Bush Basil Companion Plants Act as Plant Defense Potentiators for Cultivated Plants

Interplant interactions mediated by plant-emitted volatile organic compounds (VOCs) occur with heterospecific neighboring plants, making VOC-emitting companion plants a practical tool for pest management. In this study, we investigated the cocultivation of common bean (Phaseolus vulgaris L.) with bush basil (Ocimum basilicum L. var. minimum), which induced the expression of defense-related genes, such as pathogenesis-related protein 1, via salicylate signaling in the leaves. This coculture enhanced the defense capacity of P. vulgaris against spider mites (Tetranychus urticae) and field herbivores. Eugenol, one of the major VOCs emitted by bush basil plants, was likely responsible for conferring the antiherbivore activity on the receiver plants. Furthermore, bush basil VOCs were able to prime P. vulgaris plants to attract Phytoseiulus persimilis, a predatory mite of T. urticae, in response to T. urticae attack. Our results suggest a practical use of bush basil as companion plants in organic crop production.