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 divided into two groups (TA and TB), each of which exists as an equilibrium mixture of two structural isomers. The AAL toxins were isolated from com cultures by aqueous extraction, followed by purification on Amberlite XAD-2 resin, separation of TA from TB on silica gel and final purification on a semi-preparative high-performance liquid chromatographic (HPLC) system. A rapid, sensitive and reproducible method was developed to determine these toxins in culture material in order to monitor toxin production on com cultures. The method consisted of aqueous extraction, C18 solid-phase extraction clean-up, precolumn derivatization with o-phthaldialdehyde and reversed-phase HPLC with fluorescence detection. An isocratic HPLC system was developed that separated the structural isomers of TA and TB within a chromatographic analysis time of 24 min.