Photo-induced fungicidal activity elicited by naturally occurring thiophene derivatives

Photo-induced fungitoxicity was observed in Alternaria alternata, Aspergillus niger, Cladosporium variabile, Colletotrichum sp., Rhizopus nigricans, Pythium aphanidermatum, and Saprolegnia sp., elicited by 5-(but-3-en-l-ynyl)-2,2′-bithienyl, 2,2′: 5′,2″-terthienyl, and 2-chloro-4-5-(penta-1,3-diynyl)-2-thienyl]but-3-ynyl acetate in the presence of near ultraviolet (u.v.) radiation (320–380 nm). Conidiogenesis in A. niger, and sporangiosporogenesis in R. nigricans were depressed on media treated with 2,2′: 5′,2″-terthienyl and irradiated with near u.v. light. Radial growth of mycelia of all fungi tested was dramatically reduced by all three compounds in the presence of near u.v. light. The viability of conidia of A. niger, and R. nigricans was unaffected by 2,2′: 5′,2″-terthienyl, both in the dark and in near u.v. light. Newly emergent germ-tubes were most sensitive to toxicity mediated by u.v. light. The oomycetous fungi tested were the most sensitive to the photo-activated toxicity generated by the three compounds used. The results indicate that ED₅₀ values are dependent upon the species and the presence or absence of near u.v. light. Dramatically lowered ED₅₀ values were always observed in all systems treated with near u.v. light. The dose of near u.v. light used had no effect on the radial growth of fungi in the absence of the three compounds.