Pathogenicity of Marssonina betulae on Betula pendula and Betula pubescens

Abstract

Studies were undertaken to investigate whether Marssonina betulae is a causal agent of dieback of young birch in Scotland. Marssonina betulae was inoculated onto shoots of B. pendula and B. pubescens and symptoms monitored over several seasons. On B. pendula, but not B. pubescens, lesions developed on young shoots which often girdled to cause dieback, and secondary, sunken cankers developed on main stems. These cankers expanded during subsequent seasons, and often coalesced, girdling stems to cause death of some seedlings. A survey of 900 trees at nine planting sites in Scotland found that 50% of B. pendula and 17% of B. pubescens had M. betulae foliar infections, and that 82% of these infected trees also had sunken cankers on shoots and stems. This study has shown that M. betulae is an aggressive pathogen on B. pendula, causing sunken stem cankers and progressive crown dieback which are symptoms commonly observed on young, planted birch in Scotland.