Photoperiodic response in Origanum vulgare ssp. vulgare and ssp. hirtum letsw.: impact on development and growth

Origanum productivity (Origanum vulgare L.) is determined by the conjunction between the amount of biomass accumulated and essential oil content at harvest time. Several authors have stated that such content is maximum at flowering, but the processes that determine time to flowering is still unclear in this species. With the objective of studying photoperiodic sensinsitivity of origanum, two traditional subspecies (Compacto: Origanum vulgare ssp. vulgare and Criollo: Origanum vulgare ssp. hirtum letsw.) were grown under natural and artificialy extended photoperiod. The impact on development, duration of phenological stages and growth dynamics were evaluated. It was found that both subspecies reduced the cycle length under extended photoperiod, but in different magnitud. Criollo was the most sensitive to photoperiod. This suggests that the photoperiodic threshold to flowering induction is lower in this subspecie than in Compacto. In both of them, reduction of the duration of the vegetative stage lead to fewer number of nodes per branch and shorter branches in comparison with control treatments. Extended photoperiod resulted in a branch growth model change from linear to quadratic.