Ralstonia solanacearum and R. pseudosolanacearum on Eucalyptus: Opportunists or Primary Pathogens?

Abstract

Ralstonia solanacearum and R. pseudosolanacearum are well known primary pathogens of herbaceous crops. Reports of wilt caused by these pathogens in tree species are limited other than on Eucalyptus species. Despite the widespread occurrence of so-called bacterial wilt on eucalypts in tropical and sub-tropical parts of Africa, Asia, and the Americas, there remain many contradictions relating to the disease. Our field observations over many years in most regions where the disease occurs on Eucalyptus show that it is always associated with trees that have been subjected to severe stress. The disease is typically diagnosed by immersing cut stems in water and observing bacterial streaming, but the identity of the bacteria within this suspension is seldom considered. To add to the confusion, pathogenicity tests on susceptible species or clones are rarely successful. When they do work, they are on small plants in greenhouse trials. It has become all to easy to attribute Eucalyptus death exclusively to Ralstonia infection. Our data strongly suggest that Ralstonia species and probably other bacteria are latent colonists commonly occurring in healthy and particularly clonally propagated eucalypts. The onset of stress factors provide the bacteria with an opportunity to develop. We believe that the resulting stress weakens the defense systems of the trees allowing Ralstonia and bacterial endophytes to proliferate. Overall our research suggests that R. solanacearum and R. pseudosolanacearum are not primary pathogens of Eucalyptus. Short of clear evidence that they are primary pathogens of Eucalyptus it is inappropriate to attribute this disease solely to infection by Ralstonia species.

Metagenomics of pasteurized and unpasteurized gouda cheese using targeted 16S rDNA sequencing

“…Some of the genera identified in the Gouda cheese which was aged longer included Acidovorax , Ralstonia , Adhaeribacter , Devosia , Haemophilus , and Neisseria . Acidovorax and Ralstonia are both aerobic Gram-positive plant pathogens [ 66 , 67 ]. Acidovorax has been previously identified as a contaminant of Italian Grana cheese [ 68 ], and Ralstonia has been detected in unpasteurized milk [ 43 , 69 ] and can survive high salinity environments.…”

Antagonism of Two Plant-Growth Promoting Bacillus velezensis Isolates Against Ralstonia solanacearum and Fusarium oxysporum

“…Ralstonia solanacearum is an economically important bacterial phytopathogen 13 and infects a broad range of host plants including crops such as potato ( Solanum tuberosum ), eggplant ( Solanum melongena ), and tomato ( Solanum lycopersicum ) 14 , 15 . Tomato wilt caused by R. solanacearum is one of the most damaging tomato diseases, particularly during the hot-humid summer season in subtropical regions such as South China.…”

Comparison of bacterial communities between midgut and midgut contents in two silkworms, Antheraea pernyi and Bombyx mori

“…Bacteria in insects were originally derived from free-living environmental microorganisms 28 . Ralstonia bacteria, which are mostly related to the pathogenicity of plants, have a broad host range of over 50 families and cause serious harm worldwide 29 . Thus, we speculate that Ralstonia present in all samples surveyed in this study are derived from the leaf surface of the host plants, including Morus alba for B. mori and Quercus wutaishanica for A. pernyi.…”