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, (1)H NMR, and (13)C NMR. Four strains of A. radicina isolated from rotted carrot produced epi-radicinol as the major metabolite (up to 39414 microg/g) together with radicinol (up to 2423 microg/g), and, to a lesser extent, radicinin when cultured on carrot slices, whereas on rice they mainly produced radicinin (2486-53800 microg/g). Radicinin and epi-radicinol reduced root elongation of germinating carrot seeds at concentrations of 10-20 microg/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 degrees C and from 10 to 20 degrees C, reaching maximum levels of 60 microg/g epi-radicinol and 26 microg/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.