Étude morphologique, anatomique et ultrastructurale d'endomycorhizes synthétiques d'Erica carnea

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Abstract
Endomycorrhizae were synthesized between Erica carnea and a fungus isolated from E. vagans. Inoculated and non-inoculated plants were grown for 6 months under controlled conditions. Inoculation provokes an important stimulation of the growth and flowering of E. carnea. Under the experimental conditions reported herein, the mycorrhizae formed during the 1st month remained localised and, after 6 months, the roots usually were not colonized by the fungus. It seems probable that colonization of the whole root system requires a growth substrate that favours mycelial growth.Macroscopic and microscopic characters of the mycorrhizae obtained were studied using light and scanning (SEM) and transmission (TEM) electron microscopy. The hyphae of the responsible fungus exhibit simple septa and Woronin bodies (ascomycetes). The intracellular hyphae are characterised by the abundance of lipid globules and the presence in SEM of electron-dense granules in the vacuoles. These hyphae are wrapped in a network of fibrils particularly at the penetration points but also observed on external hyphae. These mycorrhizae seem to survive for approximately 1 month only. The importance of the inoculum as nutritional source must not be neglected since similar stimulation of the plants was also produced by inoculation with an autoclaved slurry of mycelium. We suggest that not only mycorrhizal but also saprophytic rhizosphere fungi free, by simple autolysis of their mycelia, elements that are assimilable by the plant and doubtless play a role in the mineral nutrition of the Ericaceae.