Early in vitro development of isolated microspores of four Sicilian olive cultivars.

Nowadays there is a great interest in the advancement of the studies on gametic embryogenesis in olive, as a method for obtaining homozygous material, due to the enormous effort and relevance in its genome sequencing and gene mapping. In this study, in vitro isolated microspore culture of four Sicilian olive cultivars ('Biancolilla napoletana', 'Nocellara del Belice', 'Tonda Iblea' and 'Verdello') has been carried out, investigating the influence of two polyamines (putrescine and spermidine) and of two medium compositions on pollen embryogenesis induction. During in vitro development, different structural features have been observed: uninucleated microspores, with no development, binucleated with two asymmetrical nuclei (normal gametophytic pathway: one vegetative and one generative nucleus), binucleated with two equal-size vegetative-type nuclei that had just started their sporophytic pathway, trinucleated, tetranucleated and multinucleated, indicating steps towards the sporophytic development. Moreover, the presence of several calli has been detected. A strong genotype-medium interaction has been observed: each cultivar showed a different response depending on the medium tested. This research represents an advancement in the knowledge about gametic embryogenesis in olive, towards the regeneration of homozygous olive plants.