Detection of Diplodia pinea in asymptomatic pine shoots and its relation to the Normalized Insolation index

Diplodia pinea (syn. Sphaeropsis sapinea), a common pathogenic fungus, causes considerable damage in Italy, particularly to pine stands in which trees are subjected to environmental stress. The occurrence of D. pinea in symptomless Pinus nigra shoots was investigated and related to the amount of radiation received by the trees growing on a site in a year, expressed as the Normalized Insolation index (NIi). Twenty-seven pines were selected from nine locations in Trentino (northern Italy). For each pine the incidence of the fungus in apparently healthy shoots was determined by both culturing on an agar medium and application of real-time PCR. The incidence of D. pinea determined by culturing samples taken from asymptomatic trees was 59% (16 of 27 trees), compared with 85% found using real-time PCR (23 of 27 trees). Detection of the pathogen in healthy pine tissue was positively correlated (p < 0.05) with the NIi values, using both detection methods.