Satureja montana L. essential oil, montmorillonite and nanoformulation reduce Xanthomonas euvesicatoria infection, modulating redox and hormonal pathways of tomato plants

Xanthomonas euvesicatoria (Xeu) is one of the etiological agents of bacterial spot of tomato (Bs), which is a devastating threat to tomato production worldwide. The emergence of Xeu field isolates showing resistance to agrochemicals, like copper-based bactericides, urged for developing new biocontrol strategies. Satureja montana essential oil (EO) has antimicrobial capacity against xanthomonads, and its combination with nanocarriers might benefit stability and controlled delivery in the field. The nanoclay montmorillonite (NMT) is a promising EO nanocarrier. This work aims to assess the impact of the S. montana’s EO, NMT and the nanoformulation incorporating both (EO+NMT) on X. euvesicatoria's amount, and their effects in the pathosystem (Xeu-tomato) at a molecular and physiological level. Uninfected and infected tomato plants var. cerasiforme were treated with S. montana EO, NMT and EO+NMT. The S. montana’s EO, NMT, and their EO+NMT combination were able to reduce the bacterial density and Bs symptoms. The treatment with NMT, alone or as carrier of EO (EO+NMT), also stimulated, in uninfected plants, the enzymatic antioxidant capacity and expression of some defense pathways, while EO alone induced an antioxidant effect. In infected plants, all treatments were able to downregulate key-transcripts of the oxidative, phenylpropanoid, jasmonic acid and abscisic acid pathways to levels close to those of the uninfected-untreated control. In infected plants, NMT treatment also increased the enzymatic/non-enzymatic antioxidant capacity through stimulating antiradical activity and catalase activity. Overall, these findings demonstrate the potential of NMT and S. montana EO as natural control agents of Xeu causing bacterial spot mainly due to their antibacterial capacity. These results indicate the potential to upgrading these natural compounds to new commercial products against Xeu. Furthermore, there is a potential for these products to be applied also as prophylactic treatments in field conditions.