ISOLATION AND DETERMINATION OF AAL PHYTOTOXINS FROM CORN CULTURES OF THE FUNGUS ALTERNARIA-ALTERNATA F SP LYCOPERSICI

The fungus Alternaria alternata f. sp. lycopersici produces a group of four related host-specific phytotoxins (AAL toxins) which can be divi ded into two groups (TA and TB), each of which exists as an equilibriu m mixture of two structural isomers. The AAL toxins were isolated from com cultures by aqueous extraction, followed by purification on Amber lite XAD-2 resin, separation of TA from TB on silica gel and final pur ification on a semi-preparative high-performance liquid chromatographi c (HPLC) system. A rapid, sensitive and reproducible method was develo ped to determine these toxins in culture material in order to monitor toxin production on com cultures. The method consisted of aqueous extr action, C18 solid-phase extraction clean-up, precolumn derivatization with o-phthaldialdehyde and reversed-phase HPLC with fluorescence dete ction. An isocratic HPLC system was developed that separated the struc tural isomers of TA and TB within a chromatographic analysis time of 2 4 min.