Fungal Composition and Diversity of the Tobacco Leaf Phyllosphere during Curing of Leaves

Abstract Background: Rhizopus oryzae causes tobacco pole rot in China during tobacco flue-curing. Flue-curing is a post-harvest process done to prepare tobacco leaves and involves three different stages: the yellowing stage has the lowest temperatures and highest humidity, then the color-fixing stage has higher temperatures and medium humidity, and finally the stem-drying stage has the highest temperatures and lowest humidity.Results: In this study, fungal culturing and IonS5TMXL high-throughput sequencing techniques were used to reveal the fungal community of the petioles and lamina of tobacco leaves infected with pole rot during flue-curing. A total of 108 fungal isolates belonging to 5 genera and 10 species were isolated on media. The most common fungi isolated was R. oryzae, most often found equally on petioles and laminas in the color-fixing stage, followed by saprotrophs, mostly Aspergillus fumigatus and Aspergillus flavus. High-throughput sequencing revealed saprotrophs, Alternaria being the most abundant genus, followed by Phoma, Cercospora and Aspergillus, whereas Rhizopus was the tenth most abundant genus, which was mostly found on petioles at the yellowing stage. Both culturable fungal diversity and fungal sequence diversity was higher at stem-drying stage than the yellowing and color-fixing stages, and diversity was higher with leaf lamina than petioles revealing that the changes in fungal composition and diversity during the curing process were similar with both methods.Conclusions: A better understanding of the saprotrophic fungi during curing of leaves with pole rot could result in the identification of highly competitive saproptrophs that may act as potential biocontrol agents of tobacco pole rot.