Differential responses of Cacao pathogens Colletotrichum gloeosporioides and Pestalotiopsis sp. to UVB 305 nm and UVC 275 nm

Authors: Baek, Insuck; Jang, Jae Hee; LIM, SEUNGHYUN - Orise Fellow; WANG, ZHUANGII - ARS Postdoctoral Research Associate; CHA, MINHYEOK - Orise Fellow; MAGIL, CLINT - Texas A&M University; Kim, Moon; Meinhardt, Lyndel; Park, Sunchung; Ahn, Ezekiel

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2025
Publication Date: 10/16/2025
Citation: Baek, I., Jang, J., Lim, S., Wang, Z., Cha, M., Magil, C., Kim, M.S., Meinhardt, L.W., Park, S., Ahn, E.J. 2025. Differential responses of Cacao pathogens Colletotrichum gloeosporioides and Pestalotiopsis sp. to UVB 305 nm and UVC 275 nm. Scientific Reports. https://doi.org/10.1038/s41598-025-20277-2.
DOI: https://doi.org/10.1038/s41598-025-20277-2

Interpretive Summary: Fungal diseases pose a major threat to cacao, the source of chocolate, impacting global supply and the livelihoods of farmers who depend on it. Current reliance on chemical fungicides faces challenges like pathogen resistance and environmental concerns, driving the need for sustainable alternatives. This study explored the potential of ultraviolet (UV) light, specifically UVC, as a non-chemical tool to combat key fungi (Colletotrichum and Pestalotiopsis) infecting cacao. We found that UVC light is much more effective than UVB at stopping fungal growth, although some fungi are naturally tougher against UV than others. Excitingly, we discovered that applying UVC in pulses (flashing) or combining it with ultrasound waves (sonication) can significantly boost its effectiveness, particularly against resistant fungi. Using advanced hyperspectral cameras – which see beyond visible light – we revealed how UV stress affects sensitive fungi by disrupting their biochemistry and triggering defense mechanisms like pigment production, while resistant fungi remained largely unchanged. This research highlights the promise of optimized UV treatments for sustainable cacao disease management. Understanding these fungus-specific responses, revealed through advanced imaging and analysis, is crucial for designing targeted strategies to protect this vital crop.

Technical Abstract: Fungal pathogens severely impact cacao (Theobroma cacao) production, and sustainable non-chemical control methods are needed. This study investigated the differential responses of four cacao-infecting Colletotrichum gloeosporioides isolates and one Pestalotiopsis sp. isolate (CGH5) to UVB (305 nm) and UVC (275 nm) radiation. We assessed strategies to enhance UVC efficacy, including pulsed delivery (1-20 Hz) and synergistic effects with sonication (80 kHz). Hyperspectral imaging (VIS-NIR: 430-1000 nm; SWIR: 1000-2400 nm; Fluorescence: 450-720 nm emission with 365 nm excitation) coupled with machine learning (ML) analyses characterized morphological and physiological responses to UVC stress. Results showed UVC (275 nm) was significantly more inhibitory than UVB (305 nm). Pestalotiopsis sp. (CGH5) exhibited notably higher UVC resistance compared to sensitive C. gloeosporioides isolates (e.g., CGH53). Pulsed UVC treatments enhanced growth inhibition in an isolate-specific manner, and sonication synergistically increased UVC efficacy against the resistant CGH5. Hyperspectral analyses revealed significant UVC-induced spectral changes in sensitive CGH53, consistent with photoprotective pigment production, biochemical disruption (water/lipid alterations), and oxidative stress, whereas resistant CGH5 showed minimal spectral alterations. ML models accurately classified isolates based on treatment and morphology. Our findings demonstrate the potential of optimized UVC strategies, including pulsed delivery and sonication synergy, for managing cacao fungal pathogens. The distinct spectral signatures reflect differential resistance mechanisms, underscoring the importance of pathogen-specific responses and the utility of integrating advanced sensing and analytics for developing sustainable disease control methods.