Effects of water stress and arbuscular mycorrhizal fungi inoculation on pea root rot

Summary

Root rot is a major threat to pea (Pisum sativum) production in Switzerland, caused by a pathogen complex including the oomycetes Aphanomyces euteiches and Pythium ultimum, as well as several Fusarium species. In the absence of fully resistant genotypes, farmers currently rely on partially resistant varieties. An alternative strategy is to harness the protective potential of the root microbiota. Arbuscular Mycorrhizal Fungi (AMF) are known to form beneficial symbioses with host plants and have been shown to reduce disease severity, yet their effectiveness under water stress remains poorly understood.
Here, we study whether artificial AMF inoculation reduces root rot severity more effectively than native soil AMF communities, and how hydric stress modulates plant performance and pathogen virulence while simultaneously facilitating or hindering mycorrhizal colonisation.
To answer these questions, we conducted a controlled pot experiment using naturally pathogen-infested or gamma-ray-sterilised soil. Two pea genotypes with contrasting resistance levels were subjected to three watering regimes: water deficit, optimal watering, and excessive watering; with or without artificial AMF inoculation. After 30 days, plant performance was evaluated through phenotypic measurements, while root DNA was analysed by high-throughput amplicon sequencing to characterise microbiota shifts. Mycorrhizal colonisation success and A. euteiches abundance were quantified by qPCR.
Preliminary results suggest complex, genotype-dependent responses to the interaction between hydric stress and microbial communities. Water deficit appears to reduce root rot severity, while artificial AMF inoculation does not produce the expected protective effect, showing neutral or even negative outcomes, possibly due to competition with the native soil AMF community. Ongoing microbiota composition analyses will help elucidate the mechanisms underlying these responses.