Performance of Informal Market Sweet Potato Cultivars in On-Farm Trials In
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Open Agriculture. 2017; 2: 431–441 Research Article Sunette Laurie*, Frikkie Calitz, Musa Mtileni, Whelma Mphela, Sidwell Tjale Performance of informal market sweet potato cultivars in on-farm trials in South Africa https://doi.org/10.1515/opag-2017-0047 received December 10, 2016; accepted June 5, 2017 1 Introduction Abstract: Several new sweet potato cultivars have been South Africa annually produces around 60,000 tons of released in South Africa from 2004 until 2011 with varietal sweet potato (DAFF 2014), a much lower production than traits suitable for the informal market. This paper reports most other countries in sub-Saharan Africa (FAOSTAT on results of on-farm trials conducted to evaluate the 2014). Notwithstanding, sweet potato is an important cultivars in broader agro-ecologies in the country. The indigenized root crop in South Africa and a popular trials were conducted at 15 localities across the 2011/12 traditional crop in the northern subtropical regions of the to 2014/15 planting seasons including six cultivars with country (Laurie et al. 2015b). The sweet potato industry in varying flesh colours. Data collection included marketable South Africa is notably different as there is, on one end, and unmarketable storage root yield classes, dry mass, a small number of large commercial mechanized farmers and taste acceptability. The sites were representative and, on the other end, the crop features prominently in of cool subtropical and warm temperate regions. smallholder cropping systems delivering to the informal Statistical analysis included ANOVA, AMMI, Discriminant markets. Smallholder and subsistence farmers easily analysis (DA) and Principal component analysis (PCA). include sweet potato in their cropping programmes Significant effects were detected for locality*cultivar because of its versatility, ease to cultivate and hardiness. and region*cultivar interactions for total and marketable Additionally, many people are starting to note the value yield, and for cultivar only for marketable yield. The factor of orange cultivars as rich sources of provitamin A (Laurie region was not significant. The mean marketable yield et al. 2015b). This is of great importance since Vitamin ranged from 13.1 to 19.0 t/ha, being highest for 199062.1 A deficiency (VAD) in South Africa is a national public and Ndou, while Bophelo had average stable yield over health problem with 43.6% of one- to nine-year-olds being a broad range of environments. The most prevalent vitamin A deficient (Shisana et al. 2013). The same survey unmarketable class was weevil damage (15.1%). The study also indicated that food security is at an unfavourable demonstrated PCA and DA as quick analytical tools to level, with 28.3% of the population at risk of hunger associate quality traits with cultivars to facilitate cultivar and 26.0% already experience hunger. Based on these recommendations. Bophelo and Ndou had been sold with alarming statistics, sweet potato is promoted for food and success on local informal markets and have large potential nutrition security. While the estimated informal market of to be promoted wider. 25,000 – 30,000 t for sweet potato brings an opportunity for income generation and enterprise development, Keywords: AMMI, discriminant analysis, sweetpotato, there is a large potential for processing sweet potato into yield various products, such as biscuits, doughnuts, juice and chips that can be processed on kitchen-scale (Laurie et al. 2015b, but may be scaled to commercial size with higher sweet potato production. *Corresponding author: Sunette Laurie, Agricultural Research Council- Since 1995, the ARC-VOP breeding programme Vegetable and Ornamental Plants (ARC-VOP), Pretoria, South Africa; has been focussing on high yield, good root quality, E-mail: [email protected] adaptability, high dry mass and sweet taste. Furthermore, Musa Mtileni, Whelma Mphela, Sidwell Tjale, Agricultural Research in 2003, β-carotene became the major breeding goal of the Council-Vegetable and Ornamental Plants (ARC-VOP), Pretoria, South Africa programme. Cultivars released include Ndou and Monate Frikkie Calitz, Agricultural Research Council-Biometry, Pretoria, (2003), Impilo (2007), Bophelo (2011), and Mvuvhelo South Africa (2013), while a line from the International Potato Centre Open Access. © 2017 Sunette Laurie, et al., published by De Gruyter Open. This work is licensed under the Creative Commons Attribution- NonCommercial-NoDerivs 3.0 License. 432 S. Laurie, et al. (CIP), 199062.1, is being promoted since 2010 (Laurie et al. 2.2 Planting material and trial maintenance 2015a,c). Trials at five research stations across 2008/9 to 2010/11 achieved total yield of 29.5 – 36.2 t/ha (mean 33.5 Six cultivars, as indicated in Table 2, were tested in a t/ha) and 17.3 – 24.6 t/ha (mean 20.0 t/ha) for marketable RCBD with three replicates at all 15 locations. Sweet yield. However, the cultivars needed to be tested in a potato cuttings were planted 30 cm apart in-row and 1 wider range of sites at on-farm conditions to confirm m apart intra-row. Plot size varied from 30 to 40 plants/ performance and for cultivar recommendations. plot depending on availability of cuttings. All plants were Farmers are basically interested in cultivars with used for data collection. Cuttings were produced in a field consistent superior performance on their own farms, and multiplication block at the ARC-VOP which was established those specifically adapted to farmer conditions and needs, with source material from the sweet potato disease- with a high degree of stability over time Ceccarelli 1989). tested scheme. Fertilizer mix (500 kg/ha 2:3:4 N,P,K) was However, there are specific advantages with varieties that are broadcast before planting due to the low nutrient status input-responsive as these may be able to respond to changes generally found in resource-poor farmer sites. Fertilizer in the environment in contrast to stable/non-responsive application was, however, half of the recommended dosage varieties. Popular multivariate approaches to investigate (Niederwieser, 2004) since farmers seldom afford to apply stability include the Tai stability test (Tai, 1971), Additive more. Supplementary irrigation was applied during the Main Effects and Multiplicative Interaction (AMMI) model growing season for five to six months at each site (Table 1). (Gauch and Zobel 1996) and GGE (genotype main effect plus G x E interaction) biplot model, which simultaneously represents both mean performance and stability (Yan and 2.3 Data collection Kang 2003), and variance components (Tumwegamire et al. 2016). In addition, there is potential in using additional Data collection included rating of storage root defects statistical methods (e.g. Principal Component Analysis - such as veins, constrictions, grooves (where on a 5-point PCA) to demonstrate association of variables and cultivars ordinal scale, 1=very bad, 5=very few), marketable storage and Discriminant Analysis (DA) to determine the most root yield (good quality roots between 100 and 1200 g) and prominent cultivar characteristics (Rencher, 2002). unmarketable storage root yield classes (cracked, insect Across the 2011/12 to 2014/15, commercially released damaged, long irregular, <100 g, >1200 g, mechanical cultivars for the informal market were evaluated under damaged, rotten). Two medium storage roots (250 to on-farm conditions and various agro-ecologies to identify 500 g) were sampled for determination of dry mass (dried those that perform well under farmer conditions and at in oven at 70°C for 48 hours). Taste acceptability of 3 to 4 different sites and, thus, can be widely recommended. cooked storage roots was determined with small informal This paper reports on the performance of released cultivars panels, using a rating scale: 1=excellent to 5=very bad. in on-farm trials in four provinces, their adaptability and stability, trait association and progress with vine distribution of the cultivars. The secondary purpose of 2.4 Statistical analysis the on-farm trials was to expose farmers to the improved cultivars and thereby extend production. A combined analysis of variance was performed using SAS 9.4 (SAS Institute Inc., Cary, North Carolina) with sources: cultivar, location and region and their interaction (John 2 Methodology and Quenouille 1977). The Additive Main Effects and the Multiplicative Interaction (AMMI) model was used 2.1 Sites to analyse genotype by environment interaction using Gen Stat Release 15.2 (VSN International Ltd., Hemel, On-farm trials were conducted in four provinces; nine Hempstead) for cultivar * location. “Year” was not a locations in Kwa Zulu-Natal, four in Gauteng, one in the variable because the trials were not repeated per location Eastern Cape province and one in Limpopo province. (Gauch et al. 2008). Principal component analysis was The experiments were conducted across the 2011/12 performed to demonstrate association of variables to 2014/15 planting seasons, one trial per site. The (Loadings) and cultivars (Scores) with PCA Factor scores. location information is presented in Table 1 and were A discriminant analysis (using XLSTAT 2013 (Addinsoft, representative of two regions, namely cool subtropical Paris, France) was done to determine the most prominent and warm temperate. cultivar characteristics (Rencher 2002). Table 1: Locations for on-farm trials of sweet potato conducted in South Africa 2011/12 to 2014/15 Region Loc Location name Location details Province Planting & Altitude (m) Mean Max °C Mean Max