The host-pathogen system of Gremmeniella abietina (Lagerb.) Morelet and Scots pine; effects of non-pathogenic phyllosphere fungi, acid rain and environmental factors.

Scots pine seedlings (1-yr-old) were inoculated either once, or three times, with the conidia of two saprophytic Honmmema species. After these inoculations, the seedlings were inoculated later with conidia of the pathogenic fungus Gremmeniella abietina (Lagerb.) Morelet. Seedlings received irrigation with simulated acid rain at pH 3, with water of pH 6. or no irrigation, during and after the inoculation treatments, The severity of the symptoms caused by G. abietina, and rhe isolation frequency of endophytic (symptomless) G. abietina and the saprophytes, were measured 11 months after G. abietina inoculation. The isolation frequencies of the two Hormunema species increased significantly in the seedlings inoculated three times with saprophyte conidia. Irrigation treatments did not affect the saprophytes. The disease symptoms caused by G, abietina were positively correlated with tree density. Symptomless G, abietina was isolated most often from the seedlings that had received irrigation at pH b. The isolation frequency was lowest in seedlings with acidic irrigation. The seedlings inoculated three times with conidia of Hormonema sp. 1 had a lower frequency of G. abietina isolations than other seedlings, but the difference was not statistically significant.