Effects of Tobacco “Two Black Disease” on Fungal Community Structure in Rhizosphere Soil

Purpose To study the fungal community structure in tobacco rhizosphere soil affected by black shank disease and black root rot disease (referred to as “two black disease”), respectively, and to provide theoretical support for the integrated biological control.

Methods The rhizosphere soils of flue-cured tobacco with serious black shank disease (marked as ZT3) and root black rot disease (marked as ZT5) in Zhaoyang District and Ludian County, Zhaotong City, Yunnan Province were collected, and healthy tobacco rhizosphere soil (marked as ZT2) were collected as control. The structure of fungal community in soil and its influencing factors were compared and analyzed by high-throughput sequencing technology.

Results Compared with ZT2, the fungal richness in the rhizosphere soil of ZT3 and ZT5 was higher, and their relative abundances of harmful fungi, including Olpidiomycota, Mortierella, Colletotrichum, and Rhizoctonia, were increased. The beneficial fungi Linnemannia and Talaromyces played important roles in ZT2, and their relative abundances were significantly decreased in both diseased groups. Compared with ZT2, significant differences were observed in both diseased groups, specifically manifested as increased relative abundances of unclassified_f_Mortierellaceae, Mortierella, Purpureocillium, Olpidiaceae_gen_Incertae_sedis, and Pseudoarthrographis in ZT3, while the relative abundances of harmful fungi Olpidiaster and Alternaria were increased in ZT5. Linnemannia, Talaromyces, Olpidiaceae_gen_Incertae_sedis, Pseudoarthrographis, and Alternaria were the key species significantly affecting inter-group differences. The physicochemical properties of tobacco rhizosphere soil in both diseased groups changed significantly compared with the healthy tobacco rhizosphere soil, with soil pH and organic matter content being the key environmental drivers affecting fungal community distribution differences.

Conclusion The healthy tobacco rhizosphere soil enriches beneficial fungi (Linnemannia and Talaromyces) and suppressed harmful fungi, forming a disease-suppressive microbial community structure. Both black shank disease and black root rot disease lead to the imbalance of the rhizosphere fungal community, which is characterized by a sharp decrease in beneficial bacteria and an increase in harmful bacteria. This study provides a theoretical basis for controlling soil-borne diseases through regulating the rhizosphere microecology.