Interactions of Gremmeniella abietina and endophytic fungi in shoots of Scots pine trees treated with simulated acid rain.
Detached shoots of Pinus sylvestris trees with naturally occurring endophytic fungi were inoculated with mycelium of G. abietina. The trees had been subjected to simulated acid rain (pH 3, both H2SO4 and HNO3) or control irrigation (pH 6) during the previous 5 growing seasons. The shoots were incubated in controlled conditions for 6 weeks, after which they were surface sterilized, cut into pieces and plated on agar medium. The frequency of G. abietina and endophytic isolations was measured. Shoots were often colonized by endophytic fungi, 2 Hormonema species being clearly dominant. Although the frequency of these fungi tended to be low in trees treated with simulated acid rain, the effect of this treatment was not statistically significant. The isolation frequency of Hormonema 1 increased significantly with height of the host tree. The frequency of Hormonema 2 isolations differed significantly in 2 separate sub-areas. The frequency of isolation of G. abietina was not affected by simulated acid rain treatment. G. abietina was isolated more often from shoots with Hormonema 2, which suggests that there are common factors determining the success of the endophyte and G. abietina. Alternatively, the frequency of endophytic isolations was lower than expected in those parts of the shoots invaded by G. abietina, suggesting that the latter was a stronger competitor.