EUCALYPTUS RESISTANCE EVALUATING TO BACTERIAL WILT CAUSED BY Ralstonia solanacearum

The use of resistant eucalyptus clones is the most important strategy to disease control on the field. Thus, this work aimed to evaluated methods of Ralstonia solanacearum inoculation in order to select eucalyptus resistant to bacterial wilt. The inoculation methods were selected due to ease of operation and tested in order to evaluate four clones (hybrids E. urophylla x E. grandis): i) application of 5 mL pathogen inoculum (108 cfu/mL) on the root collar of seedlings; ii) application of 5 mL of pathogen inoculum (108 cfu/mL) on the root collar of seedlings after wound of the radicular system; iii) cut of 1/3 basal of the radicular system and immersion of the roots into pathogen inoculum, at the same concentration, for 1 min; and iv) conduction of seedlings transplanted to infested sand maintained in container with application at 15 days intervals (rate of 0.25 L/m(3)) and bacterial suspension (108 cfu/mL) and submitted to collection of sprouting, similarly as it is done in commercial clonal mini-garden. The seedlings transplant to infected sand presented a higher incidence of the disease (bacterial exudation), ranging from 81 to 100%. The second trial aimed to evaluate resistance of different eucalyptus species, using the method of transplanting seedlings to the infected sand. The evaluation of the infection by exudation bacterial method was more appropriate to compare the genotypes. The bacterial wilt intensity was affected by plant and environment conditions. Every species showed disease symptoms, but E. tereticornis and E. grandis showed, respectively, the lowest (33.3%) and the highest (91.7%) percentage of infected genotypes (susceptible). The results of this work are important tools (inoculation method) and resistance sources (eucalyptus species) to bacterial wilt disease control in eucalyptus.