Pathogen-specific stomatal responses in cacao leaves to Phytophthora megakarya and Rhizoctonia solani

Authors: Baek, Insuck; LIM, SEUNGHYUN - Orise Fellow; Jang, Jae Hee; HONG, SEOK MIN - Ulsan National Institute Of Science And Technology (UNIST); Prom, Louis; Kirubakaran, Silvas; Cohen, Stephen; Lakshman, Dilip; Kim, Moon; Meinhardt, Lyndel; Park, Sunchung; Ahn, Ezekiel

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2025
Publication Date: 3/27/2025
Citation: Baek, I., Lim, S., Jang, J., Hong, S., Prom, L.K., Kirubakaran, S.J., Cohen, S.P., Lakshman, D.K., Kim, M.S., Meinhardt, L.W., Park, S., Ahn, E.J. 2025. Pathogen-specific stomatal responses in cacao leaves to Phytophthora megakarya and Rhizoctonia solani. Scientific Reports. https://doi.org/10.1038/s41598-025-94859-5.
DOI: https://doi.org/10.1038/s41598-025-94859-5

Interpretive Summary: Theobroma cacao, the source of the world's chocolate, faces a constant threat from a devastating disease known as black pod rot, caused by the pathogen Phytophthora megakarya. This study delves into the intricate world of plant-pathogen interactions, focusing on the role of stomata, microscopic pores on leaves, in cacao's defense against this disease. The research reveals an interplay between the cacao tree's genetic makeup, the specific strain of the pathogen, and environmental factors, particularly light, in determining the plant's response to infection. Two cacao varieties, SCA6 and Pound7, exhibited distinct stomatal behaviors when confronted with different strains of P. megakarya. SCA6, under specific light conditions, slightly opened its stomata wider when infected with certain strains of the pathogen, possibly a result of the pathogen's manipulation of the plant's defenses. Conversely, Pound7 consistently closed its stomata in response to infection, demonstrating a broader defense strategy. These findings have significant implications for understanding and managing black pod rot in cacao. By identifying the factors that influence stomatal behavior, targeted strategies are expected to be developed to enhance the plant's natural defenses against this disease. This knowledge could contribute to the development of disease-resistant cacao varieties and sustainable agricultural practices, ensuring the future of chocolate production. This study also highlights the power of interdisciplinary research, combining image analysis and machine learning to unravel the complexities of plant-pathogen interactions. This approach holds promise for future research in plant pathology and could contribute to the development of innovative solutions for combating plant diseases in a world facing increasing environmental challenges.

Technical Abstract: This study investigated stomatal aperture dynamics in two cacao genotypes, SCA6 and Pound7, following inoculation with different strains of Phytophthora megakarya, the causal agent of black pod rot, and a non-pathogenic fungus, Rhizoctonia solani, under varying light conditions. Image analysis and machine learning techniques were employed to analyze stomatal responses. The results revealed a complex interplay of genotype, pathogen strain, and light condition in shaping stomatal dynamics. Notably, SCA6 exhibited light-dependent stomatal opening in response to specific P. megakarya strains, suggesting a possible manipulation of stomatal aperture by the pathogen. In contrast, Pound7 displayed consistent stomatal closure in response to both pathogenic and non-pathogenic microbes, indicating a robust, broad-spectrum defense mechanism. Machine learning analysis successfully predicted stomatal area size based on morphological features and environmental conditions, with size-related traits identified as the strongest predictors. This study provides valuable insights into the intricate stomatal responses of cacao to different pathogens and highlights the potential of combining image analysis and machine learning for plant-pathogen interaction studies.