Molecular characterization of Ralstonia solanacearum infecting Eucalyptus spp. in Brazil

Abstract

SummaryAmong the bacterial pathogens of Eucalyptus in Brazil, Ralstonia solanacearum is considered one of the most important because of the characteristics of the pathogen, like the high diversity among the strains related to host range, high virulence, broad geographical distribution and its damage to the crop in recent years. Given its importance and the lack of research on this pathosystem, the present study aimed to perform a molecular characterization of different strains of infected Eucalyptus plants in Brazil. A total of 19 bacterial cultures isolated from Eucalyptus in different regions of Brazil were analysed. A 372‐bp product generated by multiplex‐PCR amplification using Nmult primers identified all the strains analysed as belonging to phylotype II. Eighteen strains were grouped into subclade IIA and one into subclade IIB. The phylogenetic tree generated from the gene sequences of endoglucanase (egl) confirmed the classification of the strains into phylotype II and separated the strains into sequevars. Strains AMC22, IBSBF2568 and IBSBF2576 were grouped into a single clade, as were strains UFV18 and UFV20, with 89% and 78% a posteriori probability, respectively, forming two new potential sequevars not yet defined. We also identified strains belonging to sequevars 41 (100% probability) and 37 (88% probability). However, most of the strains did not fit into any previously described sequevar and did not form distinct clades. The results of the analysis of fragments amplified using the ERIC‐PCR technique indicated the existence of genetic diversity among the strains studied, with a generally high correlation between similarity and the geographical origin of the strains.