یحیی تاج ور

 Drought is one of the most important environmental stresses that affects various plants such as ornamental plants. The identification and selection of ornamental tolerant genotypes is essential for landscape projects. Understanding the mechanisms that enable plants to adapt to drought stress can help to select the most tolerant genotypes for cultivation in arid and semi-arid regions.

 For this purpose, a research was conducted as a factorial experiment based on completely randomized design with eleven genotypes and two levels of irrigation (irrigation as Control and severe drought) at Ramsar Citrus and Tropical Fruits Research Institute.

 The first symptoms of drought stress were observed after 10 days in the Juniperus horizontalis (G1) genotype (the most sensitive genotype) and were not recovered and dried after 15 days. G3 and G5 genotypes (Ravande-mamouli and Ravande-setarei, respectively) showed drought stress after 28 days (most tolerant genotypes) and recovered at the end of the stress period after irrigation. Drought stress decreased photosynthetic pigments in studied genotypes. The content of soluble sugars, proline, and total soluble protein increased under drought stress conditions and the highest amount was observed in G3 genotype 30.8 mg g-1 DW, 30.5 μg g-1 DW, and 965.2 μg g-1FW, respectively. Under drought stress condition, the highest concentration of hydrogen peroxide, malondialdehyde and electrical conductivity were observed in G11, G4, and G10 genotypes respectively compared to control plants. In addition, the most enzyme activity of superoxide dismutase (85.57%), total phenol (181.09%) and total flavonoid (98.46%) was evaluated in G3, G5 and G8 respectively. Also, chlorophyll changes indicate the response of plants to environmental stresses such as drought during drought stress, the concentration of abscisic acid and ethylene increases, which stimulates the activity of the enzyme chlorophilase and causes chlorophyll degradation. The reduction of photosynthetic pigments under drought stress also seems to be related to changes in nitrogen metabolism to proline production and reduced chlorophyll synthesis because the precursor of chlorophyll and proline is glutamate. Furthermore, one of the biochemical changes that occur in plants under drought stress is the accumulation of ROS. Numerous reports have stated that drought stress increases ROS production. Drought-induced oxidative stress causes lipid peroxidation and membrane damage. It seems that in some genotypes with low levels of malondialdehyde, the membrane damage is severe and leads to more electrical conductivity. Genotypes with more electrical conductivity are more damaged by drought stress. In some genotypes, such as G2 and G11, there was a positive correlation between malondialdehyde content and electrical conductivity, but in others, such as G1, there was a negative correlation. Although the amount of malondialdehyde in this genotype is low, electrical conductivity is very high. In other words, this genotype should be a genotype sensitive to drought stress. The tolerance of the plant to various environmental stresses may be related to the level of activity of the enzymes responsible for scavenging ROS. The antioxidant response to water scarcity depends on the severity of stress and type of plant species. Therefore, different genotypes increased their antioxidant activity to reduce the effects of oxidative stress, and the high antioxidant activity was observed for G5 compared with other genotypes which can be contemplated as drought-tolerant genotype. The accumulation of compatible metabolites such as soluble sugars and proline in plants under drought conditions can help to protect them against stress. The proline and soluble sugars accumulation under stress conditions reduce lipid peroxidation and acts as a free radical scavenger. According to the results, drought stress induced accumulation of proline and soluble sugars in the genotypes of Juniperus and the highest accumulation of proline was related to G3. Therefore, this genotype can be introduced as drought-resistant genotype.

 The results of the current study showed that drought stress significantly affected some biochemical parameters in all eleven genotypes. However, a variation in drought susceptibility was observed among genotypes. The studied genotypes in this experiment had different responses to drought stress and it seems that they utilized different mechanisms for stress tolerance. Genotype of G3 (Ravande -mamouli) was the most tolerant genotype to drought stress based on the highest levels of superoxide dismutase, soluble sugars, proline, and soluble protein. Genotype of G5 was also tolerant to drought stress with high superoxide dismutase activity and the largest amount of total flavonoid production. Therefore, increasing of compatible metabolites and antioxidant system are effective protective mechanisms against oxidative damage under drought stress.

Adaptation to climate change requires appropriate knowledge. This study identifies extension programs effects and citrus farmers’ perception regarding adaptation to climate change on their knowledge. The research used a quantitative and explanatory perspective. The data were collected using interviews with a sample of 276 out of 99897 citrus farmers in the Mazandaran Province in 2021, selected by a multi-stage sampling technique. Farmers’ knowledge, perception, and access to extension programs were measured through ordinal-scaled questions. The questionnaire validity was evaluated by academic staff and researchers and its reliability was assessed using a pilot study with 30 farmers and the ordinal coefficient theta (θ = 0.92) for farmers’ knowledge. The data were analyzed using SPSSWin software and applying descriptive statistics, correlation coefficients, and ordinal regression. Results showed farmers perceived their citrus orchards’ high vulnerability to climate variability. Farmers' knowledge regarding long-term and short-term strategies to adapt to climate change was low and moderate respectively. Farmers had moderate access to extension agents and mass media and had poor access to group-based extension programs, but obtained low information on climate change from them. A significant correlation was between farmers’ communication and their information obtained. The odds ratios of the regression showed farmers' knowledge was explained by their perceptions of climate change vulnerability (R2Pseudo=2.394) and increased temperature (R2Pseudo=0.580), information obtains from researchers (R2Pseudo=1.473), and access to mass media (R2Pseudo=1.060). Policies are proposed to expand and strengthen the group-based and mass media extension programs, the interactions between researchers and farmers, and agricultural extension agents’ programs.

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.

Climate change has had broad effects on production and human societies in terms of environmental and socio-economic dimensions. In the last two decades, severe damages has been made to citrus production in the north of Iran, due to the incidence of frost, as a climatic phenomenon. However, the effects of this climatic phenomenon on citrus production and farmers’ vulnerability and resilience have not been comprehensively studied. This study aimed to understand citrus production and farmers’ vulnerability and resilience mechanisms to the climatic phenomenon of frost from the perspective of agricultural specialists and extension agents. This research used a mixed method containing a combination of case study and grounded theory. Data were collected through document analysis, focus groups and semi-structured interviews with the specialists and extension agents of the Agriculture-Jahad Organization in the Mazandaran Province working at the provincial, township and sub-county levels, who were selected using the purposive sampling technique and based on the snowball sampling method. The results indicates that extreme low tempretures have occurred much more frequently during the last two decades in the region, which hve caused many citrus orchards that are mainly sensitive to extreme low temperatures. This has increased the vulnerability of cirtrus farmers. Moreover, despite the solutions suggested by experts, the measures taken by citrus farmers to reduce their vulnerability and increase their resilience have been very limited and have not been implemented in a timely manner. The knowledge and financial, credit, institutional supports have also been insufficient and not provided timely.

In breeding programs, it is necessary having knowledge of the relatedness and genetic diversity in germplasm pools. The spread of cultivated regions and the high levels of production indicates citrus importance in the global economy. Therefore, 110 citrus genotypes were evaluated using 12 ISSR markers. Overall, 154 polymorphic bands were scored with an average of 12.8 alleles per primer. The polymorphism percentage ranged from 57 for the ISSR1 to 82 for the ISSR9. Averages of polymorphic information content (PIC), marker index (MI), gene diversity index (Nei), Shannon index (I) and number of effective alleles (Ne) were 0.48 ± 0.002, 6.14 ± 1.17, 0.42 ± 0.11, 0.61 ± 0.12 and 1.78 ± 0.27, respectively. Based on genetic diversity statistics, the studied population had high genetic diversity, and four markers (ISSR11, ISSR9, ISSR4, and ISSR5) had more potential for differentiation of genotypes. Cluster analysis and model-based structure analysis, divided the genotypes into five groups and four subpopulations based on the Neighbor-Joining method (NJ) and Bayesian approach, respectively. Based on both analyses, grouping of unknown genotypes and control cultivars in the same group probably confirms the assumption of a common genetic background between these genotypes. Results from the two analyses showed that Pummelo (C. maxima), Mandarin (C. reticulate), and Citron (C. medica), as three true citrus species, separated in different groups. In addition to the three true species, at least one species or another genus of citrus relatives is involved in the genetic makeup of the studied population. In this study, although both used analyses were effective in completing each otherchr('39')s information, by considering the degree of genetic mixing and the information of the origin of the genotypes, the effectiveness of model-based structure analysis in evaluating genetic relationships could be achieved.

Drought is one of the most prevalent and critical environmental stresses affecting a variety of plants, particularly ornamental plants. One of the useful methods to alleviate the effect of drought stress is to screen for and develop drought-tolerant varieties. In this study, a factorial experiment based on the completely randomized design was conducted to investigate the responses of 11 genotypes from different Juniperus species at two irrigation regimes (normal, drought: not irrigated for a four-week period) in terms of growth and biochemical characters.Drought stress had a significant negative impact on the assessed growth characters. The G3 and G8 genotypes had the highest root fresh weight and root dry weight at both normal and water-deficit stress conditions. G3 showed the highest root volume at normal conditions but at the drought stress, the highest root volume belonged to G1 and G8. At drought stress conditions, the leaf fresh weight and dry weight of G9, G8, G6, G4, G3 and G11 were higher than other genotypes. The stem fresh weight of G3 and G11 and the stem dry weight of G11 and G8 manifested higher values than other genotypes when water deficit stress was imposed. Stem diameter decreased in the seedlings at the drought stress, however, G2, G3, G4, G8, G9 and G11 had higher values than others at stress conditions. The relative water content decreased in the plants under stress, however, the reduction in G3, G5 and G6 were smaller than the rest of the genotypes. Among the genotypes, G5 and G3 showed the highest antioxidant activity under water-deficit stress. The genotypes G1, G6, G7 and G8 had also a notable increase in the antioxidant activity at drought stress conditions. Under drought stress, the highest increase in the proline content belonged to G3 followed by G5, G6 and G7 and the G5, G6, G10 and G8 genotypes had the highest amount of soluble sugars. In conclusion, G3 (Juniperus chinensis var. Sargentii) and G8 (Juniperus chinensis ‘Kallayʼs Compact’) showed mainly better performance under drought stress, which can be suggested as candidate drought-tolerant genotypes to be used in breeding programs for the sustainable development of urban landscape in arid and semi-arid areas. Although G5 (Juniperus procumbens ‘Nana’) had low biomass in this experiment, it showed high antioxidant activity, proline and soluble sugars at the drought stress conditions. Therefore, further investigation is needed, especially at more severe drought stress conditions, to elucidate its outstanding response to drought stress in terms of antioxidant activity and proline and soluble sugars content.

appropriate management methods in order to increase yield and water use efficiency. For this purpose, the effect of kaolin with three levels (0, 5 and 7 percent) in three levels of moisture condition (100, 75 and 50 percent of field capacity) on page mandarin as a factorial experiment based on a completely randomized design with three replications was evaluated in 2017 at the Citrus and Subtropical Fruits Research Center of Ramsar. The results showed that under moisture stress, fruit yield, water use efficiency, chlorophyll a and total contents, the relative water content of leaves, leaf water potential, and stomatal conductance were decreased significantly. While kaolin application increased the total soluble solids, fruit yield, and water use efficiency and decreased the proline content, carbohydrates, leaf surface temperature, stomatal conductance, superoxide dismutase activity, and fruit sunburn significantly. Also, in the treatment of 50% of field capacity, 5% Kaolin application, increased fruit yield (91%), chlorophyll a (70), total chlorophyll (52%), leaf relative water content (76%), stomatal conductivity (87%) and leaf water potential (19%) compared to treatment without applying kaolin. Therefore, the kaolin application in summer and severe moisture stress conditions (50% field capacity), are recommended to create a positive effect on the reduction of production of reactive oxygen species result of oxidative stress, reduction of fruit sunburn, the increase of fruit yield and water use efficiency.

Considering the limited water resources in Iran, utilization of modern methods of water conservation and preservation, such as the application of superabsorbent polymers in the soil, is one of the confront approaches of water deficit. For this purpose, in order to investigate the effect of superabsorbent on vegetative and reproductive growth of Page Mandarin in drought stress condition, a factorial experiment bases on the completely randomized design with three replications was conducted in 2016 at the Citrus and Subtropical Fruits Research Center of Ramsar. Factors were consisted of three levels of water stress (100, 75 and 50% of field capacity) and superabsorbent (0, 0.25 and 0.5% wt). The results showed that by increasing of water stress, amounts of electrolyte leakage, proline, fruit cracking and titratable acidity were increased. As well as 50% of field capacity level, 0.5% superabsorbent application was caused significantly increase leaf relative water content, total chlorophyll content, leaf water potential 60%, 15%, 23% and 87.5% and decrease electrolyte leakage and total soluble solids 65% and 22% respectively, compared with condition of treatment without applying superabsorbent. So, it seems that superabsorbent can increase the plant tolerance in counteracting moisture stress by maintaining unusable water.

Using native plants in landscape is an issue that has been neglected in the field of landscaping. Therefore, this research took place with the aim of examining the aesthetic aspect of the native tree plants of the Hyrcanian area. Field studies were carried out on 55 native tree species in 9 paths in Sari in the studied area for one year. These studies included recording appearance and aesthetic features. Registration of aesthetic features was done by observation of trees in nature and taking picture of various organs. Scoring was done according to the aesthetic indexes and then data were analyzed by SPSS software and the use of clustering method. Eventually, native tree species of the Hyrcanian region were classified based on aesthetic indexes. In the final stage, superior species was classified according to their application; finally 23 species were introduced as suitable species for street sights, 42 species for parks, 10 species for creation of productive landscapes, 19 species for use in making hinges and walls and 7 species for the margin of rivers and wet places. Summing up the results of this research, it can be concluded that, from the aesthetic point of view, some native Hyrcanian species are highly suitable for use in urban landscapes. Therefore, compatibility research for suggested species in urban environments is recommended.

Among citrus producing provinces in the country, Mazandaran province ranks first with 1.88 million tons yields. Orange is one of the horticulture crop which is sensitive to low temperature stress. Low temperature stress is one of the abiotic stresses that its negative effects is the disruption of the electron transfer process through the thylacoid membrane. Actived oxygen radicals can be reacted with methyl unsaturated fatty acid groups and produce active fatty acid radicals. Very reactive formed radicals are capable of initiating lipid peroxidation chain reactions, which leads to the accumulation of free oxygen radicals that can lead to degradation of plant chlorophylls and membrane peroxidation and disruption of photosynthesis, accumulation of ROS, damage to cell membranes, destruction of plant pigments and nucleic acids. Plants can resist against low temperature stress by water saving and utilization of antioxidant system. The amount of free proline in many plants increases in response to environmental stresses such as cold and drought stress, and this physiological response can affect the resistance of the herbal substance under stress. Due to the diversity of citrus native genotypes in the country, the aim of this study was to determine the tolerance of native genotypes against low temperature stress in north of the country.
This experiment was conducted during the years 2015_2016 at the Citrus and Semi-Traditional Fruit Research Center in Ramsar with the aim of determining the low temperature tolerance of six native pseudo orange genotypes at 4 temperature levels (3, 0,- 3,- 6), compared to The test was carried out by Unsho and Sensitive Persian Lime (low temperature stress). Therefore, in this study, the vulnerability to low-stress conditions in controlled environmental conditions was compared with that of temperature treatments (3, 0, _3 and -6 degrees Celsius) in six genotypes of native pseudo-orange (number 1-6) sensitive cultivar (Persian lime) and resistant cultivars (Unsho) were investigated. This experiment was conducted as a factorial in a completely randomized design. The results of analysis of variance showed that temperature, genotype and interaction of these two treatments were significant in lipid peroxidation, proline, antioxidant capacity, ion leakage, hydroxylation, chlorophyll a and chlorophyll content. The temperature of the device began to decrease at a temperature of 6 ° C. The temperature of the device was 1 ° C / hour, after which the samples were kept at the specified temperatures for 3 hours and at the end of this period (3 Clock) sampling was performed to measure the traits. Accordingly, the leaf aquaculture was calculated by calculating the leaf area using a leaf surface gauge device. Ionic leakage measurements were also investigated using the method of the conversation and Meg Donald method. The presence of genotypes under cold stress led to an increase in malondialdehyde. In these conditions, due to increased oxidative activity, the accumulation of antioxidant compounds such as superoxide dismutase, glutathione peroxidase and catalase increased. The data obtained from this research were based on factorial experiment in a completely randomized design with three replications of analysis of variance and then averages were compared by Tukey test at 5% level using SAS software.
Orange is a low temperature stress sensitive horticultural plant. Therefore, in this study, the vulnerability to low temperature stress in controlled environment (3, 0, 3- and -6 degrees Celsius) in six native poderotal genotypes (No.1-6) sensitive cultivars (Persian Liam) and resistant cultivars (Unsho) were studied. This experiment was conducted as a factorial in a completely randomized design. The results of analysis of variance showed that temperature, genotype and interaction of these two treatments were significant in lipid peroxidation, proline, antioxidant capacity, ion leakage, hydroxylation, chlorophyll a and chlorophyll content. Meanwhile, soluble carbohydrate was only affected by the simple factor of genotype. No effects on chlorophyll b and carotenoid pigments were significant. The highest incidences (99.33%), ion leakage (91.63%) and lipid peroxidation reaction (with a mean of 3.33 μg / kg of fresh leaf weight) were recorded in sensitive lambspeed control at 6 °C. In contrast, the highest amount of proline (32.01 mg / g leaf weight) and antioxidant capacity (73.36%) was recorded in the control group at 3 °C. Among the native pseudo-orange genotypes, in this study, different reactions were also observed under low-temperature stress conditions. Accordingly, after the control of the bird, the native pseudo-orange genotype number one was better than the one under temperature decrease. However, in most of the studied orange genotypes, in most of the destructive traits, the native pseudo-orange genotype number 6 was in the same statistical position or close to the sensitive Peninsula. The presence of genotypes under cold stress led to an increase in malondialdehyde. In these conditions, due to increased oxidative activity, the accumulation of antioxidant compounds such as superoxide dismutase, glutathione peroxidase and catalase increased.

Recent decades have witnessed the growing use of non-native plants in Iran while their use is very challenging and high-cost for the country. This raised a new approach in recent decades towards the use of native plants. Native species are precious because they possess the main ecological factors and they are already compatible with the region. Accordingly, this research was conducted to evaluate the species of woody plants that can be used in green space planning. The study focused on 55 tree species from 20 plant families in the research area. After evaluating the parameters that govern the aesthetic beauty of the studied plants in autumn, 27 tree species of Hyrcanian area were placed in the group of beautiful plants in terms of aesthetic criteria in autumn, 14 species were placed in the group of very beautiful trees, and 14 species were placed in the group of trees with average beauty. The final conclusion was that some species of Hyrcanian native trees can be used to beautify the urban landscape, especially in autumn, so it is recommended to do compatibility studies on the use of these species in urban landscape, especially in parks.

Low temperature stress is one of the most important abiotic environmental stresses that affect the growth and yield of ornamental plants. In order to investigate of some physiological and biochemical indices of four varieties of ornamental citrus used in urban landscapes under low temperature stress conditions, a factorial experiment in a completely randomized design with three replications was conducted in the Citrus and Subtropical Fruits Research Center of Ramsar in 2015. Treatments were included the temperature with four levels (3, 0, -3 and -6˚C) and four varieties of ornamental citrus including (Kumquat, Fingered citron, Calamondin and Limequat). Results showed that amounts of electrolyte leakage, water soaking, prolin content, antioxidant capacity, lipid peroxidation and superoxide dismutase activity were increased significantly by reducing of temperature, while chlorophyll a and total chlorophyll contents were decreased. Accordingly, the lowest leaf water soaking (20.92 Percent) and electrolyte leakage (30.81 Percent) amount, which are destructive indices, were showed in kamquate. Also total chlorophyll amount (2.21mgr/grFW), antioxidant capacity (60.61 Percent) and superoxide dismutase activity (26.53 IU/gr FW) that are tolerability indices were more evident in this variety. In general, Kumquat could tolerate the freezing stress up to -3°C by increasing of some indices such as proline, soluble sugars, antioxidant capacity and superoxide dismutase activity.

In this study, the vulnerability of six native genotypes of like-lime (1-6 number) with control tolerant variety of Unshiu and sensitive variety of Persian lime (to low temperature) were studied low temperature stress ( 3, 0, -3 and -6˚C), on physiological responses, in a completely randomized design with Tukey´s mean comparison. Analysis of variance showed that in the interaction between genotype and temperature, leaf water soaking, electrolyte leakage, lipid peroxidation, proline content and antioxidant capacity were significant. It was while in reaction of temperature and genotype, total carbohydrates, chlorophyll a, b, total and Carotenoids have not significant differences. Therefore, in comparison of data, the highest of leaf water soaking (91/628%), electrolyte leakage (99.3%) and lipid peroxidation (3.32 µgr/gr FW) were recorded in control sensitive plant (Persian lime) at temperature of -6˚C. Versus, the highest proline content (32.006 mg/gr leaf fresh Weight) and antioxidant capacity (73.36%) were observed in control tolerant plant (Unshiu) at temperature of -3˚C. It is noteworthy that total carbohydrate, chlorophyll a and total, were significantly different only under the influence of genotype factor. Accordingly, the maximum amount of chlorophyll a (2.359 mg/gr leaf fresh Weight), total chlorophyll (2.932 mg/gr leaf fresh Weight) and total carbohydrate (33.486 mg/gr leaf fresh Weight) were measured in in control tolerant plant (Unshiu). It should be noted that among the six native genotypes of like-lime studied, different reactions were recorded under low temperature. So that after control tolerant plant (Unshiu), native genotypes like-lime No. 6 showed better resistance against low temperature stress.

In order to evaluate the effects of potassium nitrate nutrition on some low temperature tolerance indices in Citrus aurantium seedlings a factorial experiment was conducted based on a completely randomized design with four replications at the Institute of Citrus Research in Ramsar. Treatments were potassium nitrate nutrition at four levels (0, 2.5, 5, and 10 mM) and temperature at four levels (25, 0, -3, and -6 °C). Results showed that increasing the concentration of KNO3 reduced superoxide dismutase activity and carotenoid. Concentration of 10 mM potassium nitrate also increased water content, leaf color, proline, phenol, and total chlorophyll. Maximum leaf damage, electrolyte leakage, and carotenoid were observed at -6 °C, while the highest antioxidant capacity and superoxide dismutase activity with means 37.7% and 24.4 IU. mg -1 FW, respectively were observed in Citrus aurantiumleaves at -3 °C. Highest electrolyte leakage was observed at concentration 0 mM potassium nitrate and temperature of -6 °C while highest superoxide dismutase was observed at -3 °C with the same concentration of potassium nitrate. Results revealed that concentration of 10 mM potassium nitrate increases Citrus aurantium tolerance under low temperature stress.

Citrus is a subtropical crops, therefore susceptible to freeze stress. This fruit tree has a different response to freeze stress according to the genotype and environment climate. Therefore, to evaluate the damage of freeze stress (winter 2014) on commercial citrus of Tonekabon area (Thomson Navel orange, Satsuma and Page mandarin) the morphological and physiological responses are assayed based on randomized complete block design (average was evaluated by LSD).The results showed that freeze stress can reduce chlorophyll (a, b, total) and leaf water content (p≤ 0.01). Based on data the Thomson Navel orange had the greatest reduction in these parameters. Therefore, the lipid peroxidation (1.48 µmol/g FW) and electrolyte leakage (53.06%) of Thomson Navel orange was higher than the other subjects in this study. The laboratory analysis showed that in the Satsuma mandarin prolin content (30.3 mg/g FW) and anti-oxidant capacity (73.44%) of leaves was higher than the other cultivars. But the assessment of fracture branches, most of the losses was recorded in the Page mandarin.In general, we can suggest that the Satsuma mandarin was more persistent than the other two cultivars of this study, was best tolerant to freezing stress because of lowest EC parameter in winter and best flowering in spring.

The production of reactive oxygen species (ROS) in plants under low temperature stress cause damage to plants. In order to evaluate of antioxidant responses of Page mandarin young trees (two years old) on different rootstocks under low temperatures, an experiment was conducted in a factorial plan based on completely randomized design. Treatment of temperatures were at seven levels include 9, 6, 3, 0.-3,-6 °C and 25 ± 2 °C (as control) and rootstocks were Sour orange, Citrange and Trifoliate orange. Results showed that, low temperatures increased electrolyte leakage, lipid proxidation, antioxidant capacity, superoxide dismutase, ascorbate peroxidase, catalase and peroxidase enzyme activities (P

In this study, fruits of 14 citrus varieties which damaged by freezing and 6 non damaged fruits which obtained from commercial trees were collected from germplasm collection of Citrus Research Institute. After initial evaluation, two main parts of fruit tissues were separated (peel and pulp) and after extraction procedures stored at -80 oC. Evaluating characteristics included number of seeds, peel thickness, TSS, TA, TSS/TA, total phenol, antiradical activity and amount of naringin. The results showed that the peel thickness had a positive and significant correlation with naringin content. Phenolic compounds of peel and pulp taken from non damaged fruits was higher than thus damaged fruits under freezing conditions. There were a significant correlation between peel and pulp Phenolics and antiradical activity. Naringin levels in both tissues were higher in frozen fruits than non damaged fruits. Unshiu which is known as a resistance variety to chilling injury had lower rate of naringin than other damaged fruits. Conclusion, naringin was a main compound in bitter fruits under freezing conditions, which is capable used in the processing industries.

Low temperature stress is an important environmental factor that limits citrus cultivation and yields. In this study, the effect of low temperature stress on physiological and biochemical responses of Page mandarin on citrange rootstock (on two year old plants), in incubator condition (with 65±5 relative humidity and 15000 lux Light intensity) has been investigated. Experiment was conducted using randomized design including low temperature (9, 6, 3, 0, -3 and -6°C) and control treatments (25±2°C). The comparison of treatment means showed that the lowest total chlorophyll (1.513 mg/gr leaf FW), green color (61.25%) and leaf water content (33.55% leaf FW) were related to -6°C temperature treatment. The highest accumulation of proline (48 mg/gr leaf FW) was related to -3°C temperature and maximum amount of carbohydrate (55.3 mg/gr leaf FW), was obtained with 0°C temperature treatment. Also, the highest amount of water soaking (51-75%) and electrolyte leakage (75.66%) in -6°C temperature, lipid peroxidation (2.643 MDA μgr/gr leaf FW), antioxidant capacity (63.5%) and phenol (2.863 mg/gr leaf FW) in -3°C temperature, were observed. The highest SOD enzyme activity (8.44×104 IU/gr leaf FW) was related to 0°C temperature. It could be concluded that Page mandarin (on citrange rootstock) could tolerate the freezing stress up to -3°C by increasing of proline, carbohydrate (osmotic adjustment) and antioxidant capacity.