Ralstonia solanacearum, Ganoderma australe, and bacterial wetwood as predictors of ironwood tree (Casuarina equisetifolia) decline in Guam

Abstract

Ironwood (Casuarina equisetifolia subsp. equisetifolia) trees on Guam have been in decline since 2002. This study applied proportional odds logistic multiple regression modeling to a set of biological variables in order to find significant decline predictors as a first step towards identifying pathogenic contributors. Based on the analysis of a set of 77 medium and large trees, the bacterium Ralstonia solanacearum and the fungus Ganoderma australe species complex were found to be significant predictors, with p values of <0.001 and < 0.008, respectively. Their respective values for symptomless trees were 18% and 0%, compared to 80% and 35% for those nearly dead trees of which 30% had both organisms and 15% had neither. More complex models were also fit, that included interactions. The R. solanacearum by G. australe interaction was not a strong effect, indicating additive rather than multiplicative behavior of these effects on decline severity (p value>0.087). When nine covariates were applied univariately to a data subset of 30 tree cross-sections, the significance of R. solanacearum was strongly upheld while that of G. australe was moderately reduced. Also significant were percent cross-sectional area with bacterial wetwood and the formation of ooze within 24 h. Wetwood bacteria of Klebsiella spp. and K. oxytoca were found across all levels of decline and were not significant predictors. Other enteric bacteria identified included Kosakonia, Enterobacter, Pantoea, Erwinia, and Citrobacter.

Next-generation sequencing dataset of bacterial communities of Microcerotermes crassus workers associated with Ironwood trees (Casuarina equisetifolia) in Guam

“…Casuarina equisetifolia (ironwood) trees in Guam are dying in large numbers due to ironwood tree decline (IWTD) since 2002 [ [4] , [5] , [6] , [7] ]. Bacteria such as the bacterial wilt pathogen Ralstonia solanacearum and wetwood bacteria of the genus Klebsiella ( Klebsiella oxytoca and Klebsiella variicola ) were identified in the ooze of declining trees and considered as predictors of IWTD [ 6 , 7 , 2 , 8 ]. The presence of termites was found to be significantly associated (p<0.01) with IWTD [1] and termites are known to harbor a large bacteria diversity [9] .…”

Seeing the forest for the trees: Use of phages to treat bacterial tree diseases

“…The disease can cause up to approximately 80% growth reductions, leading to reduced pulp production and considerable economic losses (Ferreira et al, 2017). It has recently been reported that R. solanacearum causes bacterial wilt in ironwood trees in Guam (Ayin et al, 2019).…”

“…It has recently been reported that R . solanacearum causes bacterial wilt in ironwood trees in Guam (Ayin et al, 2019). The third species, R .…”

Correlation Analysis of the Bacterial Community and Wood Properties of Populus × euramericana cv. “74/76” Wet Heartwood

“…A variety of pathogenic bacteria have been isolated from wet heartwood tissues. Strains of Enterobacteriaceae are most often isolated from diseased trees, particularly Erwinia and Klebsiella, as well as Enterobacter, Pantoea, Citrobacter, Edwardsiella, Lactobacillus, and Kosakonia (Carter, 1945;Hartley et al, 1961;Knutson, 1973;Schink et al, 1981b;Murdoch, 1983;Diamandis and Koukos, 1992;Zheng et al, 2006;Ayin et al, 2019;Goychuk et al, 2020). Other bacteria are also often separated from the wet heartwood of conifers and broadleaf trees, such as Bacillus, Clostridium, Bacteroides, Ralstonia, Xanthomonas, and Pseudomonas (Carter, 1945;Knutson, 1973;Schink et al, 1981b;Murdoch, 1983;Warshaw et al, 1985;Diamandis and Koukos, 1992;Kovaleva et al, 2015;Ayin et al, 2019;Goychuk et al, 2020).…”

“…I-69/55 ( Yu et al, 2019 ), Betula pendula roth ( Goychuk et al, 2020 ), Ulmus spp. L. ( Alizadeh et al, 2017a , b ), Morus ( Basavand et al, 2021 ), Casuarina equisetifolia ( Ayin et al, 2019 ), Gmelina arboreaI ( Moya et al, 2009 ), and other broad-leaved tree species. Many things have been investigated to identify the causes for development of wetwood, such as genetic variability, bacterial and fungal communities, wood physicochemical properties, and wood processing and utilization ( Schroeder and Kozlik, 1972 ; Schink et al, 1981a ; Xu et al, 2001 ; Jeremic et al, 2004 ; Zhang et al, 2005 ).…”