ABSTRACT Functional characterisation of fungal pathogen effectors is critical in designing durable resistance strategies in wheat ( Triticum aestivum ). Here, we explore the use of Ustilago hordei , a basidiomycete fungal pathogen of barley, as a surrogate system for delivery and functional analysis of effectors from other fungal pathogen species in wheat. Both the haploid wild‐type strain Uh364 and its modified solopathogenic derivative UhDS200 can grow in wheat without eliciting obvious nonhost reactions when infiltrated. We demonstrate that U. hordei can express and secrete effectors SnTOX1 and SnTOX3 from Parastagonospora nodorum into wheat and trigger within 48 h visible necrosis in cultivars having corresponding receptors, which are susceptibility factors in this inverse gene‐for‐gene pathosystem. At the molecular level, this reaction is accompanied by production of reactive oxygen species and induced expression of the wheat PR1b gene, a marker of hypersensitive cell death. However, the system showed limitations in the delivery into wheat of rust fungus effectors. When testing proven Puccinia graminis f. sp. tritici avirulence effectors PgtAVRSr35 or PgtAVRSr50, though transcripts were produced, no protein products could be detected or cell death reactions observed in cultivars harbouring the corresponding resistance genes Sr35 or Sr50 . With previous confirmation of secretion by U. hordei of effectors from Cladosporium fulvum and Fusarium species, our results show that the U. hordei secretion system provides an alternative platform for functional studies of heterologous effectors in wheat to help advance our understanding of plant–pathogen interactions and assist with breeding efforts to achieve resistance to various pathogens.
Liu et al. (2026) studied this question.