Response of microbial communities on tobacco leaf phyllosphere exposed to the broad-spectrum fungicide mancozeb

Abstract Mancozeb is a broad-spectrum fungicide frequently applied as foliar spray in tobacco fields to control fungal diseases. The response of tobacco phyllosphere microbiota toward mancozeb stress was assessed using high-throughput sequencing at four time points: before spraying, and 5, 10 and 15 days after fungicide application. Results showed that the foliar application of mancozeb had moderate but significant effect on fungal community composition of tobacco phyllosphere. In all samples, Ascomycota and Proteobacteria were the most abundant phyla, and Alternaria was the dominant fungal genus. Moreover, mancozeb significantly affected indigenous bacterial communities of tobacco leaves; Pseudomonas was predominant in untreated and before mancozeb treatment groups. An increase in abundance of Ascomycota was observed in diseased samples while healthy samples showed a reduction after mancozeb application. Increased abundance of Proteobacteria was observed in treated samples, which was much higher in diseased than in healthy groups. Increased abundance of Alternaria was observed until 15 days after mancozeb application, while successive reduction in abundance of the genus was observed in the untreated healthy group. Fungal alpha diversity indices in untreated groups increased from the first collection stage to the third, whereas a decrease in four fungal indices was observed at 5 d after mancozeb exposure. A significant difference between treated and untreated groups was observed in terms of fungal richness indices of similar samples from the previous stage. Bacterial diversity indices increased after mancozeb application while they decreased in untreated samples. Mancozeb was effective in altering the fungal community structure rather than bacterial community structure. After mancozeb treatment, the proportion of pathotroph-saprotroph-symbiotroph increased while it decreased in the untreated groups. The overall findings revealed ecological implications of the effects of mancozeb on tobacco phyllosphere microbiome; our results would provide a theoretical basis for future studies on microecological protection of phyllosphere.