Natural occurrence of Fusarium species and fumonisins in stored cassava chips

Abstract

Cassava chips are transformed products obtained following the fermentation and drying of cassava fresh roots. Once produced, chips can be stored for more than 180 days in conditions conducive for the development of toxigenic moulds. In this study, the incidence of Fusarium spp. is assessed from a set of 72 home-stored samples of cassava chips collected from farmers, during a 2-month monitoring survey period. Results from this survey enabled the recovery of 298 isolates of Fusarium spp. The Fusarium taxa detected included: Fusarium chlamydosporum, Fusarium equiseti, Fusarium verticillioides, Fusarium oxysporum, Fusarium pallidoroseum and Fusarium solani. F. oxysporum was associated with the highest level of isolation frequency (25%), whereas F. solani isolated was scanty (5%). Their level of recovery was increasingly important as the moisture content of samples increased and/or the product was stored for longer periods. Specific associations were observed to exist between the most frequently isolated Fusarium spp. The level of fumonisins further assessed showed that only 5 samples hosted this mycotoxin at concentration levels ranging between 0.22 and 1.7 mg/kg. Among the parameters used to assess its incidence, only storage duration showed significant (P<0.05) relationships with fumonisins. The occurrence of fumonisins as natural contaminants of cassava-based products is reported here for the first time. This study shows that no known fumonisin producing-Fusarium species was related to toxin occurrence in the samples collected. It can be hypothesized that any species of Fusarium infesting the samples studied could have the potential capability of producing the toxin as a result of a possible horizontal transfer of functional fumonisin gene clusters from an ancestral gene. Consequently, the present study suggests both investigations on genes responsible for plausible fumonisin formation associated with the Fusarium spp. identified from the samples collected as well as the various factors allowing their expression. Key words: Fusarium, fumonisins, cassava chips, Cameroon, rural areas.