Effect of Salicylic Acid Treatment on Disease Resistance to Coleosporium zanthoxyli in Chinese pepper (Zanthoxylum armatum)

Abstract

The Coleosporium zanthoxyli fungus causes leaf rust in the Chinese pepper (Zanthoxylum armatum). To investigate the control effect of elicitor treatment on leaf rust in this species, the impact of salicylic acid (SA) on the spores and growth of C. zanthoxyli and the induced resistance to leaf rust by Z. armatum were analyzed, and the possible defense mechanisms involved in SA induction were evaluated. The results showed that SA had no effect on C. zanthoxyli spore germination and growth; however, rust resistance was induced in Z. armatum. The optimal SA treatment concentration was 0.4 mg/mL, and the relative cure effect reached 44.56 %. SA-induced disease resistance was evident for up to 10 days, while the optimal induction interval was 48 h after stimulation. Consistent with the induced resistance, the H2O2, total protein, total phenol, and lignin concentrations, and polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), and catalase (CAT) activities were significantly increased with the SA treatment, whereas the MDA content was significantly decreased. In addition, exogenous SA promoted defense-related enzyme activities, including those of POD, CAT, and PAL, and increased the H2O2, lignin, and endogenous SA contents. Furthermore, SA induced the expression of SA signaling pathway genes such as ZaPR1 and ZaNPR1, and silencing ZaPR1 enhanced the sensitivity of Z. armatum to leaf rust. Our results demonstrated that 0.4 mg/mL SA priming increased the activities of CAT, POD, and PAL , elevated the contents of H2O2, lignin, and endogenous SA , and up-regulated the expression of SA-related gene ZaPR1, thereby enhancing the resistance of Z. armatum to leaf rust.