Effect of temperature and incubation period on production of toxic metabolites by Alternaria alternata and Alternaria radicina.

The production of toxic metabolites by four isolates of Alternaria radicina and two isolates of A. alternata in rice grains and carrot discs at 1, 10 and 20ºC was investigated. Incubation lasted 21 and 35 days or 14 and 28 days for rice grains and carrot discs, respectively. Accumulation of toxins in inoculated carrot roots stored for 24 weeks and in inoculated dried carrots stored for 48 weeks was also determined. It was found that A. radicina produced radicinin (RAD) and epi-radicinol (epi-ROH), whereas tenuazonic acid (TeA), altertoxin I (ATX I), alternariol (AOH) and alternariol methyl ether (AME) were produced by A. alternata. Although the isolates tested were capable of producing toxins in rice grains at 1ºC, none of them was detected in carrot discs. Accumulation of epi-ROH was observed in carrot roots stored for 24 weeks, whereas decreased amounts of RAD and epi-ROH were observed in dried carrots stored for 48 weeks. No A. alternata toxins were detected in stored carrot roots, whereas trace amounts of AOH were recorded in dried carrots after 32 and 48 weeks of storage.