Biocontrol Potential and Mechanisms of Cocoa-Fermentation Yeasts Against Fungal Pathogens of Cocoa Pods

This study investigated the inhibitory potential and mechanisms of four yeast isolates obtained from cocoa bean fermentation against three fungal pathogens of cocoa pods. Molecular identification revealed that the yeast isolates UNJCC Y-158 and UNJCC Y-159 corresponded to Rhodotorula alborubescens and Meyerozyma guilliermondii, respectively, while UNJCC Y-160 and UNJCC Y-161 were Pichia kudriavzevii. All four yeast isolates demonstrated inhibitory potential against the tested fungi pathogens of cocoa pods: Fusarium decemcellulare UNJCC F9, Fusarium solani UNJCC F18, and Colletotrichum siamense UNJCC F14. The results showed that Pichia kudriavzevii UNJCC Y-160 and UNJCC Y-161 exhibited the highest inhibition against the tested fungi, with inhibition percentages ranging from 12.61–34.64%. In contrast, Rhodotorula alborubescens UNJCC Y-158 and Meyerozyma guilliermondii UNJCC Y-159 displayed weaker inhibition, with inhibition percentages ranging from 2.93–10.68%. Antagonism, hyperparasitism, and the production of volatile compounds were observed as mechanisms for inhibition. Microscopic observations revealed that yeast cells attach to the fungal hyphae, causing morphological changes such as thinning and shrinking, likely due to the secretion of hydrolytic enzymes, including cellulase, produced by the yeasts. This study offers a promising alternative to chemical fungicides by utilising natural yeast isolates as biocontrol agents, thereby contributing to sustainable and environmentally friendly cocoa disease management strategies.