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2011). The minitubers are then multiplied in the field for three generations to produce basic seeds. The three
generations (1, 2 and 3) are meant to increase the amount and size of seeds. The basic seeds are distributed to
certified seed producers who produce certified seeds; the certified seeds are then sold to farmers for production of
ware potatoes (KARI, 2007). At KALRO-Tigoni, there is low efficiency in basic seed potato production. This is
mainly because minitubers are produced using the soil-filled pots; the technique has a low multiplication rate (6 to
8 tubers /plant) unlike aeroponics which can give 50 to 100 tubers per plant (Otazu, 2010; Muthoni et al., 2011).
To counter this problem, an aeroponic unit was set up at KALRO-Tigoni in 2008 by the international potato
centre (CIP) to enhance minituber production.
In addition to in vitro plantlets, minitubers can also be produced from stem cuttings as well as from minitubers.
Stem cuttings can be made on plantlets in the seedling trays so as to increase the number of plants without
incurring tissue culture costs. Stem cutting propagation is among the most productive and highly efficient low cost
potato multiplication procedures. Using stem cuttings, a single plantlet can yield up to 100,000 progenies in 6
months (Ngaruiya et al., 2013).
In light of foregoing, a study was carried out to assess minituber production from three different starter planting
materials (in-vitro, mini-tubers and stem cutting) of two potato varieties under aeroponic conditions.
2 Materials and Methods
The experiment was conducted for two successive growing periods (season one: July to December 2010 and
season two: January to May 2011) at KALRO-Tigoni. The experiment was set up as a factorial arrangement in a
randomized complete block design (RCBD) with three replications. Factor one was the starter material i.e. in-vitro
plantlets, mini-tubers and stem cutting) while factor two was the potato cultivar i.e. Asante and Tigoni. Each
aeroponic growth chamber represented a replicate consisting of six treatments combinations. Each treatment
consisted of thirty transplants at a spacing of 20 cm x 20 cm.
Plantlets originating from tissue culture (in vitro plantlets), stem cuttings and minitubers were planted in the
aeroponic growth chamber. Each sub-plot consisted of 30 transplants at a spacing of 20 cm x 20 cm.
2.1 Preparation of planting materials
1. In-vitro plantlets: Nodal cuttings (one cm) of the two cultivars (Tigoni and Asante) were cut from preceding
generation of in-vitro plantlets and cultured in Kilner jars containing 100ml Murashige and Skoog (1962) media
supplemented with glycine 0. 2 g/L, nicotinic acid 0.05 g/L, pyridoxine 0.05 g/L, inositol 10 g/L thiamine 0.01
g/L, gibberellic acid 0.001 g/L, and sucrose 30 g/L. The cultures were then incubated for three weeks in the
growth room maintained at 20 ±2°C and a 16-hr photoperiod having light intensity of 3,000 lux. The plantlets
were then transplanted into crates filled with steam-sterilized sand under greenhouse conditions for two weeks.
2. Stem cuttings: In-vitro plantlets of the two potato cultivars (Tigoni and Asante) were raised in crates filled with
steam-sterilized sand for 10 days in a greenhouse. The growing points were nipped to allow the development of
lateral shoots. When the lateral shoots attained a length of 6-10 cm, they were cut (using a sterile surgical blade).
The cut ends were dipped into a rooting hormone (Roothom H (0.6%) Indolebutyric acid) and then planted in
crates filled with steam sterilized sand for two weeks.
3. Minitubers: Minitubers (3 g each) harvested from soil-filled pots were sown in crates filled with
steam-sterilized sand at a depth of two cm. The crates were kept in a greenhouse for two weeks.
Nutrient solution containing 2.2 gms KNO3, 1.4 gms NH4NO3, 0.8 gms Ca superphosphate, 0.8 gms MgSO4,
0.036 gms Fe(EDTA) 6% and 0.048 gms Micro (Fetrilon) at a pH of 6.5 was applied to the plants for the duration
they were in the crates. The plants were then transplanted into the aeroponic boxes after attaining a height of
10-15 cm.
