Fungi are the most predominant and destructive pathogens in the forest ecosystem resulting in significant loss of biodiversity and species abundance. The incidence and severity of fungal disease symptoms at Onigambari forest reserve were evaluated. Field surveys were conducted to determine fungal diseases associated with forest trees at the reserve. Detailed assessment of tree symptoms was carried out among forest trees in the reserve using random sampling method and standard procedure. Four plots of 25m x 25m dimension were laid alternately at 50 m intervals along two transect with a total of 8 plots in the survey area. Thirty trees were carefully observed for disease symptoms from each plot resulting in a total of 240 trees spread over 15 species. Absence of water soaked lesions and ooze streaming differentiated fungal from bacterial infection. Trees were evaluated for incidence of symptoms and fungal isolates, while disease severity was determined using a rating scale. Nine disease symptoms: leaf spot, anthracnose, rust, blight, powdery mildew, dieback, root rot, heart rot and stem canker were prevalent on surveyed forest trees. Powdery mildew had the highest disease incidence of 71.6% and severity of 81.9% on Cordia millenii and Anogeissus leiocarpus leaves respectively; while leaf spot disease was most prevalent, infecting 10 different tree species. Rust disease symptoms were most severe on infected leaves of Gmelina arborea (80.9%). Tree foliage with blight symptoms had the highest mean severity of 49.2%. Eight fungal genera: Mycosphaerella, Cercospora, Botryosphaeria, Phyllactinia, Ganoderma, Cronartium, Pestalotiopsis and Glomerella were associated with 15 forest tree species evaluated. This study has provided the first report on forest tree pathology at the Reserve and forms a basis for further research on the management of the disease disorders.
Keywords: Fungi, Onigambari forest reserve, disease incidence, anthracnose.