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

We investigated the impact of the black pod rot pathogen ( Phytophthora megakarya ) and a non-pathogenic fungus ( Rhizoctonia solani ) on stomatal aperture in two cacao genotypes (SCA6 and Pound7) under varying light conditions. Image analysis revealed diverse stomatal responses, including no change, opening, and closure, that were influenced by the interplay of genotype, pathogen strain, and light conditions. Notably, SCA6 exhibited stomatal opening in response to P. megakarya specifically under a 12-hour light/dark cycle, suggesting a light-dependent activation of pathogen virulence factors. In contrast, Pound7 displayed stomatal closure in response to both P. megakarya and R. solani , indicating the potential recognition of conserved Pathogen-Associated Molecular Patterns (PAMPs) and a broader defense response. Machine learning was used to predict stomatal area size and classify pathogen treatments based on stomatal traits in cacao. Size-related traits were the strongest predictors of stomatal area size, while shape-related traits were also significant. This combined approach is promising for disease phenotyping and development of resistant crop varieties.