d-Limonene induces expression of PDF1.2 gene and resistance against Colletotrichum higginsianum in Arabidopsis ecotype Col-0. The limonene-induced expression of PDF1.2 was diminished in jar1-1 (jasmonate resistant 1-1) plants, indicating that the response of Arabidopsis depends on jasmonic acid (JA)-regulated defense signaling pathway. In fact, systemic induction of PDF1.2 was confirmed when the Arabidopsis plants harboring the PDF1.2 promotor::GUS were exposed to limonene. A similar protective effect was also observed on Japanese mustard spinach (Brassica rapa var. perviridis) challenged with C. higginsianum, suggesting that plants are capable of recognizing gaseous limonene and activate disease resistance.