الفهرس 
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Abstract
Demand for enhancing the production of different crops is great to meet the food requirements of the rapidly increase in population. New insights and techniques are required in order to achieve sufficient and sustainable yields to meet global food demand and prevent world hunger.
Wheat (Triticum aestivum.L) is the most important cereal crop in the world and in Egypt. Solving the problem of wheat production shortage to face the fast increase in population occupies the main aim of agriculture policy of Egypt government, but this increase must be accompanied by increasing in the water demands and this needs to research about new water sources. One of the new sources can be used in irrigation is seawater, but the high salinity of seawater have adverse effects one the plant and soil. Therefore, we must find efficient way to increase wheat yield by improving the salt tolerance of wheat genotypes.
The salt stress is an intricate phenomenon involving osmotic stress, specific ion effect and nutrient deficiency, oxidative stress, alteration of metabolic processes and membrane disorganization. Wheat plants are sensitive to salt stress at all growth stages and have to cope with stress imposed by the low external water potential and with ion toxicity due to accumulation of ions inside the plants.
Many new methods were used to reduce the hazard effects of seawater irrigation i.e. magnitation of water, atomic distillation, and using marine algae.
Marine bioactive substances extracted from marine algae as a biocontrol agents are used in agricultural and horticultural crops as a biofertilizers to improve their yield and quality and moreover to reduce the negative environmental impact.
So, in this investigation, we studied the response of wheat plants and the changes that might occur in germination, growth and some related physiological activities due to extract application of Ulva lactuca and Cystoseira sp in different concentrations by presoaking or spraying at two growth stages of the plant that irrigated by seawater.
A- Seedling stage experiment:
Concerning the response of wheat plants at germination stage when five seawater concentrations were combined with eight algal extract concentrations of Ulva lactuca and Cystoseira sp. The seedling experiment were carried out mainly to study the interactive effect of salinity with or without algal presoaking on growth and some related physiological characters as the enzyme activities i.e. peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD), photosynthetic pigments i.e. chlorophyll a, chlorophyll b and carotenoids and proline.
The obtained results were as follows:
1- The germination percentage of wheat grains decreased gradually with increasing seawater concentration from 10% to 50%. The percent of germination improved and increased when the wheat grains presoaked in algal extract. Cystoseira sp. caused more efficient in reducing water salinity adverse effect than Ulva lactuca.
2- The activity of enzymes CAT, POD and SOD in wheat seedlings increased with increasing salinity levels of seawater. However, grains presoaked in algal extract from 5% to 25% showed further and highly significant increase in all three enzymes, and then the activity of enzymes redecreased at algal extract concentration 50%.
3- Nitrogen carrier molecules as proline of seedlings accumulate in plants under salt stress due to irrigation with seawater. However, the content of proline decreased with application of different algal extract to alleviate the adverse effect of salinity on biosynthesis of proline.
4- The growth parameters i.e. shoot height and root length of salinized seedlings were reduced by increasing seawater concentration. On the other hand, algal extract treated wheat grains were alleviated the adverse effects of salinity and increase the growth which reached maximum level at 25% algal extract.
5- The contents of photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids) of seedling leaves decreased gradually with increasing salinization level. Grain presoaking with algal extract of two species caused a significantly stimulatory effect on the biosynthesis of pigments when compared with the corresponding treatments without algal presoaking.
B- Vegetative and harvesting stage experiments
Pot experiment is concerned with studying the effect of two concentrations of seawater and different concentrations of Ulva lactuca and Cystoseira sp extract at two growth stages (45 and 75 days old plants) and at harvest time: The results were summarized as follows:
1- Plants irrigated with two seawater concentrations (10 and 20%) showed significant decrease in growth parameters including shoot height and root length at 45 and 75 days old plant and harvest time and total dry weight, leaf number/plant and leaf area/plant at 45 and 75 days age only. But algal treatment by presoaking or spraying caused a stimulatory effect on the above mentioned parameters when compared with those of non- algal treated ones.