Effect of Water Stress on some Morphological and Physiological Characteristics of Citrus Natural Genotypes Seedling

Background and Objectives Water is a main factor in agriculture activities and almost 70 percent of world water resources are consumed in agriculture. Drought consist the most important environmental restriction to plant growth and production. Drought stress is known to change a range of physiological processes such as photosynthesis, stomatal conductance and transpiration rate. Citrus are one of sub-tropical and tropical fruits and the most important horticultural products in the world that tolerate low temperature and weak drainage but as regards Citrus growing in sub-tropical and tropical regions that often expose drought. Drought is one the environment stress factors that is caused changes in plants morphological and physiological characteristics. Study of survival time in the three citrus rootstocks in sever stress circumstances showed that this time in rootstocks poncirus, cleopatra mandarine and former-alkaeid 5 were 11, 13 , 20 days, respectively while survival time in valencia on the rootstocks was 21, 26 and 29 days, respectively. This study was performed in order to study drought tolerant in natural genotypes with the poncirus and rough lemon. And so, morphological and physiological characteristics were investigated in this genotypes. Materials and Methods This research was performed in separately two tests in Citrus and subtropical fruits research center on 2016. In the first test, survival time and total transpiration and in the second test, organs fresh and dry weight, ion leackage and leaf relative water content were assessed in factorial experiment based on randomized completely design in nucellar seedlings of 8 Citrus natural genotypes (G10, G11, G12, G16, G18, G22, G23, G25) poncirus and rough lemon under glasshouse conditions (with temperature 26-28 degree centigrade in day and 20-22 degree centigrade in night and 80-85 percent relative humidity). Factors were 10 Citrus genotypes and two treatment of irrigation (optimum irrigation and withholding irrigation for six weeks) in the second test and 10 Citrus genotypes in the first test. In this study, medium weight moisture is calculated and due to the soil moisture characteristics curve was obtained medium matric potential. The matric potential rate was in control -0.03 megapascal and in sever stresss -1.5 megapascal. Organs fresh and dry weight were measured on digital balance with accuracy 0.01 gr. (model GM 6101, Germany). S amples were dried in oven (70 degree centigrade and for 48 ho