Pantoea and Xanthomonas species associated with blight and die-back of Eucalyptus

Abstract

The pulp and paper industry is expanding world-wide to supply the needs and demands of the consumer. Due to this rapid expansion of commercial forests and our ever changing climate including the sporadic increase and decrease in rain and the increasing temperature caused by global warming, previously described and new pathogens are emerging which infect and cause diseases on commercial forest trees and agricultural crops. Research efforts are required to investigate mechanisms of disease control and eradication to prevent the propagation and rapid spread of these pathogens and ensure that there is limited economical loss of forestry and other agriculturally important plants and trees. Since both Xanthomonas and Pantoea species are becoming increasing important as emerging bacterial pathogens, their rapid and accurate identification is crucially important. Little is known about bacterial pathogens on forestry trees since the most prominent diseases of these hosts are caused by fungi. The focus of this study was to investigate and identify the bacterial pathogens associated with Eucalyptus. However, as has been seen in various studies including this one, the identification of these pathogens is not always straightforward and often time consuming. In this study the use of polyphasic identification approach was used which employs a combination of phenotypic and genotypic identification techniques. Both of the genera investigated in this study, namely Pantoea and Xanthomonas, have been found to infect a variety of agriculturally important plant hosts. Pantoea species have previously been isolated from Eucalyptus trees suffering from blight and dieback symptoms. The species isolated have included P. eucalypti from Uruguay, P. vagans isolated from Argentina, Colombia, Uganda and Uruguay and P. deleyi from Uganda. Since the first report of Pantoea on Eucalyptus trees from South Africa in 2002 it has spread locally causing sporadic outbreaks. This pathogen has also been isolated from Eucalyptus trees in other parts of the world including, Argentina, Colombia, Thailand, Uganda and Uruguay. Xanthomonas campestris pv. eucalypti was previously found to cause disease on Eucalyptus trees in Australia. Since then, three other Xanthomonas species have been isolated from Eucalyptus, namely, Xanthomonas spp. from Brazil (Goncalves et al., 2008), X. vasicola from South Africa and X. fuscans from Uruguay as seen in this study.