Micropropagation of Plectranthus edulis (Vatke) Agnew from shoot tip and nodal explants

Abstract

Plectranthus edulis Vatke belongs to the family of Lamiaceae, which occurs both as a wild and cultivated species. The major constraint in the cultivation of P. edulis is its low productivity due to shortage of planting materials and incidence of pests and diseases. In this study, an efficient protocol was established for the micropropagation of P. edulis germplasm using shoot tip and nodal explants. Explants were sterilized using different concentrations of Sodium hypochlorite (NaOCl) for different times of exposure. MS medium supplemented with different types and concentrations of auxin and cytokinin were used for culture initiation, shoot multiplication and root induction. NaOCl at a concentration of 2% and exposure time of 5 min gave 74.50±0.5% of clean culture for nodal and 69.83±0.76 from shoot tip. Six-Benzylaminopurine at 1.5 µM was found to be an optimum concentration for shoot induction, yielding 91.67±0.58% for nodal and 85.57±0.51% for shoot tip explants 3 weeks after culture. The combination of 2.0 µM BAP with 1.0 µM IAA was found to be the optimum concentration yielding 10.28±0.06 and 6.12±0.01 shoots per explants for nodal and shoot tip, respectively for shoot multiplication. Half strength MS medium with 2.0 µM IBA and 1.0 µM NAA gave the highest rooting percentage (97.00±0.28) with optimum root number (33) and length (3 cm). Up on acclimatization and transplanting, 83% survival efficiency was observed on soil mix ratio of 2:1:1 decomposed coffee husk, forest soil and sand, respectively. There were no observable variations with respect to morphology and growth characteristics to the greenhouse raised parent plants. The results obtained in this study permit the development of mass propagation protocol that could enable large scale commercial production of this highly demanded cultivar true-to type and provide a possible system towards genetic improvement of the crop.