الفهرس 
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Abstract
Two experiments were conducted during the seasons of 2015-2017. Pots experiment was conducted in the Experimental Farm of Agricultural Botany Department, Faculty of Agriculture, Ain Shams Univ. during the season of 2015 to evaluate the effect of grafting on salt tolerance of watermelon plants. Watermelon (Citrullus lanatus [Thunb.] Natsum & Nakai) cv. Aswan F1 was grafted onto the rootstock Flexifort pumpkin (Cucurbita maxima x C. moschata) and irrigated with four different concentrations of NaCl (0.0, 2000, 4000, 6000 ppm). Second experiment was conducted in the farm in Belkas, Dakahlia Governorate during the seasons of 2016 and 2017 to investigate effect of foliar applications of glycine betaine (GB) at 5, 10 mM, myo-inositol (MI) at 5, 10 mM, ascorbic acid (AA) at 50, 100 mgl-1 and sea weed extract (SWE) at 2.5, 5% on growth and productivity of grafted watermelon plants under salt stress (total salinity of soil and irrigation water was 3008 ppm). First experiment results showed that, main stem length, leaf numbers and area, branches number, root length, and shoot and root fresh and dry weights were negatively affected by salinity in ungrafted plants and this effect was directly proportional to NaCl concentrations. On the contrary, grafting positively affected the aforementioned parameters and minimized the harmful effect of salinity. Grafted plants showed decreasing in membrane permeability (MP) with 12.7 % higher relative water content (LRWC) than ungrafted plants. Under 2000, 4000, 6000 NaCl ppm salinity levels, the values of salt injury index were 15.1, 26.5 and 37.5 in ungrafted plants at 20 DAT comparing to 0.0, 6.9 and 12.9 in grafted ones. Second experiment results showed that, all foliar applications with bioregulators (AA, GB, SWE and MI) significantly increased grafted watermelon growth under saline conditions comparing to untreated plants in the two successive seasons (2016 and 2017), as indicated by plant height, lateral branches number, leaves number per main stem length, leaf area, shoot fresh and dry weights. The higher concentrations were generally better than the lower ones. At the young age (30, 45 DAT), the superiority was due to SWE and AA then GB and MI, but AA at 100 mgl-1 surpassed other treatments in subsequent sampling dates (75 and 127 DAT). Approximately, all bioregulator treatments significantly increased photosynthetic pigments; chlorophylls and carotenoids, proline, total sugars (TS), total soluble proteins (TSP) concentrations. As well as, antioxidant enzymes (POD and CAT) activities. The highest values of TSS, TSP and proline were obtained by MI at 10 mM, GB at 10 mM and SWE at 5% respectively. Ascorbic acid at 100 mgl-1 showed the best results of watermelon yield parameters; mean fruit weight, marketable fruits No./plant and fruits yield/ plant. Sea weed extract at 5% gave significant increase in the aforementioned yield parameters. Also, GB at 10 mM significantly increased fruits yield /plant. Application of AA at 100 mgl-1 and SWE at 5% are recommended for improving grafted watermelon plants growth and productivity under salt stress as they exerted their affects through counteracted the harmful effects of salinity stress, in addition to, promoting plant growth and productivity.
Key words: Watermelon, Citrullus lanatus, Salt stress, Grafting, Rootstock; Cucurbita maxima x C. moschata, Glycine betaine, Ascorbic acid, Sea weed extract, Myo-inositol.