Sweetpotato breeding

Lead Organization:

National Crops Resources Research Institute

Partner Organizations:

North Carolina State University, University of Greenwich

Community of Practice:

East & Southern Africa






In Africa and worldwide, weevils and virus diseases limit production of sweetpotato. In Uganda and Rwanda, weevils can destroy 60 to 100% of the crop. The project links U.S. sweetpotato research programs known for expertise in insect and disease resistance with programs in Uganda and other sub-Saharan countries. In addition to developing weevil and virus resistance, scientists aim to improve yield and agronomic traits and to improve food quality, nutrition, and storability, including developing sweetpotatoes higher in vitamin A.The goal of this project is to enable farmers to produce a reliable crop of more nutritious sweetpotatoes year after year.Project Highlight:Robert Mwanga, a Sweetpotato Breeding Project grantee from 1994-2009, was one of four co-recipients of the 2016 World Food Prize. Dr. Mwanga and his colleagues at Uganda’s National Agricultural Research Organization developed more than 20 sweetpotato varieties, many of which were biofortified with vitamin A. Read more about Dr. Mwanga’s work in a special interview here.

Grant Aims:

Development of insect resistant SP germplasmDevelopment of virus resistant SP (NaCRRI, NCSU)Development of co-dominant molecular markers to facilitate SP breedingDevelopment of a SP seed distribution systemSP Germplasm conservation, management, and utilizationPackage and dissemination of research outputsEnhance the SP value chainDevelopment of SP germplasm with improved quality and nutrition

Outputs and Outcomes:

The New Kawogo x Beauregard (NKB) mapping population was fully developed. The population consists of 287 progeny segregating for weevil resistance as well as other important traits; it is being maintained at NaCRRI/Uganda. One of the parents of the population, New Kawogo, is resistant to sweetpotato weevils, and the biochemicals responsible for the resistance have been identified as part of the project. Use of the mapping population will allow the biochemistry to be related to the genetics, so that resistance can be improved through marker-assisted selection.The basis of insect resistance in sweetpotato was analyzed. Weevil behavior studies with different sweetpotato varieties showed that weevils preferred Naspot1, Tanzania, ARA230 and Kakamega compared to New Kawogo and LIR302. The latter two varieties have shown to have traits resistant to weevils. The biochemical basis of the resistance was analyzed and chemicals that are involved in the resistance were identified.Three sweetpotato varieties; New Kawongo, LIR302 and ARA228 were confirmed to be resistant to sweetpotato weevil based on storage root damage data. The resistance was attributed to six phenolic compounds found in the latex of the sweetpotato parts. There is no antagonism between Bt toxins and resistance compounds. This finding suggests that the two strategies could work synergistically to combat weevil attack.The Reaching End User (REU) component of the HarvestPlus Program in Uganda has supported promotion and dissemination of orange-fleshed sweetpotato varieties bred by the CCRP project. The previously and recently released orange-fleshed sweetpotato (OFSP) varieties have replaced local varieties by proportions varying from 50% in Kamuli to 100% in Mukono and Bukedea districts in the REU project areas. The sweetpotato breeding work supported by the McKnight Foundation leading to the release of the OFSP varieties was published in the June issue of HortScience [Vol. 44(3):828-832].One of the project’s objectives is to identify root related chemicals that are involved in naturally occurring partial resistance to weevil pests, with the aim of enhancing this resistance through selection for these compounds. Hydroxycinnamic acid esters were found to influence insect resistance, including oviposition rates. Previous observations had implicated caffeic acid as a defensive compound in sweetpotato roots. This year, experiments with purified compounds combined with an artificial developed under the project showed that caffeic acid can have synergistic effects on larval mortality when combined with insecticidal proteins from the bacterium Bacillus thuringiensis. This implies that transgenic approaches, combined with breeding for natural defense compounds, could provide higher levels of resistance than each strategy used singly. Further, it was found that the volatile chemistry of sweetpotato roots changes dramatically when infested with weevils. Some of the induced compounds may have defensive roles. The project has developed molecular genetic resources aimed at improving the understanding of the inheritance of key traits and facilitating future marker-assisted breeding. The team developed the most complete molecular genetic map of sweetpotato to date using AFLP markers. The map consists of two parental framework maps based on the segregation of single-dose AFLP markers in the parental lines ‘Tanzania’ and ‘Beauregard’. In addition, multiple dose AFLP markers were placed on the map and used to identify homologous linkage groups. The TB mapping population (named for the cross Tanzania x Beauregard) is maintained in greenhouse and tissue culture formats at Raleigh and Namulonge. As part of the mapping effort, the team identified several strong quantitative trait loci (QTL) associated with resistance to root knot nematodes, dry matter, starch, beta-carotene content, and yield. A manuscript on this work has been submitted for publication.A total of 25 genotypes showed low weevil damage in the field expressed by low internal and external vine damage. These genotypes had lower damage scores than the resistant parent, New Kawogo, indicating that there was transgressive segregation for resistance.  The results also suggest that the hydroxycinnamic acid esters responsible for weevil resistance are heritable. In the laboratory bioassay, 70 genotypes had fewer (≥ 18 ) feeding holes on the roots compared to a mean of 23.5 feeding holes on New Kawogo. The resistance to sweetpotato weevils earlier reported in New Kawogo is controlled by active gene(s) that can be exploited in breeding.100 SSRa were found to be polymorphic and posted online in the USDA-ARS sharepoint. Root yields varied amongst the NBK progeny genotypes ranging from 2.2 – 4.9 t/ha. 11 clones showed transgressive segregation with an SPW severity score less than that of the resistant check (New Kawongo – Score of 2)The compounds Octadecyl-caffeic and Octadecyl-coumaric acids negatively affected feeding and oviposition of SPW biotypes from Uganda & Malawi on SP roots.They could account for resistance in tested SP varieites.Out of 47 SP clones evaluated, 22 reacted mildly to Alternaria blight, 11 had low & stable reaction to SP Virus Disease (SPVD) and 9 stable clones had high yields. The clones 316/3/2006/261, Ejumula/2006/146, Ejumula/2006/532, NAS7/2006/706, SPK004/2006/1009 & SPK004/2006/223 were stable for low reaction to SPVD and had high and stable yields231 co-dominant SSR markers have been screened for polymorphism on the parents; 172 were found polymorphic and have been used to genotype the NKB mapping population. The number of single dose markers scored against each parent is less than 8011 new OFSP clones were evaluated for yield at 4 sites. The following clones yielded highly NAS7/200/292 (14 t/ha); SOWOLA(OP)/2006/2 (14 t/ha) and SPK004/2006/1136 (28 t/ha). SPK 004 yielded much higher than the check clone NASPOT 1 (22 t/ha). SPPK004/2006/1136 was highly preferred by farmers and is being multiplied on a large scale to meet the growing demand form farmersResults of studies on weevil resistance on ten varieties of sweet potato revealed that six hydroxycinnamic acid esters (previously identified in the root latex) varied in concentration and this was strongly associated with the varietal resistance and susceptibility to sweet potato weevils observed in the fieldReleased roots and planting material of popular released varieties and orange-fleshed OFSP varieties to  farmers in Gulu, Lira and Jinja districts, with the aim of providing “starter” seed for the people returning from IDP camps so as to help them overcome hunger and vitamin A deficiency (VAD). This was during the Gulu District Agricultural Show (Northern Uganda) in March 2011 and the National Agricultural Show which was held at Jinja (eastern Uganda) in July 2011. There were distriubted to people visiting the project stall.  Demand for planting material of NASPOT 11 is also steadily increasing and as a results 289 farmers/extension/ground partners got skills in production of quality sweetpotato seed and its conservation leading to reduced requency with which farmers return to research station for seed; ie according to the project annual report 2012. Some farmers conserve limited seed under shade and rapidly multiply it at the onset of rains to get enough planting materials for field production. Varietes supplied for seed areNASPOT 10, NASPOT9, NASPOT 8, SPK 004, NASPOT 11, NASPOT 1.A new source of sweepotato weevil resistance was identified: LIR302. It was non-preferred in lab tests (choice and non-choice) and resistant in field tests.