Responses to infection by Melampsora pinitorqua and Diplodia sapinea in
Scots pine
Abstract
Diplodia sapinea causes Diplodia tip blight (DTB) and is
recognised as an opportunistic necrotrophic pathogen affecting conifers.
While DTB is associated with abiotic stress, the impact of biotic stress
in the host on D. sapinea’s lifestyle shift is unknown. Observed
co-occurrences of D. sapinea and Melampsora pinitorqua,
causing pine twisting rust on Scots pine ( Pinus sylvestris),
instigated an investigation into their interaction with and influence on
the defence mechanisms of the host. We hypothesised that M.
pinitorqua infections predispose the trees to D. sapinea by
stressing the host and altering the shoot metabolites. Trees in a pine
plantation in central Sweden were sampled over time to study pathogen
biomass and host metabolites. The symptoms of both pathogens were
consistent over years, and the preceding season’s symptoms affected the
metabolic starting points pre-infection and M. pinitorqua’s
proliferation. Symptoms of M. pinitorqua altered shoot
metabolites more than fungal biomass, with co-symptomatic trees
exhibiting elevated M. pinitorqua biomass. D. sapinea’s
biomass pre-symptoms was independent of previous disease symptoms and
infection by M. pinitorqua. Some trees showed tolerance to
M. pinitorqua, with delayed rust infections and minimal DTB
symptoms. This trait may improve the resilience of pine plantations, but
more work is needed.