When plant roots detect the presence of roots of other species, they respond in an adaptive manner: by growing away from the competing roots and increasing the expression of 14 genes implicated in the response against pathogens, according to a study.
Christoph Schmid and colleagues grew the model plant Arabidopsis thaliana with or without a mild competitor, the mouse-ear hawkweed Hieracium pilosella, and measured changes in the level of expression of approximately 22000 A. thaliana genes.
Its genetic response to the competitor's presence was in part similar to the response to the presence of plants from its own species. But surprisingly, the presence of H. pilosella also induced a genetic response in A. thaliana similar to its typical response to parasites (e.g. the oocmycote Phytophthora, which causes blight and root rot) and other forms of biological stress.
Schmid and colleagues conclude that biological stress reactions are induced by foreign organisms in general, including the roots of competing plants.