Exploration on the Mildew Conditions of Cladosporium asperulatum CY-H1, a Pathogenic Fungus on Tobacco Leaves

Aims: Mildew poses a significant threat to tobacco industry. This study focuses on a strain of Cladosporium asperulatum isolated from moldy tobacco leaves to investigate its growth under different temperature and humidity conditions, aiming to provide a theoretical basis for local prevention and control strategies against this fungus.

Methodology: Potential fungal strains were obtained from moldy tobacco leaves utilizing isolation techniques and individual colonies were cultured on PDA medium subsequently. Microscopic examination and molecular identification were employed to determine the species of the isolated strains. Isolated strain was initially inoculated with varying spore powder concentrations at water activities of 0.99, 0.95, 0.90, 0.87, 0.83, and 0.77, combined with diverse culture temperatures of 15°C, 20°C, 25°C, 30°C, and 35°C on PDA. The growth of colony area was daily measured by ImageJ software, and spore powder yield was observed after a 7-day incubation period under these specified culture conditions.

Results: (1) colony area of isolated C. asperulatum CY-H1 has a rising trend with increasing culture time at consistent temperatures. Sporulation exhibited an initial increase followed by a decrease, yet overall demonstrated an upward trajectory. The maximum value was attained at a water activity of 0.95. Under identical water activity, escalating temperatures initially augmented colony area until reaching a maximum at 25°C. Similarly, spore production displayed an initial increase followed by a decrease, with the highest production occurring at 25°C. (2) Varied concentrations of initial spore suspension influenced colony growth differently. A high concentration (initially 106 spores/mL) exhibited an earlier growth trend compared to medium (105 spores/mL) and low concentrations (104 spores/mL). (3) C. asperulatum CY-H1 did not thrive under the culture conditions of 35°C, irrespective of the initial inoculation concentration and water activity.

Conclusion: C. asperulatum assumes a crucial role as a predominant mold in tobacco storage environments. Effective prevention of fungal mildew in stored tobacco leaves is achieved by maintaining temperatures exceeding 35°C and sustaining water activity below 0.77. These findings highlight the significance of environmental conditions in controlling mold growth during tobacco storage.