Colonization and Infection of Primary Roots of Douglas-fir Seedlings by the Ectomycorrhizal Fungus Laccaria laccata
The earliest stages of the association of Laccaria laccata with seedlings of Pseudotsuga menziesii were studied by light and scanning electron microscopy. Surface sterilized germinants were planted when radicles were 1 cm long (day 0) in 32 x 200 mm tubes in a soil mix infested with (a) no organisms, (b) mycelium of the mycorrhizal fungus, (c) bacteria and actinomycetes isolated from the rhizosphere of Douglas-fir seedlings, or (b) plus (c). Colonization (development of epirhizal mycelium) and penetration of L. laccata into the radicle were observed in the absence of soil microorganisms as early as day 6, and in their presence by day 9. Infection by L. laccata, indicated by intercellular hyphae among the persistent root cap cells along the shaft of the root at regions of colonization, was first observed at day 9 and was common at day 13 in either the absence or presence of rhizosphere microorganisms. Hyphae extended as deep as 4-5 cells beneath the surface and occurred in tissues judged on the basis of distance from the root apex to be as few as 4 days old. In no case, however, did a Hartig net form in a primary root. Development of root hairs was arrested at sites colonized by L. laccata, but no other morphogenetic influence of the fungus on primary roots was noted. Lateral roots began emerging at day 18 and some fully formed ectomycorrhizae were present by days 24 or 29 in the absence or presence, respectively, of rhizosphere microorganisms. These observations showed that an intimate interaction of seedling and symbiotic fungus can be established during the early, premycorrhizal life of Douglas-fir seedlings, and that the interaction can lead to more rapid ectomycorrhizal formation than has previously been noted. Forest Sci. 27:111-124.
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Document Type: Journal Article
Affiliations: Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853
Publication date: 1981-03-01
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