Insights into the Role of Fungi in Pine Wilt Disease

Abstract

Pine wilt disease (PWD) is a complex disease that severely affects the biodiversity and economy of Eurasian coniferous forests. Three factors are described as the main elements of the disease: the pinewood nematode (PWN) Bursaphelenchus xylophilus, the insect-vector Monochamus spp., and the host tree, mainly Pinus spp. Nonetheless, other microbial interactors have also been considered. The study of mycoflora in PWD dates back the late seventies. Culturomic studies have revealed diverse fungal communities associated with all PWD key players, composed frequently of saprophytic fungi (i.e., Aspergillus, Fusarium, Trichoderma) but also of necrotrophic pathogens associated with bark beetles, such as ophiostomatoid or blue-stain fungi. In particular, the ophiostomatoid fungi often recovered from wilted pine trees or insect pupal chambers/tunnels, are considered crucial for nematode multiplication and distribution in the host tree. Naturally occurring mycoflora, reported as possible biocontrol agents of the nematode, are also discussed in this review. This review discloses the contrasting effects of fungal communities in PWD and highlights promising fungal species as sources of PWD biocontrol in the framework of sustainable pest management actions.

Phytochemicals as Biopesticides against the Pinewood Nematode Bursaphelenchus xylophilus: A Review on Essential Oils and Their Volatiles

“…PWD is an infectious forest disease, generally lethal to susceptible conifer species, caused by the direct activity of PWN, in which symptoms are worsened with the activity of associated and/or opportunistic pathogenic microbiota [19][20][21][22]. Infected susceptible trees display a reduction in oleoresin flux, progressing to a state of shoot desiccation and drooping, due to mechanisms of cavitation and subsequent interruption of sap transport, and chlorosis, as a result of a collapse in photosynthetic functions, culminating in an overall rapid tree decline [23,24].…”

Fungal Communities of the Pine Wilt Disease Complex: Studying the Interaction of Ophiostomatales With Bursaphelenchus xylophilus

“…In this sense, these communities are more likely to undergo more severe shifts in abundance and composition due to biotic and abiotic stresses (Baldrian, 2017 ). The study of the fungal communities in the PWD complex, and their intermediates, are still underrated (Zhao et al, 2014 ; Nascimento et al, 2015 ) in spite of their strong influence on PWN populations (Vicente et al, 2021 ). In this study, we present a detailed characterization of fungal communities from non-infected and PWN-infected P. pinaster trees from three contrasting PWD foci (long-term PWN presence, Companhia das Lezírias and Tróia, and transitional/recent PWN detection, Seia).…”

“…This is the first study focused exclusively on the fungal diversity in PWD affected areas, in Europe. In addition, we also characterized the adaptative response of a specific group of Ophiostomatales fungi (genus Ophiostoma, Leptographium, Graphilbum ) due to their well-recognized history with PWN (Vicente et al, 2021 ), as means to uncover their resilience in the disease complex.…”

“…A weakened pine tree is more easily attacked by the fungi transmitted by bark beetles (Coleoptera: Scolytidae) that further increase the symptomatology of wilting and function as a necessary food source for the PWN. Thus, these fungi are essential for nematode survival and reproduction (Vicente et al, 2021 ). Generally called blue-stain fungi, referring to the damage they cause, namely blue or even black discoloration of the sapwood of trees, mostly on conifers (Harrington, 1993 ; Kim et al, 2003 ; Zhou et al, 2006 ; Six, 2012 ), these bark beetle vectored fungi are also known as “ophiostomatoid fungi” (Kirisits, 2007 ).…”

Invasion History of the Pinewood Nematode Bursaphelenchus xylophilus Influences the Abundance of Serratia sp. in Pupal Chambers and Tracheae of Insect-Vector Monochamus alternatus

“…Some fungi such as Ophiostoma ips, Ophiostoma minus , and Ceratocystis sp. act as a nutritional source for the mycophagous phases of PWN (Vicente et al, 2021 ). Ophiostomatoid fungi (i.e., Sporothrix sp.…”