Foliar application of K-IBA to the Abaxial or Adaxial Leaf Surface With or Without a Surfactant Does Not Impact Root Formation in Buttonbush and Burning Bush Euonymus Cuttings

Foliar application has become a viable alternative for auxin delivery to induce adventitious rooting in cuttings. Foliar application of K-IBA to buttonbush (Cephalanthus occidentalis L.) and burning bush euonymus [Euonymus alatus (Thunb.) Siebold] cuttings improved roots per cutting compared to untreated cuttings. However, foliar application was not as effective as K-IBA applied as a basal dip. To investigate if auxin uptake could be partially responsible for the differential rooting observed between treatments in burning bush euonymus, K-IBA was applied to the adaxial (upper) or abaxial (lower) leaf surfaces with or without a surfactant. There were no differences found for rooting percentages or roots per cutting related to the leaf surface treated or inclusion of the surfactant. It has been suggested that foliar auxin is absorbed mainly through open stomates on the leaf surface during cutting propagation. The current study indicates that auxin was absorbed equally well from the adaxial and abaxial leaf surfaces in these two species and that other factors such as transport or metabolism of IBA may be influencing differential rooting related to application method. Species used in this study: buttonbush (Cephalanthus occidentalis L.), burning bush euonymus [Euonymus alatus (Thunb.) Siebold]. Chemicals used in this study: K-IBA (indole-3-butyric Acid potassium salt).