Meta-Topolin-Mediated Plant Regeneration in Giant Granadilla (Passiflora quadrangularis L.): An Underutilized Fruit Crop

The present study highlights the effect of meta-topolin (mT) on the shoot regeneration of Passiflora quadrangularis, an important ornamental, medicinal, and underutilized fruit plant. Nodal segments (3-4 cm) obtained from field-grown plants were employed as explants for shoot regeneration. The efficiency of mT and 6-benzylaminopurine (BAP) was compared during the shoot proliferation stage. Murashige-Skoog (MS) medium supplemented with 1.0 mg l-1mT was optimum for shoot proliferation. The interactive effect of mT and indole-3-acetic acid (IAA) was not effective for shoot proliferation when compared with mT alone. After the excision of the newly developed shoots and subculturing of the mother explant for different passages, shoot bud proliferation was enhanced. The maximum number of shoot buds (23.12 +/- 1.16) was formed after the fifth cycle of subculturing of the mother explant. However, a maximum of four to five elongated shoots suitable for rooting were observed after the second as well as the third cycle of subculturing. In vitro flowering was also obtained from nodal explants on mT-containing MS medium. The highest percent response for root induction was achieved when microshoots were transferred to a half-strength MS medium supplemented with 3.0 mg l-1 2-naphthoxy acetic acid (NOA) for 1 week, and NOA-treated shoots were subcultured on a plant growth regulator-free half-strength MS medium. The plantlets were hardened successfully. An improved regeneration protocol developed by replacing BAP with mT may be useful in the large-scale propagation of this recalcitrant as well as economically important plant species.