Toxin production by Fusarium species from sugar beets and natural occurrence of zearalenone in beets and beet fibers

Abstract

Fifty-five Fusarium isolates belonging to nine species were collected from fungus-invaded tissue of stored sugar beets and identified as F. acuminatum (11 isolates), F. avenaceum (1 isolate), F. culmorum (1 isolate), F. equiseti (23 isolates), F. graminearum (4 isolates), F. oxysporum (1 isolate), F. solani (4 isolates), F. sporotrichioides (7 isolates), and F. subglutinans (2 isolates). All isolates were cultured on autoclaved rice grains and assayed for toxicity by feeding weanling female rats the ground-rice cultures of the isolates in a 50% mixture with a regular diet for 5 days. Fifty-eight percent of the isolates were acutely toxic to rats, 26% caused hematuria, 18% caused hemorrhages, and 29% caused uterine enlargement. In most cases, toxicity could not be accounted for by the known toxins found. The following mycotoxins were found in extracts of the rice cultures: zearalenone (22 to 6,282 μg/g), chlamydosporol (HM-8) (68 to 4,708 μg/g), moniliformin (45 to 400 μg/g), deoxynivalenol (10 to 34 μg/g), 15-acetyldeoxynivalenol (5 to 10 μg/g), diacetoxyscirpenol (22 to 63 μg/g), monoacetoxyscirpenol (21 to 26 μg/g), scirpenetriol (24 μg/g), T-2 toxin (4 to 425 μg/g), HT-2 toxin (2 to 284 μg/g), neosolaniol (2 to 250 μg/g), and T-2 tetraol (4 to 12 μg/g). F. equiseti was the predominant species found on visibly molded beets in the field. Six of 25 moldy sugar beet root samples collected in the field contained zearalenone in concentrations ranging between 12 and 391 ng/g, whereas 10 samples from commercial stockpiles were negative for zearalenone. Zearalenone was detected in 31 of 75 sugar beet fiber samples (13 to 4,650 ng/g). Three of 31 samples contained cis-zearalenone (1 to 8 ng/g), and two contained trace amounts of trans-α- and trans-β-zearalenol. This is the first report of zearalenone in sugar beet roots and fiber.