Evaluation of the fungicide treatment with copper oxide and potassium phosphonate solutions for the sustainable management of P. pinaster trees infected with B. xylophilus

Abstract

Fungicides induce changes in the plants promising to increase tolerance of Pinus pinaster against the pathogenic pinewood nematode (PWN). To test this hypothesis, P. pinaster plants were inoculated with the PWN, treated with copper oxide (CO) or potassium phosphonate (PP), and evaluated post-inoculation for: i) the extent of foliar symptoms; ii) nematode density inside stem tissues; iii) proxies for oxidative damage and antioxidant activity, iv) mineral concentration; and v) bacterial diversity. The mortality of infected plants reached 12.5% regardless of the treatment, but plants treated with fungicides, particularly with PP, had significantly lower PWN density (up to 0.61-fold). Plants treated with PP had substantially higher concentrations of anthocyanins at 14 dai than those treated with CO and non-Treated plants (by 1.47-fold), possibly contributing to the lower PWN colonization and degree of foliar symptoms observed. CO and PP led to increased lipid peroxidation at 28 dai (by 1.84- and 1.77-fold), and PP showed higher flavonoids concentration than CO (by 1.37- and 0.49-fold), corroborating its higher potential in increasing plant antioxidative response during infection. Fungicides also induced significant changes in micronutrient accumulation in plant tissues, resulting in a decrease in Zn and P concentrations in plants treated with either fungicide as compared to infected non-treated plants. Finally, CO treatment increased the diversity of the bacterial communities, while PP decreased microbial biodiversity. Altogether, results suggest that treatment with CO and PP increases tolerance against B. xylophilus by promoting the plant antioxidant system, changing the accumulation of essential minerals, and modulating plant-associated bacterial diversity.