Bacterial communities associated to Eucalyptus plants infected by Ceratocystis fimbriata

Brazil is one of the largest producers of Eucalyptus in the world, and the demand for this wood has increasing in the last few years. The expansion of the cultivation area results in changes of factors influencing eucalyptus growth and incidence of some pathogens such as Ceratocystis fimbriata. The pathogen-plant interaction may be affected by host ecology and associated microbial communities. Therefore, we used C. fimbriata infected plants with four infestation symptoms to assess the effects of this infestation on rhizoplane and endophytic bacterial communities. The culturable bacterial diversity was assessed by isolation and 16S rRNA gene characterization by ARDRA and sequencing. Additionally, total bacterial diversity was assessed by the culture-independent approach DGGE. Results showed that healthy plants presented a higher bacterial density in the rhizoplane, while the endophytic community was higher in infected plants. Thirteen and eight ARDRA ribotypes were observed in the cultured bacteria isolated from rhizoplane and endosphere of roots, respectively. The most frequent species was Bacillus cereus. However, only the occurrence of species Pseudomonas fluorescens, P. veronii and Rahnella aquatilis were correlated with less disease occurrence. The DGGE analysis showed that the pathogen infestation interferes in the composition of the assessed bacterial communities. Principal Components Analysis (PCA) on the basis of DGGE band patterns separated samples in the four stages of disease infection. The results obtained in the present work provide information about the pathogenic-associated microorganisms and show important features related to C. fimbriata infection.