International Academy of Ecology and Environmental Sciences Proceedings of the International Academy of Ecology and Environmental Sciences 2220-8860 16 1 2026 3 1 Polyketide Synthase (PKS)-containing foliar endophytes from a traditional rice variety exhibit antagonism against Xanthomonas oryzae pv. oryzae 1-17 EN Jerick A. Viz Jobriell C. Baluyot Princess Ashley S. Tomas Roland M. Hipol http://www.iaees.org/publications/journals/piaees/articles/2026-16(1)/Polyketide-Synthase.pdf> Rice (Oryza sativa L.), a staple diet for the majority of Asians and considered one of the most crucial food crops, often suffer from diseases like Bacterial Leaf Blight (BLB), caused by Xanthomonas oryzae pv. oryzae. Endophytic fungi harbor secondary metabolites, including polyketides, which exhibit potent medicinal properties and, importantly, possess agricultural potential. In this study, we investigated the capability of ethyl acetate extracts derived from foliar endophytic fungi present in Diket red rice to produce bioactive antibacterial compounds. The extracts were tested for their in vitro antimicrobial activity against X. oryzae pv. oryzae, and the presence of polyketide synthase (PKS) genes was also examined. Among the tested isolates, namely Aspergillus spelaeus, Penicillium steckii, Penicillium chrysogenum, and Cladosporium oxysporum, the latter exhibited the most statistically (p largenr than 0.05) significant reduction in optical density (OD 600) of X. oryzae pv. oryzae broth cultures compared to positive control (Chloramphenicol), indicating possible antimicrobial activity. Out of the 16 fungal isolates, 15 were found to have the PKS gene, which may account for their antagonistic potential. These findings highlight A. spelaeus, P. steckii, P. chrysogenum, and C. oxysporum as promising candidates for the isolation of bioactive compounds aimed at controlling BLB in the future.