Migration of pinewood nematode promotes the colonization of Esteya vermicola in pine tree

Abstract

ous ecological catastrophe and economic losses to the pine forest industry. The pinewood nematode (PWN), Bursaphelenchus xylophilus, is the causal agent and is transmitted by vector beetles (Futai, 2013). The beetle Monochamus alternatus and M. galloprovincialis are the insect vectors that transmit the PWN (Akbulut & Stamps, 2012; Sousa et al., 2002). PWNs enter into the healthy host pine tree via feeding wounds of young immature beetles (Mamiya, 1983). The PWNs in the host pine tree feed on living epithelial cells and distribute throughout the tree via resin canals (Wang et al., 2011), resulting in vascular dysfunction and rapid wilt of host trees.As the first reported nematophagous fungi against PWN, Esteya vermicola has been tested to control PWD (Liou et al., 1999;Wang et al., 2011Wang et al., , 2018. Two types of conidiogenous cell and conidia (lunate and bacilloid conidia) in solid culture and blastospore in liquid culture are produced by the fungal hyphae (Wang et al., 2008). Among

Fungal Endophytes and Their Role in Agricultural Plant Protection against Pests and Pathogens

“…The conidium then produces a germination tube that penetrates the cuticle, and hyphae rapidly colonize and kill the nematode [ 136 ]. In the forestry sector, the nematophagous endophyte Esteya vermicola shows promise as a biocontrol agent of the invasive pinewood nematode ( Bursaphelenchus xylophilus ), with studies showing inoculation with E. vermicola significantly increases survival rates following B. xylophilus inoculation [ 141 , 142 , 143 ].…”

The Potential of Esteya spp. for the Biocontrol of the Pinewood Nematode, Bursaphelenchus xylophilus

“…Instead, an independent trophic hypha grows from the infection bulb, producing bacilloid conidia within the pseudocoelom, leading to a tangled mass of hyphae, reducing PWN motility and completely destroying organs and tissues from the inside out [67]. This suggests that E. vermicola can be further dispersed by infected nematodes as they migrate within their host, attracting more PWNs and initiating new infection cycles elsewhere, which are usually completed within 4 days [67,68,70]. Esteya floridanum, however, only seems to be capable of delaying tree death, as reported by Li et al [26], who noticed that larch (Larix olgensis) and Korean pines (P. koraiensis) died a few weeks later compared to positive controls, when inoculated with the fungus prior to PWN infection.…”

“…Similar enzymes are also found in PWNs and since β-1,3-glucan is the main structural component of fungal cell walls, it seems probable that β-1,3-glucanases may play an important role in their mycophagous phase [73]. Recent experiments with green fluorescent protein (GFP)-tagged E. vermicola CNU 120806 revealed that this strain is capable of germinating in and colonizing pine xylem, providing evidence for the fungus' ability to infect and kill PWNs in vivo [67,70]. The GFP-tagged E. vermicola made it possible to better understand the infection stages: once lunate conidia adhere to PWNs, they germinate, penetrate the cuticle and induce the formation of an infection bulb in the nematode's pseudocoelom, away from the attachment site and without hyphae connecting the two fungal structures.…”

“…Xue et al [78] showed that hydrogen peroxide promotes the sporulation of E. vermicola CBS 115803 conidia, under specific conditions, without them losing viability. Wang et al [70] optimized a cost-effective formula to protect spores of E. vermicola CBS 115803, containing 69.9% soluble starch, 14% wheat flour, 5% PEG8000, 0.1% Span 80, 1% arabinose and 10% skimmed milk, yielding almost 80% germination rates under desiccation stress. Although lunate conidia are significantly more resistant to stress [74], Yin et al [68] deduced that abiotic stress can be mitigated by directly injecting blastospores into pine trees.…”

“…In the prevention group, the survival rate of these pine trees was over 70%, significantly higher than that of the cure group (40%). Wang et al [70] carried out a field trial that provides evidence for a promising field application of E. vermicola. Eighty healthy 10 year-old P. densiflora were selected and randomly divided into four groups (prevention group, cure group, positive control and negative control), with twenty trees per group.…”