Prevalence of Aflatoxigenic Aspergillus Spp and Groundnut Resistance in Zimbabwe

Abstract

Aspergillus species are major causes of pre- and post-harvest spoilage of groundnut. During 2013, the presence of aflatoxigenic Aspergillus species from groundnut sold from markets in Hwange, Gwanda, Umzingwane, Insiza, Beitbridge and Matobo markets in Zimbabwe were assessed. These represent areas of high groundnut production which experience recurrent drought, a major contributory factor in Aspergillus occurrence. The samples were separately analyzed for the presence of aflatoxigenic species Aspergillus flavus and A. parasiticus. The isolation of these species was carried out using direct plating methods and their identification based on macroscopic and microscopic criteria. A total of seven Aspergillus species of and other microbes were isolated from the collected namely A. flavus, A. niger, A. oryzae, A. parasiticus, A. terreus, A. tamari, A. nidullani and Rhizopus spp. However, there were variations in the degree of occurrence of each of the two species in each of these samples. The important isolates of A. flavus and A. parasiticus that cause aflatoxins were inoculated in vitro on eleven groundnut genotypes obtained from the Crop Breeding Institute, Zimbabwe and Seed-Co Private Limited for their response to seed colonisation and infection. No variety was immune to the two Aspergillus spp, however, variety CG7 and Mwenje together with IIanda and Nyanda had a relatively longer incubation period for A. flavus and A. parasiticus respectively. During the seed resistance status test only three genotypes (Falcon, CG 7 and Nyanda) were found to be moderately resistant to infection by A. flavus and the remaining eight genotypes (Makulu Red, Tern, Teal, Mwenje, SC Orion, Flamingo and SC GV 00004) were susceptible in the laboratory tests. All the varieties succumbed to A. parasiticus during the seed resistance test. Overall, these results show the presence of aflatoxigenic Aspergillus spp in groundnuts in some Zimbabwean markets. Moreover, there is limited genetic resistance in groundnut to the A. flavus and A. parasiticus in the available genotypes implying great consumer risk.