A semiaxenic phototrophic system to study interactions between arbuscular mycorrhizal and pathogenic fungi in woody plants

Abstract

Among other benefits, arbuscular mycorrhizal (AM) fungi may increase plant tolerance to root diseases. The research on the underlying mechanisms requires growth conditions that are both controlled and realistic. To study these interactions, a semiaxenic phototrophic system was developed in which the roots grow in a controlled environment and can be inoculated with both pathogenic and symbiotic fungi. Micropropagated fig plantlets were grown in containers having shoots in the outside and roots in a growth medium without sugar, inoculated or not with the AM fungus Rhizophagus irregularis and the pathogenic fungus Armillaria mellea. Dual inoculated plants developed the mycorrhizal association and pathogen infection symptoms. Mycorrhizal inoculation lowered disease index and increased plant growth. Colonization of A. mellea in fig roots was quantified by real-time PCR, showing that R. irregularis did not significantly lower the quantity of Armillaria, suggesting that other mechanisms were involved in increased tolerance to the pathogen. The results show that the system proposed is suitable to study the triple interaction involving plant, AM and root pathogenic fungi.