The root-derived syringic acid and shoot-to-root phytohormone signaling pathways play a critical role in preventing apple scab disease.

Apple scab is a serious disease that has a huge economic impact. While some cultivars of apple are scab-resistant, most are not. Growing research has suggested that root-derived metabolites play a vital role in conferring resistance to aboveground pathogens through the long-distance signaling system between shoot and root.