Effect of three species of bacteria on damping-off, root rot development, and ectomycorrhizal colonization of lodgepole pine and white spruce seedlings

Interactions between three species of bacteria (Burkholderia cepacia, Pseud omonas chlororaphis and Pseudomonas fluorescens), an ectomycorrhizal fungus (Paxillus involutus), and three root pathogenic fungi (Fusarium moniliform e, Fusarium oxysporum and Rhizoctonia solani) were studied. Burkholderia ce pacia significantly reduced the in vitro mycelial growth of P. involutus, w hereas, B. cepacia, Ps. chlororaphis, Ps. fluorescens and P. involutus redu ced the mycelial growth of F. moniliforme, F. oxysporum and R. solani. Cult ure filtrates of B. cepacia, Ps. chlororaphis, Ps. fluorescens and P. invol utus reduced conidial germination and increased the formation of chlamydosp ores of F. moniliforme and F. oxysporum. Burkholderia cepacia also reduced the formation of ectomycorrhizal short roots by P. involutus on lodgepole p ine (Pinus contorta) and white spruce (Picea glauca) seedlings 2 months aft er inoculation However, no significance difference in mycorrhizal short roo ts was observed after 4 months. The fungicide Anchor (a mixture of carboxin e and thiram) significantly reduced root rot severity and increased the sur vival of lodgepole pine seedlings grown in a growth mix infested with F. se ven moniliforme, F. oxysporum and R. solani. Control of the diseases of whi te spruce caused by these pathogens was not as successful. Treatment of see ds with either B. cepacia or P. involutus alone significantly increased the survival of seedlings grown in a mix that was inoculated with F. monilifor me and reduced the root rot severity caused by F. moniliforme and F. oxyspo rum, but not R. solani. Higher seedling survival and lower root rot severit y were observed when conifer seeds were concomitantly inoculated with one o f the bacterial species, P. involutus and Anchor.