A seed-associated Chaetomium globosum endophyte from a susceptible wheat cultivar suppresses Septoria tritici blotch

Abstract Septoria tritici blotch (STB), caused by Zymoseptoria tritici , is among the most damaging wheat diseases worldwide and requires sustainable alternatives to intensive fungicide use. While resistant cultivars are often considered promising sources of beneficial microbiota for biocontrol discovery, the potential of endophytes associated with susceptible cultivars remains poorly explored. Contrary to expectations, a seed-associated isolate of Chaetomium globosum (HKH_AMG), recovered from the STB-susceptible wheat cultivar Taichung 29, provided the strongest disease suppression among 45 representative fungal endophytes selected for greenhouse screening from wheat, rice, and pistachio tissues. Pretreatment with HKH_AMG significantly reduced lesion development, pycnidial coverage, and pathogen biomass in the susceptible wheat cultivar Tirgan. Disease suppression was associated with reduced stomatal penetration, early hydrogen peroxide accumulation, and enhanced levels of defence-related phenolic compounds, including salicylic and gallic acids. Collectively, our findings demonstrate that disease-susceptible wheat cultivars should not be overlooked as potential sources of highly effective biocontrol endophytes. The identification of C. globosum HKH_AMG from the susceptible cultivar Taichung 29 highlights the untapped potential of seed-associated fungal microbiota for the sustainable management of STB.