Changes in Antioxidant Enzyme Activity and Viral Load in Zucchini Cultivars Infected with Papaya ringspot virus-Watermelon type

Zucchini represents one of the most important species within the Cucurbitaceous family, but diseases appear as a limiting factor. The Papaya Ringspot Virus-Watermelon type (PRSV-W) is the virus with higher occurrence in producing regions. Viral replication and disease development may promote changes involving defense-related enzymatic components. This study evaluated alterations in the oxidative metabolism as well as viral load of two cultivars of zucchini, Adele and Caserta, infected by PRSV-W. Plants were inoculated and leaf samples were collected to determine the activity of antioxidant enzymes and viral load. The intensity of the disease was measured. In local level, there was a decrease of the viral load for both cultivars, increasing significantly again at 8 days. The viral load in the new leaves of the Caserta was at least 3 times higher than in the Adele ones. Mosaic symptoms were mild in Adele and expressive in Caserta. The activity of the APX in the Caserta increased faster than in Adele in inoculated leaves, but this increase was not related to the reduction in viral load. At the systemic level, APX, presented higher activity in both cultivars, however, over time Adele reduced, which may have resulted in a lower effect of the enzyme on hydrogen peroxide and this contribute to the reduction of viral multiplication. The rapid systemic response of Adele (tolerant) and the increase in the activity of GPX and GR in the first day after inoculation, may be one of the factors that contributed to the lower load viral and severity of the symptoms. On the other hand, in the Caserta (intolerant), pronounced increases in antioxidant enzyme activity were observed over the course of disease evolution in an attempt to contain plant cell oxidative damage, which may have favored the advance of a bio trophic pathogen such as viruses.