Tese (Doutorado) - Universidade Federal de Viçosa, Programa de Pós-Graduação em Fitopatologia, 2003.

Abstract: The etiology of Eucalyptus bacterial leaf blight was studied on plants in nurseries and plantations in the states of Rio Grande do Sul, São Paulo, Minas Gerais, Bahia, Mato Grosso do Sul, Amapá and Pará. The disease is characterized by water soaked, angular and interveinal spots on the leaf limb followed by shot holes and lesions in petioles and branches. The lesions can be found along the main vein, at the leave edge and at the upper portion of the limb. Of the several isolates obtained during isolations, 25 induced hypersensitive reaction in non-host plants, and were pathogenic to Eucalyptus spp.. Identification of these isolates by biochemical tests using carbon sources (MicroLog&#63195 BIOLOG), filogenetic analysis of rDNA16S and FAME profile, revealed that 10 isolates belonged to Xanthomonas axonopodis, four each to X. campestris and Pseudomonas syringae, two each to P. putida, P. cichorii, and Rhizobium sp., and one to Erwinia sp.. When the Eucalyptus seedlings were inoculated by spraying the bacterial suspension (10 8 ufc/ml) of any isolate, only P. syringae e Erwinia sp. did not produce typical disease symptoms. Because of the higher frequency of X. axonopodis isolates, it was evaluated for its host range. Plants from the botanical families Myrtaceae (Corymbia maculata, Eugenia jambolana, E. camaldulensis, E. cloeziana, E. grandis, E. robusta, E. saligna, E. urophylla, E. urophylla x E. maidenii, E. globulus, Myrciaria jaboticaba and Psidium guajava), Caricaceae (Carica papaya), Fabaceae (Phaseolus vulgaris and Pisum sativum), Rosaceae (Prunus persicae), Rutaceae (Citrus limon) and Solanaceae (Lycopersicon esculentum) were spray inoculated with the bacterial suspension (10 8 ufc/ml). Only plants of Myrtaceae family showed susceptibility, but the symptoms developed only seedlings of Eucalyptus and Corymbia. The frequency of symptomatic plants varied among the species with E. urophylla x E. maidenii clones and E. cloeziana being the more susceptible hosts. A diagrammatic scale of eight disease severity levels was developed for disease quantification on eucalyptus leaves. The validation of the scale by three groups of inexperienced evaluators showed that although there was no accuracy in disease estimation with or without the scale, the group of untrained evaluators using the scale had higher precision.

Orientador Acelino Couto Alfenas