الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Two field experiments were carried out at El-Khielalah village, Bilquas district, Dakahlia governorate, Egypt, during the two summer seasons of 2007 and 2008 to test the alleviative harmful effect of drought stress on two cultivars of rice by using some applied antioxidants .A split split plot design with four replicates was used. The main plots were devoted to the following irrigation intervals: 1- Continous flooding (control) 2- Irrigation every 7 days 3- Irrigation every 10 day 4- Irrigation every 13 days. The antioxidants treatments were located in the sub plots as follows: Water only (control ) - Ascorbic acid (ASA) ( 300 ppm) - Humic acid ( HA) (1000 ppm) - Seaweed extract (SWE) (1000 ppm). Two cultivars were sub-sub plots: Sakha 101 (drought sensitive = C1) - Giza 178 ( drought resistance = C2). The obtained main results of our investigations are :- - The data show that increasing irrigation intervals significantly decreased growth characters of rice plant ( plant height , leaf area index ,number of tillers, shoot dry matter, crop growth rate and relative growth ) comparing with flooding ( control ) through out the two growing seasons. Irrigation every (13) days was the most effective treatment in decreasing different growth characters of rice plant cultivar . - Regarding applied antioxidants, the data show that Ascorbic acid ( ASA), Humic acid ( HA ) and Seaweed extract ( SWE ) slightly increased all rice growth para meters ( plant height , leaf area index ,number of tillers, shoot dry matter, crop growth rate and relative growth ) and ASA was the most effective in this respect. -The data show also that the two growing cultivars were different in their growth characters and C2 was more then C1 cultivar. The effect of interaction treatments of both irrigation intervals and applied antioxidants as well as cultivars on shoot dry matter of rice plant. The data show that applied antioxidants increased dry matter accumulation of shoot dry matter of two rice cultivars compared with untreated plants grown under the same condition . The data also show that applied antioxidants could partially alleviate the harmful effect of drought stress on rice growth and ASA was the most effective in this respect. -Regarding the effect of irrigation intervals combined with cultivars on crop growth rate ( CGR ) and relative growth rate (RGR) of rice plants. The data show that the interaction treatments of drought stress levels and cultivars decreased both CGR and RGR of rice plant with increasing irrigation intervals. Growth, Yield and its components: - The data show that drought stress levels decreased all Yield and its components of rice plant except unfilled grains which increased by drought stress treatments. - Applied antioxidants ( ASA, HA, SWE ) increased number of panicles, panicles length , panicles weight, 1000 grains weight and number of filled grains and grain yield (ton/fed) while decreased heading date and unfilled grains of rice plant. -It could be mention that applied antioxidants ( ASA, HA, SWE ) could be alleviate the harmful effect of drought stress on yield and its components of rice plant. The interaction treatment between irrigation intervals and cultivars slightly decreased rice grains yield. The data also show that the high drought stress level (irrigation every 13 days ) was more effective in this respect. Biochemical constituents : The data show that irrigation intervals treatments (drought stress ) increased each of soluble sugars contents, proline and phenols contents while decreased both photosynthetic pigments content and ascorbic peroxidase activity. The highest drought stress level ( irrigation every 13 days ) was the most effective in this respect. Regarding endogenous plant phytohormones , data show that irrigation intervals treatments decreased each of IAA, GA, cytokinins while increased ABA while applied antioxidants showed opposite effect which increased each of IAA, GA, cytokinins while decreased ABA . Regarding nitrogen and protein content in grain yield of rice plant, it could be show that irrigation intervals decreased while applied antioxidants increased nitrogen and protein content in the grain of rice plant.