Impact of mancozeb on tobacco leaf phyllosphere: shifts in microbial communities and functional dynamics

Mancozeb is an extensively used broad-spectrum fungicide, predominantly applied as a foliar spray in tobacco cultivation to control fungal pathogens. However, its effects on phyllosphere microorganisms remain largely unexplored. Therefore, we carefully evaluated the impact of mancozeb-induced stress on the tobacco phyllosphere microbiota at four time points: before application, and 5, 10, and 15-days post-application. The data revealed that mancozeb foliar application significantly altered the fungal community composition and had notable effects on native bacterial communities within the tobacco phyllosphere. Moreover, mancozeb exhibited a prophylactic effect in non-infected plants; the abundance of Ascomycota increased in infected samples but declined in healthy samples after mancozeb application. The invasion by Alternaria alternata, a pathogenic fungus responsible for tobacco brown spot, significantly affected both fungal and bacterial community structures and alpha diversity. Mancozeb application reduced fungal alpha diversity while augmenting bacterial diversity. Beta diversity differences between pre-treatment and post-treatment samples in both diseased and healthy leaves were diminished by mancozeb. Notably, mancozeb had a greater effect on restructuring the fungal community compared to the bacterial community. Following mancozeb treatment, the proportion of pathotroph-saprotroph-symbiotroph fungi increased, while it decreased in untreated groups. Succinctly, mancozeb had a more pronounced effect on the phyllosphere microbiota than A. alternata. These findings provide profound insights into the ecological impacts of mancozeb and A. alternata on the microbiota inhabiting the tobacco leaf phyllosphere.