INTERACTIONS OF GREMMENIELLA ABIETINA AND ENDOPHYTIC FUNGI IN SHOOTS OF SCOTS PINE TREES TREATED WITH SIMULATED ACID-RAIN

1. Detached shoots of Scots pine trees with naturally occurring endoph ytic fungi were inoculated with mycelium of the pathogenic fungus Grem meniella abietina. The trees had been subjected to simulated acid rain (pH 3, both H2SO4 and HNO3) or control irrigation (pH 6) during the p revious five 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 an d endophytic isolations was measured. 2. The shoots were often coloniz ed by endophytic fungi, two Hormonema species being clearly dominant. Although the frequency of these fungi tended to be low in trees treate d with simulated acid rain, the treatment effect was not statistically significant. The isolation frequency of Hormonema 1 increased signifi cantly with height of the host tree. The frequency of Hormonema 2 isol ations differed significantly in two separate sub-areas. The frequency of isolations of G. abietina was not affected by simulated acid rain treatment. 3. Gremmeniella abietina was isolated more often from shoot s with Hormonema 2 isolations, which suggests that there are common fa ctors determining the success of the endophyte and G. abietina. On the other hand, the frequency of endophytic isolations was lower than exp ected in those parts of the shoots invaded by G. abietina, implying th at the latter was a stronger competitor.