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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The amount of genotypic and phenotypic variability that exists in a species is important for selection and initiating breeding programs. Yam bean is grown locally in tropical countries of the Americas and Asia for their tasty storage roots, which usually have low dry matter content. The crop was recently introduced in Uganda and other East and Central African countries to supplement iron (Fe) and protein content in diets. This study aimed to estimate genetic variability for root yield and quality traits among 26 yam bean accessions in Uganda. A randomized complete block design was used with two replications across two ecogeographical locations and two seasons during 2012 and 2013. Near-infrared reflectance spectroscopy (NIRS) was used to determine quality of storage root samples. Significant differences among genotypes were observed for all traits except root protein, zinc (Zn), and phosphorus contents. Genotypic variance components () were significant for storage root fresh yield (SRFY), storage root dry matter (SRDM), storage root dry yield (SRDY), vine yield (VNY), fresh biomass yield (FBY), and storage root starch (STA) and Fe contents. For traits with significant the broad sense heritability estimates ranged from 58.4% for SRDY to 83.6% for FBY; and phenotypic coefficients of variation were high for SRFY (66%), SRDY (53.3%), VNY (60.5%), and FBY (59%), but low to medium for SRDM (22.6%), STA (15.1%), and Fe (21.3%). Similarly, the genotypic coefficients of variation were high for SRFY (56.7%), SRDY (53.3%), VNY (55%), and FBY (53.9%); and low for SRDM (20%), STA (12.4%), and Fe (17.8%). There were strong positive correlations between SRFY and both SRDY (r = 0.926) and FBY (r = 0.962), but low-to-moderate correlations among quality traits. It should be possible to breed for high dry matter yam beans by using low dry matter accessions due to the observed genetic variation ( = 9.3%2), which is important if the high dry matter Pachyrhizus tuberosus accessions (known as chuin) from Peru cannot be accessed. This study indicated substantial genetic variation for yield and quality traits in yam bean, demonstrating potential for adaptability to growing conditions and consumer needs in East and Central Africa and for genetic improvement through selection.

Sweetpotato forms a major part of the diet of both rural and urban communities in Rwanda. Moreover, the crop is expected to become more important with time as farmers engaged in mixed crop-livestock systems increasingly use vines as animal feed. Its use for both food and feed makes it attractive in areas where land availability is a constraint. Moreover, the implementation of the Rwandese government policy, which encourages use of zero grazing practice to mitigate soil erosion, emphasizes the use of sweetpotato as an alternative source of animal forage (MINAGRI, 2013).The six released cultivars have relatively high dry matter content (30%) and have good to high consumer acceptance. The cultivars also have moderate to high levels of field resistance to sweetpotato virus disease (SPVD) and Alternaria bataticola blight and yield higher (8.3 to 22.8 t • ha -1 ) than the average storage root yield of 6.0 t • ha -1 [FAOSTAT, 2011; International Potato Center (CIP), 1999]. Two of the released cultivars, RW11-2910 and RW11-2560, are orange-fleshed sweetpotato (OFSP), providing consumers with moderate to high beta-carotene (provitamin A) with potential to alleviate vitamin A deficiency. Thus, the official release of these dual-purpose sweetpotato cultivars for both food and animal feed, developed through on-station evaluation and farmer participatory selection, to augment the food and farming systems in Rwanda is reported.

The yam bean (Pachyrizhus spp) was recently introduced as a root crop with high-yield potential, considerable protein and micro-nutrient concentration to investigate its potential for food production in Rwanda. Except for Chuin types (Pachyrizhus tuberosus) which have high storage root dry matter (RDM) (26 to 36%), most accessions are consumed raw and are reported to have low RDM. The present study aimed to evaluate and identify adapted high yielding yam bean accessions in major agro-ecological zones of Rwanda. Field experiments with 22 accessions were conducted in 2012 at three research sites representing the major agro-ecologies of Rwanda. Strict reproductive pruning was followed to enhance fresh storage root yields. Across locations, ANOVA indicated highly significant differences (p < 0.01) for genotypes (G), locations (L), seasons (S) and G x L effects for storage root yield, vine yield and harvest index and accounted for 21.88%, 43.41%, 1.43% and 13.25% of the treatment sum of squares, respectively. The GGE bi-plot revealed that EC209018 is high yielding but unstable. However, genotypes, AC209034, AC209035 and EC209046, were outstanding in terms of adaptation and relative stability across the 3 locations, suggesting consistent root yields irrespective of location and environmental conditions. The GGE scatter plot showed that all genotypes formed one mega-environment for storage root yield (Karama, Musanze and Rubona) and two mega-environments for biomass yield (Karama and Rubona as one mega-environment and Musanze the second one). This study revealed that Karama is the most suitable environment for evaluation and selection of yam bean for yield components in Rwanda.

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The goal of yam bean improvement in Africa is to develop superior high yielding and high dry matter cultivars that are preferred for adoption. In this study, the estimates of variance components, heritability and response to selection were studied in F3 yam bean families selected from interspecies crosses targeting improvement of storage root dry matter and associated traits. Breeding populations were generated using North Carolina II (NC II) mating design involving high dry matter P. tuberosus chuin cultivar, low dry matter P. ahipa and the high yielding P. erosus yam beans. The progenies were advanced through selfing from F1 to F2 population and then exposed to selection at 10% selection intensity to obtain 83 high dry matter lines. The selected lines were evaluated in an F3 trial using a randomized complete block design (RCBD) with three replications at the National Crops Resources Research Institute (NaCRRI) Namulonge, in Central Uganda. The results revealed significant (P < 0.001) genetic variation for storage root dry matter (RDM), storage root fresh yield (RFY), storage root dry yield (RDY), vine yield (VNY), fresh biomass yield (FBY), harvest index (HI), starch (STA) and protein (PRO) content. High genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were obtained for VNY, RDY, FBY, RFY, RDM and STA. Narrow sense heritability was higher than 0.5 and response to selection was 15.5 to 33.1 for RDM, RFY, RDY, VNY, FBY and STA, indicating rapid genetic progress is achievable and early generation selection would be effective to improve these traits. Significant (P < 0.01) positive genetic correlations were observed between RDM, RDY, RFY, VNY, FBY and STA ranging from 0.422 to 0.963 implying that simultaneous improvement of these traits is possible in the current yam bean populations.

The current study aimed at evaluating the effect of gibberellic acid (GA 3 ) and sucrose on in vitro propagation of two elite sweet potato cultivars (Ukerewe and Gihingamukungu). Nodal explants from in vitro growing plantlets were harvested and cultured on Murashige and Skoog media supplemented with 2.5, 5, 10, 20 and 40 μM, GA 3 . In a separate experiment, sucrose was evaluated at 30, 60, 90, 120, 150, 180 and 210 mM. For Ukerewe, the explants cultured on medium supplemented with 10 µM GA 3 recorded the longest (2.78 ± 0.36 cm) microshoots. . On the other hand, cultivar Gihingamukungu explants cultured on media supplemented with 2.5 GA 3 µM produced the longest ((3.23 ± 0.40 cm) microshoots. Nodal explants from the two cultivars cultured on media supplemented with sucrose 150 mM yielded the longest microshoots (2.51 ± 0.26 and 2.34 ± 0.24 cm, respectively). From the results of the current study, it can be concluded that for micropropagation of the cultivar Ukerewe 10 µM GA 3 should be used while 2.5 GA 3 µM should be used for micropropagtion of cultivar Gihingamukungu. The regenerated plantlets were successfully weaned in the greenhouse. The protocol developed in this research will open new prospects for massive propagation of the elite sweet potato cultivars in Rwanda.