Response of Watermelon Plants Grafted onto different Rootstocks to Deficit Irrigation

The present study was conducted to examine the response of grafted watermelon (cv. Aswan) plants to deficit irrigation by using different cucurbit rootstocks viz. Giada, Shintoza, Strong toza, Ferro and Pumpkin, compared with un-grafted plants. Water treatments were applied in a field experiment under 100%, 70% and 50% of Evapotranspiration (ET). Results indicated decrease in vegetative growth (number of leaves and branches, length of the main stem), leaf relative water content, reproductive growth and fruit yield, under water stress, as compared to the control (100% ET). Results also showed reduced N, P and K contents in the leaves under water stress condition. However, proline content and antioxidant enzymes: superoxide dismutase (SOD) and catalase (CAT) were higher in water stressed plants than those receiving 100% water. Under severe water stress, all graft combinations had generally better growth and yield performance than un-grafted plants. The grafted plants of Aswan/Ferro significantly recorded the lowest decline in number of fruits/plant, total yield and flesh SSC under 50% ET irrigation treatment, as well as the lowest decline in N and P content. It is concluded that grafting watermelon plants onto specific rootstock had the potential to increase water stress tolerance. This was associated with increase in proline, and the activities of SOD and CAT in their leaves.