© 1970 by Institute of Chartered Foresters
Peridermium pini (Pers.) Lev. and the Resin-top Disease of S cots Pine
III. Infection and Lesion Development
Forestry Department, University of Aberdeen
Natural lesions of Periderinium pini could be classified into two groups, one associated with unwounded needle-bearing twigs and the other with stem wounds on tissues of all ages. Infection experiments confirmed that stem wounds can become infected, and that such infections give rise to symptoms similar to natural stem-wound infections. On the other hand, experimental needle-wound infections gave rise to symptoms similar to natural lesions not associated with stem wounds. Further experimental evidence suggests that infection of unwounded needles may take place through stomata. It is proposed that there are at least three infection pathways, namely through stomata of unwounded needles, through needle wounds, and through stem wounds. The first two accounted for about 90 per cent of the natural lesions observed in two stands in Morayshire, but the last one gave rise to a disproportionately large number of damaging stem lesions.
The factors which determine whether a lesion will reach the main stem are discussed. An estimate of the rate of growth of lesions and the rate of branch suppression at the base of the live crown is given. The distribution of lesions in the crown is shown diagrammatically. Tuberculina maxima Rost. caused a reduction in aeciospore production to about one-third of normal in one stand. Some aspects of the epidemiology of the resin-top disease are discussed.