Tobacco leaf spot diseases, caused by diverse fungal and bacterial pathogens such as Alternaria alternata, Rhizoctonia solani, and Corynespora cassiicola, threaten tobacco production in China. While Bacillus amyloliquefaciens is widely used as a biocontrol agent, its impact on non‑target phyllosphere microorganisms has remained largely unexplored.
A team led by Professor Wang Hancheng from Guizhou Academy of Tobacco Science and Professor Li Fei from Guizhou Normal University systematically evaluated the antagonistic spectrum of B. amyloliquefaciens X60 and its ecological effects on tobacco phyllosphere microbial communities. Their findings were published in Acta Microbiologica Sinica on March 31, 2026.
The strain, previously shown to inhibit Ralstonia solanacearum, exhibited potent antagonistic activity against a broad range of phyllosphere microorganisms. In vitro assays tested X60 against 20 pathogenic fungi, 15 non‑pathogenic fungi, 2 pathogenic bacteria, and 15 non‑pathogenic bacteria. X60 showed strong inhibition (60%–80%) against 13 pathogenic fungi, including Rhizopus oryzae, Colletotrichum fructicola, three Rhizoctonia solani groups, Cercospora nicotianae, Corynespora cassiicola, and Phytophthora nicotianae, among others. It also strongly inhibited 12 non‑pathogenic fungi. For bacteria, inhibition zones exceeded 20 mm against Pseudomonas syringae pv. tabaci (33 mm) and pv. angulata (30 mm), as well as against seven non‑pathogenic bacterial species.
In field trials, X60 suspension (1×10⁷ CFU/mL) was applied to tobacco leaves. Ten days later, the strain achieved 52.35% control efficacy against leaf spot diseases.
To understand ecological impacts, the team performed Illumina amplicon sequencing of bacterial and fungal communities in healthy and diseased leaves before treatment and at 1 and 10 days post‑application. The analysis revealed that X60 rapidly suppressed key pathogens. In diseased tissues, Verticillium abundance dropped from 27.44% to 0.74% at day 1 and remained at 0.53% at day 10. Overall, phytopathogenic fungal relative abundance fell from 44.87% to 6.71%.
"Bacillus amyloliquefaciens X60 possesses a broad antimicrobial spectrum and exerts strong antagonistic activity against 25 fungal and 9 bacterial species colonizing the tobacco phyllosphere," said Professor Wang. "Under field conditions, the strain provided 52.35% control and significantly reduced phytopathogen abundance, demonstrating its potential as a biocontrol agent."
The researchers observed succession among opportunistic pathogens. While Plectosphaerella decreased from 17.04% to 5.76% at day 1, it rebounded to 17.28% by day 10; Cumuliphoma was suppressed from 1.01% to 0.25% initially but surged to 27.69% at day 10, suggesting that eliminating dominant competitors may allow secondary pathogens to proliferate. However, core phyllosphere taxa—Pantoea (dominant bacteria) and Sampaiozyma (dominant fungi)—remained stable throughout, indicating good environmental compatibility.
"The application of X60 did not disrupt the stability of core phyllosphere microbial taxa," Professor Wang noted. "These findings provide a microecological basis for optimizing biocontrol strategies and integrating biological‑chemical synergistic systems."
The researchers suggest shortening the application interval to seven days to prevent secondary pathogen emergence.
ACTA MICROBIOLOGICA SINICA
Antagonistic activity of Bacillus amyloliquefaciens X60 against tobacco phyllosphere microorganisms and its impact on phyllosphere microbial community structure
4-Jul-2026