segmented model

This experiment was conducted to investigate the effects of constant temperatures and light on seed germination of white pigweed (Amaranthus albus), smooth pigweed (Amaranthus chlorostachys), redroot pigweed (Amaranthus retroflexus), and green amaranth (Amaranthus viridis) in 2018 and 2019 at Gorgan University of Agricultural Sciences and Natural Resources. In the first year, germination of different species of Amaranthus were studied monthly over a 12-month after-ripening period. In the fifth month of after-ripening, seed germination of different Amaranthus species was studied at temperatures of 10, 15, 20, 25, 30, 35, 40, and 45 °C under light and darkness conditions. In the second year, seed germination of the mentioned species was investigated at temperatures of 10, 15, 20, 25, 30 and 35 °C in four conditions: light with gibberellic acid, light without gibberellic acid, darkness with gibberellic acid and darkness without gibberellic acid. The germination percentage of different species of Amaranthus increased during the after-ripening period; although the process were varied in different species. The application of gibberellic acid also improved germination. Therefore, seed dormancy of the mentioned species is non deep physiologically. Germination percentage of different species of Amaranthus increased in temperatures of 30-35 °C, and gibberellic acid also improved their germination percentage and rate. Also, the use of gibberellic acid reduced base temperature of germination. Such responses to light and temperature ensure the germination of these plants in spring and on the soil surface. A decrease in the base temperature of germination may also cause the germination of some species of Amaranthus before spring. Low germination percentages, especially at low temperatures, are biologically important because small but significant populations of weeds may appear in the field and cause problems for farmers.

Currently, temperature and salinity stresses are spreading globally, which have a detrimental impact on the performance of various plants, particularly during seed germination and seedling growth stages. Therefore, the objective of this laboratory study was to examine the influence of temperature treatments and salinity levels on germination characteristics and initial seedling growth of kochia.

In the first experiment, temperature at nine levels (1, 5, 10, 15, 20, 25, 30, 35, and 40°C), and in the second experiment, salinity (osmotic potential at six levels (no stress, -0.4, -0.8, -1.2, -1.6, and -1.8 MPa) were considered as experimental treatments. In order to determine the cardinal temperatures (base, optimal, and ceiling) of germination in kochia seeds, non-linear regression models including the segmented, dent-like, and modified beta models were used.

In the first experiment, the response of kochia germination rate was predicted by a segmented function with R2, RMSE, and AIC (Akaike) values of 0.92, 1.32, and 65.69, respectively, which indicates the high accuracy and precision of this model in predicting the cardinal temperatures of kochia seed germination compared with the other two models. In this model, the estimated base temperature for germination was 0.7°C, the optimal temperature was 20°C, and the ceiling temperature was 44.3°C. In the second experiment, salinity stress negatively affected the characteristics of seed germination in kochia, including germination percentage, germination rate, percentage of normal seedlings, seedling length, and seedling vigor index. The highest germination percentage of kochia seeds was observed under salt-free conditions with 88.66%, which decreased to 13% under -1.8 MPa salinity conditions.

In general, the results showed that the segmented model is more efficient and accurate than the other two models in predicting germination of kochia seeds under different temperature treatments. Also, increasing levels of salinity stress significantly reduced germination potential and seedling growth of kochia seeds, so that at a stress level of -1.8 MPa, germination rate decreased by 75% compared with stress-free condition.

This study was conducted with the aim of investigating the effect of salinity stress and different temperatures on germination and determining the cardinal temperatures of germination (basic, optimal and ceiling germination temperatures) of two sugar beet cultivars. Experimental treatments included different levels of salinity stress (0, 40, 80, 120 and 160 mM) and different temperatures (5, 10, 15, 20, 25, 30, 35 and 40 °C). The three-parameter sigmoidal model was used to determine the time to reach 50% germination. The results showed that temperature and salinity stress had an effect on germination percentage and germination rate. In addition, the results showed that with increasing temperature up to optimum temperature, the germination percentage and germination rate increased, and with increasing salinity stress, the germination percentage and also the germination rate decreased. The germination percentage and germination rate in Brigitta variety was higher than that of Shokofa variety. According to the RMSE, CV, R2Adj, SE parameters, the beta model was the most suitable model for both sugar beet cultivars. In the Brigitta variety, the base temperature is between 3.67 and 5 °C, the optimal temperature is between 16.67 and 26.35 °C, and the roof temperature is between 40.10 and 40.89 °C, and in the shokofa variety, the base temperature is between 2.88 and 2.80 °C. 5.65, the optimum temperature varied between 16.11 and 26.47 °C and the ceiling temperature between 39.94 and 42.94 °C. The obtained results showed that the percentage and speed of germination in Brigitta variety under salinity stress conditions and different temperatures was higher than that of Shokofa variety, but there was no significant difference between the two varieties in terms of cardinal temperatures. Therefore, by using the output of these models at different temperatures, it is possible to predict the germination speed at different potentials.

Seed germination is one of the most important factors which determine the success of failure of crop establishment. In the absence of other environmental limiting factors such as moisture, temperature would determine the rate and overall seed germination. This research was conducted to investigate the effect of temperature regimes on seed germination, quantify the response of germination rate to temperature and determine the cardinal temperatures for different germination percentiles in Solanum lycopersicom.

Two-way factorial experiment including seven constant temperatures (5, 10, 15, 20, 25, 30 and 35 oC) and two tomato varieties (Red cherry: var. Cerasiformi and Yellow pearl: var. Yellow Pear) was conducted based on a completely randomized design arranged with thee replications at the seed technology laboratory of Agricultural Sciences and Natural Resources University of Khuzestan in 2019. Beta, segmented and dent-like functions were used to determine the relationship between germination rate and temperature. Logistic model was used to describe the suitable pattern for the germination of these two cultivars in response to each temperature level.

Results of analysis of variance showed that the interaction effect of temperature and cultivar was significant on all studied traits. Results showed that respectively at temperatures of 15, 20, 25 and 30 oC, total seed germination for yellow pearl tomato was 93%, 96%, 95% and 86% and for red cherry tomato was 95, 98, 93 and 98 percent. There was no seed germination for both tomato varieties at 5, 10 and 35 oC. Based on the results of the fitted models, it was revealed that among the tested non-linear regression models, segmented model described the germination rate of the studied tomato cultivars against the temperature the best (AICc≤70, R2=0.93). Three parameters logistic functions exhibited a reasonable fit (R2=0.96) for germination time course under temperature range of 15 to 30 oC in both cultivars. Based on the segmented model, base, optimum and ceiling temperatures of Yellow pearl and Cherry tomato were estimated 11.25, 28.72, 35.00 oC and 10.97, 28.361 and 35 oC, respectively.

Both tomato cultivars exhibited sensitivity to changes in temperature. Seed germination rate and number of the germinated seeds increased at temperatures higher than base. This increase continued until the optimum temperature and then started to decline as the temperature exceeded from optimum range. Also, results obtained from the logistic function showed that Yellow pearl cultivar is more sensitive to supra-optimal temperatures compared with Cherry tomato, and germination percentage of the 97.79 to 85.09 percent as temperature reached from 25 to 30 oC.

Swallow-wort (Cynanchum acutum) in recent years has aggressively infested sugarcane fields. Understanding seed germination behavior of this weed will save time to control it. In this investigation, germination of seeds was studied at five fruit cutting time with two weeks intervals at 14 to 70 days after fruiting (DAF) at five temperature levels 10, 20, 30, 40 and 50°C in Sugarcane research and training institute in 2017. The results showed that swallow-wort seeds were not able to germinate by the 14 DAF. From the 42 DAF thereafter, germination rate showed increasing trend and reached its highest value at 56 DAF, with 19.70 seeds per day. At the same time, the highest germination of swallow-wort seeds was 97% at temperature of approximately 30°C. By fitting the segmented model to the germination rate data, the minimum, optimum and maximum germination of mature seeds were 18.1, 32.6, and 57°C, respectively. Seeds from fruit at the 28 and 42 DAF required higher germination temperatures and showed decreasing trend with increasing the days from formation to complete ripened fruit. Based on the results of this study, it is necessary to plan for utilizing different methods of control such as removal the above ground organs as a management strategy and at maximum the second week after swallow-wort fruiting, to prevent production of seeds with ability of germination.

Determination of response function of seed germination and seedling emergence to temperature and obtaining cardinal temperatures (base, optimal and maximum) and biological day requirement (minimum day number for seed germination and seedling emergence under optimal temperature and moisture conditions) for emergence is important for crop simulation modeling. This study was carried out to survey seedling emergence response to temperature in five rapeseed cultivars that were sown on 12 sowing dates under Gorgan environmental conditions (2013-2014). Three regression models including beta, segmented and dent-like were used to describe the response of seedling emergence rate to temperature. Root mean square of error, coefficient of determination, correlation coefficient and regression of predicted versus observed values were used to develop the appropriate model. Segmented model was superior compared to beta and dent-like models to achieve the objective of this study. Estimated cardinal temperatures using appropriate model were 3.2, 26.8 and 40˚C for base, optimum and maximum temperatures, respectively. Estimation of biological day requirement in sowing depth of 2 cm showed 4.5 days. The result showed that there is no significant difference for cardinal temperatures and biological day requirement among cultivars. It was concluded that segmented model can be used to quantify the response of rapeseed sedling emergence to temperature and to obtain cardinal temperatures of emergence and thermal time or time to emergence. These parameters are required to develop prediction models for rapeseed seedling emergence under diverse temperature conditions.

Germination and seedling establishment are two critical and important stages during plants growing season. From seed technology viewpoint, germination refers to emergence and development from seed embryo, so that could produce normal seedling. Many studies have been done to determine germination cardinal temperatures and required thermal time for emergence occurrence, but there's not a lot of information about the sunflower cultivars. This study was aimed to investigate the germination response of three sunflower varieties (Farrokh, Hisan and Progress) and assessment of nonlinear regression models to determine cardinal temperatures and required biological days for germination of three aforementioned varieties. For this, Farrokh, Hisan and Progress varieties seeds were exposed to five constant temperatures (15, 25, 30, 35 and 40 0C) in Seed Research Lab., Gorgan Univ. Agric. Sci. and Natur. Res. (GUASNR) in 2012. Germination duration and percentage were measured, germination rate was calculated and biological time and thermal time for germination were estimated. In order to quantify cardinal temperatures, three nonlinear regression models (segmented, dent-like and beta) were used. Results indicated that temperature and variety simple and interaction effects had significant effect on maximum germination percentage (MGP), germination rate (reciprocal time to 50% germination), and time to 10, 50 and 90% germination. Assessment of three nonlinear regression models including segmented, dent-like and beta models revealed that segmented and beta had the same quality and selected as appropriate models for Farrokh, while dent-like model was selected as the superior model for Hisan and Progress varieties. For Farrokh, base, optimum and ceiling temperatures were estimated as 8.51, 33.26 (lower and upper optimum were 30.44, 37.05) and 48.47 0C, respectively. the base, lower optimum, upper optimum and ceiling temperatures were estimated as (8.9, 30.41, 37.77 and 45 0C) and (9.85, 28, 38 and 47 0C) for Hisan and Progress, respectively. Biological time for 50% germination for Farrokh, Hisan and Progress also were estimated as 18.14 (20.47), 18.52 and 17.05 hours. Results revealed that different sunflower varieties have different cardinal temperatures. Therefore, if we are planning to use these coefficients to quantify responses of sunflower to temperature and prediction of germination occurrence time, variety-specific coefficients should be determined and used.

This study was conducted to quantify germination response of annual savory (Satureja hortensis L.) to temperature and water potential. For this purpose، seeds were exposed to different temperature (12، 15، 20، 25، 30، 35، 37 and 40°C) and water potential (zero، -0. 1، -0. 3، -0. 5 and -0. 7 MPa) treatments in Seed Research Lab.، Gorgan University of Agricultural Sciences and Natural Resources in 2013. Results indicated that temperature and water potential and interacted effects had significant effect on maximum germination percentage، germination rate (reciprocal time to 50 percent germination)، and time to 10، 50 and 90 percent germination. Along with water potential decrement، both germination percentage and rate decreased. With temperature increasing to optimum temperature، both germination percentage and rate increased، while it decreased from optimum temperature onward. Assessment of three nonlinear regression models including segmented، dent-like and beta models revealed that the last one was selected as the superior model. Based on the superior model (Beta)، base، optimum and ceiling temperatures were estimated as 7. 56، 23. 98 and 40°C، respectively. Biological hours for control treatment (zero potential water) was calculated as 91. 17 hours. Cardinal temperatures were not affected by water potential، but biological hours for germination was delayed as 17. 64 hours per each unit water potential increment.

Cold and tropical Vetch (Vicia villosa and Vicia pannonica)are an important plants which did not do any experiment about quantification of them germination reaction to temperature. Thus, a CRD experiment performed in seed research laboratory of Urmia University with four replications which temperature treatment were eight levels of temperature as: 1, 3, 5, 10, 15, 20, 25, 30, 35 and 40 º C. Results revealed that temperature had a significant effects on germination rate and it’s percent and segmented model estimated greatly cardinal temperature (base, optimum and ceiling temperatures). Germination rate of Vicia. Pannonica in equal and less than -7.6 and equal and higher than 40.76 ºC stopped, though this thermal range for V.  villosa was equal and less than -3.8 and equal and higher than 41.2 º  C, respectively. R max were 0.027 and 0.033 h-1 for V. pannonica and V. villosa respectively. Also, results emphasized that both of Vicia species can be geminate in less than zero temperature and in V. Pannonica the base temperature was fewer than V. villosa, so, germination percent and its rate increased by upgrading in temperature to optimum temperature. Therefore, both Vicia species can geminate and emergence in  extended range of environmental thermal from -7.6 to 40.76 º C for V. Pannonica and -3.8 to 41.2 º  C in V.  villosa and thus recognized as a forage crop with acceptable production for various season and climate.