Integrated biological and chemical strategies for sustainable management of Nigrospora coryli-induced tobacco leaf spot

Tobacco (Nicotiana tabacum) leaf spot disease caused by fungal pathogens poses a major threat to crop yield and quality worldwide. Recently, Nigrospora coryli was identified as a novel causal agent of tobacco leaf spot in China, yet its biology, ecological interactions, and management strategies remained largely unexplored. In this study, we systematically characterized N. coryli through growth physiology, environmental adaptability, phyllosphere microbiome profiling, microbial interactions, and fungicide sensitivity assays. The pathogen exhibited robust environmental tolerance, with optimal growth at 28°C and pH 6.0, viability across pH 4–11, and survival at temperatures up to 57°C, while preferring soluble starch and peptone as nutrient sources. High-throughput sequencing revealed disease-associated phyllosphere shifts, including enrichment of Stenotrophomonas and Pseudomonas in symptomatic leaves and the exclusive detection of Nigrospora and Sarocladium in diseased tissues. Functional screening identified multiple antagonistic microbes, with Aspergillus niger MGM reducing lesion size by 87.6% in planta, while Pseudomonas syringae pv. angulata SLB-5-3 exacerbated disease. Among eight commercial fungicides, fludioxonil was the most potent (EC₅₀ = 0.0057 μg/mL), followed by the prochloraz-manganese chloride complex, difenoconazole, and fenaminstrobin. Synergistic interactions were observed in binary mixtures: fludioxonil + difenoconazole (1:4, SR = 1.7360), fludioxonil + fenaminstrobin (1:1, SR = 1.5365), and difenoconazole + fenaminstrobin (1:2, SR = 2.0219). These findings highlight the potential of integrating potent biocontrol agents with synergistic fungicide combinations for sustainable management of N. coryli-induced tobacco leaf spot. This study provides a comprehensive foundation for developing environmentally sound, multifaceted disease control strategies.