Screening of biocontrol agents against lily bulb rot caused by F. oxysporum and research on their fermentation process

The bulb rot disease caused by Fusarium oxysporum (F. oxysporum) in Lanzhou lily (Lilium davidii var. unicolor) is one of the most difficult diseases to detect in the early stages of cultivation, seriously threatening the yield and quality of Lanzhou lily. Currently, the main prevention method is pesticide drenching and broadcasting, apt to excessive residues, reduced quality, and environmental contamination. Thus, there is an urgent need for green and sustainable control strategies. However, screening endophytes for the development of biological control agents has been more popular in recent years owing to their strong antifungal properties and ability to settle in plant tissues asymptomatically. Initially, 21 endophytic fungal strains were isolated from healthy lilies collected in regions with high incidence of bulb rot disease in Lanzhou using the tissue separation method. Using the growth rate and plate confrontation methods, five strains (ST5, ST8, ST12, ST14, and ST20) were selected for their significant inhibitory effect on F. oxysporum, with inhibition rates exceeding 30 %. Notably, strain ST12 showed an inhibition rate of 74 %, identified as Penicillium crustosum. Simultaneously, response surface methodology optimized the ST12 fermentation process, revealing that at 27 °C, 11 d of fermentation, and at a number of the inoculated fungal cakes of 3.5, the inhibition rate against F. oxysporum reached 74.50 %. In addition to choosing a biocontrol agent for the efficient management of the F. oxysporum-caused bulb rot disease in Lanzhou lily, this study offered scientific guidance and technical assistance for the creation of biocontrol agents from plant endophytic fungi.