Isolation and identification of Rhizopus arrhizus causing postharvest bulb rot in Lilium davidii var. unicolor and its biocontrol using the endophytic bacterium Bacillus siamensis B55

Postharvest diseases in lily plants are prevalent during storage and transportation, leading to potentially catastrophic economic losses for the lily industry. Specifically, bulb rot has been observed in Lanzhou lily (Lilium davidii var. unicolor) during cold storage in Beijing, China. In this study, fungal isolates were obtained from decayed bulbs using a conventional fungal separation method, and these isolates were confirmed to be the causative agent of lily bulb rot, according to Koch postulates. A representative isolate, LZ-3-10, was selected for further identification. Based on morphological features and internal transcribed spacer sequencing results, the LZ-3-10 isolate was identified as Rhizopus arrhizus. Subsequently, an endophytic bacterial strain exhibiting robust antagonistic ability, Bacillus siamensis B55, was screened from the roots of lily plants. Evaluation of its biocontrol ability revealed that strain B55 could effectively protect L. davidii var. unicolor bulbs from infection by LZ-3-10, demonstrating a biocontrol efficacy of 51.2 ​% and significantly reducing the severity of lily Rhizopus rot. In summary, this study identifies R. arrhizus as the cause of postharvest bulb rot in L. davidii var. unicolor and, for the first time, showcases the biocontrol activity of the endophytic bacterial strain B. siamensis B55 against the isolated pathogenic fungus. These findings not only provide insights into lily bulb rot but also highlight the potential of B. siamensis B55 as a biocontrol agent for managing this disease during postharvest storage.