Data_Sheet_1_Differential Impact of the Pinewood Nematode on Pinus Species Under Drought Conditions.pdf

The pinewood nematode (PWN), Bursaphelenchus xylophilus, responsible for the pine wilt disease (PWD), is a major threat to pine forests worldwide. Since forest mortality due to PWN might be exacerbated by climate, the concerns regarding PWD in the Mediterranean region are further emphasized by the projected scenarios of more drought events and higher temperatures. In this context, it is essential to better understand the pine species vulnerability to PWN under these conditions. To achieve that, physiological responses and wilting symptoms were monitored in artificially inoculated Pinus pinaster (P. pinaster), Pinus pinea (P. pinea), and Pinus radiata (P. radiata) saplings under controlled temperature (25/30°C) and water availability (watered/water stressed). The results obtained showed that the impact of PWN is species-dependent, being infected P. pinaster and P. radiata more prone to physiological and morphological damage than P. pinea. For the more susceptible species (P. pinaster and P. radiata), the presence of the nematode was the main driver of photosynthetic responses, regardless of their temperature or water regime conditions. Nevertheless, water potential was revealed to be highly affected by the synergy of PWN and the studied abiotic conditions, with higher temperatures (P. pinaster) or water limitation (P. radiata) increasing the impact of nematodes on trees’ water status. Furthermore, water limitation had an influence on nematodes density and its allocation on trees’ structures, with P. pinaster revealing the highest nematode abundance and inner dispersion. In inoculated P. pinea individuals, nematodes’ population decreased significantly, emphasizing this species resistance to PWN. Our findings revealed a synergistic impact of PWN infection and stressful environmental conditions, particularly on the water status of P. pinaster and P. radiata, triggering disease symptoms and mortality of these species. Our results suggest that predicted drought conditions might facilitate proliferation and exacerbate the impact of PWN on these two species, through xylem cavitation, leading to strong changes in pine forests of the Mediterranean regions.

松材线虫（pinewood nematode, PWN）学名Bursaphelenchus xylophilus，可引发松材萎蔫病（pine wilt disease, PWD），是全球松林面临的主要威胁。鉴于气候因素可能加剧松材线虫导致的林木死亡，地中海地区对松材萎蔫病的担忧因未来干旱事件频发、气温升高的预测情景而进一步加重。在此背景下，深入了解松树物种在上述环境条件下对松材线虫的易感程度至关重要。为达成该研究目标，本研究在可控温度（25/30℃）与水分条件（正常浇水/水分胁迫）下，对接种松材线虫的海岸松（Pinus pinaster, P. pinaster）、意大利石松（Pinus pinea, P. pinea）以及辐射松（Pinus radiata, P. radiata）幼苗的生理响应与萎蔫症状进行了监测。研究结果表明，松材线虫的致病效应具有物种特异性：受侵染的海岸松与辐射松相较于意大利石松，更易出现生理与形态损伤。对于易感物种（海岸松与辐射松）而言，松材线虫的侵染是影响其光合响应的核心驱动因素，不受温度或水分供应状况的影响。然而，水势显著受到松材线虫与所研究非生物条件的协同作用影响：高温（海岸松）或水分限制（辐射松）会增强线虫对林木水分状态的影响。此外，水分限制会对线虫的种群密度及其在林木组织中的分布产生影响，其中海岸松体内的线虫丰度与扩散情况最为显著。在接种的意大利石松个体中，线虫种群数量显著下降，印证了该物种对松材线虫的抗性。本研究结果揭示了松材线虫侵染与环境胁迫的协同作用，尤其对海岸松与辐射松的水分状态造成显著影响，进而引发这两个物种的病害症状与死亡。研究结果表明，未来预测的干旱环境可能通过木质部空穴化作用，促进这两个松树物种体内线虫的增殖并加重松材线虫的致病效应，进而导致地中海地区松林群落发生剧烈变化。