Identification and growth-promoting effect of Paecilomyces lilacinus a biocontrol fungi for walnut rot disease

Cytospora chrysosperma is the primary pathogen responsible for walnut rot disease, affecting a wide variety of hosts. Currently, chemical agents, particularly agricultural Fungicides, are commonly utilized for the prevention and management of walnut rot. However, this practice has led to the development of drug-resistant pathogens, complicating disease control efforts. This study aimed to propose a safer and more efficient biocontrol strategy for combating walnut rot disease. The research focused on targeting C. chrysosperma, and through cross-confrontation methods, an antagonistic strain named Paecilomyces lilacinus 5-38 was isolated from walnut rhizosphere soil, exhibiting a significant inhibitory effect on C. chrysosperma with an inhibition rate of 78.71%. Results indicated that strain 5-38 not only demonstrated effective control but also displayed a broad-spectrum antifungal activity. The study also investigated the impact of different concentrations of antagonistic fermentation filtrate on C. chrysosperma mycelia, revealing a stronger inhibitory effect with increasing concentrations and a degree of thermal stability. Pot experiments demonstrated that a concentration of 150 mg/ml of antagonistic fermentation filtrate enhanced seed germination rates and various growth parameters of walnut seedlings, including seedling height, root length, root number, leaf area, and dry weight. Specifically, seedlings treated with P. lilacinus 5-38 showed significant increases of 30.12%, 33.89%, 81.89%, 6.83%, and 98.26% in these respective parameters. This study represents the first documentation of P. lilacinus as a promising biological agent for walnut rot control.