Abstract
Zucchini yellow mosaic virus (ZYMV) has a wide distribution in Mecca regions and is considered to be a serious threat on watermelon production. The aim of this study was to evaluate the antiviral activity of five medicinal plant extracts, against ZYMV-infecting watermelon plants. The experiment consisted of four application of soaking seeds, in vitro and in vivo experiments. The results of greenhouse experiments with individually treatments by decoction and infusion of Nigella sativa (NS) seeds in soaking and in-vitro experiment, bougainvillea and neem in pre-inoculation and thuja extract following nigella decoction in post inoculation were efficient to reduce and\or inhibit symptoms expression infecting watermelon seedling, whereas, decoction exhibited higher antiviral activity against ZYMV than infusion. The decoction and infusion of NS seed increased the total photosynthesis pigments, total soluble intracellular protein and total phenol contents. In conclusion, the results of the present investigation propose that the bougainvillea and neem extracts may perhaps play a central function in the mechanism of acquired systemic resistance and may produce pathogenesis-related proteins that play a significant role in watermelon seedling resistance against ZYMV.