EFFECT OF DIFFERENT TREATMENTS ON THE CONVERSION OF M.26 APPLE ROOTSTOCK SYNTHETIC SEEDS OBTAINED FROM ENCAPSULATED APICAL AND AXILLARY MICROPROPAGATED BUDS

Encapsulated buds excised from micropropagated shoots of the clonal ap ple rootstock M.26 (Malus pumila Mill.) can be considered an interesti ng example of non-embryogenic synthetic seeds. Two experiments were ca rried out to evaluate the different aptitude of apical and axillary bu ds towards encapsulation and synthetic seed production, and to find th e best treatments to enhance conversion rates. Different behaviour bet ween axillary and apical buds was observed. Synseeds from apical buds reached conversion rates of 85%, against a maximum of 25% obtained wit h the encapsulated axillary buds. A root induction treatment with 24.6 mu M IBA followed by a root initiation culture of 3 to 6 d prior to e ncapsulation with a nutrient-enriched artificial endosperm proved to b e the best protocol for enhancing rooting of the encapsulated explants . A cold treatment of 60 d was able to reduce formation of undesired c allus on the explants, which was negatively correlated with rooting.