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Two aspects of the interaction between tomato roots and the mycoparasitePythium oligandrumwere investigated, the host's response to fungal invasion and the development of fungal hyphae within the tissues. After root inoculation, hyphae developed over the root surface and penetrated the epidermis, cortex and vascular stele. Oogonia developed in great abundance over the root surface. However, the root tissue remained free from necrotic reacting cells.Pythium oligandruminfections appeared relatively non-destructive since little damage occurred to host walls even at sites of fungal penetration. Host reactions were rapid within cells but these were confined to colonized host cells or to non-infected cells adjacent to invaded ones. Host reactions took the form of a range of types of cytoplasmic networks composed of amorphous material or fibrils which surrounded the invading hyphae. Wall appositions and papillae frequently formed at sites of attempted fungal entry. Chemical compounds, possibly phenols, coated host walls and accumulated inside invaded cells. It is likely that these substances, appearing osmiophilic or electron dense, mechanically reinforce the host's walls and create a fungitoxic environment forP. oligandrum. A typical feature of this interaction was the loss of internal cytoplasmic structures by the invading hyphae which frequently were reduced to empty shells. The relationships between the host reactions and the biocontrol capabilities ofP. oligandrumare discussed. |
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