Abstract
White clover is considered amongst the most important forage legumes in temperate agricultural systems. It contributes to increased quality of pastures through its ability to fix atmospheric nitrogen, providing high nutritional feed for livestock. White clover is host to the potexvirus White clover mosaic virus (WClMV), which is readily transmitted via animal trampling/grazing and mowing. WClMV infection may strongly impact white clover's performance, affecting its ability to compete with other plants in the pasture. Understanding the extent to which the virus influences white clover's growth and yield may contribute to improve pastoral management by pointing out the importance of stress factors on pasture plant performance and herbage yield. In the current study, the effects of WClMV infection and simulated grazing on white clover's fitness, oxidative damage and the induction of antioxidants were investigated. Two cultivars of white clover, Grasslands Huia and Grasslands Kopu II, were subjected to three harvests. In response to WClMV infection and grazing-like cutting, white clover experienced oxidative stress as evidenced by the accumulation of lipid peroxides and protein carbonyls. Biomass accumulation, given as fresh weight and dry matter content, was also negatively affected. Both stresses induced an increase in ascorbate and glutathione levels and enhanced the activity of superoxide dismutase, ascorbate peroxidase, glutathione peroxidase, catalase and glutathione reductase. Glutathione S-transferase activity and the levels of reduced ascorbate and reduced glutathione were not affected by either stress.