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Germination of castor seeds of seven dwarf hybrid genotypes, compared to a 'Local' genotype, selected from a Tunisian population by the University of Catania well adapted to the Mediterranean environment, were studied at six different temperatures (8, 12, 16, 25, 32, and 40 °C). The results indicate that the optimal temperature (25 °C) and near-optimal temperature (32 °C) are the best temperatures for ensuring castor germination (final germination percentage (FGP) ≥ 82.81%). Furthermore, these temperatures positively influenced the vigour index (VI) and the radicle elongation. At a temperature of 8 °C, no germination occurred, while temperatures of 12 and 40 °C negatively affected the seed germination, which, in some genotypes, was null or negligible (<21.25%). A temperature of 16 °C allowed good results to be reached for the FGP and the other considered parameters. Overall, the dwarf hybrids performed better at high temperatures than at low temperatures, thus, making them suitable for late sowings, with the exception of the genotype 'C1020', which resulted the best performance at 16 and 40 °C, being suitable for both early and late sowings. On the other hand, the 'Local' castor genotype, being the best-performing genotype at 12 and 16 °C, and the most tolerant to low temperature (base temperature (Tb) 12.1 °C), could be used in the early sowing in spring. [ABSTRACT FROM AUTHOR]

Palm trees are propagated almost exclusively by seeds and each species germinates under a certain temperature range. In this sense, the two-way thermogradient plate may be used to determine temperature limits for germination and seed response to temperature. The objective was to define the alternating temperature regime promoting higher and faster seed germination of Carpentaria acuminata and Phoenix canariensis palms using a two-way thermogradient plate. This equipment allowed 64 combinations of alternating and constant temperatures, ranging from 6.97 to 36.42 ºC for C. acuminata, and 7.96 to 35.94 ºC for P. canariensis. Seeds were sown in Petri dishes (25 x 9 cm) containing 1% water agar. Linear regressions were estimated to determine cardinal temperatures. After 50 days, non-germinated seeds were transferred from the two-way thermogradient plate to a germination chamber at 30 °C. The temperature regime promoting highest seed germination percentage of C. acuminata was 30.45/33.00 °C (day/night), with minimum, optimum, and maximum temperatures of 9.13, 28.53, and 36.33 °C, respectively. For seed germination of P. canariensis, the most appropriate temperature regime was 29.77/17.93 °C (day/night), with minimum, optimum, and maximum temperatures of 9.53, 28.03, and 35.43 °C, respectively. [ABSTRACT FROM AUTHOR]

Population-based threshold models may aid in quantification of germination niches under stressful conditions such as salinity, temperature, and their interactions to understand seedling emergence patterns. Seeds of Sarcocornia fruticosa , Sarcocornia alpini , and Salicornia emerici were subjected to various temperatures at different NaCl concentrations. The median base NaCl concentration was roughly steady (0.68, 0.73, and 0.70 M, respectively) at sub-optimal temperatures, then decreased linearly at supra-optimal temperatures until the ceiling temperature. The estimated base, optimum and ceiling temperatures, in water, were –0.5, 15, and 29 °C for Sarcocornia fruticosa , –2.5, 11, and 24 °C for Sarcocornia alpini , and 9.5, 25, and 40 °C for Salicornia emerici , respectively. For all species, the base temperature did not change with the salinity, while both optimal and ceiling temperatures decreased. S. emerici showed rapid and synchronized germination when salinity decreased during the rainy season coinciding with favorable temperatures. • S. fruticosa , S. alpini , and S. emerici seeds were subjected to various temperatures at different NaCl concentrations. • The NaCl b(50) concentration was roughly steady at sub-optimal temperatures, then decreased linearly at supra-optimal ones. • T b , T o , and T c , in 0 M NaCl, were –0.5, 15, and 29°C for S. fruticosa , –2.5, 11, and 24°C for S. alpini , and 9.5, 25, and 40°C for S. emerici , respectively. • For all species, T b did not change with the salinity, while T o and T c decreased. • S. emerici showed rapid and synchronized germination when salinity decreased during the rainy season coinciding with favorable temperatures. [ABSTRACT FROM AUTHOR]

Conyza bonariensis is one of the most problematic weed species throughout the world. It is considered highly noxious due to its interference with human activities, and especially the competition it poses with economically important crops. This research investigated the temperature requirements for seed germination of four populations of C. bonariensis with distinct origin and the influence of daily alternating temperatures. For this, a set of germination tests were performed in growth chambers to explore the effect of constant and alternating temperatures. Seeds of the four populations (from Lleida, Badajoz and Seville, Spain and Bahía Blanca, Argentina) were maintained at constant temperatures ranging from 5 to 35°C. The final germination and cardinal temperatures (base, optimum and maximum) of each population were obtained. We also tested the influence of daily alternating temperatures on final germination. To do so, seeds were exposed to two temperature regimes: 5/15, 10/20, 15/25, 20/30 and 25/35°C night/day temperature (intervals increasing 5°C, with constant oscillation of 10°C) and to 18/22, 16/24, 14/26, 12/28 and 10/30°C night/day temperature (intervals with average of 20°C, but increasing the oscillation in 4°C between intervals). In general, all populations behaved similarly, with the highest germination percentages occurring in the optimum temperature range (between 21.7°C and 22.3°C) for both constant and alternating temperatures. In general, climatic origin affected germination response, where seeds obtained from the coldest origin exhibited the highest germination percentage at the lowest temperature assayed. In addition, we observed that the alternating temperatures can positively affect total germination, especially in oscillations that were further from the average optimum temperature (20°C), with high germination percentage for the oscillations of 15/25, 20/30, 18/22, 16/24, 14/26, 12/28 and 10/30°C in all populations. The cardinal temperatures obtained were significantly different across the populations. These results provide information that will facilitate a better understanding of the behaviour of Conyza and improve current field emergence models. [ABSTRACT FROM AUTHOR]

This study aims to explore the effect of environmental factors (temperature, light, storage time) on germination response and dormancy patterns in eight Mediterranean native wildplants, belonging to the Euphorbia L. genus. In detail, we considered E. amygdaloides subsp. arbuscula, E. bivonae subsp. bivonae, E. ceratocarpa, E. characias, E. dendroides, E. melapetala, E. myrsinites, and E. rigida. We collected seeds from natural plant populations and performed germination assays in climatic chambers at seven constant temperatures (from 5 to 35°C, with 5°C increments), and four fluctuating temperature regimes (8/15, 8/20, 8/25, and 8/30°C, with a 12/12 hr thermoperiod). Germination assays were set up both in dark (D) and in light/dark conditions (L/D, 12/12 hr photoperiod), after short and long seed storage (SS around 30 days and LS around 150 days). For all these species, except E. amygdaloides subsp. arbuscula, results show that the final germinated proportions were improved by a long storage period (>150 days), which supports the existence of nondeep physiological dormancy. Optimal temperature levels ranged from 14.3 to 21.3°C and base temperatures ranged from 5.6 to 12.1°C, while ceiling temperatures from 25.6 to 34.7°C. For none of these species, germinations were favored by an alternating daily temperature regime, while in several instances, germinations were quicker and more complete in darkness, than in an alternating light/dark regime. In some instances, extreme temperature levels (5 and 30°C) induced dormancy and germinations did not resume when seeds were exposed at optimal temperature levels. Results are discussed in terms of the dynamics of emergences and how this might be affected by climate changes. [ABSTRACT FROM AUTHOR]

The present study sought to evaluate the effect of different temperatures on germination and to determine cardinal temperatures (i.e., base, optimum and maximum) of Secale mountanum at temperatures of 3, 5, 10, 15, 20, 25, 30 and 35oC. Three nonlinear regression models (i.e., segmented, dent-like and beta) were used for quantifying the response of germination rate to temperature. The results showed that in addition to germination percentage, the temperature has a significant impact on germination rate. Given the root mean square of errors (RMSE) of germination time, the coefficient of determination (R2), the simple linear regression coefficients a and b, and the relationship between the observed and the predicted germination rates, the best models for determination of cardinal temperatures of Secale mountanum were dent-like and beta models. Base, optimum and maximum temperatures were estimated to be about 2.70 to 3.17, 21.27 to 30.00 and 35.00 to 35.05°C, respectively for the dent-like model. However, given the high value of SE for temperature base and a negative estimate of the base temperature of the beta model, one can report the dent-like model as the right model. Therefore, by using the dent-like model and the estimated parameters, it is possible to use this model for predicting germination.

Abstract: It is important to understand the effects of environmental conditions during plant growth on longevity and temperature response of pollen. Objectives of this study were to determine the influence of growth temperature and/or carbon dioxide (CO2) concentration on pollen longevity and temperature response of peanut and grain sorghum pollen. Plants were grown at daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30 and 44/34°C at ambient (350μmolmol−1) and at elevated (700μmolmol−1) CO2 from emergence to maturity. At flowering, pollen longevity was estimated by measuring in vitro pollen germination at different time intervals after anther dehiscence. Temperature response of pollen was measured by germinating pollen on artificial growth medium at temperatures ranging from 12 to 48°C in incubators at 4°C intervals. Elevated growth temperature decreased pollen germination percentage in both crop species. Sorghum pollen had shorter longevity than peanut pollen. There was no influence of CO2 on pollen longevity. Pollen longevity of sorghum at 36/26°C was about 2h shorter than at 32/22°C. There was no effect of growth temperature or CO2 on cardinal temperatures (T min, T opt, and T max) of pollen in both crop species. The T min, T opt, and T max identified at different growth temperatures and CO2 levels were similar at 14.9, 30.1, and 45.6°C, respectively for peanut pollen. The corresponding values for sorghum pollen were 17.2, 29.4, and 41.7°C. In conclusion, pollen longevity and pollen germination percentage was decreased by growth at elevated temperature, and pollen developed at elevated temperature and/or elevated CO2 did not have greater temperature tolerance. [ABSTRACT FROM AUTHOR]

Abstract: Prediction of the microbial growth rate as a response to changing temperatures is an important aspect in the control of food safety and food spoilage. Accurate model predictions of the microbial evolution ask for correct model structures and reliable parameter values with good statistical quality. Given the widely accepted validity of the Cardinal Temperature Model with Inflection (CTMI) [Rosso, L., Lobry, J. R., Bajard, S. and Flandrois, J. P., 1995. Convenient model to describe the combined effects of temperature and pH on microbial growth, Applied and Environmental Microbiology, 61: 610–616], this paper focuses on the accurate estimation of its four parameters (T min, T opt, T max and µ opt) by applying the technique of optimal experiment design for parameter estimation (OED/PE). This secondary model describes the influence of temperature on the microbial specific growth rate from the minimum to the maximum temperature for growth. Dynamic temperature profiles are optimized within two temperature regions ([15 °C, 43 °C] and [15 °C, 45 °C]), focusing on the minimization of the parameter estimation (co)variance (D-optimal design). The optimal temperature profiles are implemented in a computer controlled bioreactor, and the CTMI parameters are identified from the resulting experimental data. Approximately equal CTMI parameter values were derived irrespective of the temperature region, except for T max. The latter could only be estimated accurately from the optimal experiments within [15 °C, 45 °C]. This observation underlines the importance of selecting the upper temperature constraint for OED/PE as close as possible to the true T max. Cardinal temperature estimates resulting from designs within [15 °C, 45 °C] correspond with values found in literature, are characterized by a small uncertainty error and yield a good result during validation. As compared to estimates from non-optimized dynamic experiments, more reliable CTMI parameter values were obtained from the optimal experiments within [15 °C, 45 °C]. [Copyright &y& Elsevier]

Winter-grown canola ( Brassica napus L.) production is limited mostly by frost and winter kill in the southern canola-growing regions of the United States. Tolerance to cold and heat were assessed by studying percentage of pollen viability (PV), in vitro pollen germination (PG) and pollen tube length (PTL) for 12 field-grown cultivars. Freshly collected pollen from all cultivars were incubated on artificial solid growth media at a constant temperature ranging from 10 to 35 °C at 5 °C interval for 30 h to determine PG and PTL. A modified bilinear model best described the temperature response functions of PG and PTL. Canola cultivars showed significant variability (P < 0.001) for PV (61.3 % to 89.7 %), PG (29.0 % to 48.2 %) and PTL (463 to 931 μm). The average cardinal temperatures, Tmin, Topt and Tmax, for PG and PTL were 6.4, 24.3 and 33.7 °C, respectively. Principal component analysis revealed that maximum PG, PTL, Tmin and Topt of both PG and PTL were the most important factors in determining cold tolerance, whereas Tmax of PG and PTL, and maximum PG and PTL were more responsible in separating the cultivars for heat tolerance. The canola cultivar, KS3077, was the most cold tolerant with the lowest Tmin and the widest temperature adaptability range, and the cultivar Kadore was the most heat tolerant with the highest Tmax for the PG. The identified cold- and heat-tolerant cultivars may be useful in canola-breeding programmes to develop cultivars suitable for a niche environment. [ABSTRACT FROM AUTHOR]

Abstract: Cuphea (Cuphea viscosissima Jacq.× C. lanceolata W.T. Aiton; PSR23) is a potential new oilseed crop. Its oil is high in medium-chain fatty acids that are suitable for detergent/cleaner applications and also for cosmetics. The objective of this study was to determine the critical temperatures for cuphea seed germination. To determine the base, maximum, and optimum temperatures for seed germination, mature cuphea seeds were harvested from plants grown at Prosper, ND, in 2004, 2005, and 2006. Seeds were germinated on a temperature-gradient bar varying between 5 and 35°C. Cumulative germination was calculated for each temperature treatment. Base temperature (T b) and optimum temperature (T o) were estimated from the third-order polynomial temperature-response functions for each year. In addition, germination rate per day was used in a linear model to estimate the base temperature below which germination rate was equal to zero (T b), and the maximum temperature above which germination was equal to zero (T m). The optimum temperature (T o) was calculated as the intercept of sub-optimal and supra-optimal temperature-response functions. Through the third-order polynomial temperature-response functions and the sub-optimal/super-optimal intercept approaches, we were able to generate six estimates for each critical value. Estimates of the base temperature for cuphea seed germination ranged between 3.3 and 11°C, with the most reliable estimates between 6 and 10°C, similar to many warm-season crops such as corn (Zea mays L.) and sorghum (Sorghum bicolor L.). The optimum temperature for cuphea seed germination ranged between 18.5 and 24°C with a mean value of 21°C. The maximum temperature for seed germination ranged 33–38°C. On this basis, a cuphea planting date after 20 May is recommended for east-central North Dakota. [Copyright &y& Elsevier]

Thermal time models are useful to determine the thermal and temporal requirements for seed germination. This information may be used as a criterion for species distribution in projected scenarios of climate change, especially in threatened species like red cedar. The objectives of this work were to determine the cardinal temperatures and thermal time for seeds of Cedrela odorata and to predict the effect of increasing temperature in two scenarios of climate change. Seeds were placed in germination chambers at constant temperatures ranging from 5 ± 2 to 45 ± 2 °C. Germination rate was analyzed in order to calculate cardinal temperatures and thermal time. The time required for germination of 50% of population was estimated for the current climate, as well as under the A2 and B2 scenarios for the year 2050. The results showed that base, optimal and maximal temperatures were −0.5 ± 0.09, 38 ± 1.6 and 53.3 ± 2.1 °C, respectively. Thermal time (θ1(50)) was 132.74 ± 2.60 °Cd, which in the current climate scenario accumulates after 5.5 days. Under the A2 scenario using the English model, this time is shortened to 4.5 days, while under scenario B2, the time is only 10 hours shorter than the current scenario. Under the German model, the accumulation of thermal time occurs 10 and 6.5 hours sooner than in the current climate under the A2 and B2 models, respectively. The seeds showed a wide range of temperatures for germination, and according to the climate change scenarios, the thermal time accumulates over a shorter period, accelerating the germination of seeds in the understory. This is the first report of a threshold model for C. odorata, one of the most important forest species in tropical environments. [ABSTRACT FROM AUTHOR]