ASSESSMENT OF NUTRITIONAL VARIATION AND ESTABLISHMENT OF AN EFFICIENT TISSUE CULTURE PROPAGATION PROTOCOL FOR Vitex doniana Sweet (LAMIACEAE) FROM BENIN (WESTERN AFRICA)

Abstract

Black plum (Vitex doniana) tree is an indigenous wild species important for the livelihoods of rural populations in Benin. It is highly nutritious and rich in phytochemical compounds of health benefit. In Benin, the greatest economic potential of Vitex doniana trees probably lies in the leaves. It has emerged as a potential species for domestication. Despite some studies indicating that nutritional properties can vary according to the sample provenances, no data on nutritional variation of V. doniana leaves are available in Benin. On the other hand, the conventional methods of propagating the plant produce inadequate number of planting materials as seeds of this tree have a very weak germinating capacity and the macropropagation rate by stem cuttings is slow. Tissue culture is a reliable alternative method. Therefore, the objective of the current work was to evaluate the nutritional variation of leaves collected from different agro climatic zones and to establish a feasible in vitro propagation method for V. doniana using both somatic embryogenesis and micropropagation. During the current study, proximate, minerals and vitamin A and C concentrations were analyzed. In the Tissue Culture experiments, sterilization was evaluated using different concentrations of a commercial bleach, mercuric chloride and calcium hypochlorite at varying time intervals. For somatic embryogenesis, different growth regulators and additives were evaluated. In the micropropagation experiments, microshoots were regenerated using BAP and roots using IBA at concentrations 5, 10, 20, 40 μM. Results showed that V. doniana young leaves are highly nutritious. Protein, Calcium, vitamin A and C concentration vary significantly across agro climatic zones. The highest values of Protein, Vitamin A and C were obtained in the Sudanian zone and the highest value of calcium was obtained in the Sudano-Guinean zone. The highest number (91%) of clean leaf explants were obtained when the leaf explants were subjected to sterilization using 2% calcium hypochlorite for 30 minutes followed by a second sterilization using 2% hypochlorite for 15 minutes (double sterilization). The highest number (40%) of clean nodal explants were obtained when the explants were subjected to sterilization using 2% calcium hypochlorite for 45 minutes followed by a second sterilization using 2% hypochlorite for 30 minutes. Inclusion of 4 μM Picloram, in the medium was observed to increase the mean number of embryos per explant. Of the four amino acids tested, only tryptophan evaluated at 150 μM had significant effect on the induction of somatic embryogenesis with 6.5 embryos per explant. On the other hand, silver nitrate and casein hydrolysate at 50 μM were found to enhance the number of embryos per explant. Liquid pulsing treatment for 24 h produced the highest (9.19) mean number of embryos compared to the control (1.2). The highest mean number of shoot/explant and the highest mean length of shoot was obtained in media supplemented with 10 μM BAP. Rooting was achieved using IBA. No optimum concentration of IBA was found for root regeneration. The protocols developed during this study would be useful for the mass propagation, and genetic transformation of selected elite lines. This work provides useful information that can be used to increase domestication of V. doniana in Benin. However, further investigations need to be done on the bioavailability of nutrients from the leaves of V. doniana and the conversion and the performance in the field of both embryo-derived plantlets and plantlets obtained from micropropagation.