Occurrence of Pestalotia stevensonii on Pinus pinea in Spain

Several coniferous tree species are severely affected by fungi of the genus Pestalotia, including P. stevensonii, P. funerea and P. hartigii. In several locations around the world, Pestalotia stevensonii has been described on Pinus edulis, P. ponderosa, P. rigida, P. strobus, Abies nigra, A. pecinata and Picea excelsa (Guba, 1961). On the infected host, Pestalotia stevensonii is often found on mature needles, which become necrotic turning brown from the tips. Under conditions of high humidity, acervuli develop over the necrotic tissues of infected needles, either while they are attached to the tree or lying on the ground. Conidia are 4-celled with darker, median cells and emerge in dark spore tendrils.

Fungal isolates were recovered from necrotic needles of Pinus pinea from 41 sampling zones in the Castilla-Leon region (in west-central Spain). Isolates of P. stevensonii were identified from collections made in 28 of the sampling zones. Different spore concentrations (from 10⁴ to 10⁶ spores per ml) were used in order to evaluate pathogenic capability (Hansson, 1998). Inoculation of P. pinea nursery plants (1-2 years old) did not produce symptoms, even at high spore concentrations. Symptoms were observed only when a high concentration of spores (10⁶ spores per ml) was used on adult trees (>20 years old). P stevensonii was reisolated from all the inoculated and symptomatic plants, thus fulfilling Koch's postulates. These results indicated that P. stevensonii is a weak pathogen on this host and that P. pinea could have resistance to this fungus in the early stages of growth. To our knowledge, this is the first report of P. stevensonii being pathogenic on Pinus pinea in Spain.