Impact of benzoic acid and 2,2'-methylenebis (6-tert-butyl-4-methylphenol) on the metabolome of flue-cured tobacco and rhizosphere microbial communities: implications for continuous cropping obstacles

Background and aimsThis study examined the effects of benzoic acid (BA) and 2,2'-methylenebis (6-tert-butyl-4-methylphenol) (ME), compounds present in the root exudates of continuously cropped flue-cured tobacco, on the germination, seedling growth, and development of flue-cured tobacco. The primary objective of this study was to enhance the understanding of the underlying mechanisms of continuous cropping obstacles in flue-cured tobacco. Additionally, this study aimed to provide theoretical insights for managing continuous cropping obstacles not only in flue-cured tobacco but also in other plants.MethodsThe mechanisms governing the function of BA and ME were investigated by analyzing leaf transcriptomes and metabolomes and soil microbial communities.ResultsBA and ME significantly inhibited flue-cured tobacco seed germination, albeit with distinct concentration-dependent effects. Both compounds induced senescence and necrosis in tobacco leaves, primarily by suppressing seed germination and compromising the activity of the antioxidant system. Transcriptomic analysis revealed robust responses of photosynthesis and secondary metabolism to BA and ME, with a particular emphasis on flavonoid biosynthesis and alkaloid enrichment. Moreover, BA and ME significantly affected the richness and diversity of rhizosphere microorganisms, resulting in notable changes in microbial community structure and composition. Specifically, Actinobacteriota, Cyanobactreia, and Mucoromycot exhibited pronounced responses to flavonoid biosynthesis, particularly dihydromyricetin, while Proteobacteria, Cyanobacteria, and Mucoromycot strongly responded to alkaloid enrichment, especially with respect to tabersonine.ConclusionBA and ME induced senescence and necrosis in tobacco leaves, with dihydromyricetin in flavonoid biosynthesis and tabersonine in alkaloid enrichment having notable impacts on the rhizosphere microbial community of flue-cured tobacco.