Efficacy of selected fungicides on fungi isolated from mycotoxin contaminated maize in Kenya

Abstract

Contamination of maize by fungi represents significant health and economic problems in developing countries as well as the developed world. Fungicides are used to control plant fungal infections in fruits and vegetables but can be useful in controlling fungal infestation of maize in the field. This study was carried out to determine the in vitro efficacy of four fungicides on fungi isolated from mycotoxin contaminated maize from different regions in Kenya. A total of 138 maize samples which were part of the study KEMRI-SSC 2151 that tested positive for aflatoxin and fumonisins were subjected to mycological analysis in this study. The samples were collected from Machakos, Nairobi, Mombasa, Kitale and Kisumu. The fungicides Milraz, Antracol, Mistress and Victory were prepared according to the manufacturer’s instructions and applied on four maize kernels from each sample before direct plating on Sabourauds dextrose agar (SDA). Untreated maize kernels from each sample were also inoculated on SDA concurrently as controls. The plates were incubated at 30oC for 72 hours after which fungal growth on the kernels was examined and scored in the range of 0 to 100% infestation. Percentage germination of maize kernels on the culture plates was also scored in the range of 0 to 100%. Fungi growing on the maize kernels were identified using macroscopic and microscopic features. The activity of the test fungicides on pure fungal isolates was determined by disk diffusion method. Twenty microlitres of each diluted fungicide was impregnated on 6 mm disks and placed aseptically at the centre of the culture in three replicates before incubation at 30oC for 72 hours. Zone of inhibition on the disks was measured to the nearest millimeter. Pearson correlation analysis was used to analyze the effect of the test fungicides on maize germination. The mycotoxin positive maize samples were significantly infested by fungi of the genera Aspergillus, Fusarium, and Penicillium. There was a significant difference (p<0.05) in fungal infestation per region where Mombasa had the lowest infestation of 72.5% while those from Nairobi had the highest infestation of 99.1%. There was a significant inhibition [p<0.05 (0.00)] of fungal growth on the treated maize kernels compared to the untreated. Twenty six percent and 34% of mycotoxin contaminated maize samples treated with Mistress and Victory fungicides respectively were not xvi infested, while those treated with Milraz and Antracol were 10% and 14%respectively. Thirty one isolates were found to be resistant to more than one of the test fungicides. There was a significant positive correlation [(R2=0.054, p<0.05)] between germination and fungicide treated maize kernels. This work has demonstrated the potential use of the test fungicides for the control potentially toxigenic fungi affecting maize. The study also underscores the diversity and existence of fungicide resistant fungi in mycotoxin contaminated maize. Field experiments should be conducted to ascertain the field efficacy of the four fungicides as well as the extent of resistance to other fungicides that could impact the use of related antifungal drugs used clinical settings for treatment of fungal infections.