Floral biology in Olea europaea subsp. cuspidata: a comparative structural and functional characterization

Olea europaea subsp. cuspidata, belonging to the olive complex, is largely distributed in Asia and Africa. In this research, reproductive structures were studied at both structural and functional levels in Asian and African cuspidata accessions with the aim to broaden the knowledge about the floral biology of this subspecies. Morpho-structural observations showed that the cuspidata flower is very similar to the europaea one. Nevertheless, some biometric parameters (length of pollen, pistil, ovule, and embryo sac) significantly differed between the two subspecies. Furthermore, numerous and interesting differences were observed between Asian and African cuspidata accessions for the morphology of stigma papillate cells, degree of secondary cell wall thickenings of the endothecial cells, persistence of the tapetum, ovule and embryo sac length. At functional level, main differences were in the synchrony/asynchrony of the microsporogenesis, percentage of male meiotic abnormalities and sterile pollen, development of ovules. The influence of the growth environment on these features is discussed.