Progress in the Development of Borerresistant White-Barked Birches
Frank S. Santamour, Jr.
Abstract: This paper presents a thorough and comprehensive review of the current state of knowledge regarding the hosts of the bronze birch borer (Agrilus anxius) and biochemical and genetics studies designed to identify and develop borer-resistant white-barked birches. Both older and heretofore unpublished observations and experiments are evaluated to provide a framework for future research. Based on the hypothesis that the presence of the chemical rhododendrin in the inner bark of birches is the key to their susceptibility to the borer, the finding that Betula nigra and B.maximowicziana do not contain this compound, and that B. davurica, B. occidentalis, and B. papyrifera have low levels, increased experimentation with these species is encouraged. Some low-rhododendrin, and potentially borer-resistant, hybrids have also been discovered and are awaiting large-scale propagation for long-term trials.
Keywords: Birch; bronze birch borer, resistance; hybridization; selection.