جستجوی مقالات مرتبط با کلیدواژه « hydrotime model » در نشریات گروه « کشاورزی »

Seedling germination and establishment are one of the most sensitive stages of plant life that play a role in plant production, proper plant establishment, plant density, and uniformity and management goals. Osmotic stress has a significant effect on germination percentage and rate. Salicornia persica is an annual halophyte plant that can grow in saline environments. According to the studies and the importance of determining the tolerances of salinity and drought tolerance in germination and plant establishment, this study aimed to investigate the effect of osmotic potentials of polyethylene glycol and sodium chloride on germination and fit of time-moisture and time-salinity models of Salicornia seeds.

In order to investigate the effect of osmotic potentials caused by polyethylene glycol and sodium chloride on germination and fit of Hydrotime and Halotime models of Salicornia seeds, two experiments were conducted based on a completely randomized design at Yasouj University in 2020. The first experimental in drought stress treatments included 13 levels of osmotic potential (zero, -0.3, -0.6, -0.9, -1.2, -1.5, -1.8, -21, -2.4, -2.7, -3, 3.3 and -3.6 MPa) which were made of polyethylene glycol 6000 and second in salinity stress included 13 levels of sodium chloride concentration that was iso-osmotic with first experiment (Zero, 62, 122, 187, 249, 311, 368, 435, 498, 560, 622, 684 and 745 mM). After the end of the germination period, the characteristics of germination rate and percentage were calculated and the hydrotime model was used to describe the relationship between germination and water potential, and the halotime model was used to describe the relationship between germination and salinity. To select the best model among the osmotic potentials, root mean square parameters and R2 were used.

The results of mean comparison of effect of osmotic potentials on the percentage of germination showed that in PEG and NaCl treatment, it was almost 100% up to the level of -1.2 and -1.5 MPa, respectively, and after that, a decreasing trend was observed, so that at the level of -3.3 MP showed a decrease of about 90 and 85%, respectively. The output results of the models showed that the coefficient of the hydrotime and halotime models were 96.8 MPa.h and 16181.87 mM.h, respectively, and the drought and salinity tolerance thresholds were -3.28 MPa and 714.62 mM, respectively. The halotime model quantified the germination of Salicornia seeds better than the hydrotime model. Drought stress limits the absorption of water by seeds and affects germination by reducing the movement and transfer of seed reserves or by directly affecting the structure and synthesis of protein in the embryo. Salinity increases the osmotic pressure of the solution and reduces water absorption through the seeds. On the other hand, high salinity causes toxicity and disturbs the ionic balance and reduces seed germination by affecting the vital interactions of the seed.

The rate of decrease in germination rate and percentage in drought stress was higher than salinity stress. Based on the results of this study, using the halotime model in biological studies of halophyte plants under osmotic stress, the tolerance threshold and the time required for germination at different salt concentrations can be well determined.

In order to quantifying cardinal temperature and hydro time germination of Cuminum cyminum seeds, an experiment was conducted as completely randomized design with three replications in laboratory of Faculty of Agriculture and Natural Resources of University of Mohaghegh Ardabili in 2017. Experimental treatments were included: temperatures as, 0, 5, 10, 15, 20, 25, 30, 35 and 40 ˚C and osmotic potential as 0, -0.2, -0.4, -0.6, -0.8, -1 and -1.2 MPa. Quantifying of cardinal temperature for germination fraction of 10, 50 and 90 % were evaluated from four models as: beta, modified beta, dent-like and segmented. In this study, RMSE and R2 and AICc were used for comparison between models. Result indicted that beta model showed better responses description for germination rate of Cuminum cyminum to temperature compared with others models. However basic temperature of Cuminum cyminum was between 0.7 to 0.9 ˚C, optimum temperature about 20 to 21 ˚C and maximum temperature was 35 ˚C. In addition based on hydro time models results, θH and Ψb(50) of Cuminum cyminum were estimated 97.5 and -0.46 MPa respectively.

Seed vigor is an index of its quality. Seed vigor tests are designed to predict more accurately of seedling emergence in the field In order to predict seedling emergence more accurately, seed vigor tests are designed, depending on their prediction accuracy, each is used for different plants. This study was conducted at the seed technology laboratory in Ramin University of Agricultural Sciences and Natural Resources and field Research in 2016. In order to laboratory evaluation of seed vigor tests for predicting seedling emergence in the field, 5 safflower seed lots was used. In this study seed vigor tests include seedling establishment percent in field, standard germination test, seedling growth test, seed germination rate test and salinity test (0, 100, 200, 300 and 400 mM) The results showed that the standard germination test, seedling growth, germination rate and salinity were not significant correlated with seedling establishment percent for seed lots in the field. Therefore, these tests can not confidently used to separate the weak and strong safflower seed lots. However, the results of the comparison of the two-fold model did not succeed in distinguishing between strong and weak masses The analysis of the same data using the HydroTime model yielded results that could be separated by strong and weak safflower masses these tests can be used to separate the weak and strong safflower seed lots and used for predicting emergence in the field.

Temperature and water potential are two of the most important environmental factors regulating the seed germination. The germination response of a population of seeds to temperature and water potential can be described on the basis of hydrothermal time (HTT) model. Regardless of the wide use of HTT models to simulate germination, little research has critically examined the assumption that the base water potential within these models is normally distributed. An alternative to the normal distribution that can fit a range of distribution types is the Weibull distribution. Using germination data of Castor bean (Ricinus communis L.) over a range of water potential and sub-optimal temperature, we compared the utility of the normal and Weibull distribution in estimating base water potential (b). The accuracy of their respective HTT models in predicting germination percentage across the sub-optimal temperature range was also examined.

Castor bean seed germination was tested across a range of water potential (0, -0.3, -0.6 and -0.9 MPa) at the sub-optimal range of temperature (ranging from 10 to 35 ˚C, with 5 ˚C intervals). Osmotic solutions were prepared by dissolving polyethylene glycol 8000 in distilled water according to the Michel (1983) equation for a given temperature. Seed germination was tested on 4 replicates of 50 seeds in moist paper towels in the incubator. The HTT models, based on the normal and Weibull distributions were fitted to data from all combinations of temperatures and water potentials using the PROC NLMIXED procedure in SAS.

Based on both normal and Weibull distribution functions, hydrotime constant and base water potential for castor bean seed germination were declined by increasing the temperature. Reducing the values of base water potential showed the greater need to water uptake for germination at lower temperatures and reducing hydrotime constant indicated an increase in germination rate by increasing the temperature. Compared with hydrothermal time model based on the normal distribution, Weibull hydrothermal time model gave a better fit (RMSE=8.07%) and more accurate (AIC=-5801) to seed germination data of castor bean. Based on Weibull hydrothermal time model, base temperature and hydrothermal time constant were estimated to be 8.86 ˚C and 833/10 MPa h, respectively. The osmotic potential from which the germination begins was (μ) -1.71 MPa. The shape parameter (λ) of the Weibull hydrothermal time model implied asymmetry of base water potential data and skewness of distribution to the right. A right-skewed distribution of b(g) has important ecological implications, as it means that the seed population have a greater reserve of seeds with very high values of b(g) and are therefore slow in germination, even under optimal conditions. The HTT model assumes that the timing, rate and percentage of seed germination for a constant temperature to be controlled by the difference between water potential of the seedbed and the b for a given percentile (b(g)). Most previous studies have assumed that b(g) is normally distributed. Our results suggested that the Weibull distribution may be more suitable than the normal distribution for seed germination modeling of castor bean. Similar to the normal distribution model the parameters of the Weibull HTT model can be readily interpreted to yield information about the frequency distribution of population for b(g), enabling comparison of the germination behaviors in different seed populations. The location parameter of Weibull HTT model (μ) specifies the lowest b(g) possible value in the population ((b(0)) that cannot be derived from normal HTT model. The median (M) and mode (Mo) can be readily determined by equations of and, respectively, from the μ, scale (σ) and λ parameters. The median specifies the value of b(50) for the population and the mode will specify the location of the peak of the probability distribution function for b(g). Another advantage of the Weibull distribution in this application is that it can approximate a range of b(g) distributions through changing the shape parameter.

Results of this research were in contrast with the assumption of a normal distribution of base water potential of a seed population. Hence, before using a hydrothermal time model for predictions the distribution of base water potential within a seed sample should be examined and an appropriate equation be selected.. Due to the flexibility of the Weibull distribution, this model provides a useful method for predicting germination and determining the distribution of base water potential.

The hydrothermal time models have been widely applied to describe the germination responses of seeds to temperature and water potential. In this study, three hydrothermal time models developed on the basis of different statistical distributions (Normal, Weibull and Gumbel) were compared to describe the Phalaris minor seed germination. Results showed that Gumbel (AICc=-762.8) and Weibull (AICc=-762.6) hydrothermal time models more accurately predicted P. minor germination than Normal (AICc=-737.6) hydrothermal time model. However, there was no significant difference among values of predicted hydrothermal time constant, base temperature and median base water potential (ψb(50)) for germination of P. minor using all three models and were estimated to be 1000 MPa C h, 4.2 C and -1 MPa, respectively. Based on the Weibull hydrothermal time model, water potential threshold for the onset of germination (ψb(0)) was equal to -1.5 MPa. Also, the distribution of base water potential for germination was right skewed (λ=1.57). Weibull hydrothermal time model can be widely used to predict seed germination by considering the flexibility of distribution, the possibility of determining the base water potential distribution skewness and estimation of water potential threshold for the onset of germination.

A better understanding of the factors influencing the germination of weed seeds could facilitate the development of more effective cultural weed management practices. The aim of this research was to determine the effects of environmental factors on seed germination of Cutleaf groundcherry (Physalis angulata L.). Results showed that application of gibberellic acid (GA3) was effective treatment for seeds primary dormancy breaking. Physalis angulata seed had identical germination in either light/dark or continuous dark regimes، indicating this weed species is non-photoblastic. However، the maximum germination percentages and germination rates were observed at warmer alternating temperatures. The ranges of response to the constant temperature for germination were widened during afterripening periods. Based on the 2-piece segmented model، the base، the optimum and maximum temperatures for germination of P. angulata were estimated to be 8. 06، 35. 83 and 42. 30 ˚C، respectively. The response thresholds of P. angulata to inhibit 50% of maximum germination for salinity and osmotic potential were 59. 25 mM and -0. 29 MPa، respectively. According to the weibull hydrotime model، hydrotime constant and base water potential to initiate germination were obtained equal to 26 MPa h and -1. 45 MPa، respectively.

Germination is the first and most important developmental stage of plants which is influenced by genetic and environmental factors. Hydrotime model describes the relationship between water potential (ψ) and seed germination rate and percentage. This model quantifies the rate of germination progression (θH)، the stress tolerance of germination (ψb(50)) and the uniformity of germination (σψb). This indicators can be used to show seed lots or varieties vigor and evaluation of dormancy in seed and some treatments effects (e. g. priming، ABA or GA) on seeds vigor. Hydrotime model is not well known amongst Iranian researchers. This study aims at introducing the application of hydrotime model in germination data analysis. To achieve this، germination data of three plants (sweet clover: Melilotus officinalis، rye: Secale cereael and wheat: Triticum aestivum) in response to drought stress were used. The θH value quantifies the inherent rate of germination، which can vary among species and different physiological stages. The ψb (50) value is an indication of the average stress tolerance of the population. A population with a high ψb (50) value (less negative) will be inhibited germination at higher ψ (less stress) than will a population with a lower ψb (50) value. The value of ψb (50) for a seed population can be shifted to higher or lower values by the induction and release of dormancy. The σψb value is a quantitative estimate of the uniformity in germination in the population as greater σψb means a wider variation between the first and last seeds to germinate.