ROOT FORKING OF PINE SEEDLINGS GROWING UNDER NON-STERILE CONDITIONS

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  • (With Plate 10)

Summary

It has been demonstrated under particular pot-culture conditions that, without establishing an association, the mycorrhiza-formers Boletus bovinus, B. granulatus, Mycelium radicis nigrostrigosum, and Rhizopogon luteolus are capable of inducing short-root forking in actively growing pine seedlings, while haustorial (pseudomycorrhizal) mycelium causes forking accompanied by infection. A number of soil fungi which are not common root associates failed to bring about dichotomous root branching, but there is evidence that certain other mycelia, whose identity is not known yet, can do so.

In water-cultures of pines tryptophan induced root forking, the kind and degree of branching depending on the concentration of tryptophan.

From a morphological study of the root systems developing in pot- and in water-cultures, it would appear that two types of forking may occur in both infected and uninfected pine roots, and that one type is connected with the activity of mycorrhiza-formers, while the other seems to develop under the influence of non-mycorrhizal fungi and can also be induced by certain growth-substances and other media so far not defined.

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