Occurrence, mycotoxins and toxicity of Fusarium species from Abelmoschus esculentus and Sesamum indicum seeds

Abstract

  Seeds of two okra accessions and 17 samples of sesame seeds were examined for contamination by Fusarium species. Altogether, 37 Fusarium isolates were obtained from the two crops: 6 isolates from two okra accessions and 31 isolates from 10 sesame samples. The isolates belonged to three species: F. oxysporum, F. semitectum and F. verticillioides. All isolates from okra were identified as F. semitectum while the three species of Fusarium occurred in sesame. Six randomly selected isolates from the two crops were screened for their ability to produce mycotoxins in ofada rice culture and the crude extracts of the mycotoxins were tested on week-old Clarias gariepinus fingerlings. Six metabolites were produced by the isolates in ofada rice: equisetin (EQUS), fumonisin B1 (FB₁), FB₂, methyl-equisetin (M-EQUS), moniliformin (MON) and zearalenone (ZEA). All isolates produced EQUS at concentrations ranging 454-29,983 μg/kg. All isolates except F. semitectum BUFC 041 and F. oxysporum BUFC 024 produced MON and ZEA, while three F. semitectum isolates produced M-EQUS. Only F. verticillioides isolates produced fumonisins. There was evidence of variation within species obtained from both crops based on toxin profile and level of toxin produced. The culture extracts of all isolates induced 100% lethality to C. gariepinus fingerlings except for extracts of F. semitectum BUFC 041 which killed only 62.2% of the fingerlings, possibly due to the absence of MON. Our data suggest that okra and sesame may be potential sources of toxigenic Fusarium.