Complex response of VA‐mycorrhizae to xenobiotic substances

Abstract
The role of Vesicular‐Arbuscular mycorrhizae (VAM) in transformation of matter in the soil and their importance for plant nutrition and plant health is increasingly recognized. The complex interactions between mycorrhizal fungi, soil‐ecosystem and plant roots are, however, far from being elucidated. Ideally, the response of VA‐mycorrhizae to plant protection measures should be monitored in long‐term field studies. However, experiments under controlled conditions can contribute to elucidation of possible side effects of xenobiotics on specific processes of VAM development. A cuvette‐system has been designed to study growth of external hyphae through soil amended with selected pesticides. The same system was used to study the ability of mycorrhizal fungi to spread through natural, undisturbed soil by inserting soil monoliths, cut in the field, in the cuvettes. From four fungicides investigated in the cuvette tests, only PCNB significantly inhibited VAM formation, while SBI fungicides had no significant effect on mycorrhizal development, and captan even stimulated hyphal spread, possibly due to changes in microbial competition in the soil. The response of mycorrhizal fungi to most any changes in the soil ecosystem is very complex, and VAM‐formation is, therefore, not suitable for use as a standard requirement for pesticide registration.

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