Abstract
Pine wilt disease (PWD), caused by the pinewood nematode, is the most destructive disease in pine forest ecosystems worldwide. Extensive research has been done on PWD, but effective disease management is yet to be devised. Generally, plants can resist pathogen attack via a combination of constitutive and inducible defenses. Systemic acquired resistance (SAR) is an inducible defense that occurs by the localized infection of pathogens or treatment with elicitors. To manage PWD by SAR in pine trees, we tested previously known 12 SAR elicitors. Among them, methyl salicylate (MeSA) was found to induce resistance against PWD in Pinus densiflora seedlings. In addition, the foliar applications of the dispersible concentrate-type formulation of MeSA (MeSA 20 DC) and the emulsifiable concentrate-type formulation of MeSA (MeSA 20 EC) resulted in significantly reduced PWD in pine seedlings. In the field test using 10-year-old P. densiflora trees, MeSA 20 DC showed a 60% decrease in the development of PWD. Also, MeSA 20 EC gave the best results when applied at 0.1 mM concentration 2 and 1 weeks before pinewood nematode (PWN) inoculation in pine seedlings. qRT-PCR analysis confirmed that MeSA induced the expression of defense-related genes, indicating that MeSA can inhibit and delay the migration and reproduction of PWN in pine seedlings by modulating gene expression. These results suggest that foliar application of MeSA could reduce PWD incidence by inducing resistance and provide an economically feasible alternative to trunk-injection agents for PWD management.
Highlights
Pine wilt disease (PWD), caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus, is the most destructive disease in pine forest ecosystems worldwide
PWN can migrate within infected trees, but because they cannot move between hosts, they are transmitted through the vector Monochamus spp. (Mamiya, 1988; Kim et al, 2021)
PWN is fatal to healthy susceptible pine trees, such as Pinus densiflora, P. thunbergii, and P. koraiensis and new susceptible species are being discovered (Yang and Wang, 1989; Li et al, 2020)
Summary
Pine wilt disease (PWD), caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus, is the most destructive disease in pine forest ecosystems worldwide. PWN can migrate within infected trees, but because they cannot move between hosts, they are transmitted through the vector Monochamus spp. PWD-infected pine trees initially turn their needles yellowish to reddish-brown, and subsequently wilt and die within a few months. The serious threat posed by PWN has led to considerable efforts to control the disease. Disease control mostly relies on use of chemicals such as metam sodium for fumigation of infected trees, aerial spraying of pesticides to control pine sawyer, and trunk injection of abamectin and emamectin benzoate (Kwon et al, 2005; Lee et al, 2009; Korea Forest Service, 2013). Research on elucidating resistance mechanisms related to the relationship between pathogens and host pines is being emphasized upon
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