Evaluation of plant elicitation with methyl-jasmonate, salicylic acid and benzo (1,2,3)-thiadiazole-7-carbothioic acid-S-methyl ester for the sustainable management of the pine wilt disease.

Treatment with plant elicitors can be a promising method to induce Pinus pinaster tolerance against the pinewood nematode (PWN), Bursaphelenchus xylophilus, by promoting plant antioxidant system, micronutrient accumulation and by modulating plant-associated bacterial populations. To test this hypothesis, plants were sprayed with methyl jasmonate (MeJA), salicylic acid (SA) or benzo (1,2,3)-thiadiazole-7-carbothioic acid-S-methyl ester (BTH), and evaluated until 35 days after-inoculation (dai) for: i) extent of foliar symptoms; ii) nematode density inside stem tissues; iii) proxies for oxidative damage and antioxidant activity, iv) micronutrient concentration and v) bacterial diversity. Compared with non-elicited plants, plant elicitation, particularly with BTH, significantly decreased nematodes density inside stem tissues (by 0.63-fold). Concordantly, without elicitation plant mortality reached 12.5% while no mortality was observed in elicited plants. BTH-elicited plants had significantly higher concentrations of anthocyanins and carotenoids at the end of the assay than SA-elicited and MeJA-elicited plants, which possibly contributed to the lower PWN colonization and degree of foliar symptoms observed. Accordingly, MeJA and SA led to increased lipid peroxidation at 28 dai (by 2.64- and 2.52-fold, respectively) in comparison with BTH (by 1.10-fold), corroborating its higher potential in increasing plant antioxidative response during infection. Moreover, carotenoids showed a negative correlation with nematode migration, whereas polyphenols showed a positive correlation. Elicitors also induced changes in the bacterial community of infected P. pinaster plants, increasing the diversity of specific populations. Finally, elicitors induced significant changes in micronutrients accumulation in plant tissues, namely a decrease in the concentration of B, Mn and Ni in plants treated with BTH compared to those treated with the other elicitors. Altogether, results suggest that elicitation with MeJA, SA and, particularly, BTH, increases tolerance against B. xylophilus by promoting plant antioxidant system, changing the accumulation of essential micronutrients and modulating plant-associated bacterial diversity.
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