Effects of medium composition and the sealing material used for Petri dishes on the growth of callus of Melia azedarach L.

Little information is available on the growth of Melia azedarach L. callus during repeated sub-cultures. The present research aimed to improve our knowledge on the influence of auxins and the sealing material used for Petri dishes on the composition of the gaseous micro-environment and on the growth of callus, in order to achieve long-lasting proliferation of homogeneous callus. Continuous callus growth [to approx. six-times the initial fresh weight (FW) after 4 weeks in culture] was obtained using 4.4 µM 6-benzyladenine (BA) and 4 mg/ l (19.7 µM) indole-3-butyric acid (IBA) in 90-mm Petri dishes sealed with polyvinyl chloride (PVC) strips. Reduced callus FW and browning were observed in Petri dishes sealed with Parafilm M® (PARA), especially for callus grown on naphthaleneacetic acid (NAA)-enriched media. Data on callus growth rates in bottles were mostly in agreement with data from Petri dishes, although FWs were 25 – 35% lower, except for the NAA-PVC-dish closure combination. Moreover, high concentrations of ethylene and carbon dioxide (up to approx. µmol/ mol and 200 mmol/ mol, respectively) and low rates of callus growth were found in PARA-sealed bottles.