الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
Under arid conditions the water supply is limited and it is of prime importance to study the water economy and water use efficiency of plants. In Egypt only about 6% of the land area can be irrigated with Nile water. The rain¬fall is limited and it varies widely in the different desert regions from rainless deserts in the south to limited rain¬fall in coastal deserts where it reaches about 250 mm per annum. The agriculture in the coastal deserts depends on the rainfall, run off water accumulating in wadis and lowlands. Also the underground water is an important source of irrigation water in desert regions. The study of the drought tolerance and water use efficiency is very important under adverse cond¬itions of water supply. Previous studies showed considerable variations in the water economy and drought tolerance of the Different cultivars of the same species. Since wheat is a very important crop the present investigation is aiming to compare the water economy of five important cultivars of wheat and to find out the most productive cultivar under conditions of shortage of water supply. The increase in irrigation interval associated with increase in moisture stress resulted in reduction in vegetative growth. The studied vegetative growth criteria were, fresh and dry weight of shoot and total leaf area per plant. With decrease in water supply due to increase in irrigation interval there was a remarkable reduction in vegetative growth of all the studied cultivars. Under conditions of deficiency in water supply due to increase in irrigation interval the cultivar ” Giza 160” exhibited the greatest vegetative growth. The response of yield to water regime followed the same trend as in vege¬tative growth. There was a remarkable reduction in yield with deficiency in water supply resulting from increase in irrigation interval. The highest yield under deficiency in water supply was recorded in cultivar ” Giza 160”.
The study of the water relations of the five cultivars .revealed the decrease in transpiration rate and stomatal open¬ing in all the studied cultivars with increase in irrigation Interval. The transpiration rate and stomatal opening of all the studied cultivars exhibited a remarkable DROP before the attainment of the maximum atmospheric stress in the afternoon. Such phenomenon is of great importance in the water economy of plants since it results in avoidance of great loss of water by transpiration. With increase in irrigation interval accompanied by an increase in moisture stress the cultivar ”Giza 160” showed the least water expenditure and narrowest stomatal opening.
The relative turgidity of plant tissues decreased prog¬ressively with increase in irrigation interval. With increase in soil moisture stress the cultivar ”Giza 160” exhibited the highest relative turgidity with the least water saturation deficit.
The osmotic regulation is expressed by the degree of accumulation of soluble sugars, total ions and proline content in the plant tissues. In all the studied cultivars the content of soluble sugars, total ions and proline showed progre¬ssive increase with increase in soil moisture stress. The cultivar ”Giza 160” showed the most active osmotic regulation by greatest accumulation of the osmotica.
The cultivar ”Giza 160” proved to be the most water economic cultivar when subjected to severe moisture stress evidenced by the greatest control of water expenditure, reservation of more water content in plant tissues shown by higher relative turgidity and active osmotic regulation. All these characters account for its highest productivity under shortage of water supply. For this reason it is advisable to grow this cultivar of wheat in land areas with limited irrigation water or in coastal deserts depending on rainfall.