Improving pineapple micropropagation protocol through explant size and medium composition manipulation

Introduction. Although several pineapple micropropagation protocols have already been published, significant improvement could be achieved if the stages of the in vitro culture were better defined. Our work concerned several experiments aiming at the mass production of high quality plantlets. Materials and methods. Axillary buds were inoculated on an MS liquid culture medium added with NAA (2 μM) and BAP (4 μM). Regenerated shoots, divided into three classes of different sizes, were then used in further experiments. First, these shoots were inoculated in flasks containing the same MS culture medium with or without growth regulators. Then, four basic media, containing different salts and free from growth regulators were tested. In a third assay, the MS culture medium was compared with a half-diluted MS culture medium for studying the plantlet elongation and rooting stage. Results. In the MS culture medium supplemented with NAA and BAP, the highest multiplication rate (13.5 shoots) was obtained with the smallest shoots inoculated, while in the MS culture medium free of growth regulators, the highest plantlets (7.7 cm) were the result of the highest shoots inoculated and showed no vitrification. The normal MS culture medium, in comparison with the half-diluted one and the three other salt formulations, revealed a significant increase in the plantlet elongation and best general features. For acclimatization, the highest values of the survival rate (93.8% ) and fresh and dry weights were obtained with the transference of higher than 7.0 cm in vitro plantlets. Conclusion. Using the protocol described in this work, it is possible to obtain 1 million in vitro plantlets after 9 months from a single bud, with a 45 day subculture interval and an average multiplication rate of 10 shoots per bud