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.
Highlights
On a global scale, the contamination of agricultural products by Fusarium spp. is common and has been reported both in cold and warm ecologies (Allen and Kochman, 2001; Nganje et al, 2001; Poppenberger et al, 2003; Davis et al, 2006; Lemmens et al, 2005), suggesting that fungi in this genus can grow in a wide array of natural substrates
relative index frequency (RIF) (%) 6.4 15.4 18.8 25.2 18.8 5.4 a: data were back transformed after analysis of variance; b: Total isolation figures based on 36 samples and 580 pieces of plated cassava chips in each location
number of samples contaminated (NSC): Number of samples contaminated; total number of isolates (TNIL): Total number of isolates associated with each Fusarium species per location; RIF: relative index of the fungus: This parameter was calculated as the ratio of the number of cassava chips pieces contaminated by each Fusarium species obtained per location over the total number of Fusarium isolates, that is, 137 isolates in Yaoundé and 131 in Ebolowa
Summary
The contamination of agricultural products by Fusarium spp. is common and has been reported both in cold and warm ecologies (Allen and Kochman, 2001; Nganje et al, 2001; Poppenberger et al, 2003; Davis et al, 2006; Lemmens et al, 2005), suggesting that fungi in this genus can grow in a wide array of natural substrates. One of the most significant aspects of this genus is related to its role as a plant pathogen for a large range of botanical species. To this effect, fungi in the genus Fusarium have been reported to cause damping-off and root rot of young conifer seedlings (Jane et al, 2006). In palm trees (Elaeis guineensis), banana (Musa spp.), cotton (Gossypium spp.) and several other crops of agricultural importance, they cause wilts, whereas pre- and post-emergence blights are often reported in cereals and other graminae (Marasas et al, 1984; Davis et al, 2006). The threat connected with Fusarium spp. could be viewed in a multifaceted way: besides their implication in yield losses of agricultural crops, their role as deteriogens and significant mycotoxin producers in several food commodities has been evidenced in some studies (Kokkonen et al, 2010; Rubella and Kistler, 2005; Moss, 2002; Msikita et al, 1996)
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