Differente sealing materials for Petri dishes strongly affect shoot regeneration and development from leaf explants of quince 'BA 29'.

The effect of different sealing materials (i.e., polyvinyl chloride [PVC] transparent film, and Parafilm [PARA]) for Petri dishes was investigated on shoot regeneration from quince (Cydonia oblonga L.) 'BA 29' leaf-explants. Leaves were excised from proliferating shoot cultures, transversally scored and placed with the abaxial side down in 60-mm Petri dishes containing 10 ml of Murashige and Skoog modified medium, with 5.4 uM naphthaleneacetic acid (NAA), 4.5 uM thidiazuron (TDZ), 200 mg l-1 cefotaxime and 0.25% (wt/vol) Phytagel (IM medium) for shoot-bud induction, and cultured in darkness at 22+2 oC for 28 d. Then the explants were transferred to standard conditions (16-h photoperiod at 30 umol/ m2.s photosynthetically active radiation) on a medium similar to IM, except for lack of NAA, and with 0.65 % (wt/vol) agar instead of Phytagel, for 15 to 28 additional days. The sealing combinations PARA-PARA, PARA-PVC, PVC-PARA and PVC-PVC (in the induction-expression phases) were compared during regeneration and for their carryover effect on shoot development after transfer of explants to an elongation medium (0.9 uM 6-benzyladenine [BA]). Carbon dioxide accumulated at 27.2 mmol/ mol at the end of induction, and gradually decreased from 35.4 mmol/ mol on day 9 to 22.5 mmol/ mol on day 28 of the expression phase in PARA-sealed petri dishes, being always much higher than after sealing with PVC (1-2 mmol. mol-1). Ethylene concentration was 0.1 and 0.04 umol/ mol in the first part of the induction and expression phase, respectively, in PARA-sealed Petri dishes, and slightly decreased with duration of exposure to light during expression; while it was absent in most PVC-sealed dishes. The PARA-PARA and PVC-PVC (induction-expression) combinations gave, respectively, the worst and best results of regeneration and successive shoot development.