segmented function

  oilseed rape has a wide range of adaptation and grows well in many regions under variable temperatures. However, the ability of the varieties varies in response to the favorable and unfavorable conditions. Temperature stresses (high or low temperatures) have harmful effects on crops. Generally, temperatures below 10 ° C can damage germination and emergence. Low temperatures can also have a negative effect on the post-emergence stages of crops. The high temperatures can also reduce the total dry matter produced, the number of pods under development, the number of seeds per pod, the weight of seeds, and, finally, the yield of the plant. Also, high temperatures affect the development and maturity of the seeds, resulting in a higher level of yield. Identifying high or low tolerant cultivars can help researchers improve the new cultivars and increase the flexibility of selecting the right cultivar for farmers. There are several methods for evaluating cultivars at low and high temperatures based on farm or laboratory surveys. Field surveys are difficult, unsustainable and seasonal. Because in field conditions, temperatures and humidity fluctuate a lot. Various studies have been done to evaluate the variation of germination in heat or cold stress in different plants such as lettuce, alfalfa, sorghum, cotton, sesame, etc. However, there is not much information on canola cultivars in Iran. The aims of this study was to determine the cardinal temperatures (2) evaluate the tolerance of different genotypes at high or low temperatures and (3) and to study the secondary dormancy potential in Iranian genotypes. In order to, germination tests were conducted in fixed temperatures incubators with 5, 10, 15, 20, 25 and 30 oC on 10 oilseed rape genotypes, in 4 replications with 50 seeds. Finally, cardinal temperatures were estimated using segmented (for germination rate) and beta (for germination percentage) functions. The tolerance of genotypes to high or low temperatures were determined using estimated cardinal temperatures. Also, an experiment was conducted to investigate the potential of different cultivars for induction of dormancy, in which seeds of 10 oilseed rape genotypes were subjected to drought stress conditions to determine the percentage of total induction due to drought for each genotype. The percentage of germinated seeds, the percentage of seeds with dormancy and dead seeds can be determined. Finally, the percentage of induction of the secondary dormancy was calculated for each genotype. Statistical analysis was performed using SAS software. Marshall and Squire (1996) showed that the minimum temperature (Tb) for oilseed rape germination was about 3 °C. Soltani et al. (2013) showed that the minimum temperature for oilseed rape germination was 2.7 °C and under dry conditions up to 6.7 °C at -0.8 MPa increased. Also, they showed that the average thermal time for germination (TT50) increased from 29.5 °C/day at 0 MPa to 57.9 °C/day at -0.8 MPa. Results indicated that mean of base (Tb), optimum (To) and ceiling (Tc) temperatures for germination percentage were 4.99, 18.23 and 34,20 oC and also mean of base (Tb), optimum (To) and ceiling (Tc) temperatures for germination rate were 6.18, 24.76 and 39.40 oC. The Heat and Cold tolerance indexes were also different in different cultivars. Okapi cultivar was the most tolerant in heat tolerance index (5.95) and in cold tolerance index (8.48). X-Power had the lowest tolerance to heat (4.78) and cold (6.50). The potential of secondary dormancy induction also was at the highest level in Okapi (about 40 %). It seems that there was connection between secondary dormancy induction and tolerance to temperature stresses which needs more studies.

In order to examine the germination response of basil medicinal plant’s seeds (Ocimum basilicum L.) to temperature and determination of cardinal temperatures for germination percentage and rate, a compound decomposition experiment was performed through a fully random design with four reptile and six thermal levels (8, 15, 20, 25, 30, and 35 degree centigrade) in seed technology laboratory of Abou-Reyhan campus in Univerity of Tehran. In this study, 22 Basil masses were evaluated including “Tehran”, Green Shahr-e-Rey”, “Green Birjand”, “Purple Birjand”, “Green Shiraz”, “Green Zabol”, “Zahedan”, “Green Zahedan”, “Kermanshah”, “Green Pishva”, “Purple Pishva”, “Green Malayer”, “Khash”, “Local green Tonekabon”, “Green Isfahan II”, “Purple Isfahan II”, “Green Isfahan III”, “Green Isfahan IV”, “Green Mash’had”, “American green Napolta”, “Italian Genovese”, and “Switzerland” . Based on the results of variance analysis, temperature impact, genotype, and their interaction on germination percent and germination rate was significant at the 5% level. Optimal range of temperature for germination percent and germination rate was obtained as 19.10-27.78 and 20.32-29.89 degrees centigrade, respectively. In most masses, the highest germination rate was observed at 25 degrees centigrade. Among all evaluated masses in current research, Isfahan III was appropriated the highest germination rate in all temperatures. The results of experiment showed that the response of germination percentage and germination rate to temperature was well described through Beta function and segmented function, respectively, and cardinal temperatures can be determined for Basil using these two models.

This study was conducted to evaluate the effects of water potential and temperature on seed germination rate of lemon balm (Mellissa officinalis L.). The seeds were incubated in various temperatures of 20, 23, 25, 27, 30 and 32ºC and water potentials of 0, -0.2, -0.4, -0.6 and -0.8 MPa in three replications. This study was conducted in Seed Laboratory, College of Agriculture and Natural Resources, University of Tehran in Karaj in 2015. Data were analyzed using combined statistical design in a completely randomized design in several places. Segmented function was evaluated to describe cardinal temperatures. The base, optimum and ceiling temperatures of lemon balm were 17.30, 30.9 and 35ºC under optimum conditions of water potential, respectively. The base temperature increased gradually with decreasing water potential and increased to 21.25°C in -0.8 MPa water potential. The optimum temperature decreased to about 28°C by decreasing water potential to -0.6 MPa. Lemon balm seeds did not germinated in 5, 10, 15 and 35°C in any moisture levels. The R2 value of hydrothermal time model was 0.55. The hydrothermal value was 71.41 MPa oday and According to this model seed germination of lemon balm needs to 71.41 MPa oday. The results can be used for future studies on the seed biology and ecology of lemon balm.

This study was conducted to evaluate the effect of salinity and temperature on seed germination characteristics of lemon balm (Mellissa officinalis L.) in various temperatures of 20, 23, 25, 27, 30 and 32ºC and water potentials of 0, -0.2, -0.4, -0.6 and -0.8 MPa were used as treatments in Seed Laboratory, College of Agriculture and Natural Resources, University of Tehran in 2015. Data were analyzed using combined statistical design. Percentage of germination decreased as salinity increased at each level of temperature. Estimate of threshold point for salinity was -0.132 MPa. Segmented function was evaluated to describe cardinal temperatures. The base, optimum and ceiling temperatures of lemon balm were 17.30, 30.9 and 35ºC under optimum conditions of water potential, respectively. Response curve of the base temperature increased linearly from 17°C (control) to about 23°C (-0.8 MPa) by decreasing water potential. The base and optimum temperature and the biological time for germination were increased by increasing salinity. The results showed that Melissa officinalis L. is sensitive to salinity in germination stage.