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Tissue culture has been used to produce high quality and clean planting material. In addition to viral elimination, tissue culture offers other advantages such as rapid multiplication of seed stock for basic seed production within a short period of time. The method is also useful for germplasm conservation. Although, in-vitro multiplication of potato was started 40 years ago and is promising, extensive use in developing countries has been limited by the high costs of media. There is thus need to explore cheaper alternatives without compromising on quality of in-vitro plantlets. A study was carried out to compare the effects of the liquid medium and solid medium on performance of three popular Kenyan potato cultivars i.e. Dutch, Kenya Sifa and Tigoni. Liquid medium consisted of Murashige and Skoog medium supplemented with normal vitamins and sucrose while solid medium consisted of the same chemicals into which phytagel were added to solidify the medium. Data taken were number of roots, nodes and leaves per plantlet over time. From the results, the liquid medium gave more roots, more nodes and more leaves per plantlet than the solid medium. The results therefore indicated that liquid media have a significant effect on the plant growth. In addition, liquid medium was found to be cheaper than solid media by USD 1.65. It appears more economical to use liquid media than solid media for in vitro micro-propagation of potato. However, the experiment needs to be repeated especially with different potato cultivars so as to come up with useful recommendations.

An experiment was conducted at KALRO-Tigoni to assess the effect of starter plant material (in-vitro plantlets, stem cuttings and minitubers) on minituber production of two potato cultivars Asante and Tigoni under aeroponic conditions. The experiment was set up in the aeroponic unit at KALRO-Tigoni in randomized complete block design (RCBD) replicated three times. Data were collected at each harvest on the number of minitubers produced per plant; the minitubers were later graded into three weights (0.1-5g, 5.1-12g, >12g). Cultivar Tigoni produced a higher total number of minitubers (49.96) and (52.67) compared to Asante which produced (39.63) and (46.39) minitubers in season one and two respectively. Additionally, in-vitro propagation materials gave the highest number of minitubers (56.44 and 62.94) compared to stem cuttings (43.53 and 51.44) and minitubers (34.42 and 34.19) during the two seasons respectively. The results of this study suggest that the starter materials have a significant effect on the number of potato minitubers produced under the aeroponic system regardless of the potato cultivar. Use of in-vitro plantlets as starter material optimizes minituber production in the aeroponic system. However, the study should be repeated so as to come up with concrete results.Keywords Aeroponics Asante; Potato minitubers; Starter material; Tigoni BackgroundIn Kenya potato (Solanum tuberosum L.) is the second most important staple crop after maize and plays a major role in national food and nutritional security (Janssen et al., 2013). Potato is grown by about 800,000 farmers cultivating about 161, 000 hectares per season with an annual production of about 3 million tonnes in two growing seasons (GTZ-PSDA, 2011;MoALF, 2016). The annual potato crop is valued at KSh. 50 billion (USD 500 million) at farm gate prices (GTZ-PSDA, 2011;MoALF, 2016). Beyond the farm, the industry employs about 3.3 million people as market agents, transporters, processors, vendors and exporters (ANN, 2009;MoALF, 2016). In addition potato is a vital source of calories, proteins, vitamins, potassium and fiber.Most potato producers are small scale famers; it is estimated that 90% of them own less than 1 ha (Janssen et al., 2013). Most of these farmers depend on rainfall to produce their crops. Yields are low [4.4 to 10 t ha-1 with an average of 7.7 t ha-1 (MoA, 2008;Muthoni et al., 2010; Janssen et al., 2013)]. Low yields are mainly due to use of poor quality seed potato, low soil fertility, low and erratic rainfall, pests and diseases (Janssen et al., 2013). Certified seed potato is expensive (about US$ 30 for a 50 kg bag) yet one requires 16 such bags to plant one acre. In addition, certified seeds are scarce; certified seed potato producers supply less than 5% of the national demand. Consequently, most farmers plant seed tubers from informal sources such as own harvests, neighbours and local markets with own harvests being the major source of seed for most farmers. Continuous cultivation of these farm-saved seeds encourages build...

There is limited information on the performance of Kenyan potato varieties under aeroponic systems. Experiments were therefore carried out at the Kenya Agricultural Research Institute (KARI), Tigoni, under an aeroponic system in 2012 and 2013 to evaluate the growth and mini-tubers production of five varieties commonly grown in Kenya and differ in vegetative and reproductive characteristics. The experiment was set up in a randomized complete block design (RCBD) replicated three times. Plant growth expressed by plant height differed among the varieties and these differences became more pronounced with plant age. The effect of variety on number of mini-tubers per plant and total weight of mini-tubers per plant was significant. The number of mini-tubers per plant ranged from 62.2 to 19.2 in season 1 and 56.8 and 17.1 in season 2. Correlations between the number of mini-tubers per plant and the total weight of mini-tubers per plant with days to tuberization, days to senescing, days to maturity, plant height measured at 80 days after transplanting and plant vigor, were positive and significant. The correlation between the number of mini-tubers per plant and total weight of mini-tubers per plant was also positive and significant. It is concluded that mini-tubers production under aeroponic system was variety dependent with Tigoni, Asante and Kenya Mpya being the most productive varieties irrespective of the season. Evaluation of a variety's suitability/adaptability to the system is therefore necessary to determine the most adapted varieties before embarking on large scale production as this will ultimately affect production costs, with higher yielding varieties more likely to result in lower mini-tubers production costs.