The Ratio and Concentration of Two Monoterpenes Mediate Fecundity of the Pinewood Nematode and Growth of Its Associated Fungi

Abstract

The pinewood nematode (PWN) Bursaphelenchus xylophilus, vectored primarily by the sawyer beetle, Monochamus alternatus, is an important invasive pest and causal agent of pine wilt disease of Chinese Masson pine, Pinus massoniana. Previous work demonstrated that the ratios and concentrations of α-pinene∶β-pinene differed between healthy trees and those trees containing blue-stain fungus (and M. alternatus pupae). However, the potential influence of the altered monoterpene ratios and concentrations on PWN and associated fungi remained unknown. Our current results show that low concentrations of the monoterpenes within petri dishes reduced PWN propagation, whereas the highest concentration of the monoterpenes increased PWN propagation. The propagation rate of PWN treated with the monoterpene ratio representative of blue-stain infected pine (α-pinene∶β-pinene = 1∶0.8, 137.6 mg/ml) was significantly higher than that (α-pinene∶β-pinene = 1∶0.1, 137.6 mg/ml) representative of healthy pines or those damaged by M. alternatus feeding, but without blue stain. Furthermore, inhibition of mycelial growth of associated fungi increased with the concentration of the monoterpenes α-pinene and β-pinene. Additionally, higher levels of β-pinene (α-pinene∶β-pinene = 1∶0.8) resulted in greater inhibition of the growth of the associated fungi Sporothrix sp.2 and Ophiostoma ips strains, but had no significant effects on the growth of Sporothrix sp.1, which is the best food resource for PWN. These results suggest that host monoterpenes generally reduce the reproduction of PWN. However, PWN utilizes high monoterpene concentrations and native blue-stain fungus Sporothrix sp.1 to improve its own propagation and overcome host resistance, which may provide clues to understanding the ecological mechanisms of PWN's successful invasion.

Performance of Sirex noctilio ’s biocontrol agent Deladenus siricidicola , in known and predicted hosts

“…Fast drying has also been postulated as a possible explanation for low D. siricidicola performance in areas with warm dry winters (Bedding, 2009) Although we identified some differences in chemical profiles of the two taxa, we did not detect any differences in performance of nematodes inoculated onto plates of each, suggesting that these differences in plant chemistry did not directly impact their survival. Propagation of the pine wilt nematode, B. xylophilus, is influenced by monoterpene concentrations in P. massoniana (Niu et al, 2012) but the taxa investigated in our study did not differ in their concentrations of these.…”

A native fungal symbiont facilitates the prevalence and development of an invasive pathogen–native vector symbiosis

“…It is these fungi, including Ophiostoma ips, O. minus, and Ceratocystis sp., reported from wood infested with the nematode and vector beetles in Japan, Korea, and America, that provide food for the mycophagous phase of the nematode life cycle (Kobayashi et al 1974, Wingfield 1987, Hyun et al 2007). Ophiostomatoid fungi identified in dead trees positively influence reproduction of the pinewood nematode and the interactions of nematode and host pine trees (Maehara 2008, Maehara and Futai 2000, Niu et al 2012. This is especially true for native Ophiostoma minus, which was isolated in Japan and was shown to strongly and positively influence the reproduction of the nematode and consequently the number of nematodes dispersed by beetles (Maehara and Futai 2000).…”

Gene family expansion of pinewood nematode to detoxify its host defence chemicals

“…Nematodes inhabit a diversity of habitats and can be free‐living ( Caenorhabditis elegans and C. briggsae ), animal‐parasitic ( Strongyloides stercoralis in mammals, Brugia malayi and Enterobius vermicularis in humans) and plant‐parasitic ( Meloidogyne incognita and M. hapla in many crops and Globodera pallida in potatoes among others) (Coghlan, ). Consequently, nematodes experience a much greater array of deleterious xenobiotic exposure in soils (Lindblom & Dodd, ) and insect haemolymph (Zhou et al, ) and to plant defence chemicals (Niu, Zhao, Lu, Zhang, & Sun, ). Thus, xenobiotic detoxification is necessary for survival.…”