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

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. 
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 hours). RWC is measured by using of fresh weight, dry weight and turgid weight in this formula: RWC= [(FW-DW) / (TW-DW)] × 100. Ion leackage was determined by use of 4 equal leaf segments and measuring of primary and secondary ion leackage in this fomula: EL (%) = (EL1/EL2) × 100. The first research was included of 10 treatment, six replication and one seedling in every plot and the second research was included of 20 treatment, three replication and two seedlings in every plot. SAS software (ver. 9.1) and Duncan test were used to variance analysis and mean comparison. Excel software was used to graphs drawing.
The results showed that in first test, poncirus (with 125 days) and G11 (with 78 days) have longer survival time and are more tolerant and so rough lemon (with 38 days) and G12 (with 44 days) were more susceptible. Others were intermediate. Slowest of water consumption time in poncirus and the most quick in rough lemon, and so maximum of total transpiration in G25 and minimum in poncirus was observed. In second test, decrease maximum of leaf, shoot and total fresh weight in G22 (arranged by 0.37, 0.47 and 0.42) and decrease minimum in G11 (arranged by 0.48, 0.54 and 0.52), decrease maximum of root fresh weight in G22 (with 0.35 fold) and decrease minimum in G18 (with 0.52 fold), decrease maximum of root/shoot fresh weight in G18 (with 0.61 fold) and decrease minimum in G23 (with 0.65 fold) and increase maximum of root/shoot dry weight in G16 (with 1.56 fold) and increase minimum in poncirus (with 1.3 fold) was observed in compared with control. In stress, G18 (with 32.32 percent) and G12 (with 34.37 percent) had leaf relative water content minimum in compared with control. G12 (with 78.59 percent) and G18 (with 73.16 percent) had maximum and poncirus (with 31.85 percent) minimum ion leackage percent in compared with control. Therefore, rough lemon, G12 and G18 as susceptible and poncirus and G11 as tolerant to drought were introduced.
In stress conditions, poncirus has longer survival time, slower water consumption time, minimum total transpiration and minimum ion leackage percent and is most tolerant. Rough lemon has shower survival time, more rapid water consumption time and is most susceptible. Other genotypes locate in after grades. Therefore poncirus and rough lemon can be used as rulers in tests of drought study.