Radicinols and radicinin phytotoxins produced by Alternaria radicina on carrots

The phytotoxin epi-radicinol, a diastereomer of radicinol, was isolated from large cultures of Alternaria radicina grown on carrot slices and identified by GC-MS, LC-MS, H-1 NMR, and C-13 NMR. Four strains of A. radicina isolated from rotted carrot produced epi-radicinol as the major metabolite (up to 39414 mug/g) together with radicinol (up to 2423 mug/g), and, to a lesser extent, radicinin when cultured on carrot slices, whereas on rice they mainly produced radicinin (2486-53800 mug/g). Radicinin and epiradicinol reduced root elongation of germinating carrot seeds at concentrations of 10-20 mug/mL. Carrot samples naturally infected by A. radicina contained detectable quantities of epi-radicinol also in combination with lower levels of radicinin or radicinol. Accumulation of radicinols and radicinin in stored carrots, either naturally contaminated or artificially inoculated with A. radicina, was stimulated by successive temperature rises from 1 to 10 degreesC and from 10 to 20 degreesC, reaching maximum levels of 60 mug/g epi-radicinol and 26 mug/g radicinin. This is the first report on the production of radicinols by A. radicina and its natural occurrence in carrots in association with radicinin.