IN VITRO REGENERATION FROM PUMMELO (CITRUS GRANDIS OSBECK.) COTYLEDON-DERIVED CALLUS

Pummelo, a citrus fruit, is an underutilized fruit crop with a potential for commercialization in warm humid climates. Improvement of crops through bio-technological approaches mainly involves availability of efficient in vitro regeneration protocols. A study was conducted to develop a regeneration protocol for a local cultivar of pummelo under cultivation in Devanahalli, Bangalore, India, using cotyledon explants obtained from six-week-old in vitro grown seedlings. Callus was induced on MS (Murashige and Skoog) media by use of α-naphthaleneacetic acid (NAA) at 1, 3 and 5 mg/L, and 2,4-dichlorophenoxyacetic acid (2,4-D) at 0.5, 1 and 2 mg/L, each one individually and also in combination with 6-benzyl adenine (BA) at concentrations of 0.5 and 1 mg/L. The best callusing was obtained in media containing 5 mg/L NAA plus 0.5 mg/L BA (100% callusing with 1.2 g callus fresh weight per explant). In order to induce shoots in the calli, they were transferred in MS media containing each of BA (1 to 8 mg/L) and Adenine Sulphate (AdS) (1 to 40 mg/L), with or without 0.25 mg/L indole-3-butyric acid (IBA). 2,4-D-induced calli showed ability of regenerating shoots better than NAA-induced calli which failed almost totally. Shoot regeneration was best (90% with average 1.9 shoots/explant) when BA was used at 5 mg/L alone. AdS was less effective than BA in shoot induction in the calli though its best result, 70% shoot induction with average of 2 shoots/explant at 20 mg/L, was also considerable. Presence of IBA in the media with each of the two cytokinins used, generally, affected shoot regeneration negatively. The regenerated microshoots were rooted in half strength MS medium supplemented with 4 mg/L IBA. The produced protocol in this study can be useful for improvement of pummelo through biotechnological techniques which involve callus tissue.