Can Copper Oxide or Potassium Phosphonate Increase Pinus Pinaster Tolerance to Bursaphelenchus xylophilus?

Abstract

Fungicide application may improve Pinus pinaster (Maritime pine) defenses against Bursaphelenchus xylophilus (pinewood nematode, PWN). To test this hypothesis, we evaluated the effects of copper oxide (CO) and potassium phosphonate (PP) on PWN-infected P. pinaster plants. The overall mortality rate of infected plants was 12.5%, regardless of the treatment. PP-treated plants displayed a significant reduction in nematode densities (up to 61%) and foliar symptoms compared to untreated controls. Twenty-eight-day post-infection, CO and PP increased oxidative stress proxies, such as lipid peroxidation (1.84- and 1.77-fold increases, respectively), and PP also enhanced antioxidant defenses, particularly flavonoid concentrations, which were 1.37-fold higher than those in CO-treated plants. In addition, both CO and PP reduced zinc and phosphorus concentrations in plant tissues, compared to controls, and CO treatment led to an increase in plant endophytic bacterial diversity, while PP reduced it. These findings demonstrate that CO and PP enhance P. pinaster tolerance to PWN by promoting the plant oxidant system, modulating mineral uptake, and altering plant–endophyte interactions. This study also highlights the potential to enhance resource use efficiency by extending fungicide applications beyond fungal pathogens to include nematodes, such as the PWN, offering a valuable approach for the integrated management of multiple pests.