2017 ASHS Annual Conference

Vegetative propagation by cuttings allows for clonal propagation of valuable horticultural genotypes. Adventitious root formation relies on translocation of carbohydrates from the cutting to root primordia and expanding roots. A lack of information exists on the temporal relationships among carbon translocation, photosynthesis, and water status as vegetative cuttings develop callus and roots. Our objectives were to determine relationships among cutting water status and gas exchange and investigate the translocation of photosynthates produced both pre- and post-severance as adventitious rooting occurred on cuttings of Hibiscus acetosella. Stock plants were ¹³C labelled before, and cuttings labeled after being taken, to track movement of carbohydrates from the cutting to adventitious roots. Cutting water potential (Ψ) remained similar over the 21 d, likely because cuttings were held under mist. Net photosynthesis (Pn) and stomatal conductance (gs) both increased over the course of the study, while leaf intercellular CO₂ concentration (Ci) remained mostly unchanged. This suggests that the low photosynthetic rate prior to adventitious root formation was not the result of low Ψ or gs. Instead, we postulate that the low Pn during the early rooting phase was the result of low sink strength. This is supported by a strong correlation between root growth rate (and thus sink strength) and Pn. Based on translocation of ¹³C from the cuttings to the newly formed roots, it was determined that both pre- and post-severance-produced photosynthates are used for adventitious root growth. We conclude that new root growth of H. acetosella cuttings uses both pre- and post-severance-produced photosynthates. However, photosynthesis during the early phase of new root growth appears to be limited by a low sink strength.