Fungal species diversity in juvenile and adult leaves of Eucalyptus globulus from plantations affected by Mycosphaerella leaf disease

In recent years Mycosphaerella leaf disease (MLD) has become very common in Eucalyptus globulus plantations in Galicia, Northwest Spain. The etiology of MLD is complex and is associated with several species of Mycosphaerella and Teratosphaeria. A survey of the fungal mycobiota associated with juvenile and adult leaves, and with leaf litter of the same trees in MLD affected plantations was made. The goal was to identify pathogens and endophytes, to determine if the mycobiota of each leaf type differed, and if leaf litter might be a reservoir of MLD inoculum. Fungi belonging to 113 different species were isolated from leaves of juvenile and adult trees sampled at 10 locations; 81 species occurred in juvenile and 65 in adult leaves. The average number of species obtained from juvenile leaves was significantly greater (p>0.01) compared with adult leaves. This difference suggested that juvenile leaves are not only more susceptible to a group of pathogens, but to a wide range of fungi. Therefore, a general resistance mechanism might be lacking or be less effective in juvenile than in adult leaves. Several pathogenic species were identified in both leaf types. Leaf litter and living leaf mycobiotas were very different. However, some of the species they shared were MLD pathogens, suggesting that leaf litter could contribute inoculum of MLD.