Apple replant disease (ARD) can remain in orchard soil for decades, weakening newly planted apple trees and making it difficult for growers to judge whether a site is safe to reuse. A large-scale study now identifies a set of gene-expression signals that could provide a biological readout of disease severity. By testing apple plants in soils collected from 151 sites, the researchers found that the root response was far more consistent and informative than the leaf response. Twelve root genes eme