A Comparison of Irrigation System, Basal Temperature and Auxin Concentration on Rooting of Stem Cuttings of Ilex glabra L.

Abstract

Basal stem temperature and auxin treatment effects on rooting percentage, root number, length of the longest root, and basal stem necrosis of hardwood stem cuttings of Ilex glabra L. (inkberry holly) were compared between a recirculating subirrigation propagation system and a conventional intermittent mist propagation system. Recirculating subirrigation maintained basal temperature and medium moisture content better than conventional intermittent mist. While rooting percentages were significantly greater for cuttings rooted in the recirculating subirrigation system, root number, and length of the longest root were higher for cuttings rooted under intermittent mist. A basal temperature of 32C (90F) was supra-optimal, resulting in significantly lower rooting percentages. However, rooting temperature had no effect on root number or basal stem necrosis. Basal stem necrosis of rooted cuttings was greater in the recirculating subirrigation system, and increased with temperature in both irrigation treatments, but appeared to have no significant effect on root number. Increasing auxin concentration increased rooting percentage, root number, and length of the longest root of rooted cuttings, though the response differed with irrigation treatment. Cuttings of Ilex glabra L. can be rooted successfully in a recirculating subirrigation propagation system where the rooting process appears to be less sensitive to rooting temperature and auxin concentration than for cuttings rooted under intermittent mist. However, overall root growth was greater on cuttings rooted under intermittent mist, perhaps because of the lower medium moisture content in that system. This suggests that optimal rooting of hardwood cuttings can be achieved without intermittent mist using a recirculating subirrigation system with modifications to the moisture content of the rooting medium.