Thesis (M.Sc.)--Chulalongkorn University, 2006

Screening of antifungal activity against two phytopathogenic fungi; Phytophthora palmivora and P. parasitica, PDA was incorporated with four natural products: N-acetylglucosamine, glucosamine, gallic acid and berberine at concentration of 1,000 ppm. Among them, berberine exhibited the most potent antifungal activity against both fungi by 100 percent inhibition. Berberine was extracted from (C. fenestratum (Gaertn.) Colebr) and investigated the antifungal activity against six phytopathogenic fungi; Alternaria porri, Cercospora sp., Colletotrichum gloeosporioides, Fusarium oxysporum, P. parasitica and Pythium deliense was further investigated and IC [subscript 50] values were determined as 101, 653, 1011, 599, 48 and 284 ppm, respectively. Seven derivatives of berberine: canadine, 8-methoxy-7,8-dihydroberberine, 8-trichloromethyl-7,8-dihydroberberine, acetonylberberine, 8-cyano-13, 14-dehydrocanadine, 13-benzylberberine and 13-methylberberine were manipulated by introducing various groups at C-8 and C-13 of berberine. Four berberine derivatives: acetonylberberine, 8-cyano-13,14-dehydrocanadine, 13-benzylberberine and 13-methylberberine displayed better antifungal activity against selected phytopathogenic fungi than berberine. Spore germination and phytotoxicity bioassay were also investigated. 8-Cyano-13,14-dehydrocanadine and 13-benzylberberine revealed completely inhibition of spore gerimantion of P. parasitica while 13-benzylberberine showed relatively no evident on phytotoxic effects.