SUMMARY
Water relations and ultrasound acoustic emissions were measured before, during and after a cycle of water stress, in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings infected with two xylem pathogens (Phomopsis occulta and Diplodia pinea). After 150 days from the inoculation no significant differences in water relations parameters and ultrasound emissions were found between infected and control plants.
INTRODUCTION
Modifications of climate may create more favourable conditions for the development and spread of fungal pathogens. On the other hand, plants may become more susceptible to pathogens if stress conditions (for instance water stress) occur as a consequence of climate changes (Palti, 1981).
Recently, two fungi species (Phomopsis occulta Trav. and Diplodia pinea (Desm.) Kickx) were found to infect the cambium and the xylem of Douglas-fir (Pseudotsuga menziesü (Mirb.) Franco) trees grown in Southern Italy (Basilicata); this observation represents a new record for this region.
Phomopsis occulta causes a definite die-back of young branches and shoots, a typical stem girdling where chromatic alterations are evident with a definite canker of limited growth on the trunk (Wilson & Hahn, 1929). Diplodia pinea, chiefly important as a cause of die-back in pines, is recognized as causing a “blight” of Douglas-fir seedlings (Peace, 1962).
As microorganisms which probably infect both the parenchyma and the xylem, these fungi may determine a reduction of hydraulic conductivity of stem and branches, either by physically blocking the xylem conduits or by promoting the formation and spread of gaseous emboli within the conduits (Zimmermann, 1983; Tyree & Sperry, 1989).