Seasonal timing and recurrence of methyl jasmonate treatment influence pine weevil damage to Norway spruce seedlings

Abstract

Defense can be induced in conifer seedlings to reduce pine weevil (Hylobius abietis) damage, by treatment with the plant hormone methyl jasmonate (MJ). Few studies have addressed important practical issues regarding the use of MJ such as treatment incidence and timing, seedling age and its compatibility with plant nursery practices. We examined if levels of pine weevil damage depend on seasonal timing and recurrence of MJ treatment, and if the observed effects depend on plant age. Norway spruce (Picea abies) seedlings from two age cohorts (1 year and 1.5 years old) received four MJ treatments: MJ application before winter storage in the previous year, after winter storage but before spring/summer planting, repeated MJ application (both before winter storage, and before planting) or no MJ application at all. Pine weevil damage was evaluated in a lab and field experiment. We found that the timing and recurrence of MJ treatment affected the amount of damage inflicted by pine weevils in different ways, but these effects were consistent among age cohorts. MJ application before winter storage provided the most effective protection, and this reduction in damage was comparable to that provided by a currently used physical protection method against pine weevil feeding. Our results indicated that MJ can be applied in line with nursery practices (before winter storage) and provides adequate protection for two growing seasons.

Variation in Methyl Jasmonate-Induced Defense Among Norway Spruce Clones and Trade-Offs in Resistance Against a Fungal and an Insect Pest

“…Our results are in line with previous studies on MeJA-induced resistance in P. abies and other conifers species. Decreases in pine weevil damage ranging from 50 to 70%, for example, have been shown to occur after consecutive treatment with 10 mM MeJA in Norway spruce seedlings ( Chen Y. et al, 2020 ). For other species such as Pinus pinaster , pine weevil damage was reduced by 80% after treatment with 100 mM MeJA ( Moreira et al, 2009 ), and reduced by 30–60% for P. pinaster , P. radiata , P. sylvestris , and P. abies seedlings treated with 25 mM MeJA ( Zas et al, 2014 ).…”

“…Protection against pine weevil damage is necessary for only a few years after planting, since pine weevils cause high mortality only at the seedling stage. In terms of applicability, several studies have shown that treating seedlings with MeJA can be compatible with nursery practices ( Fedderwitz et al, 2019 ; Chen Y. et al, 2020 ). Infection by E. polonica occurs when mature trees are attacked by the spruce bark beetle, and it would be important for these trees to be constitutively more resistant to infection.…”

“…We chose two concentrations of MeJA (25 and 50 mM) based on previous studies in our group and on the size of the plants. Smaller Norway spruce plants (average height: 20 cm, average diameter: 3 mm) have often been treated with concentrations ranging from 5 to 15 mM MeJA ( Fedderwitz et al, 2019 ; Chen Y. et al, 2020 ). Larger and thicker plants (average heights above 25 cm, and diameters above 5 mm) as those used in our experiment, have been treated with higher concentrations (25 mM MeJA, Lundborg et al, 2016b ; 50 mM MeJA, Fedderwitz et al, 2016 ).…”

“…Treatment with methyl jasmonate (MeJA), for example, induces the formation of traumatic resin ducts and synthesis of terpene and phenolic-based compounds ( Krokene et al, 2008 ; López-Villamor et al, 2020 ). These MeJA-mediated changes have been shown to increase resistance against bark-feeding insect pests like the pine weevil Hylobius abietis ( Heijari et al, 2005 ; Zas et al, 2014 ; Fedderwitz et al, 2016 ; Chen Y. et al, 2020 ), and the spruce bark beetle-blue stain fungus complex Ips typographus - Endoconidiophora polonica ( Zhao et al, 2011 ; Schiebe et al, 2012 ). However, responses to MeJA can vary with plant genotype ( Zeneli et al, 2006 ; Moreira et al, 2013 ; López-Goldar et al, 2018 ), with some genotypes showing greater or lesser levels of inducibility relative to their constitutive state.…”

Comparing Exogenous Methods to Induce Plant-Resistance Against a Bark-Feeding Insect

“…The effect of MeJA treatment on pine weevil damage has been shown to be dose dependent (Moreira et al, 2009;Zas et al, 2014). In one of our previous experiments, a higher dose of MeJA (three consecutive sprayings of 10 mM MeJA) resulted in greater Norway spruce resistance to pine weevil damage relative to plants receiving a lower dose (one spraying of 10 mM MeJA) (Chen et al, 2020). The low dose of MeJA in our previous study on Norway spruce was the same as the low dose used in this study on Scots pine seedlings, and the amount of debarked area received by these two conifer species were similar in both studies.…”