Photo‐induced fungicidal activity elicited by naturally occurring thiophene derivatives

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Abstract
Photo‐induced fungitoxicity was observed inAlternaria alternata, Aspergillus niger, Cladosporium variabile, Colletotrichumsp.,Rhizopus nigricans, Pythium aphanidermatum, andSaprolegniasp., 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 inA. niger, and sporangiosporogenesis inR. nigricanswere 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 ofA. niger, andR. nigricanswas 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 ED50values are dependent upon the species and the presence or absence of near u.v. light. Dramatically lowered ED50values 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.