The Influence of Water Stress and Insect Defoliation on the Development of Disease in Abies grandis Seedlings Inoculated with Armillaria ostoyae : Root and Butt Rots

Uppsala

International Union of Forest Research Organizations, Swedish University of Agricultural Sciences

1994

S. 52-64

35 Lit. Ang.

Bandaufführung

73434

This greenhouse study used three-year-old Abies grandis (Dougl.) Lindl. seedlings to evaluate the influence of separately and simultaneously imposed water stress and western spruce budworm (Choristorneura occidentalis Freeman) defoliation on the incidence of infection and mortality by Armillaria ostoyae (Romagn.) Herink. Insect caused defoliation has been earlier reported to enhance successful colonization of Armillaria spp. on deciduous trees in the forests of the NE United States; the positive response of the fungus was attributed to a weakened tree condition. Conversely, althougs this study conclusively found water-limited trees to have increased susceptibility to Armillaria ostoyae, defoliation significantly lowered Armillaria-caused infection and morality. The decline in infection success is attributed to defiliation-caused reduction in plant water stress and an alteration of root phenolics and carbohydrate chemistry. Total pheolics and soluble sugars were higher in roots of undefoliated, water-stressed seedling. Root starch was higher in defoliated trees, possibly due to the mode of defoliation. Unlike many forest defoliators, western spruce budworm consumes only current year foliage leaving a complement of older foliage to produce and transport photosynthates. Short-term defoliation appeared to enhance the physiological condition of water-stressed trees by reducing transpiration loss and utilization of reserve carbohydrates.