Micropropagation of Alocasia longiloba Miq and Comparative Antioxidant Properties of Ethanolic Extracts of the Field-Grown Plant, In Vitro Propagated and In Vitro-Derived Callus

In this study, an efficient micropropagation protocol was developed for A. longiloba and the antioxidant properties of field-grown plant, in vitro-derived greenhouse-grown plant and in vitro-derived callus extracts were compared. The A. longiloba seeds tested using tetrazolium chloride salt exhibited 89% viability. Due to poor germination capacity of A. longiloba seeds, the seeds were treated with gibberellic acid (GA₃) or sulfuric acid (H₂SO₄). The maximum seed germination of 87% was observed at 30% H₂SO₄ treatment after 19.00 d, whereas GA₃ treatment showed maximum germination of 53% after 22 d. In vitro shoot multiplication was carried out using various types of cytokinins alone or in combination with auxin. Among them, 6-benzyl amino purine (BAP) single treatment was found to be the best hormone. The highest shoot-length (7.26 cm) and maximum number of shoots per explant (18) were recorded at 3-mg L^-1 BAP. For in vitro rooting, indole-3-acetic acid at 0.5-mg L^-1 was found to be the optimum concentration. Callus was induced using various types of auxins alone or in combinations with cytokinins. The highest percentage of callus of 91 and fresh weight of 6 g was obtained with 3-mg L^-1 IAA. The plantlets produced in the current study were subjected to acclimatization. The combination of topsoil and peat moss at 1:2 ratio was found to be the best soil media. In this study, in vitro-derived callus extract showed the highest phenolic content (538 mg GAE), followed by extracts of field-grown plant parts, i.e., fruit and petiole (504 and 300 mg GAE) while in vitro plant extract showed the lowest (98 mg GAE). Meanwhile, the highest flavonoids was recorded in petiole extract. Comparative antioxidant activity study shows, in vitro-derived callus exhibited better DPPH-radical-scavenging activity (IC₅₀: 0.113-mg mL^-1) whereas the extracts of petiole, fruit and in vitro plant showed 0.126-, 0.137- and 0.173-mg mL^-1, respectively. At the same time, the fruit extract showed better (IC₅₀: 0.088-mg mL^-1) ABTS radical scavenging activity than all extracts tested. In conclusion, the in vitro-derived callus extract could be favored for high TPC and better DPPH scavenging activity. Hence, the present study was conducted to establish an efficient micropropagation protocol and to compare the antioxidant activity of the field-grown plant, in vitro plant and in vitro derived callus extracts of A. longiloba.

Keywords: Alocasia longiloba; antioxidant; callus extract; keladi candik; micropropagation.