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The paper-sandwich technique for simultaneous inoculation of populations of root apices, was used to produce numbers of synchronously developing ectomycorrhizas, and to permit direct time-sequencing of stages in the infection process in eucalypts. After one day there was evidence of chemical interaction between fungus and host. By two days, sheath formation had started in the cap region, cap cells were invaded by fungus, and apical root tissues commenced to swell. By four days all the anatomical features of an ectomycorrhiza were present, including the Hartig net. Thereafter, mycorrhizal features were merely enhanced and perpetuated by subsequent acrogenous development of the fungus-root dual organ. The process of mycorrhizal perpetuation involved the same sequence of events (sheath development at the apex associated with invasion of cap cells, modification of other root tissues, then finally formation of Hartig net) as did the initial infection process. [ABSTRACT FROM AUTHOR]

Summary: Vesicular‐arbuscular (VA) mycorrhizal fungi and ectomycorrhizal fungi were observed together in the same root system, and even within the same root apices, of seedlings of Eucalyptus dumosa A. Cunn. ex Schau. On a population basis, there was a succession of two overlapping mycorrhizal epidemics‐VA mycorrhizas followed by ectomycorrhizas. This succession was interpreted as follows. Early build‐up of VA mycorrhizas was related to initial higher inoculum potential of that fungus and to rapidity of colonization of individual roots. The ectomycorrhizal fungus was more successful later in achieving secondary infections by hyphal spread and in colonization of lateral root branches. The ectomycorrhizal fungus had no difficulty infecting pre‐existing VA mycorrhizas, but the ectomycorrhizal sheath provided a barrier to subsequent VA mycorrhizal infections. While the proportion of VA mycorrhizas to ectomycorrhizas changed between two and five months, the overall proportion of mycorrhizal roots remained constant, suggesting that there could be competition between the different fungi for limiting substrate. [ABSTRACT FROM AUTHOR]