Abstract

The pinewood nematode (PWN) Bursaphelenchus xylophilus is the causal agent of the pine wilt disease (PWD) and represents one of the major threats to conifer forests. The detection of the PWN in Portugal, associated with Pinus pinaster, increased the concern of its spread to European forests. Despite its susceptibility to PWD, genetic variability found among P. pinaster populations has been associated with heritable PWD resistance. Understanding the mechanisms underlying tree resistance constitutes a valuable resource for breeding programs toward more resilient forest plantations. This study investigated changes in anatomy, chlorophyll a fluorescence (ChlF), and primary metabolism in susceptible and resistant P. pinaster half-sib plants, after PWN inoculation. Susceptible plants showed a general shutdown of central metabolism, osmolyte accumulation, photosynthetic inhibition, and a decrease in the plant water status. The ChlF transient rise (OJIP curve) revealed the appearance of L- and K-bands, indicators of environmental stress. In contrast, resistant plants revealed a regulated defense response and were able to restrict PWN migration and cellular damage. Furthermore, the accumulation of γ-aminobutyric acid (GABA) and succinate suggested a role of these metabolites in PWD resistance and the possible activation of the GABA shunt. Altogether, these results provide new insights to the role of primary metabolism in PWD resistance and in the selection of resistant phenotypes for disease mitigation.

Highlights

  • The pinewood nematode (PWN) Bursaphelenchus xylophilus is the causal agent of the pine wilt disease (PWD), and represents a major threat to worldwide conifer forests, especially Pinus spp., with significant ecological and economical losses

  • At 28 days after inoculation (DAI), more than half of the plants scored level 3 or 4; that is, plants exhibited at least 50 % of needle discoloration and/or wilting

  • The integration of photosynthetic and metabolic data allowed to identify specific traits possibly associated with P. pinaster resistance to PWN, as a valuable resource for future studies

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Summary

Introduction

The pinewood nematode (PWN) Bursaphelenchus xylophilus is the causal agent of the pine wilt disease (PWD), and represents a major threat to worldwide conifer forests, especially Pinus spp., with significant ecological and economical losses. The PWN is vectored by long-horned beetles (Monochamus spp.) and spread into healthy trees during maturation feeding or into decaying trees through oviposition (Evans et al, 1996, 2008). The PWN is native to North America and was introduced in Japan in 1905 where the PWD was first reported in Japanese red pine (Pinus densiflora) (Futai, 2008). The PWN has reached Spanish border territories, thereby increasing the concern of its spread to European forests (Abelleira et al, 2011)

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