Induction of superoxide dismutase, malate dehydrogenase and phenylalanine ammonia-lyase during enhancing resistance of common bean against Xanthomonas axonopodis pv. phaseoli by exogenous salicylic acid

Bacterial blight of common bean caused by Xanthomonas axonopodis pv. phaseoli (Xap) is one of the most devastating diseases and causes serious yield losses worldwide. To extend our understanding for the efficacy of salicylic acid (SA) as a therapeutic agent against bacterial diseases, we have studied the impact of exogenous SA treatment on disease incidence and development during the course of Xap infection. In this study, an enhanced resistance response induced by SA was detected in common bean infected with Xap. On the other hand, SA did not have direct antibacterial effect in vitro. Additionally, we examined the effects of SA on expression of superoxide dismutase (SOD), malate dehydrogenase (MDH) and phenylalanine ammonia-lyase (PAL). SA-pretreated leaves had higher expression of MDH after Xap infection when compared with their counterparts pretreated with water (control). SA/Xap treatments showed more expression of SOD at 24, 48 and 72 h post-pathogen inoculation (hpi) compared to water/Xap samples, whereas PAL expression was significantly different only at 24 hpi. The results showed the contribution of SA as an effective resistance activator and may provide an additional approach in bacterial blight integrated diseases management programs.