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26 July, 2016

Two Ralstonia species associated with bacterial wilt of Eucalyptus

Ralstonia solanacearum sensu lato causes bacterial wilt in many economically important agronomic crops and tree species. Eucalyptus is one of the recorded hosts but despite the losses to forestry, little is known regarding the disease. The aim of this study was to identify theRalstonia species that are associated with bacterial wilt of Eucalyptus trees growing in different parts of the world. Phylotyping, sequevar and multilocus sequence analysis (MLSA) were used to identify and determine the genetic diversity of the available isolates. The isolates obtained from Africa and Asia grouped in phylotype I and those isolates from South America, in phylotype II. Following the recent re-classification of R. solanacearum sensu lato, these results show that there are two Ralstonia species associated with bacterial wilt ofEucalyptus, namely, R. solanacearum and R. pseudosolanacearum. Our isolates from South America represented R. solanacearum and those form Africa and Asia, R. pseudosolanacearum. Analysis of the endoglucanase (egl), transcriptional regulator (hrpB) and DNA mismatch repair (mutS) gene regions supported this finding. In addition, one previously unidentified sequevar was identified using partial endoglucanase (egl) gene sequence analysis of those isolates obtained from Colombia. This study raises questions regarding the aetiology of the two Ralstonia species found on Eucalyptus, their importance relating to quarantine, potential impact and management of the disease with which they are associated.

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