Can copper oxide or potassium phosphonate increase Pinus pinaster tolerance to Bursaphelenchus xylophilus?

Fungicide application may improve Pinus pinaster (Maritime pine)defenses against Bursaphelenchus xylophilus (pinewood nematode,PWN). To test this hypothesis, we evaluated the effects of copperoxide (CO) and potassium phosphonate (PP) on PWN-infected P. pina-ster plants. The overall mortality rate of infected plants was 12.5%,regardless of the treatment. PP-treated plants displayed a significantreduction in nematode densities (up to 61%) and foliar symptomscompared to untreated controls. Twenty-eight-day post-infection, COand PP increased oxidative stress proxies, such as lipid peroxidation(1.84- and 1.77-fold increases, respectively), and PP also enhancedantioxidant defenses, particularly flavonoid concentrations, whichwere 1.37-fold higher than those in CO-treated plants. In addition,both CO and PP reduced zinc and phosphorus concentrations inplant tissues, compared to controls, and CO treatment led to anincrease in plant endophytic bacterial diversity, while PP reduced it.These findings demonstrate that CO and PP enhance P. pinaster toler-ance to PWN by promoting the plant oxidant system, modulatingmineral uptake, and altering plant–endophyte interactions. Thisstudy also highlights the potential to enhance resource use efficiencyby extending fungicide applications beyond fungal pathogens toinclude nematodes, such as the PWN, offering a valuable approachfor the integrated management of multiple pests.