Introduction

Indigenous fruit tree species (IFTs) are trees with edible fruits, which naturally grow within a specific geographic location and are often characterized by limited development relative to their potential (Mabhaudhi et al. 2017). South Africa has rich plant species diversity with numerous hotspots such as Maputaland and Pondoland Albany (Boon 2010). Some of these centers of plant endemism have a rich diversity of IFTs with economic potential as food crops. The exploitation of these species as a food source in certain rural areas of South Africa such as in Mpumalanga is well documented (Mashile et al. 2019). However, these species are still harvested from the wild despite their food security potential (Muok 2019). Therefore, there is a need to prioritize and introduce them as resources for small-scale farmers to ensure their continued contribution to food and income security (Jusu and Cuni-Sanchez 2017).

The domestication of IFTs starts by identifying priority species that have economic potential (Nieminen et al. 2017). The selection criteria for IFTs cultivation used by local farmers in Uganda is primarily based on cash value, food provision and to a lesser extent on medicinal value, length of the fruiting period, ease of propagation and drought resistance (Agea et al. 2007). Adansonia digitata L., Parinari curatellifolia Planch. Ex Benth., Sclerocarya birrea, Strychnos coculoides DC ex. Perleb and Uapaca kirkiana Muell. Arg. are perceived as the most important species for domestication in Malawi, Tanzania and Zimbabwe based on ethnobotanical surveys (Bvenura and Sivakumar 2017). However, the prioritization of IFTs differs based on the geographic location (Jusu and Cuni-Sanchez 2017).

Ethnobotanical studies and scorecard assessment methods are widely used for prioritizing IFTs with domestication and commercialization potential at a local level (Franzel et al. 2007; Jusu and Cuni-Sanchez 2017; Nieminen et al. 2017). However, such studies are few in South Africa. Therefore, the objective of this study was to prioritize IFTs with this potential in northern KwaZulu-Natal, South Africa, using focus group discussions, scorecard assessment and ranking system methods. One research question was addressed to plant experts: what should be the most preferred or prioritized IFTs in northern KwaZulu-Natal?

Materials and methods

Focus groups and ranking system

A list was compiled from the literature based on tree species that produce edible fruits, which are of African origin and are commonly found in South Africa including KwaZulu-Natal province (Table 1). Discussions with focus groups were held with representatives from organizations including the Council for Scientific and Industrial Research (CSIR), University of Zululand, the Agricultural Research Council (ARC), iSimangaliso Nature Reserve, Ezemvelo KwaZulu-Natal Wildlife, Siyazisiza Trust, Owen Sithole College of Agriculture, Transnet as well as independent consultants. The choice of representatives from these organizations was based primarily on people working predominantly with edible plants regarding their natural resources, propagation measures, and development of products from these plants. Therefore, these groups included agronomists, botanists, ecologists, hydro-scientists, food scientists and plant physiologists. Participants in four groups of six people each were informed that the purpose of the study was to prioritize species with domestication and commercialization potential. They were also invited to add other species through local taxonomy (naming of plants using isiZulu vernacular and/or English common names) if they were not included in the species list provided (Table 1). Scientific taxonomy through the recording of family, species and other common names; geographic distribution as well as uses of the added species were conducted using the literature.

Table 1 Taxonomy, distribution and uses of indigenous fruit tree species with domestication and commercialization potential
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Each group identified, with reasons for selection, a maximum of ten presumed most important species, either from the species list provided or from their own experience. The ten selected species were then ranked 1–10 by each group corresponding to weights of 100–10% such that 1 was the highest rank given the weight of 100% and 10 was the lowest rank given the weight of 10%. The results from all groups were then tallied and the number of times a species was given a particular rank was noted. An overall score was calculated as the sum of the products of the rank (%) and the number of citations of a given species with that rank.

Scorecard assessment

A scorecard assessment, with individual species assigned eight different attributes, modified from Brehm et al. (2010) and Nieminen et al. (2017), was used to further trim the top ten species to seven, to score them based on the objective of this study (Table 2). Each attribute was given a pre-determined weight value from 2 to 5, where 2 was the lowest value, indicating least desired attribute, and 5 the highest value indicating the most desired attribute for this study. A score out of eight for each attribute was assigned to each species, with the highest number always indicating the highest priority. The overall score for each species was calculated as the sum of the product of the weight and assigned score (out of 8) for each attribute. A further reference group meeting was held with experts in horticulture, ecology, hydro-sciences and plant genetics to discuss the feasibility of domesticating the seven prioritized species.

Table 2 The attributes and pre-determined weight values used in the scorecard assessment
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Data analysis

Data from literature search and participants were classified into different categories (Tables). Data from focus group discussions and ranking system were analysed descriptively using frequency citation and rank order priority percentages, where frequency citation was the number of groups which selected and ranked the same species. Scorecard data were analysed using Microsoft Excel and simple descriptive statistics.

Results and discussion

Indigenous fruit trees with domestication and commercialization potential

A total of 29 IFTs with domestication and commercialization potential were recorded, of which 20 were sourced from the literature and nine (represented by asterisks) were identified by participants in focus and reference groups (Table 1). A comparable study carried out in 15 villages of Limpopo listed 52 utilized fruit tree species, where only 33 were indigenous while 19 were exotic (Mashile et al. 2019). As the participants were given a species list to help with group discussions and invited to add any species not included, they probably concluded that species they initially found on the list were enough and added fewer species. Free-listing of species in the current study area could probably have yielded more species as in Rasethe et al. (2013).

The species recorded in the current study belonged to 29 genera and 23 families. Sapotaceae was the most dominant family, represented by four species, followed by Anacardiaceae (3 species) and Rhamnaceae (2 species), whereas the remaining families were represented by only one species each. All four species within the dominant Sapotaceae family (Englerophytum magalismontanum, Inhambanella henriquesii (Engl. & Warb.) Dubard, Manilkara discolour (Sond.) J.H. Hemsl. and Vitellariopsis dispar) (N.E.Br.) Aubrev. were contributed to the list through focus group discussions than literature (Table 1), which is a benefit to numerous species documentation through the free-species listing (Rasethe et al. 2013). The dominance of species belonging to the Sapotaceae, Anacardiaceae and Rhamnaceae families was also recorded in the selection of preferred IFTs by rural communities in Mpumalanga (Mashile et al. 2019). These families, which mostly consist of trees, have a high economic value and are much preferred for their use as a source of fruits, firewood, medicine, timber and crafting (Rasethe et al. 2013). On the other hand, in Uganda, Arecaceae was the most dominant family represented by three species in which Phoenix reclinata Jacq. was within these species (Nieminen et al. 2017). Species endemism might have contributed to the other two species (Borassus aethiopium Mart. and Pseudospondias microcarpa Engl.) to be recorded only in Uganda.

Recorded species are known by different vernacular names across five ethnic groups namely, Afrikaans, English, Zulu, Xhosa and Tshivenda. Among these, a quarter of the species are known by the same vernacular name by at least two ethnic groups. Similar findings were recorded in Tanzania, where people use vernacular names in their languages for the indigenous species they use (Otieno et al. 2015). Rich vernacular diversity due to the broad ethnic spread of users’ help to safeguard indigenous knowledge (Otieno et al. 2015).

Recorded species are distributed throughout the provinces of South Africa with KwaZulu-Natal being the most represented location with the frequency index of 86% followed by Limpopo (76%) and least represented in Northern Cape (10%). Most of these species thrive in warm and dry climatic conditions which are more experienced in KwaZulu-Natal and Limpopo provinces (DAFF 2013). All species also occur in at least one African country in addition to South Africa. This suggests that Africa has a rich diversity of IFTs with domestication and commercialization potential. Fifty-five percent of listed species are processed into various products such as culinary oils, beverages, jams, jellies and sweets. A comparable study reported that most IFTs have the potential to produce new food products for local and international markets (Van Wyk 2011).

Focus groups and ranking system

The participants identified; with their reasons, Strychnos spinosa, Syzygium cordatum Hochst. ex Krauss, Sclerocarya birrea, Dovyalis caffra, Ximenia caffra Sond., Vangueria infausta, Harpephyllum caffrum Bernh., Englerophytum magalismontanum, Garcinia livingstonei and Berchemia zeyheri as ten priority species that belong to nine families (Table 3). Comparable studies from Limpopo (Rasethe et al. 2013) and Mpumalanga (Mashile et al. 2019) recorded; among others, H. caffrum, S. birrea, S. spinosa and V. infausta as the most utilized or preferred IFTs. These similarities in local preferences may be linked to the abundance and usefulness of these species in different areas (Jusu and Cuni-Sanchez 2017).

Table 3 Rank values assigned by each group and reasons for selection for the top 10 species in descending order
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The Anacardiaceae was the most represented family with two species, namely, H. caffrum and S. birrea whereas the remaining families were presented by one species each. Similar findings on the utilization of plant resources were noted where the Anacardiaceae was represented by the most species (Rasethe et al. 2013). Two groups ranked S. birrea as the first most important species whereas two groups ranked S. spinosa as the second-most important species. However, S. spinosa had the highest score (320) compared to S. birrea (260); B. zeyheri had the lowest score (80).

The reasons for selection included species abundance, drought resistance, high commercial value and food value. Forty percent of the prioritized species were chosen because they have multiple-uses. This finding is in agreement with studies in Limpopo (Rasethe et al. 2013). Provided that most of these species are still harvested from the wild, multi-utilization can lead to overharvesting and extinction (Fukushima et al. 2010). Ethnobotanical studies, through focus group discussions alone, are not able to identify indigenous fruit tree species with commercialization potential as participants list species based on only personal preferences such as taste. In a study carried out in Bushbuckridge, Mpumalanga, 55% of participants preferred certain indigenous fruits based on taste whereas only 3% accounted for economic value as a reason for preference (Shackleton et al. 2002). Focus group discussions should be accompanied by preference rankings taking into account the objectives of the study other than only personal preferences (Nieminen et al. 2017).

Scorecard assessment

The top seven IFTs identified in order of the most to the least preferred species were S. spinosa, G. livingstonei, E. magalismontanum, S. birrea, D. caffra, V. infausta and B. zeyheri (Table 4). Similarly, in Malawi, Tanzania and Zimbabwe, S. birrea was one of the five most prioritized species (Bvenura and Sivakumar 2017). Preference of this species at a countrywide level is probably due to value-added opportunities that have been explored in numerous industries including, beverages and cosmetics (Akinnifesi et al. 2006). In contrast, A. digitata and P. curatellifolia that were among the five prioritized species in Southern Africa (Bvenura and Sivakumar 2017), and were on the main list of plants in the current study, were not prioritized. These species might not be abundant in KwaZulu-Natal, and thus participants probably opted for species widely distributed in the area of interest. Species that are more abundant are more likely to be prioritized (Nieminen et al. 2017).

Table 4 The top 7 species in descending order
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Seventy percent of the prioritized species in the current study are from the species list generated from literature whereas, 30% came from the participants added species. Participants tend to probe for species on the provided list (Nieminen et al. 2017). Strychnos spinosa was ranked as the first most preferred indigenous fruit tree species with a final score of 151 whereas B. zeyheri was ranked least with a final score of 146.1. Although these species are ranked in descending order, they are all equally preferred because their final scores are relatively similar. In a scorecard assessment species may have identical scores for entirely different reasons (Brehm et al. 2010). Although S. spinosa was ranked as the first most preferred species, it scored the lowest in the species abundance attribute (4/8). Similarly, this species was ranked number 12 in the top 15 species prioritized for on-farm cultivation by Uganda farmers based on taste and its scarcity on farms might have led to such a ranking (Agea et al. 2007).

Vangueria infausta scored 8 in the yield quality and quantity attribute. A comparable study recorded that the fruit yield of V. infausta is prolific and superior to some equally important IFTs (Mng’omba et al. 2011). G. livingstonei, E. magalismontanum, S. birrea and B. zeyheri were scored as the most priority species with market demand for the products. This attribute suggests that it is easier to sell the products of these species (Nieminen et al. 2017). D. caffra followed by S. spinosa are easier to propagate and regenerate. Consequently, less labour is required when domesticating such species, thus more likely to be prioritized for cultivation (Mashela and Mollel 2001). Species were scored from 1–3 in the pests, diseases and drought resistance attribute in which S. spinosa was the most prioritized species in this attribute. Frequent irrigation is expensive, thus prioritization of drought-tolerant species is often favoured (Ngemakwe et al. 2017). B. zeyheri has numerous uses and scored 5 whereas S. spinosa scored least in this attribute. However, if a species has other uses in addition to food use, it is likely to be prioritized but can be prone to numerous factors such as overharvesting (Nieminen et al. 2017).

Conclusion and recommendations

According to scorecard assessment, all the IFTs assigned priority status, namely; Strychnos spinosa, Garcinia livingstonei, Englerophytum magalismontanum, Sclerocarya birrea, Dovyalis caffra, Vangueria infausta and Berchemia zeyheri, qualify for domestication programmes in northern KwaZulu-Natal. The next step is to find sites which harbour these species in that part of the province and study their phenology, yield and water use requirements prior to domestication initiatives.