Kaitera, J. 2007. Effect of tree susceptibility on Peridermium pini lesion development and sporulation on Scots pine. Baltic Forestry 13 (1): 45-53

Susceptibility of Scots pine progenies to pine stem rusts may be an important factor in rust epidemics. This study is an investigation of the susceptibility, lesion development, and sporulation of a resin-top disease fungus, Peridermium pini, on Scots pine seedlings originating from the seeds of trees showing various degrees of susceptibility to pine stem rusts. The resin-top disease symptoms and rust sporulation induced after artificial inoculation, i.e. Peridermium pini aecia, stem swelling and spermatial fluid, were recorded in 1995 - 2003.
The tree susceptibility was found to have little or no effect on the disease rate or other disease and sporulation variables. Aecial sporulation lasted longer on seedlings from resistant trees when compared to seedlings from healthy trees, but the annual lengths of stem bearing aecia and swellings were greater on the seedlings raised from healthy trees than those raised from resistant trees. The spore source was found to significantly affect the disease and sporulation variables. The northernmost spore source induced higher disease rates, greater frequency of seedlings bearing aecia and swellings, and the resultant seasonal sporulation lasted longer than when using the southern spore sources as inocula.

Key words: aecia, Cronartium flaccidum, lesions, Peridermium pini, Pinus sylvestris, resin-top disease, resistance, Scots pine, spermatia, sporulation, susceptibility, swelling