Fusarium verticillioides and microbiome responses in maize ears driven by chemical and biological fungicide treatments

Yield losses caused by fungal pathogens are an aggravating problem in global crop cultivation. Fusarim verticillioides causes ear rot and produces a specific fumonisin type mycotoxin that causes qualitative and quantitative losses in maize production. In tropical agriculture, high yielding maize is only assured through foliar protection using fungicides due to the high pathogen pressure. However, the use of chemical fungicides alone does not guarantee the protection of grains Recently, a co-application of fungicides with a Bacillus subtilis strain was identified as a promising strategy to ensure better grain quality. We have employed an integrative approach to assess changes in the microbiome of maize subjected to the novel treatment and contrasted it to conventional treatments. This was complemented with molecular and analytical monitoring of the pathogen and mycotoxin levels. Two sampling times were analyzed (10 days after application of treatments and at harvest) and two maize fields were implemented to account for regional differences. A comparative analysis indicated a treatment-specific occurrence of bacterial and fungal OTUs in the plants. Both, pesticide as well as combined treatments were characterized by the occurrence of unique OTUs that were not present in the controls. Treatments resulted in up to 22 introduced OTUs. The lowest values of total fumonisinals were observed in the combined treatment (field 1 = 0.29 ppm and field 2 = 0.77 ppm) while the conventional pesticide treatment had the highest values (field 1 = 3.84 ppm and field 2 = 10.02 ppm). This provided strong evidence that conventional treatments of maize with fungicides can promote mycotoxin levels in grains. Moreover, we could show that alternative treatments with implementation of biological control agents not only significantly decrease mycotoxin levels but are also followed by distinct microbiome responses that might have implications for the plant's susceptibility.