آرش مامدی

Iran's arid and semi-arid regions span over 1.5 million km², accounting for nearly 92% of the country's total area. Drought is one of the most critical abiotic stresses affecting these areas. Due to challenges faced in breeding improved drought-tolerant genotypes, the domestication and cultivation of drought-resistant plants have emerged as the best solution to prevent the extinction of wild species and restore pastures. Selecting drought-tolerant plants during the germination stage is crucial for successful plant establishment. Seed germination is the first and most important developmental stage, that is influenced by genetic and environmental factors. The hydrotime model describes the relationship between water potential (ψ) and seed germination rate and percentage. This model quantifies the rate of germination progression (hydrotime constant: θH), the uniformity of germination (standard deviation of the base water potential: σψb), and the stress tolerance of germination [base osmotic potential for 50% germination: ψb(50)]. These indicators can be used to determine seed vigor and seed dormancy and the effects of treatments on seed viability. This study aimed to use hydrotime model to predict of germination response of three medicinal species of Nepeta haussknechtii, N. pogonosperma, and N. glomerulosa subsp. staffina to water potential. 

For each species, six water potential levels (0, -0.3, -0.6, -0.9, -1.2, and -1.5 MPa) were applied using a completely randomized design with three replications in 1402 at the Seed Technological Research Laboratory of the Natural Resources Gene Bank, Iran. Seed germination of species was recorded daily at a temperature of 25°C. Since no germination was observed at a potential level of -1.5 MPa, this treatment was excluded from the analysis. The hydrotime model was then fitted to the germination data, and the hydrotime constant (θH), base osmotic potential for 50% germination ψb(50), and standard deviation of the base water potential (σψb) were quantified. 

The analysis of variance revealed significant effects of drought (at five levels of 0, -0.3, -0.6, -0.9, and -1.2 MPa) on all seed germination characteristics of all three Nepeta species (P<0.05). The hydrotime model results showed that the germination rate under drought stress was higher in N. haussknechtii (θH=48.32) than in N. glomerulosa (θH=52.13) and N. pogonosperma (θH=56.57). Furthermore, the germination uniformity of N. haussknechtii (σψb=0.18) was higher than that of N. glomerulosa (σψb=0.39) and N. pogonosperma (σψb=0.24). In terms of drought resistance, N. pogonosperma (ψb(50)=-1.006) exhibited greater resistance compared to N. haussknechtii (ψb(50)=-0.69) and N. glomerulosa (ψb(50)=-0.77).

Osmotic stress significantly impacted the germination pattern, timing, and rate of Nepeta seeds. Since seed quality concerning drought resistance determines the speed and uniformity of germination, the output of the hydrotime model, including parameters θH, σψb, and ψb(50), was effective in predicting germination percentages under drought stress conditions. Drought-tolerant genotypes were identified using the hydrotime model, with N. pogonosperma being the most resistant species, followed by N. haussknechtii and N. glomerulosa. The hydrotime model is a tool in breeding programs for identifying high-efficiency genotypes' resistance to stress conditions.

Quinoa has attracted a lot of attention in recent years due to its low ecological needs and rich nutritional value. Therefore, the variability of germination components to temperature and determination of cardinal temperatures were performed by seed germination test at different constant temperatures from -1 to 45°C.The results of the dent-like model showed that the base temperature and ceiling temperature of quinoa were -03.04 and 45.45°C, respectively, and the optimum temperature was from 20 to 35°C. To investigation the effect of salinity and drought stress on germination at 25°C, the seeds were exposed to osmotic potentials from 0 to -28 bar, which were made of sodium chloride (NaCl) and polyethylene glycol (PEG), respectively, to induce stresses. The results showed that the reduction of osmotic potential up to -12 bar was not able to significantly reduce the germination components compared to normal conditions. However, with decreasing osmotic potential to -18 and -24 bar, the germination percentage decreased significantly. The germination was completely stopped at -24 bar of drought-induced, while 24% germination was observed at the same point of the salinity-induced osmotic potential. Therefore, seed germination capacity under salinity-induced stress was more tolerant than drought-induced stress at all levels of osmotic potentials. Most likely, due to the fact that quinoa is halophyte, by absorbing the ionic elements of salt, required for the maintenance of the cell turgor, which concurrent increase in cytosolic osmolality. Thus, this species has a great potential for distribution to other areas such as provinces with dry climate.

Canada thistle (Cirsium arvense) is a noxious weed and one of the most problematic weeds in field crops, orchards, vegetables, pastures and grasslands in Iran. Determining the ecological factors of this grass weed will contribute to development of its control programs. In order to study germination characteristics to water and salinity stress conditions at different temperatures, an experiment was conducted. Temperatures regimes included 5, 10, 15, 20, 25, 30 and 35°C. For each temperature the treatment, for salinity and water stress was 4 potentials (zero, -4, -8, and -12 bar) of NaCl and 4 potentials (zero, -4, -8, and -12 bar) of PEG. Results showed that increasing salinity stress decreased significantly germination rate and percentage. Tb germination was increased from 11°C to 22°C in -12 salinity potential and Tc decreased from 42°C to 33°C. Result showed that seed germination under drought was more sensitive, so that germination percentage at -8 bar was zero.  Obtained germination data for high salinity and drought clearly showed that the permissive temperature range for germination was limited.

The prediction of seed viability is important for seed producers, and its prediction in storage depends on the understanding of the quantitative relationships between seed loss, seed moisture and storage temperature. In order to study the effect of temperature, seed and time on the deterioration of the anise seed, and also quantitative characterization of this effect and determining the coefficients of life, this study was carried out in a randomized complete block design in a factorial experiment in the Agricultural Laboratory of Tehran University. The temperature was measured at 4 levels (5, 15, 25 and 35 o C), soil moisture contents in 4 levels (5, 9, 13 and 17%) and six times (one, two, three, four, five and six months) as the factors were this test. The results of analysis of variance showed that the effect of temperature on seed moisture content was significant for germination indices at 1% level. With increasing temperature and humidity, germination declined over time. Life coefficients after six months of storage showed that survival curves can be plotted with a single source. Also, the results showed that by increasing the moisture content at any temperature, especially at higher temperatures, the life expectancy decreases with increasing moisture content. Using the life-time equation, the coefficients KE=4/21, CW =1-66, CH =0 038/0 and CQ =0,00039 were calculated.

The main goal of seed storage is to maintain its quality from harvesting to sowing time. Among all factors, storage temperature and seed moisture content are the most important factors affecting seed longevity. This experiment was conducted at University of Tehran, Department of Agronomy and Plant Breeding during 1394 to determine the Ellis and Roberts deterioration model of Chenopodium quinoa seeds and introduce constants of viability equation. Seed viability and initial moisture content was measured and after that seeds were adjusted to 5, 9, 13 and 17% moisture content and sealed hermetically in Nano packets. Storage temperatures were 5, 15, 25 and 35˚C. The interval of sampling depended on the storage conditions. Seed viability constants were estimated to predict seed longevity in this species and relationship between sigma and moisture content and temperatures was determined. After probit analysis, survival curves were depicted in each condition. Results showed that seeds with 5% moisture content stored at 5°C had the highest germination percentage, and after 8 months seed viability decreased from 98% to 94%. But, seeds which were stored at 17% moisture content and 25 and 35°C had the highest deterioration rate. Estimates of KE, CW, CH and CQ were 2.93, 0.51, 0.019 and 0.00031, respectively. Also, the results showed that seed longevity decrease with increased seed moisture and temperature.

Quinoa (Chenepodium quinoa Willd.) is a grain-like crop which has a high grown potential in Iran. Due to it's seed have high nutritional value, therefore, compared to milk nutrition by the FAO. This study aims to determine the seed dormancy and pre-harvest sprouting three cultivars of quinoa. This plant was planted in a randomized complete block design at the research farm of university of Tehran and, phonological traits were recorded. Then the related studies such as seed dormancy and pre-harvest evaluation resistance were conducted in two 15 and 25°C constant temperatures in seed laboratory. The results shown that there is significant genetic variation for pre-harvest sprouting and other traits. The results demonstrate that Titicaca and Santamaria have lowest and highest germination in cluster, respectively. Also, Titicaca cultivar related to the other cultivars have had high percentage of seed dormancy. The results shown that it is possible to handle the quinoa crop in such areas which have frequent risk of PHS.

This study was conducted to quantify germination response of onion (Allium cepa) to temperature. For this purpose, seeds were exposed to Various constant temperatures (5, 10, 15, 20, 25, 30, 35 and 40ºC) treatments in seed lab, the university of Tehran, in 2015. The effects of temperatures on rate and percentage of germination was significant. With temperature increasing from 5 to 30ºC, both germination percentage and rate increased, while it decreased with increasing temperature from 30 to 35ºC. Cardinal temperatures of seed germination were estimated by using four regression models including dent-like, segmented, beta modified and beta Models. The best model for estimating cardinal temperatures was dent-like and beta modified models that by used dent-like model The base, under optimal, upper optimal and ceiling temperatures were 0.3, 24.99, 33 and 35.89 °C, respectively, and following beta modified model, The base, optimal and ceiling temperature were 0.2, 26.87 and 35.51°C. For predicting time of germination at different constant temperatures used Thermal-time that constant coefficient of Thermal-time was 3191.43 (°Cd).

The aim of this study was to quantify the response of germination rate to temperature and to find cardinal temperatures required for different germination percentiles in Papaver somniferum. Four models of non-linear regression [Quadratic, Segmented, Beta and Dent-like] were evaluated to describe the relationships between germination rate and temperature of P. somniferum over 7 constant temperatures (3, 5, 10, 15, 20, 25 and 30 ˚C). Different statistical indices [Root Mean Squares of Error (RMSE) and coefficient of determination (R2)] were used to compare models performance. The Dent-like was found to be the best model to predict germination rate (RMSE=000.35, R2=0.87). The base, sub optimum, supra optimum and the ceiling temperatures for P.somniferum  seed germination were estimated 3, 7, 20 and 31˚C, respectively. The cardinal temperatures depended on the model used for their estimation. Overall, Dent-like was better suited than the other models to estimate the cardinal temperatures for germination of P. somniferum seed. The highest germination percentage (72) and germination rate (0.86) was observed in 10 and 15 ˚C, respectively.

Quinoa (Chenepodium quinoa Willd) is a grain-like crop which has a high production potential in Iran. Due to its seeds high nutritional value, it is compared with milk by the FAO. In order to study the effects of temperatures on seed germination of Quinoa seeds under salinity stress conditions, an experiment was conducted in Seed Lab of the University of Tehran in Karaj. Temperatures regimes included 5, 10, 15, 20, 25, 30 and 35°C. At each temperature four salinity treatments (zero, -4, -8 and -12 bars) using NaCl were used. Results showed that increasing salinity stress decreased significantly germination rate but did not affect germination percentage except in 35°C at -12 bar. Basal temperature (Tb) for Quinoa germination was increased in high salinity potentials, but ceiling temperature (Tc) decreased. The germination data indicated that high salinity resulted in the narrow germination temperature in Quinoa seed.