Basic density, extractive content and moisture sorption properties of Pinus pinaster wood infected with the pinewood nematode, Bursaphelenchus xylophilus

The pinewood nematode（PWN）, Bursaphelenchus xylophilus, has become one of the most severe threats to pine forest worldwide. Nematodes, migrating through resin canals and feeding on the living cells, induce rapid metabolic changes in ray parenchyma cells, create cavitation areas, decrease xylem water content and oleoresin exudation, and cause necrosis of parenchyma and cambial cells. This study focused on the impact of PWN infection on technological parameters of wood and evaluated the impact of anatomic and biochemical incidences of tree defense reactions on basic density, extractive content and moisture sorption properties of Pinus pinaster wood.Samples of infected and uninfected wood were studied.The presence of nematodes reduced wood basic density by2 % and decreased the total content of extractives in infected wood as compared with uninfected（5.98 and8.90 % of dry wood mass, respectively）. Extractives in infected trees had inverse distribution along the trunk as compared with uninfected trees. The adsorption isotherms for infected and uninfected wood had similar positioning.We recorded differences（some statistically significant） in the equilibrium moisture content of infected and uninfected wood under varying environmental conditions. Despite the verified differences in wood basic density, extractive content and moisture sorption properties, the overall conclusion is that the PWN had a slight impact on these characteristics of wood.

A new bacteria-free strategy induced by MaGal2 facilitates pinewood nematode escape immune response from its vector beetle

Symbiotic microbes play a crucial role in regulating parasite–host interactions;however,the role of bacterial associates in parasite–host interactions requires elucidation.In this study,we showed that,instead of introducing numerous symbiotic bacteria,dispersal of 4th-stage juvenile(JIV)pinewood nematodes(PWNs),Bursaphelenchus xylophilus,only introduced few bacteria to its vector beetle,Monochamus alternatus(Ma).JIV showed weak binding ability to five dominant bacteria species isolated from the beetles’pupal chamber.This was especially the case for binding to the opportunistic pathogenic species Serratia marcescens;the nematodes’bacteria binding ability at this critical stage when it infiltrates Ma for dispersal was much weaker compared with Caenorhabditis elegans,Diplogasteroides asiaticus,and propagative-stage PWN.The associated bacterium S.marcescens,which was isolated from the beetles’pupal chambers,was unfavorable to Ma,because it caused a higher mortality rate upon injection into tracheae.In addition,S.marcescens in the tracheae caused more immune effector disorders compared with PWN alone.Ma_Galectin2(MaGal2),a pattern-recognition receptor,was up-regulated following PWN loading.Recombinant MaGal2 protein formed aggregates with five dominant associated bacteria in vitro.Moreover,MaGal2 knockdown beetles had up-regulated prophenoloxidase gene expression,increased phenoloxidase activity,and decreased PWN loading.Our study revealed a previously unknown strategy for immune evasion of this plant pathogen inside its vector,and provides novel insights into the role of bacteria in parasite–host interactions.

Fertilization and clear-cutting effects on greenhouse gas emissions of pinewood nematode damaged Masson pine plantation

Introduction:Management practices are essential for maintaining forest ecological functions under increasing diseases and pest disasters.The effects of nitrogen fertilization(NF)and clear-cutting(CC)on the soil microbial community structure and greenhouse gases emission were investigated of pinewood nematodes(Bursaphelenchus xylophilus)-infected Masson pine(Pinus massoniana)plantations.Outcomes:CC increased the soil microbial biomass carbon(SMBC)and soil microbial biomass nitrogen(SMBN)contents relative to the control(CK).NF increased the SMBN but had no significant effect on the SMBC content.The total fungal and bacterial abundances increased in the CC treatment compared with the CK,but there was no significant difference between the NF and CK.The cumulative soil CO_(2)emission(-2.35 t C·hm^(-2))was higher than that of CK(1.65 t C·hm^(-2))in summer,and the cumulative annual N_(2)O emission(16.90 kg N·hm^(-2)yr^(-1))of NF was approximately 47 times of CK(0.36 t N·hm^(-2)·yr^(-1)).CC increased the CO_(2)flux(-2.21 t C·hm^(-2))in summer but have no significantly effects on N_(2)O emission.Conclusion:These results indicated that NF and CC practices changed forest soil microbial community structure and affected soil greenhouse gas emissions in pinewood nematodes-infected Masson pine plantations.The CO_(2)emission rates increased in the NF and CC treatments,which reduced the carbon sequestration function of forests and had a negative impact on climate change.

Pine wilt disease: a short review of worldwide research

This article summarizes the results of the research papers presented at the International Symposium on pine wilt disease （IUFRO Working Party Meeting 4.04.03） held in July 2009, at Nanjing, China. The general topics covered were on pine wilt disease （PWD）, its causal organism, the pinewood nematode （PWN） Bursaphelenchus xylophilus, plus other PWN-associated microorganisms that play a significant role in PWD such as bacteria （e.g. Pseudomonasfluorescens）. Most of the papers that are reviewed are based on work on PWD-PWN in East Asia and Russia. Specific topics covered include： 1） the fundamental conceptions of PWD development, 2） pathogenicity, 3） host-parasite relationships including the histopathology of diseased conifers and the role of toxins from bacteria-nematode ecto-symbionts, 4） PWN life cycle and transmission, 5） B. xylophilus dissemination models, 6） associations （with other nematodes）, 7） diagnostics, 8） quarantine and control of the PWN and 9） biocontrol of the PWN.