Pathogenicity ofMarssonina betulaeand other fungi on birch

Abstract

Marssonina betulae,Discula betulina,Melanconium bicolorandFusarium avenaceumwere inoculated onto shoots of 1‐ and 2‐year‐old seedlings ofBetula pendulaandB. pubescensand symptom development monitored over several seasons.Marssonina betulaecaused disease onB. pendula, but not onB. pubescens. OnB. pendulasymptoms included discrete lesions, which often girdled, causing dieback of inoculated leading shoots, and the development of secondary sunken cankers on the main stems, which were usually centred around a dead sideshoot. Cankers on the main stems expanded during subsequent growing and dormant seasons, and often coalesced, girdling stems and causing the death of some seedlings. All isolates ofM. betulaecaused disease onB. pendulaand conidia were able to infect young shoots in early flush without requiring a wound.Discula betulinacaused lesions and dieback onB. pendulaandB. pubescenswithin 3 months of inoculation, but disease did not progress thereafter and all inoculated seedlings recovered.Melanconium bicolorandF. avenaceumcaused very little disease on either birch species. This study showed thatM. betulaeis an aggressive pathogen onB. pendula, causing sunken stem cankers and progressive crown dieback, which are symptoms commonly observed on young, planted birch at field sites across Scotland.