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EFFECT OF SILVER THIOSULPHATE AND PHOTOPERIOD ON IN VITRO TUBERIZATION OF THREE POTATO (SOLANUM TUBEROSUM L.) CULTIVARS

The experiment was carried out to study the effect of 6 concentrations of silver thiosulphate (STS) and photoperiod on in vitro tuberization of three potato cultivars, namely, Herms, Spunta and Santana. The experiment was conducted in tissue culture laboratory, Vegetable Crops Dep., Fac. Agric., Cairo Univ. Tip meristems in each cultivar were excised and cultured on MS media. In vitro plantlets of all cultivars were multiplied as per routine by sub culturing twice. In microtuberization stage, nodal cuttings from second subculture were cultured on MS media with 0, 0.4, 0.8, 1.2, 1.6 or 2 mM of STS. The treatments were kept under dark or light conditions. STS at 0.4 and 0.8 mM recorded the tallest microplants. The highest number of leaves and branches per plantlet were obtained with 0.4mM STS. On the other hand, the STS at 2 mM recorded the lowest values of plantlet height, number of leaves and branches per plantlet. The highest percentage of microtuberization was recorded with STS at 0.4 mM under dark conditions, and at 2 mM under light one. At dark, Spunta with 1.6 mM STS produced significantly the highest number of microtubers/plantlet. Whereas at light, the maximum number of microtubers/plantlet was obtained with 0.4, 0.8 and 1.2 mM STS in Herms, Spunta and Santans, respectively. In‘Spunta’, application of STS at 0.4 mM under light folded the number of microtubers/plantlet 2.9 compared with dark. In Santana, number of microtubers/plantlet of 0, 0.8, 1.2, 1.6 and 2 mM STS were higher in light comparing to dark. STS applied at 0.8 and 1.2 mM produced significantly the highest value of microtuber fresh weight in Spunta and Santana, respectively under dark. In ‘Spunta’, the applications with 0, 1.2, 1.6 and 2 mM STS at light conditions recorded fresh weight of microtuber higher than in dark. Keywords; Potato, in vitro tuberization, silver thiosulphate, dark and light conditions.