Abstract
Livingstone potato (Plectranthus esculentus N.E.Br) is an underutilised indigenous root vegetable grown by communal farmers in the eastern provinces of Zimbabwe. It is vegetatively propagated using unimproved retained tubers from the previous season. The risk of disease carryover is therefore high, leading to poor yields. The objective of the study was to exploit the tissue culture technique of micropropagation to produce a mass supply of healthy planting material for improved productivity. Two experiments were conducted: firstly, to determine the best explant type and secondly, to determine the best landrace and plant growth regulators for the growth of plantlets. The landraces, namely, Ndurwe, Musande, Chibanda, and Chizambezi, were sourced from communal farmers in the stated production areas. Naphthalene acetic acid (NAA) and benzyl amino purine (BAP) were the auxin and cytokinin used, respectively. The first experiment was laid out as a randomized complete block design (RCBD) with two factors: landrace and explant type (shoot tips, nodes, and leaves). After culturing the explants on a plain Murashige Skoog (MS) medium for ten weeks, the best explant was the node with regards to the number of nodes, shoots, and roots of the plantlets which were significant (P<0.05). The second experiment was laid out as a RCBD with two factors: landraces and the plant growth regulator combinations. The nodes were subcultured on an MS medium supplemented with the 16 combinations of plant growth regulators (0 mg/l, 0.5 mg/l, 1 mg/l, and 2 mg/l BAP concentrations: 0 mg/l, 0.2 mg/l, 0.5 mg/l, and 1 mg/l NAA concentrations), respectively. Chizambezi performed best and is, therefore, highly recommended for the rapid multiplication of Livingstone potato. Results from this study have clearly demonstrated that the addition of NAA: BAP at varying concentrations was significant and is essential for optimizing the growth media for micropropagation of Livingstone potato in Zimbabwe. Commercial production of plantlets can, therefore, be carried out to provide healthy planting material for the communal farmers for improved productivity while preserving the germplasm of the underutilised crop at the same time.
Highlights
Livingstone potato or wild potato (Plectranthus esculentus N.E.Br) is a perennial herbaceous plant, which belongs to the Lamiaceae family and is grown for its edible tubers. e crop can be propagated sexually using seed, but the development of the crop is slow and the offspring is heterogeneous [1]
Effect of Landrace and Explant Type on the Average Shoot Number. e landrace, explant type, and the landrace x explant type interaction effects were significant (P < 0.05) on the mean shoot number. e interaction resulted in Musande nodes producing the highest mean shoot number which was not significantly different (P > 0.05) from that of the Musande shoot tip. e Ndurwe leaf explant produced the least number of shoots which performed statistically the same with the leaf and shoot tips from the other landraces as well as the nodes from Chibanda and Chizambezi (Table 2)
Musande nodes produced shoots with the highest number of nodes which was statistically similar to that of the Ndurwe shoot tip. e Ndurwe leaf explant produced the least number of nodes per shoot, and this was not significantly different to the leaf and shoot
Summary
Livingstone potato or wild potato (Plectranthus esculentus N.E.Br) is a perennial herbaceous plant, which belongs to the Lamiaceae family and is grown for its edible tubers. e crop can be propagated sexually using seed, but the development of the crop is slow and the offspring is heterogeneous [1]. Communal farmers in Zimbabwe produce the crop asexually using small tubers which are retained from last season’s crop [2, 3] This ensures the maintenance of lines, the risk of disease carryover into the season is very high and eventually leads to a decline in potential yield. For root vegetable crops like Livingstone potato, the availability of adequate disease-free planting material is a constraint to increased productivity, and as such, the crop remains neglected and underutilised in Zimbabwe [2]. Underutilised crops such as Livingstone potato are characterized by low yields [1,2,3]. Tindall [6] stated that the yield of Livingstone potato can be as low as two to six tonnes per hectare, while Schippers [1] highlighted yield potentials of Advances in Agriculture up to 60 t/ha under optimal experimental conditions using tissue culture produced plantlets in South Africa [7]
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