Copper and nickel pollution: frequency of endophytic fungi in Scots pine shoots and endophyte growth in vitro

The frequency of endophytic microfungi was measured from current-year shoots of Scots pine trees growing in Harjavalta, a heavily polluted area in western Finland. The copper (Cu) and (Ni) concentrations in bark plus phloem and needles of the same trees were measured. The frequency of isolates of endophytic taxa were either negatively (Hormonema sp. 2 and Sterile sp. 1) or positively (Hormonema sp. 1, BL132) correlated with the Cu and Ni concentration of bark plus phloem. Isolates of the most common endophytic taxa and the pathogenic Gremmeniella abietina from Harjavalta were grown in vitro in different levels of Cu (0.6 – 126 μg/mL) and Ni (0.3 – 50 μg/mL) separately and in combination. This experiment included also isolates of G. abietina and Hormonema sp. 1 from the northern (unpolluted) area. The concentrations of Cu and Ni that reduced the linear growth to 50% of control were estimated. The endophyte taxa with positively correlated frequency with increasing concentration of Cu and Ni in the shoots were able to withstand elevated levels of Cu and Ni in vitro. Compared with most of the other fungi, G. abietina isolates were particularly sensitive to addition of Ni. No evidence for intraspecific adaptation of G. abietina and Hormonema sp. 1 to Cu and Ni was found. Key words: endophyte, Gremmeniella, heavy metal, Hormonema, Scots pine.