Bacteriostatic Activity and Resistance Mechanism of Artemisia annua Extract Against Ralstonia solanacearum in Pepper

The destructive bacterial wilt disease caused by <i>Ralstonia solanacearum</i> leads to substantial losses in pepper production worldwide. Plant-derived pesticides exhibit advantages of high efficiency and broad spectrum when compared to traditional chemical pesticides. <i>Artemisia annua</i> and 'Tai Jiao' No. 1 were used as the experimental materials, and treated with 0.75 g·mL^-1, 1.5 g·mL^-1, and 3 g·mL^-1 of <i>A. annua</i> extract and inoculated with <i>R. solanacearum</i> at a concentration of OD600 = 0.1 for 14 days. The inhibitory activity of <i>A. annua</i> extracts against <i>R. solanacearum,</i> as well as the disease index, defense enzyme activities, and defense-related substances contents of pepper seedlings were determined. The results showed that the Minimum Inhibitory Concentration (MIC) of the <i>A. annua</i> extract was 3 g·mL^-1. As the concentration of <i>A. annua</i> extract increased, the extent of <i>R. solanacearum</i> cell crumpling intensified, accompanied by a gradual decline in its biofilm-forming ability. On the 14th day after treatment, the disease severity index and incidence rate were significantly reduced when the <i>A. annua</i> extract was applied at concentrations of 0.75 g·mL^-1 and 3 g·mL^-1. At both the 7th and 14th days after treatment, the application of <i>A. annua</i> extract at concentrations of 0.75 g·mL^-1 and 3 g·mL^-1 led to enhanced activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in peppers at different stages. Simultaneously, it reduced the levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), effectively scavenging reactive oxygen species and alleviating cellular lipid peroxidation. Furthermore, the extract increased the activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL), as well as elevated the contents of soluble protein, flavonoids, and total phenols, ultimately enhancing the disease resistance of peppers. Considering the development costs, the application of <i>A. annua</i> extract at a concentration of 0.75 g·mL^-1 demonstrates great potential for green control measures against bacterial wilt in peppers.