Effect of growth regulators on in vitro potato multiplication and production of mini-tubers under aeroponics.
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Potato production in Uganda has remained very low with the production stagnanted at 7.0 t/ha. The seed system depends conventional means to propagate potatoes through the use of tubers which is characterized by a low multiplication ratio requiring several field multiplications to generate large quantities of seed to meet the seed potato industry. Tissue culture and aeroponics are excellent technologies that can allow rapid multiplication of potatoes. Potato production through these technologies is also known to be higher though the system in Uganda hardly growth regulators making the production of seed potato to remain low. However, the use of plant growth regulators is known to influence potato production leading to mass production. In order to increase the potential of tissue culture for rapid production of planting material and rapid production of potato seed through aeroponics method, this study aims at optimizing protocols for rapid propagation and production of seed potato for the most popularly grown and farmer preferred varieties such as Kachpot-1, Kinigi, and Victoria. Eight hormonal combinations, N1 – N4 and B1 – B4, composed of MS supplemented with different hormonal combinations were formulated in the tissue culture laboratory. N1 and B1 were composed of MS only, N2, MS+3mg/l GA3+0.005 mg/l NAA), N3, MS+4mg/l GA3+0.01 mg/l NAA), N4, MS+5mg/l GA3 +0.02 mg/l NAA, B2, MS + 3mg/l GA3 + 1.5 mg/l BAP, B3, MS+4mg/l GA3 + 2.0mg/l BAP and B4, (MS+5mg/l GA3 + 2.5 mg/l BAP). Ten shoot tips from in vitro raised plantlets were excised and transferred to each of these hormonal combinations, three replicates were made and laid in the completely randomized design. The tissue culture plantlets raised on these hormonal combinations N1 – N4 and B1 – B4 were planted in the sand – soil mixture (1:1) for acclimatization and root hardening. Plantlets raised on N1 – N4 developed a strong root system and were later transplanted onto the aeroponic units. Together with the in vitro plantlets raised on N1 and B1, tuber sprouts and stem cuttings were planted in the aeroponics unit. In the aeroponics unit, six plants were fixed on top of the aeroponics boxes and replicated three times. In the laboratory, data were collected on the number of shoots, shoot height, number of buds, leaves, roots and nodes. Data on growth vigour, the numbers of shoots, shoot height, number of days to tuber formation and number of stolons per plant and number of mini-tubers were taken in the aeroponics screen house. Results showed that the GA3 and NAA hormonal combination is the best for development of complete plantlets and increased multiplication capacity of the studied cultivars. The hormonal concentrations vary from variety to variety. For Kinigi, hormonal combination N3 produced the highest mean number of nodes (6.42), mean number of buds (4.32) and tallest plantlets (mean height, 7.38 cm). In Kachpot 1, hormonal combination N4 produced the tallest plantlets (6.67 cm), the highest mean number of nodes (8.14) and leaves (8.71) were produced by N1 and B1 while highest mean number of buds (5.36) and roots (6.28) were produced by N2. For Victoria, N4 produced the tallest plantlets (7.19 cm), highest mean number of buds (5.88), nodes (7.66) and roots (5.76). The hormonal combinations; N1 – N4 did not significantly differ from each other in each variety on the number of mini-tubers per plant with mean ranging from 37.47 – 32.06 for Kachpot 1, 28.47 – 23.74 for Kinigi and 43.23 – 30.72 for Victoria. Amongst the starter planting materials, TC generated plants produced a significantly higher number of mini-tubers per plant than TBS and SC generated plants across all the varieties. TC generated a mean number of 43.64 in Kachpot 1, 32.91 in Kinigi and 39.95 mini-tubers per plant in Victoria. TBS generated a mean number of 37.34 in Kachpot 1, 21.15 in Kinigi and 34.95 mini-tubers per plant in Victoria. SC generated the lowest number of mini-tubers per plant across all the varieties with a mean of 20.24 in Kachpot 1, 13.81 in Kinigi and 21.25 mean number of mini-tubers per plant in Victoria. The results obtained from the present study suggest the use of GA3 and NAA hormonal combination in order to increase the rate of multiplication in shoot tip culture by increasing the plantlet height, the number of nodes and buds on the plantlets obtained. Application of these growth regulators at the tuber initiation stage or after emergence would increase the production of mini-tubers of the aeroponically grown potatoes Foliar application of the growth regulators may also increase mini-tuber numbers. The yield produced by TBS generated plants in Kachpot 1 and Victoria was above the potential mini-tuber yield in aeroponics. TBS generated plants can therefore be used as alternative starter planting materials for Kachpot 1 and Victoria in aeroponic production of mini-tubers. The mini-tuber yield of TBS generated plants in Kinigi and SC generated plants across all the varieties was below the potential mini-tuber yield in aeroponics and therefore should not be used as alternative starter planting materials for aeroponic production of potato mini-tubers for Kinigi.