Differential effects of nutrient availability on the secondary metabolism of Austrian pine (Pinus nigra) phloem and resistance to Diplodia pinea

Nutrient availability can modulate the incidence and severity of plant diseases. We examined the effects of fertility on (i) host resistance and (ii) secondary metabolite production in the Pinus nigra Arnold – Diplodia pinea (Desm.) Kickx pathosystem. Following preconditioning of trees to one of three fertility levels for one growing season, phloem tissue of one branch was harvested for chemical analyses while another branch on the same whorl was inoculated with the fungus to assess resistance. Nutrient availability had concave and convex quadratic effects on concentrations of total monoterpenes and total phenolics respectively, but had no effect on fungal lesion lengths. Lesion lengths were negatively correlated with lignin, suggesting that this compound is an important factor in resistance. Counteracting effects of nutrient availability on phenolic and terpenoid pathways may explain why fertility had no effect on expression of disease resistance.