The occurrence of bacterial wilt caused by Ralstonia solanacearum in eucalyptus clonal hedges in the Brazilian states of Bahia, Espírito Santo, Maranhão, Minas Gerais and Pará, from April to September, 2005 resulted in loss of 553,991 rooted cuttings, 6,837,691 cuttings at rooting stage and 11,266,819 cuttings, with a total loss estimated to be at least six million reais (US$ 2.7 M). In clonal minihedges, the disease is characterized by foliar necrosis, annular or complete wood darkening, wilt and death of rooted-cuttings. Leaf symptoms are similar to those observed during the gradual death of rooted-cuttings subjected to drastic pruning or with malformed root systems. In the rooting phase, infected minicuttings can present redning of leaf blade veins and cutting rot. In the field, the disease is characterized by leaf browning and necrosis, basal leaf loss, internal wood darkening and plant death, with onset generally occurring four months after transplant. Disease severity is generally higher in trees with entangled roots and overplanting. The causal agent of the disease was confirmed through exudate tests, scanning electron microscopy, bacterial isolation, PCR/RFLP analyses, hypersensitive reactions (HR) in tobacco seedlings, pathogenicity tests in eucalyptus and tomato plantlets and reisolation of the bacteria. The production of cuttings offers a highly favorable environment for bacterial multiplication. This, combined with the lack of knowledge on genetic resistance and other disease control strategies, makes it essential to avoid introduction of this bacterium in clonal nurseries.
bacterial wilt; vascular wilt; Eucalyptus spp.; clonal propagation; PCR/RFLP; DNA
