Occurrence of Aspergillus Species in Groundnut (Arachis hypogaea L.) along the Value Chain in Different Agro-Ecological Zones of Eastern Ethiopia

摘要

Groundnut is an important cash crop for domestic markets as well as for foreign trade in several developing and developed countries. It is also one of the most valuable cash crops in eastern Ethiopia. However, its production is constrained by Aspergillus species, which cause quantitative losses and produce highly toxic and carcinogenic chemical substances known as aflatoxins. A reconnaissance survey was conducted in 2014 cropping season with a research objective to determine the levels of infection of groundnut seed by Aspergillus species along the groundnut value chain in different agro-ecological zones of eastern Ethiopia, including three major groundnut growing areas, namely Babile, Gursum and Fedis Districts of East Hararghe Zone, Oromia Regional State. In this study 210 groundnut seed samples were collected from farmers’ fields, farmers’ stores, market retailers and vendors at Babile, Fedis and Gursum districts in 2014 cropping season, and were tested for seed moisture content using electronic moisture meter. The frequency of Aspergillus species contamination on groundnut seeds was determined using plate counting methods. The seed moisture data showed that the moisture contents of seed samples ranged between 3 and 15%; the lowest was obtained from groundnut seed samples collected from vendors at Babile district and the highest was from farmers’ fields at harvest in Fedis district The proportion of seed contamination by Aspergillus species varied from 30% in seed collected from vendors to 85% in seed samples from farmers’ fields in Babile, Fedis and Gursum districts. Groundnut seed samples collected from farmers’ fields was the first (85%), where as from farmers’ stores had the second highest seed contamination with 80% infection, and groundnut samples collected from that of market retailers had 60% contamination. Five different Aspergillus species were associated with 210 groundnut seed samples along the groundnut value chain actors. Of the several Aspergillus species isolated from the groundnut seed samples, A. flavus and A. niger were the most prevalent mycotoxigenic fungi across the farmers’ fields, farmers’ stores, market retailers and vendors at Babile, Fedis and Gursum districts in the five agro-ecological zones of eastern Ethiopia such as low-land dry (LLD), low-land moist (LLM), mid-land dry (MLD), mid-land moist (MLM), and high-land humid (HLH). The occurrence of these two species ranged from 22.05-49.05% (A. flavus) and 23.83-48.11% (A. niger). Their relative dominance in number of isolates from the total associated fungi was 23 and 22%, respectively. On the other hand, A. parasiticus, A. ochraceus, and A. tamarii occurred rarely. The highest frequencies of occurrence of A. flavus and A. niger were on groundnut seed samples from farmers’ fields in Fedis district in mid-land moist agro-ecological zone and the least was from roasted groundnut seed samples from vendors in Babile, Fedis and Gursum districts in all the five agro-ecological zones. From the present findings, it could be concluded that there was high occurrence of aflatoxigenic fungi along the groundnut value chain actors. Also, the current results imply the urgent need for application of management measures against aflatoxigenic fungi to maintain the quality of groundnut in the various value chain processes and to avert human and animal health risks.