Biofortification of common bean as a complementary approach to addressing zinc deficiency in South Africans

ABSTRACT

Deficiencies of vitamin A, iodine, iron and zinc (Zn) in humans are caused partly by the consumption of food that has insufficient quantities of these. Their deficiency has a negative impact on the health, wellbeing, social and economic status of human beings. A national survey conducted in 2012 identified deficiencies of vitamin A, Fe, and Zn among other nutrients in South Africans and regarded the deficiencies of vitamin A and Fe as a moderate but not Zn. This review discusses causes of Zn prevalence in low-income South Africans and that it is largely caused by the low content of Zn in their diets. Initiatives to reduce Zn deficiency include fortification of wheat products and maize meal which has failed to address it successfully. Weaknesses of fortification include high cost of fortified food products to low-income populations, poor regulation in ensuring compliance in fortification, non-fortification of sorghum meal, and leaching of fortified nutrients during processing. This review suggests Zn-biofortification of locally-preferred common bean cultivars as an alternative strategy to compliment fortification. The review also discusses advantages of adopting biofortified Nutritional Andean common beans. Furthermore, the review suggests initiatives including evaluation of the common bean genotypes’ adaptation to different agro-ecologies.

KEYWORDS:

• Biofortification
• fortification
• zinc deficiency
• zinc
• South Africa

Introduction

In 2009, the World Health Organisation (WHO) ranked vitamin A, Zn and Fe deficiencies among leading risk factors responsible for deaths in the world (WHO 2009). A few years later, the 2014 Rome Declaration on Nutrition and the International Food Policy Research Institute (IFPRI) (2016) confirmed that diet-related health challenges were increasing across all income groups in the world. Diet-related illnesses are largely caused by deficiencies of vitamin A, iodine, iron and zinc and negatively affect the health, wellbeing, social and economic status of humans. In order to address these deficiencies, countries need to adopt an approach that includes empowering poor farmers and food consumers (Thompson and Cohen 2015). Taking the diet-related challenges and the suggested suggestions into consideration, this review paper outlines solutions that are achievable. This includes the biofortification of locally-grown cultivars of common bean or adoption of Fe-and Zn-biofortified common beans by the South African government. This would ensure that the biofortified beans are available even to low-income villagers who can afford and those that have land and can cultivate. Secondly, if the government adopted the Fe-and Zn-biofortified common beans, it could form part of existing dietary-related solutions in South Africa. Although our main focus is addressing Zn deficiency, we acknowledge that micronutrient and vitamin A deficiencies co-occur. As noted by the Rome 2014 declaration, ensuring food security would include eradication of malnutrition in all its forms, including undernutrition, overweight, obesity, and micronutrient deficiencies.

A South African National Health and Nutrition Examination Survey conducted in 2012 concluded that vitamin A deficiency was a moderate public health problem given the decrease in its prevalence nationally (Shisana et al. 2012). Furthermore, the survey indicated that anaemia and iron status had improved substantially relative to that shown in results of a national survey conducted in 2005. The substantial improvement in anaemia was also confirmed by a study which showed that it was indeed a minor health problem in South Africa (Phatlhane et al. 2016). Despite the reported decline in anaemia, poor scholastic performance by Primary School learners was related to iron deficiency anaemia (Hlatswayo et al. 2016). Moreover, a recent review reported that South African children showed a prevalence of anaemia, vitamin A deficiency, as well as zinc and iodine deficiencies (Harika et al. 2017). There are various initiatives that are suggested to form part of dietary-based solutions which if adopted and promoted, could help reduce the vitamin A and micronutrient deficiencies in the country (Govender et al. 2017; Gurmu et al. 2017; Laurie et al. 2017). Despite a few reports which showed findings that are contrary to the conclusions of the 2012 national survey (Hlatswayo et al. 2016; Harika et al. 2017), it should be noted that the survey acknowledged the existence of vitamin A and Fe deficiencies, but, indicated that these were a moderate public health problem. Based on the moderate public health ranking of vitamin A and Fe deficiencies by the South African government, the focus of this review will therefore suggest initiatives that can contribute towards reducing Zn deficiency.

Zn is needed by humans in relatively small but adequate amounts starting from the embryogenesis stage and throughout the human life (Terrin et al. 2015). Its deficiency negatively affects the health, wellbeing, social and economic status of humans. Specifically, Zn deficiency leads to poor health, night blindness, behavioural disorders, immune deficiencies, delays sexual maturity, and contributes significantly to the morbidity and mortality of young children among many other symptoms (Caulfield et al. 2006; Bevis 2015). Results of surveys conducted in South Africa show that there is a prevalence of inadequate dietary Zn intake mainly by low-income people living in villages (Labadarios et al. 2005; Kolahdooz et al. 2013; Joy et al. 2014; Mchiza et al. 2015; Motadi et al. 2015; Steyn et al. 2016). Of the Zn-deficient South Africans, the most affected are mothers and children (Kolahdooz et al. 2013; Motadi et al. 2015; Harika et al. 2017; Hess 2017).

There are a variety of factors that are responsible for the low zinc content in South Africans which is not unique to them but also to billions other people in the rest of the world. With regards to low-income South Africans residing in villages, dietary Zn deficiency is largely caused by the following factors.

Low intake of a diverse and balanced diet

Compared to their peri-urban and urban counterparts, low-income rural dwellers largely depend on a diet that is not diverse, fresh nor nutritious (von Bormann 2016; Chakona and Shackleton 2017). Results from literature indicates that in general, rural dwellers consume 8.3–9.3 mg Zn whilst urban dwellers consume 9.6–10.0 mg Zn (Kolahdooz et al. 2013; Hattingh et al. 2008). In the main, their diet is limited in Zn-enhanced food products but also a generally low and not regular intake of fruits, vegetables, grain legumes, red meat, poultry, sea food, and dairy products (Labadarios et al. 2003; Pareira 2014). Without a doubt, consumption of such a diet would supply a human's body with high-quality protein and bioavailable micronutrients (de Bruyn et al. 2016). Unfortunately, a diverse and balanced diet is neither affordable nor available on a regular basis to low-income villagers given that most depend on grants which are not enough for them to can afford it on a regular basis.

The most common staple foods for low-income populations are maize or sorghum meals. The finely-ground powder of these meals is made through grinding or milling of the cereal grain. Such a process coupled with storage of the ground maize or sorghum meal lead to denaturing of proteins, removal of B vitamins, decrease of gluten quality and oil content (McKevith 2004). It is partly on this background that the type of cereal-based diet that low-income rural populations depend on contains low proteins, vitamins, and Zn content but a high content of phytate (Caulfield and Black 2004; Mamabolo et al. 2006). Such a diet also represents a shift from traditional African diets which include cereal grain, leafy vegetables, grain legumes and from time to time include root tubers, fresh and fermented milk and poultry products (Mukhala et al. 1999). It is rather a combination of these food products that ensures sufficient intake of proteins and micronutrients. Although native African grain legumes such as cowpea and Bambara groundnut are still cultivated by smallholder farmers in South Africa (Mohale et al. 2014; Govender et al. 2017), largely, these are neglected. The crops are largely neglected by researchers, funding agencies as well as commercial farmers who focus on specialised cash crops. Smallholder farmers also show less interest in cultivating large hectares of these grain legumes because of factors such as postharvest losses (Chibarabada et al. 2017). An example of this includes areas where un-improved landraces of cowpea are grown for its grain. Given the grain's susceptibility to attack by weevil and the general lack of knowledge on affordable techniques to deal with this challenge, farmers in such areas hardly cultivate the crop anymore, despite its agronomic potential and nutritional benefits. The fact that smallholder farmers dedicate a small piece of their cropping land to cultivation of grain legumes is because a larger part is used for cultivation of staple crops such as maize or sorghum, and legumes planted as intercrops to the main cereal crops. Lastly, a diet that is based on grain legumes is in some parts of the country associated with poverty and referred to as a ‘poor man's meat’. All these are among factors that contribute to the low intake of pulse legumes with village population missing out on vitamins, proteins and micronutrients.

Cultivation of food crops in soils containing low Zn concentration

The Zn deficiency prevalence in South African low-income village dwellers is partly as a result of eating food that is cultivated in cropping fields that contain low concentration of zinc (van der Waals and Laker 2008). The link between Zn content in soil, food and humans is that crops planted in low-Zn soils most likely also contain lower concentration of Zn and humans that eat such crops eventually become Zn deficient. This means that addressing Zn deficiency in cropping fields addresses the Zn concentration in commonly eaten plants and its availability in humans would improve. Generally, the low Zn levels in cropping fields cultivated by low-income populations is caused by cultivating soils derived from parent material that contain low concentration of Zn, soil that is highly weathered, have high pH (>7), and pedologically old (Alloway 2009; de Valença et al. 2017; Gregory et al. 2017). It is important to note that the Zn status in South African cropping fields is different between that cultivated by smallholder to that by commercial farmers. Although smallholder farmers in southern Africa apply inorganic and organic fertilisers (Orchard et al. 2017), where applied, the rates are hardly sufficient to meet crop requirement (Machete et al. 2004; Mnkeni et al. 2010). Reasons to this include a general lack of professional expertise on fertiliser management (Radebe 2014), large quantities of organic fertilisers required and high cost of chemical fertilisers (Odhiambo and Magandini 2008). Literature on Zn levels in South African soils is scanty and include that of topsoil collected from ten selected smallholder farmers’ fields under dry bean production in the Limpopo Province which contained 1.34 to 4.31 mg/kg, and fourteen smallholder farmers’ fields in the Eastern Cape Province under dry bean and cereal production which recorded 0.77 to 1.76 mg/kg (Habinshuti 2015). Soil analyses results of topsoil collected from a smallholder farm in the Thukela region of the KwaZulu-Natal Province of South Africa showed Zn levels that ranged from 3.8 to 5.3 mg/l (Mthembu et al. 2018). In contrast to smallholder cropping systems, crop production by most commercial growers includes comprehensive fertilisation programmes (Van Biljon et al. 2010). For example, selected farmers’ fields under commercial soybean production in the KwaZulu-Natal, North-West and Mpumalanga Provinces recorded between 2.1 and 18.2 mg/kg topsoil (Mapope and Dakora 2016).

Intervention in addressing micronutrient and vitamin deficiencies in South Africa

Over the years, the South African government has attempted to address the Zn challenge through fortification of certain food stuffs. For example, in 2003, a regulation was enacted and mandated that maize meal and wheat flour be fortified with vitamins A, B1 (thiamin), B2 (riboflavin), B6 (pyridoxine), Niacin, Folic acid, Fe and Zn (Department of Health 2003). In the government gazette, this is published under Act No 54 of 1972: Foodstuffs, Cosmetics and Disinfectants. The national mandatory food fortification programme was aimed at addressing vitamin and micronutrient deficiency. Maize meal and wheat flour were selected because they were considered as the two most commonly eaten food items, including by people in the lower income bracket. As part of compliance, an official fortification logo had to be put on packaging and advertising materials of fortified products used, on a voluntary basis. Currently, implementation of the Act is not consistent in South Africa for both maize meal and wheat flour. For example, it is not all wheat flour that is fortified in South Africa, but only wheat flour produced for use in making bread is fortified. The wheat flour for use in making cake is not fortified.

Challenges facing food fortification

Although maize meal sold in formal markets is fortified, this is not common across the country. For example, for the majority of smallholder farmers who cultivate maize, once the maize is harvested, it is stored and left to dry and once dry, it is shelled and later milled using local small-scale millers. The small-scale milling industry in South Africa is deregulated (Abu and Kirsten 2009) and largely does not involve fortification of the maize meal. This means, the maize grain milled by such millers and consumed by a significant percentage of South African rural dwellers is not fortified. The second challenge is that the price of fortified products especially bread and maize meal is high for low-income families who mainly depend on government grants. The high prices are as a result of additional costs added from product transfer from agro-processors to retailers in villages. Thirdly, the South African government has no regulation to ensure that sorghum meal, the second-most consumed after maize meal, is fortified. This means that people who eat sorghum meal do not have access to fortified vitamins and micronutrients. Apart from these inconsistencies, during cooking or boiling of fortified food, a large percentage of nutrients introduced through fortification are lost, at times with an average retention of 39.8% (Kuyper 2000; Pretorius and Schönfeldt 2012). This background indicates that the current fortification strategy in South Africa has disadvantages and is also not as successful in increasing Zn concentrations, including in diets of infants (Faber et al. 2005; Alamu et al. 2006).

Alternative strategies to addressing Zn deficiency in South Africa

In this review paper, we suggest that the South African government consider other means to addressing especially Zn deficiency apart from the fortification of maize meal and wheat products. This includes Zn-biofortification of crops that are available to both the urban and village populations of the country, commonly consumed and affordable. One such crop is common bean as it is cultivated at both smallholder and commercial sectors across the nine provinces of South Africa. It is also sold in both the formal and informal markets. Zinc biofortification of common bean can be achieved through two strategies namely agronomic and genetic biofortification. Genetic biofortification includes the development of new crop cultivars with embedded and enhanced Zn into cells of the edible part of the target crop (Steur et al. 2017). For dry bean, the edible parts include the seed coat, cotyledons and embryo, all which are consumed as the pulse seed is consumed whole, which is advantageous (Sperotto and Ricachenevsky 2017). Agronomic biofortification on the other hand involves application of Zn fertilisers and this can be achieved through seed treatment, foliar application or soil application (Cakmak 2008; de Valença et al. 2017; Zaman et al. 2017). This approach however is costly to low-input crop farmers given the cost of zinc inorganic fertilisers (Mpai and Maseko 2018). Alternatives to application of the costly Zn fertiliser alone include where it is applied along organic nutrients and N and P fertilisers which increased Zn concentrations in cowpea grain (Manzeke et al. 2017). Although this approach resulted in increased nutritional value of the legume, the combination of the fertilisers used in the study may not be affordable to low-input crop farmers. On the other hand, application of inorganic or organic fertilisers in combination with plant biostimulants or plant biostimulants alone resulted in improved physico-chemical properties of soils, and increased the growth and yield of crops (Choukr-Allah et al. 2016; Ansari and Mahmood 2017; Mumtaz et al. 2017; Thonar et al. 2017; Moloto et al. 2018). The increase nutrient solubilisation along with plant growth and yield by application of biostimulants without fertilisers seem an affordable option. Caution should be taken on the application of biostimulants as fertilisers because there is not much literature that studied their long-term effect on nutrient reserves in soils and on overall soil security. Whatever the case, the ultimate goal of Zn biofortification includes developing edible plant parts, mainly leaves and grains, with higher Zn content and lower content of non-essential elements for human consumption or animal feed. Although the bioavailability of biofortified Zn and other nutrients to human body is being debated (Bechoff and Dhuique-Mayer 2017), it has multiple advantages compared to fortification of nutrients. These include its success in limited leaching of the embedded nutrients during cooking, storage and processing (de Valença et al. 2017; Diaz-Gomez et al. 2017).

Common bean production in South Africa

Common bean is normally grown in the summer or rainy season in southern Africa and its grain is the most widely consumed of known grain legumes across the world (Bhandari et al. 2017). That is why it is widely cultivated at both smallholder and commercial level across South Africa (Figure 1). The Grain South Africa has records of commercial common bean production since the 1990/1991 cropping season. For example, in the 1990/1991 cropping season, average provincial area under dry bean production, tons produced, and tons/hectare were 78.272 ha, 99.098 t, and 1.266 t/ha, respectively (Grain South Africa 2017). In contrast, there were 45.050 ha, 68.450 t, and 1.519 t/ha recorded in the 2016/2017 cropping season. This showed a 33.222 ha decline in area under cultivation, a 30.648 decline in tonnage and a 0.253 t/ha increment (Grain South Africa 2017). Major producing provinces in the 2016/2017 cropping year included the Free State, Limpopo, and Mpumalanga whilst the least yield was recorded in the Western Cape, Northern Cape and Gauteng (Grain South Africa 2017). There are no official figures of yield or land under dry bean cultivation by smallholder farmers in South Africa. Although only figures from commercial dry bean production are available in South Africa, there has hardly been enough grain produced to meet the country's dry bean consumption demand (Department of Agriculture, Forestry and Fisheries (DAFF) 2015; Figure 2). This is because, over the past years, the demand or consumption of common bean in the country has always outstripped local production. The higher demand is met through importation from countries such as Malawi, Mozambique, China, Tanzania and Thailand (DAFF 2015). In the eastern part of South Africa for example, the high demand of dry bean is partly met through importation from Swaziland.

Figure 1. Tons of common bean produced across the nine provinces of South Africa from the 2011/2012 cropping season to the 2016/2017 cropping season. Data was sourced from Gran SA, 2017.

Figure 2. Tons of common bean produced in South Africa showing variation in production, import, and consumption, from the 2009/2010 cropping season to the 2013/2014 cropping season. Data was sourced from Gran SA, 2017.

Given the popularity, demand and nutritional importance of the pulse, the government introduced a programme aimed at assisting smallholder farmers to improve production. The programme has different names across the Provinces and in the Mpumalanga Province for example, it was referred to as ‘Masibuyele emasimini’ but is currently being renamed ‘Phezukomkhono mlimi’. Through the programme, almost a hectare of cropping land is ploughed for each smallholder farmer, chemical fertilisers mostly NPK and LAN, and seeds (including dry bean) are supplied by government (Shabangu 2015). Where managed well, the initiative has had a positive impact including increased grain yield and an increase in the number of smallholder farmers showing interest to participate. There has also been a number of challenges which with better planning, can be overcome. These include fewer resources such as operational machinery, machinery that break and remain unfixed for longer, poor planning, and ploughing late in the cropping season when rains are almost gone.

Value of common bean in South Africa

Common bean is planted as either a sole or an intercrop and the grain used as food for humans and the straw as feed for livestock. The intercropping system practiced at the smallholder sector is self-sustaining and of low-input in that, it enhances the amount of biomass that is harvested from a given piece of land (Masvaya et al. 2017). Other advantages include provision of cover to soil surfaces and that the soil particles that attach to roots of intercrops become bound and that promotes soil conservation (Tsubo et al. 2003; Dwivedi et al. 2015). Common beans are mainly intercropped with maize or sorghum, a combination that makes better utilisation of sunlight, water and nutrients given their differences in use of other resources which support their growth and development (Mukhala et al. 1999). Where intercropped with these non-legumes, benefits include increased rhizosphere P availability of intercrops and enhanced grain yield of the cereal (Lalati et al. 2014), which in turn can supply Zn and Fe to the legume (Xue et al. 2016). There is also transfer of N from the dry bean to the cereal as well as enhancement of N fertility of soils (Stagnari et al. 2017). Although not as efficiently but such a cropping system result in reduced pest, weed pressure and disease incidences (Nurk et al. 2017). Besides the above mentioned benefits largely to cropping systems, there are benefits that farmers gain in intercropping dry beans with cereals and these can be of financial nature where the beans are sold, diversify in household food and therefore diet, sustained food availability especially during the dry or winter season. The need to maintain food availability during the dry or winter period is from the fact for inland parts of South Africa, such a season is associated with no rainfall. This means that farming is hardly possible unless farmers have enough water and available facilities to can provide supplementary irrigation. Other benefits are associated with the crop being used as a feed for livestock where once shelled, the chaff is used as feed to livestock. This is crucial during the dry winter season because grass and most shrubs dry up due to lack of rainfall. The chaff of intercropped cereals exhibit enhanced protein content, which result in improved protein quality of the feed but also reduces farmers’ costs for providing protein supplements to livestock (Eskandari et al. 2009). Lastly, intercropping common beans with cereals provides insurance against crop failure especially given the current extremely hot weather conditions experienced in most parts of South Africa (Elum et al. 2017).

As food, the grain provides protein, carbohydrates such as starch and sugars, vitamins including thiamine, folic acid, riboflavin and vitamin B6 and minerals, and minerals such as iron, copper, phosphorus, manganese and magnesium (Ribeiro et al. 2012). The grain is one of the most commonly sold in both formal and informal markets in a both canned and dry grain forms. Of all available grain legumes cultivated and available locally, common beans are the most bought and consumed. Although adopted from America, in South Africa today, these beans play an important role as a staple food and serve as a source of income to farmers (McDermott and Wyatt 2017). The raw grain, largely the speckled in colour is boiled and various sauces made from it. Nationally, dry beans are used in soups, chilli dishes, casserole recipes, paste, and salads. Even though different tribes use the pulse for different dishes, there are common dishes such as where it is boiled and mixed with maize meal to prepare a porridge called ‘umnxushu’ in isiXhosa, or ‘sishwala’ in siSwati.

Adoption of biofortified dry beans as part of the solution to addressing Zn deficiency

Despite the popularity and large consumption of commonly-grown dry bean cultivars in South Africa, the country's low-income population as well as most village dwellers suffer from Fe, Zn and vitamin A deficiency. Reasons to this are multi-fold including the fact that it takes long-term nutrition with adequate levels of NPK fertilisers to realise increased grain nutrient levels. For example, long-term (>30 years) nutrition of crops with NPK fertiliser along with compost or manure enhances micronutrient accumulation in cropping fields and edible parts of crops (Brar et al. 2015; Kuppusamy et al. 2018). In South African smallholder cropping fields however, the long-term and short-term benefit of applying government-subsidized NPK fertilisers is unlikely to result in increased nutrient content given the inconsistent supply of these fertilisers and the incorrect application rates. There is therefore a need to consider biofortification of locally-produced dry beans or adoption of already biofortified common beans. The International Centre for Tropical Agriculture (CIAT), through its HarvestPlus programme, developed red-mottled dry beans. The red mottled bush beans, named NUA (Nutritional Andean) lines are characterised by higher mineral content, higher yield content and resistance to drought and disease attacks (CIAT 2008). Generally, common beans contain 3.14–12.07 mg/g Fe and <1.89–6.24 mg/g Zn (Marles 2017). However, the NUA genotypes contain 40–90 mg/kg Fe and 10–35 mg/kg Zn (CIAT 2008). The higher Fe and Zn contents in leaves of the test NUA genotypes make them a rich feed material for livestock as well. Since their release, the NUA dry beans have been evaluated under different field conditions in various regions including Latin America, eastern and southern Africa as part of the HarvestPlus and Agrosalud programmes for biofortification (CIAT 2008; Blair et al. 2010). Results have shown for example that NUA35 and NUA56 contain markedly greater seed Zn content than commonly cultivated commercial cultivars in Uganda, Rwanda, Colombia, Bolivia, Costa Rica, and Guatemala when tested under different climate, altitude and soil types (Sharma et al. 2017). These genotypes are currently being tested in various eastern and southern African countries including Tanzania, Kenya, Malawi, Zambia, Zimbabwe, and Swaziland.

Since 2008, the NUA dry bean genotypes have been tested for disease resistance and drought tolerance at the Cedara and Makhathini Research Stations in the coastal KwaZulu-Natal Province of South Africa (CIAT 2008). The fact that South African institutions are assessing testing these genotypes is an indication that the South African government has intentions of adopting the Fe and Zn-enhanced beans. Besides disease resistance and drought tolerance, hopefully, evaluations will include their acceptability by South Africans. The assessments should include evaluation of the beans’ performance in different agro-ecologies and planting dates. These factors are important because research results indicate that in future, the Northern Hemisphere will be more favourable than the Southern Hemisphere for production of dry beans (Foyer et al. 2016; Ramirez-Cabral et al. 2016). It is therefore crucial that research on common beans in the Southern Hemisphere also focus on identifying more areas that are suitable for the crop's production under the generally unpredictable climatic conditions. Equally important is ensuring that the evaluations involve initiatives that include a comprehensive fertiliser subsidisation programme. Such should include fertiliser bags where macronutrients and micronutrients are mixed in one bag as has been tested in neighbouring countries (Chianu et al. 2011). Such an initiative, if adopted and tested on the on-going evaluation of NUA common bean genotypes in South Africa would ensure that the challenge of micronutrient deficiency is addressed at both the diet level and smallholder cropping fields. Furthermore, it would avert mining of nutrients because it is possible that biofortified seeds take up more nutrients from cropping fields than their non-biofortified counterparts. According to the 2008 CIAT report, in South Africa, crosses were being made where traits of the NUA common beans were combined with locally-preferred cultivars for enhanced micronutrient content. This approach is likely to result in the desirable outcome which is, in case the NUA beans are not accepted by South Africans, their enhanced Fe and Zn traits would have been embedded on locally-preferred cultivars.

Conclusion

In most South Africans the prevalence of Zn deficiency is caused by eating food low in Zn concentrations as well as growing crops in soils deficient in Zn. Zn deficiency is one of risk factors responsible for human deaths across the world. The South African government has strategies in place aimed at combating the deficiency of Zn and this includes its fortification in wheat products and in maize meal. The approach has not been as successful particularly in eradicating Zn deficiency because fortified nutrients are reduced during cooking, storage and processing. Furthermore, maize meal produced by a significant number of small-scale millers is largely not fortified, and, sorghum meal, a staple food to many South Africans, is not fortified. The review suggests that along with the current fortification programme, the government considers Zn-biofortification of local common bean cultivars or adopting biofortified NUA dry beans. Common beans are available in almost every shop across the country, preferred by consumers and popularly grown grain legume including by poor farmers across the country. The crop has multiple benefits including enhancing the fertility of cropping systems, and nutritional benefits to humans and livestock. In South Africa, there are on-going experiments that evaluate NUA dry beans for adaptation to drought and resistance to diseases. We suggest that in addition to these on-going evaluations, there is a need to have experiments intended at assessing these across different South African agro-ecologies. Moreover, as researchers have begun assessing a possibility of enhancing locally-preferred cultivars with Zn and Fe, these should further be evaluated under different soil conditions. Lastly, we suggest that as government has on-going programmes aimed at motivating smallholder farmers grow dry beans, such should include fertilisers made of a combination of macronutrients and micronutrients. This would ensure that micronutrient deficiency is not only addressed at the diet level only but also in cropping fields, particularly that cultivated by smallholder farmers.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Rebahlotse Mapula Moloto is a graduate student in Department of Crop Sciences at the Tshwane University of Technology, South Africa.

Lesiba Harry Moremi is a graduate student in the Department of Crop Sciences at the Tshwane University of Technology, South Africa.

Puffy Soundy is a professor and Head of Department of Crop Sciences at the Tshwane University of Technology, South Africa. His research focus is on the agronomy of aromatic plants, medicinal plants and vegetable crops under protection.

Sipho Thulane Maseko is an academic at the Tshwane University of Technology, South Africa, and his research focus is on food legumes, soil fertility and plant nutrition.

Additional information

Funding

This work was supported by Tshwane Univeristy of Technology, Department of Crop Sciences.