Effects of harvest maturity on microbial community composition, enzyme activities, and phenolic acids in upper tobacco leaves after curing

The upper leaves of flue-cured tobacco are an important raw material for cigarette production, and harvest maturity is one of the important factors affecting tobacco leaf quality.This study used Illumina MiSeq high-throughput sequencing, conventional physicochemical assays, and gas chromatographymass spectrometry analysis to investigate the effects of different harvest maturities on the microbial community composition, enzyme activities, phenolic acid contents, and main aroma and chemical components of tobacco leaves after curing.The results showed that Proteobacteria, Actinobacteria, and Ascomycota were the dominant bacteria and fungi in the cured tobacco leaf samples.At the genus level, Unclassified_k_Fungi was the dominant fungal genus in the conventional harvesting treatment; Altemaria, Leptosphaerulina, and Stagonosporopsis were the dominant fungal genera in the 7-d delayed harvesting treatment, Aspergillus, Symmetrospora, and Filobasidium were the dominant bacterial and fungal genera in the 14-d delayed harvesting treatment.Correlation analysis revealed that the dominant bacterial and fungal communities at the genus level showed a high correlation with the enzyme activities, phenolic acid contents, aroma component contents, and chemical component contents in the tobacco leaves.For example, the content of the neutral aroma substance neophytadiene was significantly positively correlated with Aspergillus, Symmetrospora, and Curtobacterium, while the nicotine content was extremely significantly negatively correlated with Aspergillus, Symmetrospora, and Pseudomonas and significantly positively correlated with Massilia.Finally, we found that the enzyme activities, phenolic acid contents, and aroma component contents in the tobacco leaves in the 14-d delayed harvesting treatment were higher, the nicotine content was the lowest, and the chemical composition was more consistent.In the microbial community, Aspergillus, Symmetrospora, and Filobasidium promoted the improvement of tobacco leaf quality to a certain extent.Our study evaluated the effect of harvest maturity on tobacco leaf quality from multiple perspectives and emphasized the important role of the endophytic microbial communities in the development of tobacco leaf quality.The objective is to offer scientific support for the ensuing modification of the harvest period for flue-cured tobacco and the use of the microbial community to enhance the quality of tobacco leaves.K e y w o