Development of autotrophy and tolerance to acclimatization of Myrtus communis transplants cultured in vitro under different aeration

The behaviour of myrtle (Myrtus communis L.) plantlets during the last phas e of in vitro culture before transplanting was studied. Myrtle plants were sampled from Mediterranean shrubland vegetation. (In vitro growth of myrtle microcuttings was evaluated during the rooting phase using 500 cm(3) conta iners fitted with two different types of closures. The number of gas exchan ges and time in which aerated and closed vessels lose half of their gas con tent were calculated. Both types of vessel closure allowed photosynthetic a ctivity in myrtle cultures even though the higher aeration rate induced hig her net photosynthetic rate (PN) during all the culture. In vitro morphogen etic ability and rooting of myrtle microcuttings were affected by the diffe rent environment conditions inside the culture vessels: plantlet growth and root formation of myrtle explants increased in aerated vessels in comparis on with closed ones. The well developed root system. the higher PN and dry mass accumulation during the pre-acclimatization phase in aerated vessels i nduced a better ability to face the transplant stress.