Population of Aspergillus flavus and Fusarium verticillioides and contamination of maize with associated mycotoxins under push-pull cropping system in Siaya County, Western Kenya

Push-pull cropping system is a companion cropping system that effectively controls stemborers, fall armyworm and Striga weed, resulting in increased yield in cereal crops like maize and sorghum. Siaya County is one of the administrative localities where push-pull cropping system has been adopted by smallholder farmers practising mixed cropping. The aim of this study was to assess the population of Aspergillus flavus, Fusarium verticillioides and levels of aflatoxin and fumonisin in maize under push-pull cropping system in Siaya County. A total of 57 maize samples i.e., 27 push-pull and 30 non-push-pull, were collected at harvest between January and February 2017. Ten to 20 maize cobs were collected from standing crop from each farm. Fungi were isolated from ground homogenized maize samples on low strength potato dextrose agar amended with chloramphenicol, streptomycin and tetracycline and identified based on their cultural and morphological characteristics. Levels of aflatoxin and fumonisin were determined from 20g of maize composite samples using EnzymeLinked Immuno-Sorbent Assay (ELISA). Fusarium, Aspergillus and Acremonium spp. were the most prevalent fungal genera in maize samples from both push-pull and non-push-pull cropping systems. The population of F. verticillioides and A. flavus was significantly lower in maize samples from push-pull cropping system. All the samples from push-pull cropping system had aflatoxin levels below the Kenyan threshold (10 parts per billion). The proportion of maize samples with high fumonisin levels above the threshold set by European Commission (1000 ppb) was 10.6%, which was lower in maize from push-pull cropping system. The findings of this study showed that there were significantly lower populations of A. flavus and F. verticillioides and lower levels of aflatoxin and fumonisin from maize samples collected from farms practising push-pull cropping system. These findings imply possibility of a mechanism of control of mycotoxigenic fungi and associated mycotoxins by the push-pull cropping system. The high population of F. verticillioides in maize was an indicator of the risk of further fumonisin production in storage and hence exposure of the toxin to humans and animals.