Antimicrobial and herbicidal properties of the fruticose lichen ramalina from Guimaras Island, Philippines

Lichens, a unique symbiosis between two or three organisms, are known to produce metabolites that can be tapped as biopesticides for agriculture. In this research study, the fruticose lichen Ramalina was collected within Guimaras Island, Philippines. A total of 195 specimens were collected and characterized using conventional morphological and chemical analyses. These lichens were identified as Ramalina farinacea, R. roesleri, and R. nervulosa. To test for potential application in agriculture, nine lichen specimens were extracted with acetone and assayed for its inhibitory activities against test bacteria, fungi, and weedy plants. All lichen extracts inhibited Pseudomonas aeruginosa (>19 mm ZOI) while only seven lichen extracts inhibited Staphylococcus aureus (13-19 mm ZOI). No inhibitory activity was observed against the fungal plant pathogens Fusarium oxysporum, F. solani, F. verticillioides, Colletotrichum capsici, and C. gleosporioides, and the Gram-negative bacteria Escherichia coli and Pectobacterium carotovorum var. carotovorum. Furthermore, there was also a decrease in the root (up to 27% reduction) and shoot (up to 39% reduction) lengths, and leaf chlorophyll content (up to 44% reduction) of Fimbristylis miliacea, Leptochloa chinensis and weedy rice (Oryza sp.). These results, therefore, suggested the potential of lichen extracts from Ramalina as a biological control for weed management.