Effect of seedbed steaming on Cylindrocladium floridanum, soil microbes and the development of white pine seedlings

The Egedal® bed steamer produced sufficient heat to kill mierosclerotia of Cylindrocladium floridanum at 5 and 10 cm soil depths in one bareroot forest seedling nursery. At a second nursery, the buried inoculum was killed only to a depth of 5 cm. Soil steaming did not affect the mierosclerotia at 15 cm. The steaming reduced populations of fluorescent pseudomonas to undetectable levels to a depth of 20 cm and populations of Trichoderma species were significantly reduced in the upper 10 cm of the seedbed. Density of white pine seedlings sown in the steamed beds was significantly higher (P= 0.05), and height, root collar diameter, shoot weight and root weight were significantly greater (P= 0.05) 4 months after steaming than that of control seedlings sown in unsteamed beds.

Protection of black spruce seedlings against Cylindrocladium root rot with ectomycorrhizal fungi

Cylindrocladium floridanum Sobers and Seymour, principal causal agent of root rot of conifers in forest nurseries, was grown in vitro with four species of ectomycorrhizal fungi, Paxillus involutus, Hebeloma cylindrosporum, Laccaria bicolor, and Tricholoma sp. The effect of inoculating black spruce seedlings (Picea mariana (Mill.) B.S.P.) with P. involutus was also investigated. Tricholoma sp. and especially P. involutus and H. cylindrosporum inhibited growth of C. floridanum in Petri dishes, while L. bicolor was inhibited and completely covered by C. floridanum. Hyphae of the pathogen in the contact zone were deteriorated in the presence of P. involutus and H. cylindrosporum. The inoculation of P. involutus reduced the number of infected black spruce seedlings by approximately 50%. However, the simultaneous inoculation of two different strains of P. involutus did not significantly reduce disease development. Linear regression demonstrated that the percentage of infected plants was negatively correlated with mycorrhiza formation. The relation between these two variables also showed that even if colonization by P. involutus is poor or null, it has some inhibitory effect against Cylindrocladium root rot.Key words: Paxillus involutus, Cylindrocladium floridanum, root rot, ectomycorrhizal fungi, biological control, Picea mariana.