Effect of agronomic practices and weather conditions on mycotoxins in maize: a case study of subsistence farming households in Zimbabwe

Maize is susceptible to many mycotoxigenic fungi and mycotoxins, being prone to Fusarium spp. infection and subsequent mycotoxin contamination. Fumonisin B-1 (FB1) is the predominant mycotoxin in Zimbabwean subsistence-grown maize and results of mycotoxin analyses indicated FB1 to be significantly higher compared to other mycotoxins. To fully elucidate maize agronomic practices influencing FB1 contamination of maize produced by Zimbabwean subsistence farming populations, an investigative field survey was conducted in the selected provinces of Mashonaland West and Manicaland. Agronomic data and associated climatic data were collected during the 2014/2015 agricultural season. A total of 158 maize samples were collected from households' harvest, three months and six months post-harvest. Analysis and quantification of mycotoxin contamination in the maize samples was performed using a validated multi-mycotoxin analysis method with a scope of 23 mycotoxins. Maize was mainly contaminated by FB1. There was low mycotoxin co-occurrence in Zimbabwean maize, which was typically of Fusarium toxins. FB1 occurred in 23, 47 and 47% of samples at harvest, three and six months post-harvest, respectively. The corresponding means of positive samples were 609, 597 and 289 pg/kg, respectively. Regarding fumonisins, the choice of seed and fertiliser application were significant in modulating FB1 contamination. There was no significant difference in mean FB1 contamination during post-harvest maize storage. Daily temperatures were key factors influencing FB1 incidence and levels. High temperatures were associated with high FB1 contamination particularly at the flowering stage of maize. Rainfall was positively correlated with FB1 contamination. Good agricultural practices attributed to low FB1 contamination in maize pre-harvest. Post-harvest practices such as preserving seed integrity by preventing pest infestation using grain protection chemicals are important in achieving lower mycotoxin contamination and in particular, FB1, in maize grain.