Characterization of Rhizoctonia Species Associated with Foliar Necrosis and Leaf Scorch of Clonally-propagated Eucalyptus in Brazil

The objective was to identify and characterize the causal agent of foliar necrosis and leaf scorch of Eucalyptus spp. in Brazil. Nineteen putative isolates of Rhizoctonia obtained from Eucalyptus plants during clonal propagation were compared with isolates from other hosts and with tester strains of anastomosis groups of Rhizoctonia solani. Features compared were morphological characteristics of anamorphs and teleomorphs, numbers of nuclei per cell in the vegetative hyphae, anastomosis of hyphae, and ability to produce necrotic lesions on cuttings and damping-off of E. grandis×E. urophylla hybrid seedlings. Rhizoctonia solani AG1 (AG1-IB like) was the most frequent causal agent isolated from Eucalyptus plants and cuttings with symptoms of leaf scorch and foliar necrosis respectively. These isolates were highly virulent on Eucalyptus cuttings and presented naturally epiphytic growth on Eucalyptus shoots. Binucleate isolates and isolates of R. solani AG4 were also virulent on cuttings and were most virulent on Eucalyptus seedlings causing pre- and post-emergence damping-off. Virulence on Eucalyptus cuttings and seedlings was not restricted to a single species or anastomosis group of Rhizoctonia.