Hidden diversity of mycoparasitic fungus assiociated with the coffee leaf rust fungus (Hemileia Vastatrix) and it's relation to wellbeing of small coffee productors in Brazil

Coffee leaf rust (Hemileia vastatrix) is one of the most serious threats to coffee production worldwide, particularly affecting smallholder farmers who rely on coffee for their livelihoods. This research investigates the hidden diversity of mycoparasitic fungi associated with H. vastatrix and evaluates their potential as sustainable biological control agents. The study focuses on the identification and characterization of Paranectriella hemileiae, a mycoparasitic fungus observed colonizing rust pustules on coffee leaves. Microscopic examination revealed that P. hemileiae grows directly over H. vastatrix lesions, suggesting a parasitic interaction that may suppress rust development. To complement the biological analysis, interviews with eight smallholder coffee producers in Brazil explored farmers’ motivations, challenges, and perceptions regarding non-conventional agricultural practices. Results showed that health, environmental, and ethical concerns were the main motivations for adopting biological or organic methods, while labour intensity and input availability were cited as barriers. The study concludes that P. hemileiae represents a promising biological control candidate for coffee leaf rust and that integrating such fungal agents with participatory, farmer-driven strategies could strengthen sustainable coffee systems. Together, these findings highlight the importance of linking biological innovation with social adoption to promote ecological resilience and improve the wellbeing of small coffee producers.