الفهرس 
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Abstract
Through investigating the physiological roles of chitosan (CHT) in germination of Brassica napus seeds, three concentrations (3000, 5000, and 7000 ppm) were chosen based on a preliminary experiment. On the basis of the results obtained the relatively low applied concentrations of CHT enhanced B. napus seed germination, germination rate index, induced reduction in time required to attain 50% germination, decreased percentage of infected seeds via activating biochemical activities particularly the rate of glyoxylate cycle, as it was traced from the significant increase encountered in its key enzyme namely isocitric lyase, which play crucial role in the germination of fatty seeds where it finishes the embryo with its germination requirement of sugars and other major metabolites. Also, CHT belonging to oligosaccharide family, may act as signaling molecule, acting as a buffer, control and regulate the rate of water uptake, thus decreasing imbibitional injury recorded at the rapid and fast imbibition of dry seeds of water. Moreover, CHT at the relatively low concentrations significantly increased the activity level of antioxidant enzymes which reduce oxidative stress associated with imbibition of water of dry seeds. Moreover, CHT at the relatively low concentrations decreased seeds susceptibility to infection via the changes induced in protein banding pattern of B. napus seedlings in response to CHT reflecting an effect on gene expression. Thus, unique proteins were expressed only in seedlings developed from seeds pre-soaked in CHT, which had acquired the seedlings defense against fungal invasion as β-1,3 glucanase, chitinase, PAL, JIPs, systemin. Increased content of B. napus seedlings of IAA, GA3, ABA and cytokinins in response to low concentrations of CHT participate in enhancement of seedlings growth. A reverse pattern of change in above attributes was recorded on applying the relatively highest concentration (7000 ppm) which may be explained on the basis of accumulation of high percentage of CHT molecules within structural components of membrane which may altered its major characteristics as increase in its permeability and leakage of solutes into germination media, inducing growth of pathogens, a decrease in major requirements of seeds germination. The physiological roles of CHT in growth and development of B. napus plants grown in reclaimed sandy soil were also investigated at two successive seasons. The results obtained in the first season (2018/2019) indicated a significant increase in different attributes of growth, flowering, and yield in response to the different applied concentrations of bulk and nano chitosan, with a magnitude of response attained at 5000 ppm (bulk CHT) and 50 ppm (nano CHT). In response to different applied concentrations of bulk or nano CHT there was a significant increase in percentage of yield per feddan, compared with the control, with the maximum increase (86.2%) attained on using 5000 ppm of bulk CHT and 72.15% upon using 50 ppm of nano-CH. Treatment with bulk or nano-CHT lead to earliness of flowering and beginning of fruit set and hence shortening of the life cycle of the treated plants. In the second season of cultivation (2019/2020) and based on the results obtained in the first season, other range of concentrations were chosen for the purpose of achieving variable response and of attaining an inhibitory concentration. In response to the applied low concentrations of bulk CHT (3000, 5000 7000 ppm) and nano CHT (25,50,75 ppm) there was a significant increase in major growth, flowering, and yield attributes with 5000ppm of bulk CHT and 50ppm of nano CHT giving the optimum response. On the other hand, treatment with the highest concentration (9000 ppm) of bulk CHT and 200 ppm of nano CHT lead to a significant decrease in the above-mentioned parameters. Different treatments lead to earliness of flowering and fruiting of treated plants. There was a significant increase in plant yield which achieved 85.93% in using 5000
ppm of bulk CHT and 71% in case of using 50 ppm of nano CHT. Analysis of the yielded seeds indicated that treatments with 3000, 5000, 7000 ppm of bulk-CHT and 25,50 ppm of nano-CHT
induced significant increase in their content of total CHO, oils, N, P and K. Fatty acids profile of yielded seeds refer to a significant increase in oleic acid and linoleic acid content in response to 3000, 5000 and 7000 ppm of bulk CHT and in response to all concentrations used of nano CHT. Moreover, all applied concentrations of nano-CHT significantly decreased erucic acid content of yielded seeds achieving 50% reduction at 25 and 50 ppm. Bulk CHT, on the other hand, induced significant decrease only on applying 5000 and 7000 ppm. Analysis of the seed cake refer to, in general, a significant decrease in its content of glucosinolate in response to different concentrations applied of bulk and nano CHT. Assaying changes in major mechanical properties of soil induced by bulk CHT indicate a significant increase in soil porosity and water holding capacity and obvious decrease in percolation rate. Nano CHT led to a marked increase in water holding capacity via decreasing soil porosity and percolation rate.