Abstract
A Myriad of biotic and abiotic factors inevitably affects the growth and production of tobacco (Nicotiana tabacum L.), which is a model crop and sought-after worldwide for its foliage. Among the various impacts the level of disease severity poses on plants, the influence on the dynamics of phyllospheric microbial diversity is of utmost importance. In China, recurring reports of a phyto-pathogen, Didymella segeticola, a causal agent of tobacco leaf spot, accentuate the need for its in-depth investigation. Here, a high-throughput sequencing technique, IonS5TMXL was employed to analyze tobacco leaves infected by D. segeticola at different disease severity levels, ranging from T1G (least disease index) to T4G (highest disease index), in an attempt to explore the composition and diversity of phyllospheric microbiota. In all healthy and diseased tobacco leaves, the most dominant fungal phylum was Ascomycota with a high prevalence of genus Didymella, followed by Boeremia, Meyerozyma and Alternaria, whereas in the case of bacterial phyla, Proteobacteria was prominent with Pseudomonas being a predominant genus, followed by Pantoea. The relative abundance of fungi, i.e., Didymella and Boeremia (Ascomycota) and bacteria, i.e., Pseudomonas and Pantoea (Proteobacteria) were higher in diseased groups compared to healthy groups. Healthy tissues exhibited relatively rich and diverse fungal communities in contrast with diseased groups. The infection of D. segeticola had a complex and significant effect on fungal as well as bacterial alpha diversity. FUNGuild analysis indicated that the relative abundance of pathotrophs and saprotrophs in diseased tissues proportionally increased with disease severity. PICRUSt analysis of diseased tissues indicated that the relative abundance of bacterial cell motility and membrane transport-related gene sequences elevated with an increase in disease severity from T1G to T3G and then tended to decrease at T4G. Conclusively, the current study shows the typical characteristics of the tobacco leaf microbiome and provides insights into the distinct microbiome shifts on tobacco leaves infected by D. segeticola.
Highlights
Given its commercial importance, tobacco is cultivated extensively all across the globe and categorized as a non-food agricultural crop, mainly consumed as cigarettes, cigars, snuff, etc. (Liu et al, 2017)
The ITS region of rDNA and V3-V4 hypervariable regions of the 16S rRNA were amplified to detect the dynamics of microbial diversity to different disease severity levels of D. segeticola infection, which manifests as leaf spots in tobacco
The dynamics of fungal operational taxonomic units (OTUs) were opposite to the bacterial OTUs with the disease severity advancement, which might be related to the factor of leaf nutrition leading toward the competitive relationship between microorganisms
Summary
Tobacco is cultivated extensively all across the globe and categorized as a non-food agricultural crop, mainly consumed as cigarettes, cigars, snuff, etc. (Liu et al, 2017). Its leaves are susceptible to damage by fungal, bacterial, and viral pathogens during growth and development. Morphological deformations, such as leaf spots induced by microflora, could result in heavy economical losses (Zhu, 2002). Didymella segeticola was first reported by Chen et al (2015), while its pathological characteristics were explained by Zhao et al (2018) as being a causal agent of leaf spot on tea plants in China. A study carried out by Guo et al (2020) revealed that D. segeticola causes leaf spot disease in tobacco plants as well. Diseased tobacco leaves affected by this pathogen exhibit sandy beige-colored lesions with dark-brown edges, circular, elliptical, or irregular in shape, usually surrounded by yellow halos (Guo et al, 2020)
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