In vitro production of trichothecenes and zearalenone by Fusarium isolates from equatorial barley ( Hordeum vulgare l.) grown in Kenya

摘要

Fusarium head blight (scab) is a devastating disease of wheat and barley throughout the world. The disease has been reported worldwide wherever cereals are grown, cutting across diverse ecological and geographical distribution. In addition to being pathogenic to plants, which may cause severe crop yield reduction, many Fusarium species are also capable of producing mycotoxins deleterious to human health as secondary metabolites. Fusarium toxins are commonly detected in wheat, barley,maize, rice and beer. Traditionally malted barley (Hordeum vulgare L.) is the principal ingredient in clear beer and Fusarium toxins incidences are of major concern. Moreover, the spent grain from the brewing industry is used as feed and presence of mycotoxins can lead to harmful effects on domestic animals and also find a way into the human food chain. Studies carried out in Kenya have revealed presence of various Fusarium species with ability to produce mycotoxins and presence of Fusarium toxins in wheat and maize and beer. Based on the ubiquitous nature of Fusarium mold and the fact that barley production takes place in maize and wheatgrowing areas, this study set out to investigate the occurrence of Fusarium molds in Equatorial barley grown in Kenya and the ability of the isolates to produce selected mycotoxins. Grain samples were obtained from newly delivered barley lots originating from two regions and stored grain awaiting malting after break of dormancy from Kenya Maltings Ltd., Nairobi. The Fusarium isolates were identified to species level based on cultural and morphological characteristics. Additionally, they were screened in-vitro on rice cultures for their ability to produce Type A trichothecenes (T–2 toxin, HT–2 toxin, Diacetoxyscirpenol), Type B trichothecenes (deoxynivalenol and nivalenol) and Zearalenone. Samples from all sources were contaminated with Fusarium, but at varying magnitudes - 50%, 33.3% and 25% for barley kernels originating from Timau, Olchoro and in-storage grain with no common history of origin, respectively. The distribution of the species showed some regional specificity. F. graminearum and F. poae predominated in kernels sourced from Olchoro region. All strains of F. graminearum produced both deoxynivalenol and zearalenone. F. poae strains and F. chlamydosporum did not produce detectable amounts of the screened mycotoxins. However, two inconclusively identified isolatesof Fusarium spp. isolated from Timau samples produced deoxynivalenol only. The study revealed that a number of toxigenic Fusarium spp. do occur in Equatorial barley grown in Kenya.