Fungal Contaminants Affecting Oyster Mushroom (Pleurotus ostreatus) Cultivation in Luzon Provinces, Philippines and Their Potential Biocontrol Using Pleurotus-Associated Bacteria

Oyster mushroom (Pleurotus ostreatus) cultivation is an emerging industry in the Philippines, providing both nutritional benefits and livelihood opportunities. However, production is hindered by fungal contaminants that impede mycelial growth during different developmental stages. This study provides insights into the diversity of fungal species affecting oyster mushroom cultivation in Luzon provinces, and screened Pleurotus-associated bacteria as biocontrol agents against prime fungal contaminants identified. From a total of 41 fungal contaminants isolated, molecular analyses coupled with inhibition assays revealed Trichoderma pleuroti and T. virens as the most predominant and aggressive contaminants. Dual-culture and grain-spawn assays showed that T. virens completely inhibited P. ostreatus under both in vitro and in vivo conditions, respectively. Diversity analysis indicated a correlation between fungal prevalence and specific climatic zones, suggesting that environmental factors influence contaminant distribution. To combat these contaminants, 74 bacterial isolates were screened, wherein 8 demonstrated promising antagonism. In vivo grain-spawn assay demonstrated that isolates Bacillus sp. SUB_QZN 4-2-1 and Paenibacillus lautus SUB_CAV 4-1-6, when incorporated at 0.01%, enhanced P. ostreatus colonization in the presence of T. pleuroti, compared with T. pleuroti + P. ostreatus controls at α = 0.05. Enzymatic profiling revealed non-lytic modes of antagonism (cellulase, protease, and lipase), while chitinase activity was absent in all isolates. The effective bacterial isolates were identified as members of the genera Bacillus, Lysinibacillus, and Paenibacillus. Despite promising in vitro results, bacterial treatments were ineffective against T. virens in vivo, indicating the need to further optimize dosage, timing, and isolate combinations. Overall, these findings support the potential use of Pleurotus-associated bacterial antagonists as biocontrol agents in mushroom cultivation and lay a foundation for sustainable disease management.