Benzothiadiazole-elicited defense priming and systemic acquired resistance against bacterial and viral pathogens of pepper under field conditions

Like the innate immunity in mammals, plants have developed an induced resistance, referred to as systemic acquired resistance (SAR). Recently, defense priming that is not related to the direct activation of defenses, but instead elicits more rapid induction of resistance mechanisms following trigger application, has been proposed to explain the long-lasting effect of SAR. However, the majority of previous studies have focused on understanding the molecular mechanism underlying priming under in vitro and laboratory conditions. This study examined whether defense priming occurred and was detectable with SAR marker genes by a chemical elicitor, benzothiadiazole (BTH), under field conditions. Pepper seedling application of 0.5 mM BTH was sufficient to prime the CaPR4 gene for 20 days as well as to induce SAR against bacterial spot caused by Xanthomonas axonopodis. Transcriptome analysis revealed to prime defense hormonal signaling and antimicrobial compound production genes. At the end of the season, when bacterial spot and Cucumber mosaic virus disease outbreaks naturally occurred, BTH-treated plants demonstrated less disease symptoms. Our results indicate that the priming of SAR genes plays a critical role in plant protection against pathogens under natural conditions.