الفهرس 
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Abstract
Plants are subjected to several harsh environmental stresses that adversely affect growth, metabolism and yield. Several biotic and abiotic stresses affect the growth in higher plants [1 and 2]. Drought, salinity, extremes of temperature, flood, pollutants and radiation are the important abiotic stress factor limiting the productivity of crops [3]. Of these drought is a major abiotic factor that limits agricultural crop production [4 and 5].
▪ Drought
Drought is undoubtedly one of the more important environmental stresses limiting the productivity of crop plants around the world [6]. Drought is a world wide problem, constraining global crop production seriously [7, 8, 9 and 10] and recent global climate change has made this situation more serious [11, 12, 13, 14 and 15].