An efficient inoculation method of Ralstonia solanacearum to test wilt resistance in Eucalyptus spp.

摘要

The variation in disease incidence of bacterial wilt caused by Ralstonia solanacearum among eucalypt clones (Eucalyptus spp.) in the field indicates that the disease may be controlled by planting resistant material. However, efficient inoculation methods for bacterial wilt on eucalypt are scarce and have low replicability. In this work, we developed an effective protocol for inoculation of R. solanacearum, which was subsequently validated on different eucalypt clones. Three methods were tested: (i) soil infestation with bacterial cell suspension; (ii) immersion of wounded roots in the bacterial cell suspension; and (iii) injection of bacterial cell suspension in the base of the stem. The injection method proved to be the most efficient for inoculating eucalypt with R. solanacearum. Differentiation between resistant and susceptible clones was observed 30 days after inoculation in independent assays. Base stem inoculation of 21 eucalypt clones showed that four clones, classified as resistant, did not exhibit wilt symptoms or bacterial ooze at the end of the experiment. Although no wilting symptoms were observed, four other clones were considered susceptible because at least one plant showed bacterial ooze from the inoculated tissue. The remaining 13 clones were highly susceptible, presenting typical wilt symptoms and bacterial ooze.