Optimizing IBA concentration and stem and segment size for rooting of hybrid hazelnuts fromhardwood stemcuttings

Germplasm improvement of woody crops through plant breeding depends on effective methods of vegetative propagation, both for evaluation of candidate germplasm and for dissemination of improved varieties. Hybrid hazelnuts [Corylus americana (Walter) x C. avellana (L.)] are being developed as a new crop for the Upper Midwest for their ecological and economic value, but lack of economically viable propagation methods is a significant bottleneck to their wide scale adoption. This paper describes two trials to optimize propagation from hardwood stem cuttings in low-cost humidity tents, using dormant crown suckers collected in the fall. We found that: 1) 2 g.L^-1 (2,000 ppm) indole-3-butyric acid (IBA) in a 50% ethanol solution is the best concentration for rooting cuttings of a range of sizes and 2) rooting declines with increasing basal diameter of stems, but increases with increasing length of stem. The thicker cortex of large diameter stems may present a physical barrier to emergence of adventitious roots. Conversely, longer stems have larger stores of carbohydrates, which are essential both for keeping the stems alive until roots can be developed, and for providing the building blocks for growing those roots.