Effect of Medium, Iron-Chelating Agent and Plant Growth Regulator on Micropropagation of Pomegranate (Punica granatum L.)

Pomegranate (Punica granatum L.) is a fruit tree that originated from Iran and has been cultivated since ancient times. Classical propagation methods of pomegranate like stem cutting and air-layering have seasonal timing and a higher risk of pathogens contamination. Micropropagation by tissue culture could be considered a method for production of steady and pathogen free plants in this species. However, factors such as lack of rooting and browning due to the oxidation of phenolic components under invitro culture can limit its micropropagation efficiency. To overcome these problems, the effects of various factors, including media, iron-chelating agent, and plant growth regulators, were examined on the pomegranate propagation through in vitro conditions.

To obtain sterile explants, stem cuttings of the pomegranate cultivar Shishe Cap Ferdos were treated with different disinfection treatments. Then, the effect of DKW, MS and WPM basal media and two types of iron chelating agents (EDDHA and EDTA) were evaluated to decrease the secretion of phenolic compound from explant and subsequent browning. In the next step, the effect of plant growth regulators treatments, including 1-2 mg/l of BA in combination with 0.2 mg/l of various auxins (IAA, NAA or IBA) on shoot development and proliferation was studied. After that, rooting of regenerated plantlets was explored at WPM medium supplemented with 0.5 or 1 mg/l IAA, IBA or NAA. Finally, pomegranate plantlets were transferred to different soil mixtures, including eat moss and perlite (2:1), cocopeat and perlite (2:1), peat moss and vermiculite (2:1) and cocopeat and vermiculite (2: 1) for acclimation.

The results indicated that sterilization with 2% sodium hypochlorite for 15 minutes followed by washing with 1g/l carbendazim for 10 minutes, and finally culturing the explants in the medium containing 1 g/l carbendazim had the best effect on reducing explant contamination. Among different basal media and iron chelating agents, WPM resulted in the lowest explant browning. Also, EDDHA was more efficient compared to the EDTA so that explant browning in WPM media containing Fe-EDDHA reduced by 55.8% compared to DKW containing Fe-EDTA. In addition, WPM basal medium supplemented with 2 mg/l BA and 0.2 mg/l IAA induced higher shoot proliferation in node explant of pomegranate. For rooting treatments, after 45 days, WPM supplemented with 1 mg/l IAA induced higher rooting percentage, root length and number in pomegranate shoots. Among different acclimatizing treatments, plantlets that grew on peat moss and perlite (2: 1) had the highest leaf number and stem height.

Our results suggested that the medium composition and chelating agent affected pomegranate explants browning. EDDHA appears to have a positive effect on reducing browning by chelating copper, which is a phenol oxidase cofactor. Also, EDDHA was more efficient compared to the EDTA.