Can methyl jasmonate treatment of conifer seedlings be used as a tool to stop height growth in nursery forest trees?

Abstract

A plant's induced defense system can be triggered by the application of the plant hormone methyl jasmonate (MeJA), and recent research suggest that MeJA treatment may become a tool for protection of conifer seedlings against insect herbivory (e.g. by the pine weevil Hylobius abietis). A side-effect of MeJA application is temporarily reduced height growth. This has generally been considered as negative, but in forest tree nurseries this could instead be beneficial since it is commonly desired to stop the growth of nursery seedlings in late summer. Artificially longer dark periods (long nights/short days) are widely used in high-latitude nurseries to terminate height growth and induce freezing tolerance. However, long night treatment requires specialized nursery equipment and are labor intensive. Therefore alternatives are sought after. We compared long-night and MeJA treatments by following the growth of Norway spruce (Picea abies) seedlings throughout one season. The regulatory effect of MeJA on height growth was similar if not even better than that of long nights, i.e. it was terminated faster. However, MeJA treatment also reduced root growth and delayed the development of freezing tolerance. MeJA may therefore not replace long-night treatments, but it could facilitate a more flexible application of long nights by gaining a longer time interval during which this treatment can be used without risking the seedlings growing too large.

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

“…Moreover, it seems that induced resistance can be better achieved by several sprayings of MeJA at lower concentrations instead of one application with a higher concentration. Concentrations higher than 10 mM can be detrimental to seedlings, and result in treatment-related damage (e.g., loss of needles, needle browning in Norway spruce; Fedderwitz et al, 2019), and we indeed observed some needle-browning in seedlings treated with 15 mM MeJA (Supplementary Figure 8D). Our results are thus, an important contribution to development of methods for optimum use MeJA as a seedling protection tool.…”

“…Our results are thus, an important contribution to development of methods for optimum use MeJA as a seedling protection tool. Finding the MeJA treatment concentration and frequency that provides effective resistance, minimizes phytotoxicity and is compatible with nursery needs and practices is essential for MeJA implementation ( Fedderwitz et al, 2019 , Chen et al, 2020 ).…”

“…Different letters above means indicate statistically significant differences (P < 0.05) between mean estimates. and practices is essential for MeJA implementation (Fedderwitz et al, 2019, Chen et al, 2020.…”

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

“…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 ).…”