Nutritional water productivity of cucumis myriocarpus in context of climate -smart agriculture

Thesis (Ph.D. (Plant Production)) -- University of Limpopo, 2022

Malnutrition continues to pose a serious threat to humankind and their animals, and this is inextricably exacerbated by the irrevocable incident of climate change. Due to the latter, adaptation efforts for achieving the first Goal of the eight Millennium Development Goals appear to be unequivocally remote. The first Goal intends to eliminate hunger by ensuring that humankind is provided with nutritional food, thereby eliminating hidden hunger, which is malnutrition. Globally, malnutrition is widespread since best agricultural practices that increase yield do not necessarily correlate with increased nutrition in plant produce. The concept of nutriconclusiotional water productivity (NWP) links the accumulation of certain functional nutrients to the amount of water (m3) used in their bio-accumulation. Due to high nutrient deficiencies in exotic crops that were bred for high yield under best agricultural practices, attention is being redirected to certain indigenous underutilised crops, which had for centuries survived marginal conditions. Such underutilised crops had been, without empirically-based information, viewed as potential candidates for positively contributing towards the achievement of the first Goal of the eight Millennium Development Goals in lieu of biofortification. In the northern region of Limpopo Province, South Africa, one such underutilised crop is wild cucumber (Cucumis myriocarpus), a leaf vegetable indigenous to the northern semi-arid region of South Africa. The plant, due to its short stem, has attributes of a “stolon”, with drought-tolerance and nematode-resistant attributes, and had served as a leaf vegetable with various medicinal uses among the local people. The plant, therefore, has inherent potential benefits of promoting functional nutritional security under various conditions. Due to a lack of empirical information to advance the production of this underutilised crop, a decision was taken to investigate the production of the crop in relation to NWP of mineral malnutrition (MMN) elements and micronutrient malnutrition (MNMN) substances under conditions that had been predicted through modelling to be threatening inland South Africa with the advent of increasing intensity of global warming. The objectives of the study were, therefore, five-fold, namely, to investigate the responses of NWP of MMN elements in C. myriocarpus leaf tissues to (1) planting density, (2) irrigation interval, (3) population density of root-knot (Meloidogyne species) nematodes, (4) chloride salinity and (5) inoculation with arbuscular vascular mycorrhiza (VAM) under various conditions. In all objectives, soil water content was measured using soil moisture profile probes, connected to an HH2 Moisture Meter (Delta-T Devices, UK). At 56 days after initiating the treatments, 20 healthy mature leaves were harvested per plant, oven-dried at 70°C for 72 h and ground in a Wiley mill, with the extraction of nutrient elements performed using the digestion method from 0.4 g material. Selected MMN elements were quantified using the Atomic Absorption Spectrophotometer ICPE-9000, with related NWP values. In three of the five objectives, MMN elements versus independent variables (i.e. planting density, irrigation interval or salinity) exhibited significant (P ≤ 0.05) quadratic relationships, which offered the opportunity to compute the optimisation point using x = –b1/2b2 relations, derived from Y = ax2 + bx + c quadratic equation. In contrast, in the remaining two objectives, MMN elements versus independent variables (i.e. nematodes or Biocult) did not exhibit significant relationships, except that occasionally, population densities of M. javanica linearly reduced NWP of Fe. In conclusion, the findings in the current study demonstrated for the first time that nutritional quality in harvestable produce, as articulated using the concept of NWP of MMN elements is not aligned with the philosophy of high yield (quantity) as pronounced in best agricultural practices. The provided models showed that although certain cultural practices could be disadvantageous to the producers in terms of quantity, stressful conditions could to a certain extent be advantageous to consumers in terms of the nutritional value of the produce.

Land Bank Chair of Agriculture – University of Limpopo, National Research Foundation of South Africa (NRF) the Flemish Interuniversity Council (VLIR) of Belgium and the Agricultural Research Council-Universities Collaboration Centres