Sweetpotato selection releases: Lessons learnt from Uganda

The National Sweetpotato Programme of the National Agricultural Research Organisation (NARO) in Uganda released 14 sweetpotato cultivars between 1994 and 2005. Of the released cultivars, six have gained importance in local Ugandan markets and in export trade to Europe and two are being used as parental sources for high drymatter (>30%), sweetpotato virus disease (SPVD) and nematode resistance in hybridization schemes, and in the genetic mapping work in joint international collaborative research. Two orange-fleshed sweetpotato (OFSP) cultivars, namely, Ejumula, and SPK004 (Kakamega), high in beta-carotene (the precursor for vitamin A) arespreading rapidly for combating widespread vitamin A deficiency in Uganda. The major steps leading to the release of Kakemega and Ejumula are used to illustrate the experience of the Ugandan sweetpotato breeding programme sustained activities for a decade, and lessons learnt are highlighted. The sustained breeding activitieshave led to a vibrant and robust program, increased international and south to south collaboration, increased partnership and alliances; shifted research focus from production to production per se and quality (nutrition), resulting into significant and relevant agricultural research. The lesson here is that it takes a long time to develop technologies, disseminate and commercialize them. It also requires commitment by the donor, government, scientists, farmers and other stakeholders for effective commercialization of the developed technologies

Identification of simple sequence repeat markers for sweetpotato weevil resistance

The development of sweetpotato [Ipomoea batatas (L.) Lam] germplasm with resistance to sweetpotato weevil (SPW) requires an understanding of the biochemical and genetic mechanisms of resistance to optimize crop resistance. The African sweetpotato landrace, ‘New Kawogo’, was reported to be moderately resistant to two species of SPW, Cylas puncticollis and Cylas brunneus. Resistance has been associated with the presence of hydroxycinnamic acids esters (HCAs), but the underlying genetic basis remains unknown. To determine the genetic basis of this resistance, a bi-parental sweetpotato population from a cross between the moderately resistant, white-fleshed ‘New Kawogo’ and the highly susceptible, orange-fleshed North American variety ‘Beauregard’ was evaluated for SPW resistance and genotyped with simple sequence repeat (SSR) markers to identify weevil resistance loci. SPW resistance was measured on the basis of field storage root SPW damage severity and total HCA ester concentrations. Moderate broad sense heritability (H2 = 0.49) was observed for weevil resistance in the population. Mean genotype SPW severity scores ranged from 1.0 to 9.0 and 25 progeny exhibited transgressive segregation for SPW resistance. Mean genotype total HCA ester concentrations were significantly different (P < 0.0001). A weak but significant correlation (r = 0.103, P = 0.015) was observed between total HCA ester concentration and SPW severity. A total of five and seven SSR markers were associated with field SPW severity and total HCA ester concentration, respectively. Markers IBS11, IbE5 and IbJ544b showed significant association with both field and HCA-based resistance, representing potential markers for the development of SPW resistant sweetpotato cultivars

Evaluation of promising sweetpotato genotypes for high altitude, cool, moist agroecologies of Uganda

No Abstrac

Advances in breeding for sweetpotato virus resitance in Uganda

No Abstrac

Insights into population structure of East African sweetpotato cultivars from hybrid assembly of chloroplast genomes.

Background: The chloroplast (cp) genome is an important resource for studying plant diversity and phylogeny. Assembly of the cp genomes from next-generation sequencing data is complicated by the presence of two large inverted repeats contained in the cp DNA. Methods: We constructed a complete circular cp genome assembly for the hexaploid sweetpotato using extremely low coverage (<1×) Oxford Nanopore whole-genome sequencing (WGS) data coupled with Illumina sequencing data for polishing. Results: The sweetpotato cp genome of 161,274 bp contains 152 genes, of which there are 96 protein coding genes, 8 rRNA genes and 48 tRNA genes. Using the cp genome assembly as a reference, we constructed complete cp genome assemblies for a further 17 sweetpotato cultivars from East Africa and an I. triloba line using Illumina WGS data. Analysis of the sweetpotato cp genomes demonstrated the presence of two distinct subpopulations in East Africa. Phylogenetic analysis of the cp genomes of the species from the Convolvulaceae Ipomoea section Batatas revealed that the most closely related diploid wild species of the hexaploid sweetpotato is I. trifida. Conclusions: Nanopore long reads are helpful in construction of cp genome assemblies, especially in solving the two long inverted repeats. We are generally able to extract cp sequences from WGS data of sufficiently high coverage for assembly of cp genomes. The cp genomes can be used to investigate the population structure and the phylogenetic relationship for the sweetpotato