Understanding pine wilt disease: roles of the pine endophytic bacteria and of the bacteria carried by the disease‐causing pinewood nematode

Abstract

Pine wilt disease (PWD) is one of the most destructive diseases in trees of the genus Pinus and is responsible for environmental and economic losses around the world. The only known causal agent of the disease is the pinewood nematode (PWN) Bursaphelenchus xylophilus. Despite that, bacteria belonging to several different genera have been found associated with PWN and their roles in the development of PWD have been suggested. Molecular methodologies and the new era of genomics have revealed different perspectives to the problem, recognizing the manifold interactions between different organisms involved in the disease. Here, we reviewed the possible roles of nematode‐carried bacteria in PWD, what could be the definition of this group of microorganisms and questioned their origin as possible endophytes, discussing their relation within the endophytic community of pine trees. The diversity of the nematode‐carried bacteria and the diversity of pine tree endophytes, reported until now, is revised in detail in this review. What could signify a synergetic effect with PWN harming the plant, or what could equip bacteria with functions to control the presence of nematodes inside the tree, is outlined as two possible roles of the microbial community in the etiology of this disease. An emphasis is put on the potential revealed by the genomic data of isolated organisms in their potential activities as effective tools in PWD management.

Pseudomonas associated with Bursaphelenchus xylophilus, its insect vector and the host tree: A role in pine wilt disease?

“…This compound was previously described as being produced by nematode-associated bacteria causing wilting symptoms (Proença, Grass, & Morais, 2016). In the genomes of P. yamanorum (accession number LT629793) and P. extremaustralis strains (accession numbers FUYI00000000.1, LT629689 and AHIP00000000.1), we found genes coding for enzymes for the complete degradation of benzoate, a common intermediate in the anaerobic metabolism of toxic compounds, like phenols and other aromatic metabolites produced by the tree as a defence mechanism.…”

“…The genomes of the four Pseudomonas strains had genes coding for the necessary enzymes for phenylacetate production. This compound was previously described as being produced by nematode-associated bacteria causing wilting symptoms (Proença, Grass, & Morais, 2016). This is the first study analysing the diversity of Pseudomonas associated with PWD.…”

Induction of resistance against pine wilt disease caused by Bursaphelenchus xylophilus using selected pine endophytic bacteria

“…It has been suggested that the bacteria, which produce a pine wilt toxin, along with the nematode are responsible for the rapid wilting of Japanese pine resulting from PWD (Oku et al ., ). These results and other findings indicate that bacteria associated with nematodes are essential for disease development (Zhao et al ., ; Proença et al ., ). On the other hand, pine endophytic bacteria were suggested to be part of the plant–nematode interaction by growth promotion or induction of resistance in pine trees (Nascimento et al ., ).…”

“…These bacterial species have several roles in disease development, such as their ability to produce phytotoxins that damage plant cells (Han et al ., ). For pine endophytic bacteria, it has been suggested that such bacteria could have a role in induction of plant resistance, possibly by bacterial produced lipases (Nascimento et al ., ; Proença et al ., ). Moreover, analysis of the pine tree microbiome revealed several orthologues for traits related to plant growth promotion and plant defence factors such as chitinases (Alves et al ., ).…”

Bacillus pumilus and Stenotrophomonas maltophilia as two potentially causative agents involved in Persian oak decline in Zagros forests (Iran)

“…The PGPR and biocontrol potentials have been proved for S. maltophilia in a number of studies (Elo, Maunuksela, Salkinoja-Salonen, Smolander, & Haahtela, 2000;Ruiu et al, 2017;Tashi-Oshnoei, Harighi, & Abdollahzadeh, 2017). The recent studies on pine wilt disease have shown that association of this bacterium with nematodes is the major causing factor of such diseases in pine wood (Arbuzova, Kulinich, Mazurin, & Zinov'eva, 2014;Cheng et al, 2013;He et al, 2016;Proença, Grass, & Morais, 2017). The recent studies on pine wilt disease have shown that association of this bacterium with nematodes is the major causing factor of such diseases in pine wood (Arbuzova, Kulinich, Mazurin, & Zinov'eva, 2014;Cheng et al, 2013;He et al, 2016;Proença, Grass, & Morais, 2017).…”