H2O2 metabolism during sweet orange (Citrus sinensis L. Osb.) ‘Hamlin’ Xanthomonas axonopodis pv. citri interaction

Sweet orange (Citrus sinensis L. Osb.) ‘Hamlin’ is a canker (Xanthomonas axonopodis pv. citri: Xac) susceptible citrus genotype grown commercially worldwide. Canker causes severe economic losses and restricts the marketability of crop for export. Little is known about the role of oxidative stress in canker development. In the present investigation, sweet orange ‘Hamlin’ leaves were artificially inoculated with Xac to determine the impact of Xac infection on hydrogen peroxide (H2O2) metabolism. Characteristic symptoms following artificial inoculation were water soaking of the infiltrated zone between 2 and 8 days after inoculation (dai); raised epidermis accompanying tiny yellow colored bacterial colonies at 8 dai; and yellowing and necrosis of the infected zone by 12–16 dai. In planta Xac population increased 1000 fold by 14 dai from an initial population of 7.3 × 106 cfu cm−2 (0 dai). Peak concentrations of H2O2 were observed at 24 h and between 8 and 10 dai and coincided with higher activity of total superoxide dismutase (SOD). Lower levels of H2O2 in infected leaves were maintained by Xac induced higher activities of catalase (CAT), ascorbate peroxidase (APOD), and guaiacol peroxidase (POD). It appears Xac altered H2O2 metabolism in C. sinensis L. Osb. ‘Hamlin’ to enhance survival and growth.

► Citrus canker is an economically important disease worldwide.
► H2O2 degradation was increased in canker infected ‘Hamlin’ leaves.
► Activity of catalase, ascorbate peroxidase, and peroxidase was higher during Xac-‘Hamlin’ interaction.