Repellent activity of estrogenic compounds toward zoospores of the phytopathogenic fungus Aphanomyces cochlioides

Screening chemical compounds, we found that a xenoestrogen, bisphenol A, sh owed potent repellent activity against the zoospores of Aphanomyces cochlio ides. Based on this finding, we tested a number of androgenic and estrogeni c compounds (e.g. testosterone, progesterone, estradiols, diethylstilbestro l, estrone, estriol, pregnenolone, dienestrol etc.) on the motility behavio r of A. cochlioides zoospores. Interestingly, most of the estrogenic compou nds exhibited potent repellent activity (1 mug/ml or less by the "particle method") toward the motile zoospores of A. cochlioides. We derivatized some of the estrogens and discussed the relationship between the structure of a ctive molecules and their repellent activity. Apparently, aromatization of the A ring with a free hydroxyl group at C-3 position of a steroidal struct ure is necessary for higher repellent activity. Interestingly, methylation of diethylstilbestrol (DES) yielded completely different activity i.e. both mono- and di-methyl ethers of DES showed attractant activity. Moreover, th e attracted zoospores were encysted and then germinated in the presence of di-methyl ether of DES. The potential usefulness of this repellent test is discussed for the detection of estrogenic activity of naturally occurring c ompounds, and the possible role of phytoestrogens in host/parasite interact ions. So far, this will be the first report of repellent activity of estrog enic compounds toward trivial fungal zoospores.