Contrasting Root Fungal Communities and Pathogen Loads in Asymptomatic and Symptomatic Faba Bean Plants During a Severe Drought Year

Drought is increasingly recognized as an important factor shaping plant-associated microbiomes, yet field evidence linking variation in root microbial communities to contrasting plant health outcomes under drought conditions remains limited. During the 2022 growing season, an extended drought period coincided with the occurrence of severely symptomatic faba bean plants growing alongside asymptomatic plants within the same plots. Because soil type, management, plant genotype, and field history were identical, this provided an opportunity to examine whether differences in the root-associated fungal community were associated with contrasting plant health states. We combined ITS1 amplicon sequencing with quantitative PCR (qPCR) targeting major root rot pathogens and arbuscular mycorrhizal fungi (AMFs) in roots of asymptomatic and symptomatic plants. Although the pathogen spectrum was similar in both health states, qPCR revealed substantially higher abundances of Fusarium spp. and Didymella pinodella in symptomatic plants. Symptomatic plants showed significantly lower fungal species richness and a distinct community structure compared with asymptomatic plants. Indicator species analysis identified 23 taxa associated with asymptomatic plants, including Mortierella spp. and several other taxa previously linked to plant stress tolerance, whereas only three taxa were associated with symptomatic plants. Asymptomatic plants also showed higher AMF abundance. These findings demonstrate that asymptomatic and symptomatic faba bean plants occurring during a severe drought year harbored contrasting root fungal communities and pathogen loads. Although the observational nature of the study precludes conclusions regarding causality, the results highlight a close association between environmental factors, plant health status, and fungal community composition under field conditions. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .