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Biological characterization and in vitro fungicide screening of a new causal agent of walnut leaf spot in Guizhou Province, China

Summary

Researchers in China discovered that a fungus called Didymella segeticola is causing a serious leaf spot disease in walnut trees in Guizhou Province. They studied how this fungus grows under different conditions and tested 20 different fungicides to find the most effective treatments. Two fungicides—difenoconazole and tetramycin—were found to be particularly effective at stopping the fungus, offering practical solutions for protecting walnut crops.

Background

Walnut leaf spot disease is a serious threat to walnut cultivation in Guizhou Province, China, causing significant economic losses. In July 2022, a severe outbreak of walnut leaf spot was observed in Hezhang County, with disease incidence rates of 65-75%. The causal agent needed to be identified and characterized for effective disease management.

Objective

To identify the causal agent of walnut leaf spot disease in Hezhang County, Guizhou Province through morphological and molecular characterization; to determine the biological characteristics of the pathogen including effects of temperature, light, carbon/nitrogen sources, and humidity; and to screen fungicides for effective control of the disease.

Results

The causal agent was identified as Didymella segeticola, marking the first report of this pathogen on walnuts worldwide. Optimal conditions for pathogen growth were: 20°C for mycelial growth, 6:18 h photoperiod (light:dark) for spore production, maltose as best carbon source, and beef extract as best nitrogen source. Among 20 screened fungicides, difenoconazole showed the best inhibition with EC50 of 0.0007 μg/mL, followed by tetramycin with EC50 of 0.0009 μg/mL.

Conclusion

This study provides the first comprehensive characterization of D. segeticola as a walnut leaf spot pathogen in China and elucidates its biological preferences for future management strategies. The identification of effective fungicides, particularly difenoconazole and tetramycin, provides practical tools for disease control. These findings establish a foundation for sustainable and effective management of walnut leaf spot disease in Guizhou Province.
  • Published in:Frontiers in Microbiology,
  • Study Type:Experimental Study,
  • Source: PMID: 39450284, DOI: 10.3389/fmicb.2024.1439487
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