Journal of Agricultural, Life and Environmental Sciences ISSN:2233-8322(Print) 2508-870X(Online)

Lettuce (Lactuca sativa L.) is a popular vegetable. While there is growing concern about the safety of agricultural goods for human health and the environment, there is only limited information on the control of lettuce leaf spot pathogen Alternaria alternata in a safe and eco-friendly manner. Therefore, in this study, we tested the inhibitory effects of seven plant extracts and an antagonistic microbe (Bacillus velezensis UK1) on A. alternata KL-1. The most effective plant extract was Goldthread 80%, which exhibited 72% and 99% mycelial growth inhibition at concentrations of 100 µg/mL and 1,000 µg/mL, respectively, followed by clove tree 70%, soapnut 40% + cinnamon oil 20%, and Lysimachia foenum-graeci Herba 5%. In contrast, rhubarb 92% + castor oil 3%, cinnamon oil 28% + tea plant 25%, and (Goldthread + rhubarb) 7% exhibited relatively low inhibitory effects, inhibiting mycelial growth by 52%, 40%, and 12%, respectively, at a concentration of 1,000 µg/mL. We also identified an effective antagonistic microbe, B. velezensis UK1. The inoculation of 10 µL of bacterial suspension at an OD₆₀₀ of 1.0 exhibited approximately 47% mycelial growth inhibition when bacteria were inoculated 1 day before inoculation of the fungi on media. Our results demonstrate that plant extracts and the antagonistic microbe B. velezensis UK1 both have the potential to be utilized to control the pathogen that causes leaf spot, A. alternata.