Cytokinin preconditioning enhances multiple shoot regeneration in Pongamia pinnata (L.) Pierre - a potential, non-edible tree seed oil source for biodiesel

Abstract

An efficient, highly reproducible protocol for multiple shoot induction and plant regeneration of Pongamia pinnata has been successfully developed using cotyledonary node explants. This study also demonstrates that preconditioning of explant stimulates production of multiple shoots from cotyledonary nodes of P. pinnata. The highest direct shoot regeneration (90%) with an average of 18.4 ± 3.1 shoots/explant were obtained when cotyledonary node explants were excised from seedlings germinated on Murashige and Skoog (MS) media supplemented with benzyladenine (BA) 1 mg l^-1, and subsequently cultured on MS media with 1 mgl^-1 thidiazuron (TDZ). Scanning electron microscope observations of cotyledonary node (CN) explants excised from pre-conditioned and normal seedlings, revealed larger buds with rapid development in BA-preconditioned CN explants. The addition of adenine sulphate significantly increased the average number of shoots per explant. The highest direct shoot regeneration (93%) with an average of 32.2 ± 0.93 shoots/explant was obtained from BA-preconditioned CN when cultured on MS media supplemented with 1 mg l^-1 TDZ and 200 mg l^-1 adenine sulphate (ADS). Repeated shoot proliferation was observed from BA preconditioned CN explants up to 3 cycles with an average of 15 shoots/explant/cycle when cultured on MS media supplemented with 1 mgl^-1 TDZ and 150 mg l^-1 L-glutamine, thus producing 45 shoots/CN explant. Shoots were elongated on hormone free MS media and rooted on ½ MS media supplemented with 1 mg l^-1 of IBA. Rooted shoots were successfully acclimatized and established in soil with 80% success. The highly regenerative system developed in this investigation for this important tree could be a useful tool for genetic transformation.