Saffron ( Crocus sativus L.) suffers substantial yield losses due to polymicrobial corm rot, a disease with unresolved aetiology. To clarify the contribution of the rhizosphere microbiome to disease expression, the present study presents the first integrated field survey that concurrently profiles bacterial (16S rRNA) and fungal (ITS2) communities along with soil geochemistry across a natural gradient of corm-rot severity (0 to >70% plant mortality). Severe disease was associated with pronounced fungal dysbiosis, characterised by a marked depletion of saprotrophic guilds, increased dominance of pathotrophs (68% vs . 46% in healthy fields), and an unusually high relative abundance (mean 58%) of Rhexocercosporidium panacis, a putative pathogen not previously reported at such levels in saffron systems. In contrast, bacterial communities in diseased soils displayed higher alpha diversity but greater compositional instability consistent with the Anna Karenina principle, shifting from iron-mobilising taxa (for example, Bacillus ) toward stress-tolerant, iron-sequestering lineages (notably Gammaproteobacteria ). Predictive metagenomic analysis supported this taxonomic turnover, indicating enriched ferroxidase-associated functions in healthy rhizospheres, which coincided with higher bioavailable soil iron. Diseased soils were enriched in non-heme ferritin and stress-response serine/threonine kinases. Collectively, these patterns suggest an iron–microbiome–disease axis in which chronic iron limitation in calcareous soils is associated with rhizosphere dysbiosis and a functional shift from iron mobilisation to iron hoarding, thereby potentially intensifying plant stress and vulnerability to opportunistic pathogens. These findings provide the first field-based evidence that microbiome-mediated iron cycling is a key determinant of corm-rot outcomes in saffron and establish a mechanistic basis for microbiome-centred, iron-informed management strategies in this high-value crop. • First integrated field-scale profiling of bacterial and fungal communities in the saffron rhizosphere • Rhexocercosporidium panacis dominates diseased fields at previously unreported levels • Iron limitation in calcareous soils is associated with rhizosphere microbiome dysbiosis • Healthy rhizospheres show markedly higher predicted ferroxidase activity and elevated bioavailable Fe • Microbiome-informed microbial inoculants are proposed as a sustainable strategy for corm rot suppression
Yeganeh et al. (Fri,) studied this question.