Aims:The main objectives of the study were to establish the current production practices, constraints, and identity of the different landraces of Livingstone potato (Plectranthus esculentus) that are grown in Zimbabwe as well as the potential for improvement of the indigenous traditional vegetable in the small holder-farming sector. Study Design: A questionnaire based survey was conducted.

In Zimbabwe, the average sweet potato yield (6 t/ha) is relatively low when compared to Asian counterparts (17 t/ha). These low crop yields have been blamed on weevil infestations and viral infections which account for 60-90% of sweet potato yield losses in Africa. Meristem tip culture, a Centre for Potato Improvement (CIP) initiated tissue culture technique, has been widely used to eradicate viruses from clonally propagated crops and has been noted to be one of the instrumental techniques that helped China to increase sweet potato yields. In an effort to adopt the meristem tip culture technique for the production of virus-free planting material of a local sweet potato (cv Brondal), a study was conducted to evaluate the effect of Benzylamino purine (BAP), 1-Naphthaleneacetic acid (NAA) and Gibberellic acid (GA3) (either alone or in combination) on cultured Brondal meristems. The different hormonal treatments were assessed on the following parameters: plantlet regenerative capacity, multiple plantlet production, shoot height, average leaf number per shoot and average node number per shoot, ten weeks after meristem culture. All treatments containing a combination of BAP (1 mg -L) and GA3 (at either 5 mg -L, 10 mg -L, or 20 mg -L) had a significantly (p<0.01) higher plantlet regenerative capacity of 33-66% when compared to other treatment combinations. Only treatments, 10 mg -L GA3 + 1 mg -L BAP and 20 mg -L GA3 + 1 mg -L BAP were capable of inducing multiple plantlet formation, producing an average of three plantlets/meristem and two plantlets/meristem respectively. Overall, treatment 10 mg -L GA3 + 1 mg -L BAP gave rise to significantly (p<0.01) taller shoots (20 mm) compared to the rest of the treatments used. For average leaf number per shoot, all GA3 treatments (5 mg -L, 10 mg -L, or 20 mg -L) supplemented with 1 mg -L BAP gave significantly (p<0.01) higher numbers of leaves (six leaves/shoot) than the rest of the treatments. Treatments 10 mg -L GA3 + 1 mg -L BAP and 20 mg -L GA3 + 1 mg -L BAP gave rise to the highest number of nodes per shoot, producing an average of three nodes per shoot. In sharp contrast to treatments containing a combination of BAP and GA3, all treatments containing a combination of BAP and NAA performed poorly in all parameters tested for plant regeneration of Brondal sweet potato variety. In conclusion, the best hormonal treatment for culturing Brondal meristems proved to be 10 mg -L GA3 + 1 mg -L BAP.

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.

The Livingstone potato (Plectranthus esculentus), a tuberous root vegetable indigenous to Africa, remains a neglected and underutilised crop species (NUCS). Of late, there has been a shift in how the NUCS are viewed as consumers become increasingly aware of their nutritional and medicinal value. The objective of the review was to highlight research developments of the Livingstone potato and to identify existing research gaps in a quest to unlock the potential of this crop. Traditionally, the vegetable has been utilised for food, economic and medicinal benefits. However, recent research developments in Africa have demonstrated that the Livingstone potato is highly nutritious and can provide raw materials for the agro and pharmaceutical sectors. While these are notable developments, more needs to be done, especially in Zimbabwe where there is very little researched information on its production and utilisation. The economic impact could potentially be at household, farmer and national level through establishing strong value chains. This is important in order to increase awareness and promote the crop, whose production is on the decline. The diversity and nutritional value of the Livingstone potato needs to be evaluated in Zimbabwe, as a step towards crop improvement, which is key to improved productivity. Continuous production at a large scale will help preserve the germplasm and prevent the genetic erosion currently taking place. This review echoes previous calls for the government of Zimbabwe to take bold steps to support the NUCS, such as the Livingstone potato, at policy level and to fund programmes that deal with such crops.

Somatic embryogenesis (SE) and organogenesis are crucial in the development of disease free plants and genetic engineering. An investigation was conducted on the ability of treatments containing a combination of 2,4-D and Kinetin to induce either SE or organogenesis from cultured sweet potato cv Brondal leaves. Ten treatments were evaluated and each treatment had an exclusive combination of 2,4-D (at 0.05, 0.1, 0.2, 0.5 or 1 mg/L) to kinetin (at either 0.1 or 0.5 mg/L). Callus initiation occurred earlier in treatments containing higher hormonal concentrations. The 2,4-D to Kinetin ratio had a highly significant ( p = 0.001 ) effect on callus growth and proliferation. Increasing 2,4-D to Kinetin ratio promoted profuse explant callusing while increasing Kinetin to 2,4-D ratio suppressed callusing but encouraged organogenesis, in particular shoot production (treatment containing 0.05 mg/L 2,4-D and 0.5 mg/L Kinetin). Embryogenic calli were formed seven weeks after leaf culture in the treatment containing 0.5 mg/L 2,4-D and 0.1 mg/L Kinetin. The embryogenic calli that developed from this treatment emerged from previously nonembryogenic calli. Plantlets produced via the SE pathway proved to be weak and unviable and died within four weeks of germination. In contrast, plantlets produced under organogenesis were strong, grew vigorously, and could be subcultured several times. This disparity may be accounted for by the fact that the cv Brondal embryos that developed under SE were not exposed to an embryo maturation staged before plantlet germination was initiated. The maturation stage would have assisted embryos to reach physiological maturity and a desired level of desiccation, both being critical elements in embryo to plantlet conversion. In this experiment, cv Brondal regeneration from leaf explants was successfully achieved via organogenesis using 0.05 mg/L 2,4-D and 0.5 mg/L Kinetin, and tentative steps towards development of SE based regeneration protocol were established using 0.5 mg/L 2,4-D and 0.1 mg/L Kinetin.