Identification of Botrytis cinerea as a Walnut Fruit Rot Pathogen, and Its Biocontrol by Trichoderma

Walnut (Juglans regia L.) fruit rot significantly impacts yield and quality, yet the pathogens responsible for it remain insufficiently characterized. In this study, we identified several fungi associated with the disease and characterized their morphology and physiology. Pathogenicity tests at two developmental stages of the walnut fruit were performed for the newly described pathogen. Among the Botrytis, Alternaria, and Penicillium species, Botrytis cinerea sensu lato stands out as a newly identified pathogen of the cultivated walnut. Growth assessments revealed variability in B. cinerea strains, with consistent patterns found across different temperatures. Pathogenicity of the isolated B. cinerea strains differed: one strain caused husk necrosis, three strains caused kernel necrosis in younger fruits, while two strains induced kernel necrosis in the later developmental stages. Additionally, we evaluated the biocontrol potential of Trichoderma strains against B. cinerea and demonstrated their efficiency in suppressing each isolated B. cinerea strain (76–100% inhibition), highlighting their potential in sustainable disease management in walnut production.