Healing of bark wounds in Norway spruce seedlings can be negatively affected by treatment with methyl jasmonate

Key message

Treatment with methyl jasmonate can slow down the healing of stem bark wounds in Norway spruce seedlings.

Abstract

In woody plants, healing of bark wounds is a tolerance trait involved in recovery from stem damage. Yet, little is known on how wound healing may be affected by plant protection treatments such as methyl jasmonate application (MeJA, a plant hormone triggering increased resistance to pests). Here, we examined if MeJA can affect healing of an existing and a subsequently inflicted stem wound on Norway spruce (Picea abies) seedlings, the effect of treatment on plant growth, and potential trade-offs between healing and resistance to insect damage. Seedlings from 18 full-sib families were mechanically wounded (or not) on the lower stem and treated with MeJA (or water) one week after. Two months later, another wound was inflicted and wound area was measured during six months. Growth of non-wounded and wounded seedlings were compared, and correlations between family estimates of healing rates and field insect damage were examined. We found that MeJA slowed down wound healing. For the first and second wound, respectively, MeJA-treated seedlings experienced 15% and 9% slower healing rates, and wounds remained 58% and 69% larger in size compared to water-treated seedlings. Stem wounding and MeJA together were more detrimental to seedling diameter than height growth, relative to each treatment alone. Finally, resistance to field insect damage and wound healing rates were not significantly correlated. We conclude that MeJA-mediated seedling protection may trade-off with bark wound healing, which may be negative for seedling vigor. However, further studies are needed to evaluate if such effects outweigh the benefits that MeJA provides.