Influence of different transplant times on the acclimatisation process of micropropagated artichoke [Cynara cardunculus L. subsp. scolymus (L.) Hayek]

Acclimatisation of in vitro globe artichoke plantlets is one of the most critical phases of the micropropagation process. Indeed, in vitro plants usually show low survival rates when transferred to soil as a consequence of extensive water losses, due to poor stomatal functioning, epicuticolar wax formation and water transport. Moreover, most in vitro developed roots usually die during acclimatisation and a new root system should develop. The environmental conditions characterising the Mediterranean area allow plant acclimatisation even under cold greenhouses or very simple and cheap apparatus such as shading nets, where plantlets are protected against aphids (virus vectors) or other pest attacks. In these conditions, the choice of the most appropriate transplant time seems to be determinant. In this paper, the influence of five different acclimatisation times (July 29, September 19, December 20 and March 7) and mycorrhizal symbiosis on in vivo survival of globe artichoke cv. Romanesco plantlets, was evaluated. After in vitro rooting, at each transplant date, plantlets were transferred under a shading net apparatus, in sterilised alveolate trays, filled with commercial peat mixture and perlite (peat:perlite 3:1). Transplanted plants were subjected to a thirty-day period of progressively decreasing soil moisture. The highest percentage of acclimatised plants (71%) was attained in the September plantation time, when plants encountered the most favourable thermal conditions i.e. mean air temperatures close to 19 degrees C, with minimum never below 12-13 degrees C and maximum never exceeding 28 degrees C. According to other authors, mycorrhizal symbiosis always positively affected acclimatisation, determining, when excluded the first sowing date, an increase in the percentage survival ranging from +21 to +57 units as compared to the control (uninfected roots).