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Two orange-fleshed landrace sweetpotato [Ipomoea batatas L. (Lam.)] cultivars named ‘SPK004’ (‘Kakamega’) and ‘Ejumula’ were approved for release by the Ugandan Plant Variety Release Committee in Apr. 2004 (Mwanga et al., 2004a). This is the third lot of sweetpotato cultivars to be officially released by the sweetpotato program in Uganda, the first two being released in 1995 and 1999 (Mwanga et al., 2003). ‘Ejumula’ and ‘SPK004’ are Ugandan and Kenyan landrace germplasm, respectively, selected from a batch of 25 orange-fleshed sweetpotato (OFSP) clones of different origins (Table 1). Both cultivars have good storage root shapes if grown in light soils, high dry matter content, and excellent consumer acceptance, especially among children and women. The cultivars have low to moderate levels of field resistance to sweetpotato virus disease (SPVD) and Alternaria blight (Tables 2 and 3) and high storage root yields compared with the average national root yield of 4 t·ha−1 (International Potato Center, 1999). The release of these two cultivars provides consumers and farmers with high-quality sweetpotatoes of orange flesh for combating vitamin A deficiency in the country (Mwanga et al., 2004a, 2004b).
The two landrace cultivars were designated ‘SPK004’ (‘Kakamega’) and ‘Ejumula’ during laboratory and field evaluations at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda. These two landraces were selected from a set of 25 OFSP clones assembled in 2001, and the set consisted of 1) five landrace cultivars [a) ‘Ejumula’ was collected from Aterai village, Wera Sub-county, Amuria County, Katakwi District (Abidin, 2001, 2004); b) ‘SPK004’ was introduced as pathogen-tested mini cuttings from the Seed Unit of the International Potato Center (CIP), Muguga, Kenya; and c) three other local OFSP Ugandan landraces (‘Sudan’ collected from Luwero, ‘Kala’ from Soroti, and ‘Mahuri’ from Kabarole)]; 2) one OFSP breeding line (Sowola-6) from the sweetpotato program in Uganda; and 3) 19 OFSP clones introduced from CIP, Lima, Peru, in Feb. 2001 (Table 1) (Mwanga et al., 2004a). The pedigrees of ‘Ejumula’ and ‘SPK004’ are not known but they are assumed to be chance seedlings selected by farmers. By the time of the official release, the two cultivars were spreading quickly through farmer–to-farmer exchange or purchase of planting materials and promotions by nongovernment organizations, schools, farmer groups, and government departments and had already reached 28 districts in Uganda (Apac, Arua, Bundibugyo, Entebbe, Gulu, Iganga, Jinja, Kabale, Kabarole, Kampala, Kamuli, Katachwi, Kayunga, Kibale, Kumi, Lira, Luwero, Masaka, Masindi, Mbale, Mbarara, Mpigi, Mukono, Ntungamo, Palisa, Soroti, Tororo, and Wakiso) (Mwanga et al., 2004a).
In communities that have had interventions to promote OFSP, there has been significant uptake of these cultivars. On average, OFSP has increased from 3.2% in 2004 to 22.4% of total production in 2006 in intervention communities. The frequency of farmers that produce OFSP increased from 21.7% in 2004 to 64.3% in 2006. Similarly, the frequency of farm households that consume OFSP increased from 25% to 69% (Yanggen and Nagujja, 2006).
Main standard morphological descriptors [International Potato Center (CIP), Asian Vegetable Research and Development Center, and International Board for Plant Genetic Resources, 1991] of the two cultivars are listed in Table 2. Important quality attributes, disease and insect pest reactions, and agronomic traits are presented in Table 3. Both cultivars have spreading vines and vigorous growth with dense foliage that suppresses aggressive weeds. The flower color in both cultivars is the same, pale purple limb with purple throat. Flowering is moderate in ‘SPK004’ and sparse in ‘Ejumula’, whereas capsule formation and seed set are sparse in both cultivars, enabling crosses to generate breeding populations under NaCRRI conditions without special treatment.
Both cultivars have high root dry matter content (greater than 30%) and a dry texture with a sweet taste when cooked. Flesh color ranges from light orange (orange with yellow patches) in ‘SPK004’ to deep orange in ‘Ejumula’ with intensity varying according to age of roots, location, agroclimatic factors such as soil type, and season (wet/dry).
Mwanga et al. (2004a, 2004b) have presented the data for official release of ‘SPK004’ and ‘Ejumula’ in Uganda. Details of the release information include descriptions of pedigree, cultivar, test site, materials and methods, planting materials, on-station and on-farm trials, planting and harvesting dates, pest and disease evaluation procedures, farmer selection, acceptability evaluation, experimental designs, stability analysis, dry matter determination, beta-carotene determination by spectrophotometry and high-performance liquid chromatography, corresponding results, and cultivar maintenance.
The following description is a summary of the release data.
The released cultivars were tested for eight seasons on-station and on-farm during 2001 to 2003 in replicated, standard multilocation yield trials in: 1) the warm, subhumid short grasslands where weevils and drought are important; 2) the warm, moist, tall grasslands where viruses are severe; and 3) the cool, moist, southwestern highlands where Alternaria stem blight and low soil fertility problems are widespread. A total of 10 multilocational on-station and 14 on-farm trials were conducted under rainfed conditions (Mwanga et al., 2004a). The cultivars were routinely evaluated for resistance to SPVD, Alternaria stem blight, and sweetpotato weevils, Cylas puncticollis (Boheman) and C. brunneus (Fabricius) (Table 3). Classifications of the relative resistance to disease and weevil damage were based on field evaluation under natural disease pressure and weevil populations with the level of infection varying from low to high depending on agroecology. Storage root dry matter content, root yield, taste, and desirable agronomic attributes (e.g., earliness, root size, shape and stability of root traits) were also evaluated (Table 3). ‘SPK004’ has moderate field resistance to SPVD, whereas ‘Ejumula’ is susceptible to the devastating disease at NaCRRI where high natural SPVD inoculum pressure is prevalent. Both cultivars are susceptible to sweetpotato weevils, but ‘SPK004’ is less susceptible than ‘Ejumula’ under field conditions. Both cultivars are highly susceptible to the pests in no-choice tests under laboratory conditions. Both cultivars, however, are potentially valuable as sources of beta-carotene in a high dry matter content background, and they have already been distributed by CIP to several countries in sub-Saharan Africa. These cultivars are expected to perform well in agroecologies with low to moderate SPVD pressure and with well-distributed rainfall for at least 3 months during growth.
The cultivars are maintained as pathogen-tested plants in the screenhouse at the Kenya Quarantine Station, Muguga, and are maintained in the field by NaCRRI in Uganda. Requests for these cultivars should be addressed to: Seed Unit, CIP, P.O. Box 25171, Nairobi, Kenya. Requests for planting materials within Uganda should be directed to: Sweetpotato Program, NaCRRI, P.O. Box 7084, Kampala.
Contributor Notes
This work was supported, in part, by a grant from The McKnight Foundation, Collaborative Crop Research Program.
Current address: Tarthorst 519, 6708 HS Wageningen, The Netherlands.
Former CIP sweetpotato breeder. Current address: Kansas State Univ. Horticulture Research and Extension Center, 35230 W 135th Street, Olathe, KS 66061.
To whom reprint requests should be addressed; e-mail rmwanga@naro-ug.org.
