SUMMARY
Aim of the study: We tested alternative active principles to the most widely used resin tapping stimulant which contains sulphuric acid. We also studied the effect of wounding in five-year-old Pinus pinaster seedlings with a microtapping method.Area of study: The experiment was carried out at the Universidad Politécnica de Madrid in Spain.Material and Methods: The experiment consisted of six treatments: control (no stimulant no wounding), wound (no stimulant), and pines stimulated with sulphuric acid, ethrel, salicylic acid and citric acid. We evaluated the resin yield differentiating between released resin and internal resin (resin retained within the xylem), and the physiological status of the tree.Main Results: Wounded plants produced on average three times more resin than control plants. Plants stimulated with salicylic and citric acids showed the highest resin yield and produced on average 15% more resin than those stimulated with sulphuric acid, mainly because the released resin was higher. Tree diameter affected resin yield and thicker trees produced more resin. We did not observe any significant effect of the treatments on stomatal conductance and only a marginal significant effect (p<0.10) on water potential.Research highlights: Salicylic acid and citric acid seem to be promising stimulants for the resin tapping activity to be further tested in field experiments with adult trees.Keywords: sulphuric acid; ethrel; pine resin; microtapping; wounding; water potential; stomatal conductance.Abbreviations used: TR: total resin content; RR: released resin; IR: internal resin; gs: stomatal conductance; ?leaf: midday leaf water potential.