Origin

During sweetpotato PPB trials on-farm (Gibson et al., 2008) and in on-station evaluations in major selected agroecologies in Uganda (Mwanga et al., 2010), ‘NASPOT 11’ was coded as NIS/2003/NKA1081L, in which NIS = Namulonge Ipomoea selection, 2003 = the initial year the clone was selected, NKA = New Kawogo, the female parent, 1081 = the selection (genotype) number, and L = Luwero District, the district where the farmer group initially selected the seedling and cloned it. ‘NASPOT 11’ is a seedling selection by farmers in the PPB trials from bulked seed obtained from an open-pollinated polycross nursery of 24 parents grown between 2000 and 2001. The 24 parents consisted of 10 released cultivars, three introductions, five advanced clones from the Ugandan sweetpotato breeding program, and six landrace cultivars described in detail by Mwanga et al. (2009). These 24 parents were for improvement or as sources of one or a combination of genes for control of desirable traits such as high DM (30% or greater), resistance to SPVD and Alternaria stem blight (Alternaria bataticola), and earliness (3 to 4 months). ‘NASPOT 11’ is a progeny of ‘New Kawogo’ as the female parent from open-pollinated seed; thus, its male pedigree is unknown.

Description and Performance

Selected descriptors of the International Potato Center (CIP), Asian Vegetable Research and Development Center, and International Board for Plant Genetic Resources (1991) were used to describe ‘NASPOT 11’. The main descriptors and gross morphology (in parentheses) of ‘NASPOT 11’ are as follows: 1) plant type (semierect); 2) predominant vine pigmentation (green); 3) secondary color vine pigmentation (purple nodes); 4) mature leaf shape general outline (triangular); 5) lobe type (no lateral lobes); 6) mature leaf size (small, less than 8.0 cm); 7) mature leaf color (green); 8) vein color (all veins mostly or totally purple); 9) immature leaf color (purple on both surfaces); 10) petiole pigmentation (green with purple spots throughout petiole); 11) flowering habit (sparse); 12) stigma exertion (inserted); 13) seed capsule set (sparse); 14) storage root formation (dispersed); 15) storage root shape (long elliptic); 16) storage root skin color (intermediate purple–red, no secondary color); and 17) root flesh color (cream, no secondary color) (Fig. 1). Data and detailed information on ‘NASPOT 11’ officially released in Uganda in April 2010 are described by Mwanga et al. (2010). The release information included detailed descriptions of test sites, materials and methods, cultivars, pedigree, PPB procedure, planting materials, on-station and on-farm trials, planting and harvesting dates, pest and disease evaluation protocols, farmer selection criteria, acceptability assessment, experimental designs, stability analysis, dry matter estimation, production package, and cultivar maintenance.

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Morphological characters of ‘NASPOT 11’, (A) flower, (B) shoot and storage roots, and (C) storage root attachment, shape, and flesh color.

Citation: HortScience horts 46, 2; 10.21273/HORTSCI.46.2.317

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In 2003, sweetpotato PPB was initiated with three farmer groups in Luwero, Mpigi, and Kiboga Districts in Central Uganda to assess the benefits of PPB (Gibson et al., 2008). This includes the time it would take to deliver improved cultivars to farmers and to determine the advantages of PPB. Each group received 2000 to 6000 pre-germinated sweetpotato seeds of at least two families (New Kawogo and Bunduguza) depending on the availability of scientific staff, technicians, and willingness of the groups to handle segregating populations from the seedling nursery and subsequent large numbers of clones in the initial stages of the PPB trials. Each selected seedling, based on vigor, root flesh color, and absence of disease symptoms, furnished five vine cuttings that were planted at each of the six sites on ridges, 1 m apart, and 30 cm between the plants. Subsequent clonal selections based on additional desirable traits such as high DM and storage root shape were planted on mounds or ridges in 2004 onward. By 2005 onward, the remaining selected clones were planted on at least three farms at each site. During clonal evaluation, 2005 to 2008, the farmers and researchers evaluated the selected clones in PPB trials in the three districts Luwero, Mpigi, and Kiboga. In Luwero, nine farmers each hosted the trials. Each farm consisted of a household that planted one to three ridges (50 plants per ridge), 1 m between ridges, 30 cm between plants on the ridge, with Dimbuka and NASPOT 1 as control cultivars. At harvest, 5 months after planting, taste ranking was done by 12 farmers (eight females, four males) in which 1 = best (most preferred) and 9 = least preferred, based on pairwise selection of the nine clones. In Mpigi, 15 farmers (farms) each hosted the PPB trial (13 females, two males) who planted four ridges (30 plants per ridge), 1 m between ridges, 30 cm between plants on the ridge. Taste ranking was done by 15 farmers (12 females, three males): 1 = best (most preferred) and 11 = least preferred as described previously. In Kiboga, one farmer hosted the PPB trial but a group of nine farmers (eight females, one male) were involved, planting the on-farm trial in three replications, on mounds (three plants per mound), 1 m between centers of the mound.

The promising advanced clones in the PPB trials were evaluated on-station at Namulonge, Kachwekano, Ngetta, and Serere and on-farm in Soroti and and Kabale Districts between 2006/2007 and 2008/2009. The routine procedure of the National Sweetpotato Program for evaluating advanced sweetpotato clones was followed (Mwanga et al., 2009). The clones were planted on four ridges, 5.4 m long, 1 m between ridges, one vine cutting per planting point on the ridge, 0.3 m between plants (18 plants/ridge) (plant density, ≈33,330 plants/ha), in a randomized complete block design (RCBD) with four replications. All outside rows of the experimental plots had border plants to minimize experimental error resulting from competition by border plants in adjacent plots. SPVD and A. bataticola blight were scored at 2 months after planting, whereas vine and total root and biomass yield were computed from plot yields. DM of storage roots was expressed as the average percentage of dry weight of fresh weight. DM was determined after weighing two replications of 500-g samples of sliced roots and oven-drying to a constant weight at 65 °C.

The PPB trials on-farm and on-station comprised three broad agroecologies: 1) the warm, sub-humid short grasslands (Ngetta and Serere stations; Lira and Soroti Districts) where sweetpotato weevils and drought are significant; 2) the warm, moist, tall grasslands (Namulonge station; Luwero, Mpigi, and Kiboga Districts) where SPVD is prevalent and severe; and 3) the cool, moist, southwestern highlands (Kachwekano station; Kabale District) characterized by Alternaria stem blight and low soil fertility stresses. In the trials, ‘NASPOT 11’ was evaluated to confirm resistance to SPVD, Alternaria stem blight, and sweetpotato weevils, Cylas puncticollis (Boheman) and C. brunneus (Fabricius) (Tables 1 through 3). Categories of the resistance to disease and weevil damage were based on field tests under natural disease inoculum and weevil population pressures as described by Mwanga et al. (2002, 2009). Disease infection and pest attack on-farm and on-station varied from low to high in the different agroecologies that had low to high SPVD, Alternaria blight, and weevil population pressures (Tables 2 and 3). Storage root DM, taste, and desirable agronomic attributes such as earliness, biomass, root size, shape (Fig. 1; Tables 1 through 3), and storage root yield were also evaluated. The mean root yield of ‘NASPOT 11’ varied across sites in the different agroecologies in PPB trials on-farm and on-station (Tables 2 and 3), but they were above the national average of 4.0 t·ha⁻¹ and the local checks. On average ‘NASPOT 11’ had better storage root yield and stability parameter estimates, namely regression coefficient (b), deviation from regression (S²d), and Tai's test stability criteria (α and λ) (Tai, 1971) compared with the local checks Magabari, New Kawogo, and Dimbuka (Table 4). A cultivar is considered to have stable performance if the slope of the regression line is close to 1 and the deviations from the regression line (mean square deviations) are small. In Tai's (1971) stability analysis, the interaction term is partitioned into two components: the linear response to environmental effects, which is measured by a statistic α, and the deviation from the linear response, measured by another statistic λ. A perfectly stable cultivar has (α, λ) = (−1,1) and a cultivar with average stability is expected to have (α, λ) = (0,1). Tai's analysis also provides a method of obtaining the prediction interval for α = 0 and a confidence interval for λ values. Although on average the root yields of ‘NASPOT 11’ were similar to the yields of ‘NASPOT 1’ released in 1999, the former was more reliable based on stability estimates (Table 4), and higher resistance to SPVD and Alternaria blight (Table 3).

Table 4.

Average storage root yield and estimates of stability parameters by regression analysis and Tai stability test for 10 sweetpotato clones during two seasons, 2006/2007 to 2008/2009 in four sites, Namulonge, Kachwekano, Ngetta, and Serere in Uganda.

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From the on-farm and on-station trial results (Tables 2 and 3), ‘NASPOT 11’ was as good as or better in performance for the desired traits than the local checks in specific locations and in the four agroeclogies represented by the four research stations. The taste ranking varied with location and community, suggesting that although ‘NASPOT 11’ in general performed well, it had superior performance where it was more specifically adapted such as in Kabale (Table 2) and at Namulonge (Table 3). These PPB trials demonstrate the potential for significant rapid progress in sweetpotato breeding, especially in specific environments, with the PPB approach complementing conventional sweetpotato breeding (Ashby, 2009). In the third year (2005) of clonal selection, participating farmers had started consuming storage roots from the promising PPB sweetpotato materials in their homes. In the fourth year (2006), PPB participating farmers started selling ‘NASPOT 11’ in their local markets in Zirobwe, Luwero District. This is a big plus for the PPB approach in ensuring that cultivars identified are well adapted to specific conditions and are highly client-oriented. Other PPB clonal selections had negative traits such as poor storage root shape, so they could not be sold in local markets. These results demonstrate the value of PPB and are in agreement with Belay et al. (2008), Gabriel et al. (2000), Gibson et al. (2008), Ssemakula et al. (2003), Thiele et al. (2001), and Witcombe et al. (2003). Sweetpotato consumption and exchange by participating farmers [participatory variety selection (PVS)] in the so-called conventional breeding would normally start only in Year 6 or 7 (Mwanga et al., 2009).

Insect and Disease Resistance

‘NASPOT 11’ is susceptible to sweetpotato weevils in no-choice laboratory tests and during field evaluation in dry seasons although its storage roots are mostly produced at moderate depth where they are protected from attack. The cultivar has moderate field resistance to SPVD under Namulonge conditions where SPVD inoculum pressure is high and high field resistance to Alternaria stem blight at Kachwekano where high A. bataticola blight pressure is prevalent. Both SPVD and A. bataticola blight are devastating to susceptible clones. ‘NASPOT 11’ is expected to perform well in agroecologies with low to high SPVD and low to high Alternaria blight pressure with well-distributed rainfall for at least 3 months from planting and during the early growth cycle. ‘NASPOT 11’ is expected to be a source parent for resistance to SPVD and A. bataticola blight in sweetpotato breeding schemes.

Diffusion of ‘NASPOT 11’

‘NASPOT 11’ is currently grown in the areas where PPB trials were conducted and where participatory trial evaluations on-farm were conducted together with on-station trials to generate stability performance data in Luwero, Mpigi, Soroti, Kiboga, Kabale, and Lira Districts. The spread of the cultivar is mainly through farmer-to-farmer exchange or sale of planting materials. In the absence of special promotions by development agents, its spread is expected to increase faster compared with other sweetpotato cultivars tha are not orange-fleshed (Mwanga et al., 2009).

Availability

‘NASPOT 11’ is maintained as pathogen-tested plants in a screenhouse at the Quarantine Station, Muguga, in Kenya as well as in the field and screenhouse by NaCRRI in Uganda. Requests for this cultivar should be addressed to: Seed Unit, CIP, P.O. Box 25171, Nairobi, Kenya. Requests for planting material within Uganda should be directed to: Sweetpotato Program, NaCRRI, P.O. Box 7084, Kampala.