Effects of fertilization on red pine defense chemistry and resistance to Sphaeropsis sapinea

Sphaeropsis sapinea (Fr.:Fr.) Dyko & Sutton in Sutton is a fungal pathogen that causes shoot blight and canker disease throughout the world on conifers predisposed by stress. Fertilization is often recommended to reduce stress, and presumably increase disease resistance. We examined the effects of fertilization on red pine (Pinus resinosa Aiton) resistance to S. sapinea, and on concentrations of constitutive and pathogen-induced secondary metabolites putatively involved in disease resistance. Wounded branch tips were inoculated with agar plugs colonized by the pathogen; noncolonized plugs were used for controls. Fertilization increased lesion size (P < 0.05) and foliar nitrogen (P < 0.01), and decreased foliar C:N ratio (P < 0.01), constitutive lignin levels both locally (P < 0.05) and distally (P < 0.05), and total soluble phenolics distal to the inoculation point (P < 0.01). At the infection court, inoculation significantly increased accumulation of total soluble phenolics (P < 0.01), and the induction or depletion of several individual phenolics (P < 0.05). Distally, inoculation was also a significant factor (P < 0.05) in the accumulation or depletion of some of the individual phenolics investigated. These results show that fertilization decreases resistance of red pine to S. sapinea, and suggest that lignin and soluble phenolics might be involved in host defense.