Characterization, distribution and pathogenicity of bacteria isolated from chlorotic white spruce (Picea glauca (Moench) Voss)

Abstract

Several genera of bacteria were isolated from the foliage, twigs, bark and wood of stems of chlorotic 10 - 12 years old white spruce (Picea glauca (Moench) Voss). Most of the isolates were nonspore-forming, aerobic or facultative anaerobic rods. Ninety-four percent of all isolates were gram-negative and six percent gram-variable. From 16 isolates, five belonged to the genus Enterobacter (Erwinia), four were Serratia spp., three Pseudomonas spp. and two isolates resembled the genus Pasteurella. Two isolates could not be classified. The bacteria were found throughout the entire trees, but qualitative and quantitative differences existed between sections of the trees. The number of bacteria varied from 2.3 X 10[superscript3] to 6.0 X 10[superscript5] / g.d.w., higher concentrations being present in the fine roots and brown spots of bark. Inoculations with the selected bacterial isolates, alone or in combination, induced pathological responses on young germinants and rooted cuttings of white and black spruce. Stunting, discoloration, localized swellings, tip necroses of hypocotyl, reduced root growth and needle deformation were induced by dip inoculation of seed and hypocotyl. When the inocula were applied to green cuttings the rooting of cuttings and the number and length of developing roots were significantly reduced. Re-isolations yielded the original bacterial types used for the inoculations. The observed pathogenic effects were consistently associated with the Enterobacter isolates and one unknown isolate (U[subscript1]). The pathogenicity tests showed that many of the bacteria inhabiting white spruce have the capacity to affect the growth and development of young roots of black and white spruce and thus plausibly to contribute to the chlorosis syndrome of white spruce.