Phylloplane as a potential Erwinia psidii inoculum reservoir

Erwinia psidii is an airborne and waterborne bacterium that causes eucalyptus bacterial blight, a destructive disease occurring in eucalyptus forests in Brazil. To design assertive and efficient control strategies to reduce or eliminate the incidence of the disease, it is necessary to understand the ability of the plant-pathogenic bacterium to survive in phylloplane conditions. We investigated the survival of E. psidii on the phylloplane of Eucalyptus urophylla (SUZBA1175), E. urophylla (SUZBA1922), E. grandis × E. urophylla (FA6825), Lantana camara , Brachiaria decumbens , Conyza bonariensis , Digitaria insularis, Psidium guajava , and Eugenia uniflora plants. On the phylloplane of eucalyptus genotypes, the survival of the bacterial pathogen varied between 35 and 56 days. On the phylloplane of E. uniflora and P. guajava , E. psidii was recovered for up to 77 and 85 days, respectively. Bacterial cells were recovered for up to 7 days on B. decumbens and D. insularis . On the other hand, on L. camara and C. bonariensis , the bacterium survived for up to 21 days. In this study, we showed that E. psidii can persist as an epiphyte on the leaf surface of eucalyptus genotypes, on plants from the same botanical family as eucalyptus, and on weeds. This brings us the important information that the phylloplane is a putative reservoir for E. psidii and can serve as a primary inoculum source for new infections or contribute to the increase of bacterial blight in eucalyptus forests.