Five sweetpotato [Ipomoea batatas L. (Lam.)] cultivars named NASPOT 7 (Namulonge Sweetpotato 7), NASPOT 8, NASPOT 9 O (Namulonge Sweetpotato 9 orange-fleshed), NASPOT 10 O, and Dimbuka-Bukulula were approved for release by the Ugandan Plant Variety Release Committee in July 2007 (Mwanga et al., 2007a). This is the fourth group of sweetpotato cultivars to be officially released by the Sweetpotato Program in Uganda. The first three groups were released in different years, six in 1995 (Mwanga et al., 2001), six in 1999 (Mwanga et al., 2003), and two in 2004 (Mwanga et al., 2007c). The five cultivars released in 2007, described here, have acceptable storage root shapes when grown in light soils. They also have high dry matter content (≈30%) and good to excellent consumer acceptance, particularly among children younger than 6 years old and women (Mwanga et al., 2007b, Odongo et al., 2002; Potts and Nagujja, 2007; Wamaniala, 2008). The cultivars have low to moderate levels of field resistance to sweetpotato virus disease (SPVD) and Alternaria bataticola blight and high storage root yields compared with the average national storage root yield of 4.0 t·ha−1 (International Potato Center, 1999). The release of these five cultivars provides consumers and farmers with high-quality sweetpotatoes with cream- and orange-fleshed storage roots and moderate to high provitamin A contents with potential to alleviate widespread vitamin A deficiency in Uganda and other developing countries (Jaarsveld et al., 2005; Low et al., 2007; Ruel, 2001; UDHS, 2001) and contribute to food security (Mwanga et al., 2007a).
Origin
Throughout evaluation at the National Crops Resources Research Institute (NaCRRI), Namulonge, and in on-station and on-farm trials in major selected agroecologies in Uganda, the five clones were coded using the following nomenclature: Namulonge Ipomoea selection (NIS)/the initial year selected/the female parent/the selection (genotype) number/similarity code number (if present). The codes for the releases were ‘NASPOT 7’ (NIS/2002/SPK004/1), ‘NASPOT 8’ (NIS/2002/SPK004/1/1), ‘NASPOT 9 O’ (NIS/2002/SPK004/6), ‘NASPOT 10 O’ (NIS/2002/SPK004/6/6), and ‘Dimbuka-Bukulula’ (Dimbuka). ‘Dimbuka-Bukulula’, collected from Bukulula subcounty in Masaka District, is a superior Ugandan farmers' cultivar selected out of 1256 landrace germplasm accessions. The sweetpotato germplasm was collected from 21 major sweetpotato-producing districts in Uganda and assembled at NaCRRI in 2006. The pedigree of ‘Dimbuka-Bukulula’ is not known, but it is assumed to be a chance seedling or sport selected by farmers. The other four cultivars, NASPOT 7, NASPOT 8, NASPOT 9 O, and NASPOT 10 O, are seedling selections from the sweetpotato program at NaCRRI and were selected from bulked seed from an open-pollinated polycross nursery of 24 parents grown during 2000 to 2001. The 24 parents in the polycross block consisted of 10 released cultivars, three introductions, five advanced clones from the Ugandan sweetpotato breeding program, and six landrace cultivars (Table 1). The three introductions, Zapallo (PI 420027), Jewel (PI 440031), and Beauregard (PI 440132), were received from the International Potato Center (CIP), Lima, Peru, as pathogen-tested in vitro plantlets. The six landraces and the districts (in parentheses) from where they were collected were ‘Arivumaku-2’ and ‘Ngujja’ (Arua), ‘Kala’ (Kumi), ‘Kanyasi’ (Kabale), ‘Araka’ (Soroti), and ‘Bunduguza’ (Kamuli). The 24 parents were included in the polycross nursery for improvement or as sources of one or a combination of genes for control of desirable traits such as orange-fleshed roots (provitamin A), high dry matter (30% or greater), resistance to SPVD and Alternaria stem blight, and early maturity (3 to 4 months) (Table 1). The four released breeding lines described here were all progenies of ‘Kakamega’ (‘SPK004’) as the female parent, but because seed was open-pollinated, their male pedigrees are not known.
Origin and main attributes of 24 sweetpotato parents used in the 2001/2002 polycross nursery at Namulonge, Uganda.
Diffusion of Cultivars
The global HarvestPlus Program (HarvestPlus, 2007; Pfeiffer and McClafferty, 2007) was involved in an effectiveness case study to promote orange-fleshed sweetpotato (OFSP) to alleviate vitamin A deficiency in Uganda. The OFSP high provitamin A cultivars, NASPOT 9 O and NASPOT 10 O (Bengtsson et al., 2008), were given new names, ‘Vita’ and ‘Kabode’, respectively, in the HarvestPlus project areas (Wamaniala, 2008).The adoption rates for both ‘NASPOT 9 O’ and ‘NASPOT 10 O’ in three target HarvestPlus project area districts in Uganda reached 100% (3261) in Bukedea, 90% (3504) in Kamuli and 80% (3511) in Mukono; the numbers in parentheses were households growing both cultivars by Sept. 2008, three seasons after the farmers received them (Wamaniala, 2008). Spread of the other released cultivars in the three and other districts was not as fast and was mainly through farmer-to-farmer exchange or sale of planting materials and promotions by nongovernment organizations, schools, farmer groups, and government departments. In the absence of a seed company that deals in sweetpotato-planting materials, the released cultivars have already reached the following 22 districts in Uganda: Amuria, Bukedea, Busia, Jinja, Kabale, Kampala, Kamuli, Karamoja, Katakwi, Kayunga, Kumi, Lira, Manafwa, Masaka, Mayuge, Mpigi, Mukono, Nakasongola, Padel, Soroti, Tororo, and Wakiso (Potts and Nagujja, 2007; Wamaniala, 2008).
Description and Performance
The five released cultivars were evaluated for five seasons on-station at Namulonge in seedling, observation, preliminary and intermediate trials between 2002 and 2004, and for three seasons in on-station and on-farm trials between 2004 and 2006 in replicated, standardized, multilocation yield trials in three major agroecologies: 1) the warm, subhumid short grasslands where sweetpotato weevils and drought are important; 2) the warm, moist, tall grasslands where SPVD is severe; and 3) the cool, moist, southwestern highlands where Alternaria stem blight and low soil fertility stresses are prevalent. Mwanga et al. (2007a) provided detailed descriptions of pedigree, test sites, cultivars, planting materials, on-station and on-farm trials, planting and harvesting dates, farmer selection criteria, experimental designs, stability analysis, production package, and cultivar maintenance.
A total of eight multilocational on-station and 13 on-farm trials were conducted under rain-fed conditions, but only data for years 2004/2005–2006 are presented where the original number of clones (68,874) selected from the seedling nursery had been reduced to less than 10 for on-farm trials (Mwanga et al., 2007a). In the trials, the cultivars (Table 2) were evaluated to confirm resistance to SPVD, Alternaria stem blight (Tables 3 and 4), and sweetpotato weevils, Cylas puncticollis (Boheman) and C. brunneus (Fabricius) (Table 5). Classifications of the relative resistance to disease and weevil damage were based on field evaluation under natural disease and weevil population pressures as described by Mwanga et al. (2007b, 2002). The level of infection varied from low to high depending on agroecology, represented by Namulonge for high SPVD pressure, Kachwekano for high Alternaria blight pressure, and Serere and Ngetta for high weevil populations during dry periods. Storage root dry matter content, root yield, taste, and desirable agronomic attributes such as earliness (90 to 120 d to maturity), root size, shape (Tables 1 and 2), and storage root yield were also evaluated (Tables 3–5). The mean root yields of the released cultivars across sites varied in on-station (Table 4) and on-farm trials (Table 5), but they were above the national average of 4.0 t·ha−1. In over 70% of the cases, the yields of the cultivars were as good as or better than the local control cultivars (Tables 3–5) in the different agroecologies. ‘NASPOT 9 O’ and ‘NASPOT 10 O’ varied in root yield and biomass, but they have orange fleshed-storage roots with more provitamin A than Dimbuka-Bukulula and Tanzania, which have cream-fleshed roots that have very little provitamin A (beta-carotene) determined by spectrophotometry and high-performance liquid chromatography (Fig. 1; Table 3). Compared with the local checks, Dimbuka-Bukulula had higher root yields on station at most sites and gave equal or better yields on farm. Yield trends reported here are similar to the sweetpotato yield trends reported by Abidin et al. (2005), Grüneberg et al. (2005), and Manrique and Hemann (2002) who pointed out the need to select under high yielding and marginal environments when breeding for wide and specific adaptations. Although relative ranking in taste evaluations varied on different farms, the released cultivars had high acceptability on most farms (Table 5).
Morphological descriptors of five sweetpotato culivars released in Uganda in July 2007.z
Yield, quality attributes, and disease and insect pest reaction of five sweetpotato cultivars released in Uganda in July 2007.
Yield of ‘NASPOT 7’ to ‘NASPOT 10 O’, ‘Dimbuka-Bukulula’, and ‘Tanzania’ in four sites in Uganda.
Performance of ‘NASPOT 7’ to ‘NASPOT 10 O’, ‘Dimbuka-Bukulula’, and local checks in on-farm trials in Uganda.
Cross section of root and shoot of ‘Dimbuka-Bukulula’ (A and F) compared with ‘NASPOT 7’ (B), ‘NASPOT 8’ (C), ‘NASPOT 9 O’ (D), and ‘NASPOT 10 O’ (E).
Citation: HortScience horts 44, 3; 10.21273/HORTSCI.44.3.828
The five released cultivars are susceptible to sweetpotato weevils in no-choice laboratory tests and under dry season field condition evaluations. To date, there are no sweetpotato cultivars with high resistance to sweetpotato weevils in the world sweetpotato germplasm collections. The five released cultivars have moderate field resistance to Alternaria stem blight. ‘Dimbuka-Bukulula’ is susceptible to SPVD at Namulonge where the natural SPVD inoculum pressure is high and devastating to susceptible clones, but the NASPOT cultivars have moderate field resistance to the disease. These released cultivars are expected to perform well in agroecologies with low to high SPVD pressure and with well-distributed rainfall for at least 3 months soon after planting and during the early growth cycle.
Availability
The cultivars are maintained as pathogen-tested plants in the screenhouse at the Quarantine Station, Muguga, Kenya, 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.
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