced alterations in early shoot and root development of 59 sweetpotato genotypes was evaluated in the tissue culture laboratory at the Kenya Plant Health Inspectorate Services, Quarantine station, Muguga, Kenya. These genotypes were obtained from Lima, Peru and were evaluated against two known Kenyan check varieties, Marooko (drought tolerant) and K566632 (drought susceptible). Plantlets of each genotype were raised on Murashige and Skoog basal solid medium, from an original node consisting of a 0.2-0.5 cm stem segment. These were exposed to polyethylene glycol (PEG 6000) at three different concentration levels: 0, 10 and 15 g/l. The experiment was laid out in a factorial completely randomized design with three replications. Data on shoot and root growth were recorded during tissue regeneration lasting over a period of 4 weeks per regeneration cycle. Analysis of variance indicated genotypes, salt levels and salt level × genotype interaction, were highly significant (P<0.01) with respect to all the traits. At 15 g/l concentration of PEG, genotypes 189135.9, 194515.5, 440024, 441724 and 440001 had roots that were longer than those of Marooko. Genotypes 194515.5, 194539.36, 441724, 441538, 189135.9, 41768, 192033.5 and 440429 recorded greater leaf expansion, greater stem length elongation, greater root and shoot growth and high dry matter production at all salt levels indicating their ability to withstand severe water stress conditions. Genotypes 189151.38, 420027, 440132, 440104, 440034, 421111, 440166 and 441755 were identified as susceptible. The technique was found to be a useful tool for screening a large number of sweetpotato genotypes within a relatively short period of time.