Mellein and its derivatives isolated from the basidiomycete mushroom Lentinus tigrinus exhibit inhibitory activity against plant pathogenic microorganisms.

AIMS: Plant diseases caused by pathogenic microorganisms are among the major challenges in global agricultural production, necessitating the search for bioactive natural compounds with effective antimicrobial activity. This study investigates the potential of Lentinus tigrinus culture filtrate extract for the discovery of compounds active against agriculturally important pathogens.

METHODS AND RESULTS: The culture filtrate of the mushroom L. tigrinus was subjected to bioassay-guided fractionation, leading to the isolation of five compounds. These were identified by mass spectrometry, nuclear magnetic resonance, and optical rotation analyses as (R)-mellein (1) and its derivatives: (R)-5-methoxycarbonylmellein (2), (3S,4S)-4-hydroxymellein (3), (3R,4S)-4-hydroxymellein (4), and (S)-8-O-methylmellein (5). All compounds were tested in vitro against four plant pathogenic fungi and four plant pathogenic bacteria. Compound 2 exhibited the strongest antifungal activity, particularly against Pyricularia oryzae, inhibiting conidial germination (IC₅₀ 30.2 μM) and germ tube elongation (IC₅₀ 20.7 μM). In vivo, compound 5 suppressed rice blast lesion symptoms caused by P. oryzae. Compound 1 showed the most potent antibacterial activity. Based on IC₅₀ values, all compounds were more effective against fungi than bacteria.

CONCLUSIONS: The inhibitory activities of the five isolated compounds against plant pathogenic fungi and bacteria suggest their potential as lead compounds for agrochemicals for managing plant diseases.