Cardinal Temperatures Research Articles

Optimizing multi-environment trials in the Southern US Rice belt via smart-climate-soil prediction-based models and economic importance.

Rice breeding programs globally have worked to release increasingly productive and climate-smart cultivars, but the genetic gains have been limited for some reasons. One is the capacity for field phenotyping, which presents elevated costs and an unclear approach to defining the number and allocation of multi-environmental trials (MET). To address this challenge, we used soil information and ten years of historical weather data from the USA rice belt, which was translated into rice response based on the rice cardinal temperatures and crop stages. Next, we eliminated those highly correlated Environmental Covariates (ECs) (>0.95) and applied a supervised algorithm for feature selection using two years of data (2021-22) and 25 genotypes evaluated for grain yield in 18 representative locations in the Southern USA. To test the trials' optimization, we performed the joint analysis using prediction-based models in four different scenarios: i) considering trials as non-related, ii) including the environmental relationship matrix calculated from ECs, iii) within clusters; iv) sampling one location per cluster. Finally, we weigh the trial's allocation considering the counties' economic importance and the environmental group to which they belong. Our findings show that eight ECs explained 58% of grain yield variation across sites and 53% of the observed genotype-by-environment interaction. Moreover, it is possible to reduce 28% the number of locations without significant loss in accuracy. Furthermore, the US Rice belt comprises four clusters, with economic importance varying from 13 to 45%. These results will help us better allocate trials in advance and reduce costs without penalizing accuracy.

The Germination Performance After Dormancy Breaking of Leucaena diversifolia (Schltdl.) Benth. Seeds in a Thermal Gradient and Its Distribution Under Climate Change Scenarios.

Climate change models predict temperature increases, which may affect germination, an important stage in the recruitment of individuals in agroecosystems. Therefore, it is crucial to conduct research on how temperature will impact the germination of multipurpose native species. Leucaena diversifolia (Schltdl.) Benth. is native to America and is commonly cultivated around the world due to having a high protein content in seeds, and their trees are used in agrosilvopastoral systems because they fix nitrogen and provide shade and cattle feed. However, climate change affects the critical phases of its life cycle and influences its growth, reproduction, phenology, and distribution. To assess the germination performance of Leucaena diversifolia under different temperatures throughout thermal times, we estimated germination variables and determined cardinal temperatures and thermal time; we also analysed germination and potential distribution under two climate change scenarios. We found significant variations in seed germination (78-98%) and differences in cardinal temperatures (Tb = 5.17 and 7.6 °C, To = 29.42 and 29.54 °C, and Tc = 39.45 and 39.76 °C). On the other hand, the sub-optimal and supra-optimal temperature values showed little differences: 51.34 and 55.57 °Cd. The models used showed variations in germination time for the analysed scenarios and the potential distribution. We confirm that the populations and distribution of L. diversifolia will be altered due to climate changes, but the species retains the ability to germinate under warmer conditions.

Factors Influencing the Variation of Plants' Cardinal Temperature: A Case Study in Iran.

The establishment and spread of plants in their native or alien geographical ranges are determined by their germination. This study investigated the impact of different factors on variations in cardinal temperatures. We used the lm procedure and measured the effect size by the Eta-square approach to find the association of different factors (species, ecotypes, origin (native/alien), year, and life cycle) with the cardinal temperatures of 31 species. Our results showed that the base, optimum, and maximum temperatures responded differently to these factors. The base temperature was less impacted by ecotypes compared with the optimum and maximum temperatures, whereas the species had a higher impact on the variation in the base temperature. The effect of the origin of weedy plants on the base temperature was higher than the optimum and maximum temperatures. The effect of the year on the optimum temperature was more prominent than that on the base and maximum temperatures. The results confirmed that weedy alien plants preferred high and narrow ranges of base, optimum, and maximum temperatures and probably will be more problematic in summer crops. The results indicate that alien plants can benefit from warmer conditions in invaded areas at the germination stage. These findings lay the foundation for further studies to elucidate which factors are more important.

Germination responses of Lens Culiunaris L. seeds to osmotic potentials at cardinal temperatures using hydrothermal time model

BackgroundLentil is a significant legume that are consumed as a staple food and have a significant economic impact around the world. The purpose of the present research on lentil was to assess the hydrothermal time model’s capacity to explain the dynamics of Lens culinaris L. var. Markaz-09 seed germination, as well as to ascertain the germination responses at various sub-optimal temperatures (T) and water potentials (Ψ). In order to study lentil seed germination (SG) behavior at variable water potentials (Ψs) and temperatures (Ts). A lab experiment employing the hydrothermal time model was created. Seeds were germinated at six distinct temperatures: 15 0С, 20 0С, 25 0С, 30 0С, 35 0С, and 40 0С, with five Ψs of 0, -0.3, -0.6, -0.9, and − 1.2 MPa in a PEG-6000 (Polyethylene glycol 6000) solution.ResultsThe results indicated that the agronomic parameters like Germination index (GI), Germination energy (GE), Timson germination index (TGI), were maximum in 25 0C at (-0.9 MPa) and lowest at 40 0C in 0 MPa. On other hand, mean germination time (MGT) value was highest at 15 0C in -1.2 MPa and minimum at 40 0C in (-0.6 MPa) while Mean germination rate (MGR) was maximum at 40 0C in (0 MPa) and minimum at 15 0C in (-0.6 MPa).ConclusionsThe HTT model eventually defined the germination response of Lens culinaris L. var. Markaz-09 (Lentil) for all Ts and Ψs, allowing it to be employed as a predictive tool in Lens culinaris L. var. Markaz-09 (Lentil) seed germination simulation models.

Cardinal temperatures of populations developed from native maize (Zea mays L.) from central and southern, Tamaulipas, Mexico

Objective: To estimate the cardinal temperatures of native maize populations from Tamaulipas. Design/Methodology/Approach: Ten genotypes developed from native germplasms were established in Güémez, Tamaulipas, on 12 planting dates (2019 and 2020). The cardinal temperatures (Tb, To, and Tu) of each of the cultivars were estimated through the decomposition of a quadratic model, using the days from sowing to tasseling and the average temperature of each sowing date from that period. Results: From sowing to tasseling, the evaluated cultivars recorded 15.7-18.1 °C base temperatures (Tb), 28.3-30.1 °C optimum temperatures (To), and 32.3-34.4 °C threshold temperatures (Tu). The Tb and To values represent the high thermal requirement of the germplasm, while Tu stands for its resistance to high temperatures. The L3, L4, L5, and VHA cultivars stood out for their broader adaptation range (16.2 to 34.4 °C), while the L3, L4, and L6 cultivars have a higher resistance to high temperatures (average Tu: 34.5 °C). Study Limitations/Implications: The cardinal temperatures determined in this study depended on the evaluated genotypes and the environment in which they developed. Findings/Conclusions: The maize germplasm evaluated in this study was resistant to high temperatures. As a result of its adaptation to the conditions of central and southern Tamaulipas, this germplasm is a source of variation for the characteristics that provide resistance to the stress caused by high temperatures.

Predicting temperature ranges for the initial development of two native Brazilian tree species using multiple sowing dates

Accurate data on development responses to air temperature are essential to feed development and productivity models through which it is possible to analyze the global warming impacts. The cardinal temperatures – base (Tb), optimum (Topt), and maximum (TB) - delimit the temperature range in which development occurs, while the phyllochron (ºC day per leaf) defines the thermal requirements necessary for leaf appearance and development rate of tree species. Field experiments employing multiple sowing dates provide a wide range of temperature regimes closer to natural field conditions and, at the same time, allow obtaining accurate and reliable estimates of cardinal temperatures and phyllochron values. This study estimated the cardinal temperatures – Tb, Topt, and TB – and the phyllochron of tree species Cybistax antisyphilitica (Mart.) Mart. and Platycyamus regnellii Benth., both native to Brazil, using multiple sowing dates. For this, leaf appearance data from field experiments conducted outdoors during the 2017 and 2018 growing seasons with twelve sowing dates were used. C. antisyphilitica develops properly among 13 °C (Tb), 20 °C (Topt), and 48.4 °C (TB) temperature ranges, and P. regnellii among 13.7 °C (Tb), 21.5 °C (Topt) and 43.4 °C (TB). The phyllochron for leaf appearance was different between the two species. On average, C. antisyphilitica needs to accumulate 88.2 °C day to emit a leaf on the main stem, while P. regnellii needs to accumulate 109.7 °C day per leaf, and both values correspond to a development rate of 0.0134 and 0.0091 leaf per ºC day, respectively. Information about cardinal temperatures provides valuable insights into the development patterns and thermal requirements, which can be used in development models to project the development under future climates.

Modeling the effect of temperature on rhizome sprouting in the invasive weed silverleaf nightshade (Solanum elaeagnifolium)

AbstractSilverleaf nightshade (Solanum elaeagnifolium Cav.), a noxious, highly invasive perennial weed, poses a significant threat to irrigated summer crops, vegetables, and orchards. This weed has the ability to reproduce both sexually through seed production and asexually via an extensive underground rhizome network, the latter playing a major role in the weed’s invasion, establishment, and persistence. Our aims were thus to assess the impact of temperature on rhizome sprouting for fragments of different lengths and to model the sprouting dynamics. The influence of temperature on the sprouting of rhizome fragments (2.5-, 5-, 7.5-, or 10-cm long) was investigated in growth chambers at eight temperatures ranging from 10 to 45 C. The highest sprouting proportions for 10-cm rhizome fragments were recorded at 30 and 35 C in complete darkness. The highest sprouting time for all fragment lengths was observed at 15 C in complete darkness. Modeling sprouting rates as a function of temperature gave the cardinal temperatures for the four different rhizome fragment lengths, with Tb (base temperature) values of 12.80, 9.34, 9.14, and 9.50 C, To (optimal temperature) values of 38.9 $$0$$ , 36.60, 35.16, and 34.86 C, and Tc (ceiling temperature) values of 39.80, 40.08, 40.50, and 40.80 C for rhizome lengths of 2.5, 5, 7.5, and 10 cm, respectively. Based on these findings, the potential for S. elaeagnifolium to spread to new areas and possible new management strategies are discussed; these offer a novel approach for informed decision making regarding the control of this weed.

The temperature optima for pollen germination and pollen tube growth of coconut (Cocos nucifera L.) strongly depend on the growth temperature

Abstract Understanding trait variation in response to temperature is important to predict how crops respond to rising temperature. Although we have a sound understanding of the effects of increasing temperature on growth and development of crops, a robust assessment of how crop reproductive processes are affected by climate warming is still lacking. In this study, we experimentally investigate how the growth temperature affects the cardinal temperatures of in vitro pollen germination of widely distributed tree crop species Cocos nucifera L. (cultivar Sri Lankan Tall). We hypothesize that temperature optima for pollen germination and pollen tube growth would be determined by the growth temperature. Our results showed that the temperature optima of pollen germination and pollen tube growth were higher at relatively warmer sites (sites where the mean annual temperature ∼ 28°C) compared to the cooler sites (sites where the mean annual temperature ∼ 22°C). The two processes were better coordinated at warmer sites. We speculate that tropical tree species that are currently growing in relatively cooler environments may have the capacity to perform their reproductive physiological functions in future warmer climates without any substantial negative impacts. Findings of this study should prove useful in quantifying the potential impacts of climate warming on tropical agro-ecosystems, improving the representation of plant reproduction in crop models.

Determination of Cardinal Temperatures and Phenological Stages of Two Species of Spiny Cocklebur (Xanthium spinosum) and Common Cocklebur (X. strumarium) Based on Growing Degree-Day

Determination of Cardinal Temperatures and Phenological Stages of Two Species of Spiny Cocklebur (Xanthium spinosum) and Common Cocklebur (X. strumarium) Based on Growing Degree-Day

Epidemiology of Powdery Mildew of Apple caused by Podosphaera leucotricha (Ell.and Ev.) Salm. in Kashmir, India

Apple is an economically important horticultural crop that is affected by a number of diseases, including powdery mildew. The disease spread is affected by the environmental conditions during the growth period. The germination and appressoria formation of conidia of powdery of apple initiated after 2 and 4 h, respectively at 20 ±2oC in moist saturated atmosphere. Sporulation started 96 h after incubation on susceptible apple leaves. Cardinal temperatures for powdery mildew development were 10, 20 and 30 oC. Relative humidity levels of 32 percent and above favoured development of powdery mildew. Temperature had negative significant correlation, whereas relative humidity had positive non-significant correlation with incidence of disease.

Cardinal Temperatures and Thermal Time for Germination of Sarawak Traditional Rice

Germination of two rice landraces, namely Bario Sederhana and Biris, was determined from twelve temperatures (12.5 – 40 ºC) in a series of incubation experiments. The cardinal temperatures and thermal time for germination were estimated from a ‘broken-stick’ linear model. Both landraces had a Tb of 10 ºC, Topt between 32 – 33 ºC, and Tmax of 43 ºC. At the sub-optimal temperatures, the thermal time for germination was 62 ºCd for Bario Sederhana and 53 ºCd for Biris. Within the supra-optimal range (Topt to Tmax), both landraces required 27-29 ºCd for seed germination. The maximum final germination for Bario Sederhana was 93% at 30 ºC while Biris had 100% seeds population germinated at 27.5 ºC.

The seed germination spectrum of 486 plant species: A global meta-regression and phylogenetic pattern in relation to temperature and water potential

The germination niche of plant species depends primarily on the seeds’ responsiveness to temperature and water potential. However, to appreciate future climate risks to natural regeneration through germination, a global level synthesis across species is needed. We performed a meta-regression and phylogenetic patterning of primary data from 377 studies on 486 species, including trees, grasses, crops and wild species, to determine patterns and co-correlants in the cardinal values that define species’ germination niches. We found positive correlations between base temperature and other germination traits related to cardinal temperatures suggesting that plant species alter base temperature values in harmony with other thermal traits as a highly efficient adaptation strategy to coping with harsh conditions. A negative correlation was found between thermal time and base temperature, and positive correlations between other cardinal temperatures and base temperature. Mean values of thermal time indicate that annual crops germinate more rapidly compared to wild species, potentially as a consequence of domestication, and tropical tree seeds the slowest. Dryland species (Cactaceae and Agavaceae) have the widest upper thermal and lower moisture niches, indicative of abilities to grow under harsh conditions, while forages have the narrowest thermal and moisture niches, suggesting higher sensitivity to frost or drought. We propose a new conceptual framework for future research on germination niche as shaped by thermal and moisture traits. Our database represents a unique source of information to further determine the vegetation boundaries of wild or cultivated species, including within simulation studies on plant species adaptations under changing land-use and climate.

ZONAREA CULTURII SPECIILOR GOJI, DUD, KIWI ȘI BANANA NORDULUI ÎN ROMÂNIA, ÎN CONDIȚIILE SCHIMBĂRILOR CLIMATICE

The warming trends of Romania's climate create increasingly favorable conditions for the cultivation of some new and subtropical species. However, the absolute minimum temperatures in the winter period do not follow a statistically assured increasing trend in all months, and this is not similar throughout the country. The objective of this work was to identify the areas in Romania where the climatic conditions are suitable for growing goji berry (Lycium barbarum L. and L. chinense Mill.), mulberry (Morus rubra L. and M. alba L.), kiwi (Actinidia deliciousa A. Chev., A. arguta Siebold & Zucc and A. kolomikta Rupr. et Maxim.) and pawpaw species (Asimina triloba (L.) Dunal), by using mathematical models. The areas where the minimum and cardinal temperatures of the growing season, its duration and annual rainfall are the most suitable for the growth and development of new species have been identified. The winter absolute minimum temperatures were recorded with a probability of 25%, which falls below the frost resistance limit of the species Actinidia deliciousa A. Chev. (-17°C), Lycium chinense Mill. (-23°C) and Lycium barbarum L. (-25°C), represented the limiting climatic factor of the spatial distribution of these species. Most of Romania's territory, except for mountainous areas, is suitable for growing mulberry, pawpaw (Asimina triloba (L.) Dunal), Actinidia kolomikta Rupr. et Maxim. and Actinidia arguta Siebold & Zucc species, which have frost hardiness limits of -28°C, -30°C, -39°C and -31°C respectively. Irrigation of all studied crops increased the whole country's average suitability score from 1.56 to 2.35 in the 0-4 range (0 unsuitable and 4 highly suitable) and expanded the areas of species' suitability. The heterogeneity and dynamics of climatic factors on the territory of Romania emphasize the importance of models for computing climate suitability as a decision tool in the establishment of goji berry, mulberry, kiwi, and pawpaw orchards.

One-step analysis of growth kinetics of mesophilic Bacillus cereus in liquid egg yolk during treatment with phospholipase A2: Model development and validation

Liquid egg yolk (LEY) is often treated with phospholipase A2 (PLA2) to improve its emulsifying capacity and thermal stability. However, this process may allow certain pathogens to grow. The objective of this study was to evaluate the growth kinetics of mesophilic Bacillus cereus in LEY during PLA2 treatment. Samples, inoculated with B. cereus vegetative cells, were incubated isothermally at different temperatures between 9 and 50 °C to observe the bacterial growth and survival.Under the observation conditions, bacterial growth occurred between 15 and 48 °C, but not at 9 and 50 °C. The growth curves were analyzed using the USDA IPMP-Global Fit, with the no-lag phase model as the primary model in combination with either the cardinal temperatures model (CTM) or the Huang square-root model (HSRM) as the secondary model. While similar maximum growth temperatures (Tmax) were determined (48.4 °C for HSRM and 48.1 °C for CTM), the minimum growth temperature (Tmin) of the HSRM more accurately described the lower limit (9.26 °C), in contrast to 6.51 °C for CTM, suggesting that the combination of the no-lag phase model and HSRM was more suitable to describe the growth of mesophilic B. cereus in LEY.The root mean square error (RMSE) of model validation and development was <0.5 log CFU/g, indicating the combination of the no-lag phase model and HSRM could predict the growth of mesophilic B. cereus in LEY during PLA2 treatment. The results of this study may allow the food industry to choose a suitable temperature for PLA2 treatment of LEY to prevent the growth of mesophilic B. cereus.

Influence of environmental factors on seed germination and seedling emergence of Amaranthus blitoides S. Watson and A. hybridus L.

AbstractAmaranthus blitoides S. Watson and A. hybridus L. are common herbaceous annual summer weeds in different regions of Iran, which produce a large number of small seeds per plant. The goal of these experiments was to determine seed germination cardinal temperature and investigate the effect of constant temperature, osmotic and salt stresses, stratification, flooding duration, after‐ripening and seed planting depth on seed germination and seedling emergence. Two‐piece segmented, dent‐like and beta four‐parameter models were used to investigate the relationship between germination rate and constant temperature. The dent‐like model showed the best description of the effect of constant temperature on seed germination rate of both A. blitoides and A. hybridus. Optimal seed germination of A. blitoides occurred at 35°C, but in A. hybridus optimum germination was observed in a range of constant temperatures from 30 to 40°C. Osmotic and salt stresses and flooding adversely affected seed germination of both species. After ripening for 6 months increased germination percentage of both A. blitoides and A. hybridus. Maximum seedling emergence of A. blitoides (42.8%) and A. hybridus (44.9%) occurred at a planting depth of 3.3 cm, whereas further increased planting depth minimized seedling emergence of both weeds. Information obtained from this study will help us to develop effective techniques for management of A. blitoides and A. hybridus.

Crop productivity estimation by integrating multisensor satellite, in situ, and eddy covariance data into efficiency-based model.

Accurate and quantitative regional estimates of the carbon budget require an integration of eddy covariance (EC) flux-tower observations and remote sensing in ecosystem models. In this study, a simple remote sensing driven light use efficiency (LUE) model was used to estimate the primary productivity for major cropping systems using multi-temporal satellite data over the Saharanpur district in India.The model is based on radiation absorption and its conversion into biomass. The LUE model was implemented for major crop rotations derived from the time-series of Sentinel-2 and Landsat 8 with monthly satellite-based spatially explicit fields of photosynthetically active radiation (PAR), fraction of absorbed PAR (fAPAR) and down-regulated light use efficiency. Incident PAR and fAPAR were estimated on monthly basis from the ground-calibrated empirical equation using INSAT-3D insolation product and remote sensing-based vegetation indices, respectively. Spatial LUE maps created by down-regulating maximum LUE (EC tower-based) with water and temperature stressors derived from land surface water index (LSWI) and EC-based cardinal temperature, respectively. LUE-based modeled GPP over the sugarcane-wheat system was found higher than the rice-wheat system in Saharanpur district. This is because C4 crop (sugarcane) has very high photosynthetic efficiency compared to C3 crops (rice and wheat). Modeled GPP over the sugarcane-wheat system was found in good agreement with observed EC tower-based GPP (Index of Agreement = 0.93). Further regionally calibrated remote sensing-based LUE model well captures gross photosynthesis rates (GPP) over cropland ecosystem compared to globally modeled MODIS GPP product.

Germination response of Oat (Avena sativa L.) to temperature and salinity using halothermal time model

Seed germination is a complex physiological process influenced by abiotic stresses such as drought, temperature, salinity along with other biological and physical means. Halothermal time model (HaloTT) permitted quantitative assessment of seed germination at different water potential (ψ) and temperature (T). The present study aimed to evaluate the reliability of HaloTT model and to find cardinal temperature values for seed germination of Oats under various Ts and ψs. Avena sativa L. Var. Swan seeds were incubated at seven constant Ts under five various ψs prepared through sodium chloride (NaCl) at Plant Physiology Lab., University of Peshawar, Pakistan. The cardinal Ts measured through HaloTT model for Oats seed germination were 10, 30 and 40 °C for the base (Tb), optimum (To) and ceiling (Tc) temperatures correspondingly in distilled water (0 MPa). The maximum halotime constant (θHalo) was recorded as 48 MPa °Ch−1 at 30 °C in distilled water (0 MPa). The highest value of halotime and thermal time of germination rate was observed at -2.0 MPa at 40 °C. Germination percentage (GP), germination rate index (GRI), germination energy (GE), coefficient of velocity of germination (CVG), timson germination index (TGI), mean germination rate (MGR) and coefficient of variation of germination time (CVt) was observed maximum in 0 MPa at 30 °C, while minimum in -2.0 MPa at 40 °C. Contrarily the high rate of mean germination time (MGT) and time to 50 % germination (T50 %) was reported in -2.0 MPa and -1.5 MPa at 10 and 40 °C, while in distilled water (0 MPa) is lowest at 25 and 30 °C. Thus, we concluded that HaloTT model precisely interpret germination responses to various ψs across different Ts and may be used as an accurate and simple method to predict germination parameters under natural field conditions.

Limiting temperatures of embryo growth and seed germination of Fraxinus excelsior L. (Oleaceae): a threshold model approach

Key messageWe have examined thermal control for embryo growth and seed germination in European ash. Using historical data (span of 36 years) of embryo index in matured seeds, we showed that maturation is not influenced by the annual average temperature. Secondary dormancy in ash’s seeds is easily induced, and the thermal window for both embryo growth and seed germination was between 10 and 20 °C.ContextSeed germination plays a crucial role in establishing plant communities. Ash seeds are characterized by deep morphophysiological dormancy, usually overcome by 32 weeks of stratification. Observed climate changes might disrupt ash’s thermal window for embryo growth and seed germination. Thus, proper examination of seed adaptability can be important for forest management.AimsWe investigated the effect of temperature on the embryo index (ratio between embryo and seed length) as well as embryo growth and germination of European ash (Fraxinus excelsior L.) seeds under different thermal conditions.MethodsWe used seeds collected at the same site in Poland between 1985 and 2021 to first analyze the influence of the growing season on the initial embryo index in mature seeds. Subsequently, we examined embryo growth and germination of seeds at constant temperatures of 3°, 10°, 15°, 20°, 25°, and 30 °C from seeds collected in 2021. Using the modeled rate of embryo growth and germination, we predicted the cardinal temperatures for those processes in ash seeds.ResultsThe embryo index of ash seeds varied; however, there was no relationship between the index and year of seed collection. The base temperature for embryo growth was 1.4 ± 1.1 °C, with a ceiling temperature of 29.9 ± 2.0 °C and an optimal temperature of 15.7 ± 0.3 °C. The base temperature for germination was at − 1.8 ± 0.3 °C. Due to the induction of secondary dormancy, the ceiling temperature of germination was impossible to establish.ConclusionsThe initial embryo index of mature ash seeds seems to be an individual trait and was not affected by local average annual temperatures. The most effective temperature ranges for embryo growth and germination were similar, however narrow (between 10 and 15 °C). Temperatures above 20 °C inducted secondary dormancy, hampering embryo growth as well as germination. Such a narrow thermal window for embryo growth can potentially act as a limiting factor for the natural regeneration of ash seeds.

Seed Fatty Acid Changes Germination Response to Temperature and Water Potentials in Six Sesame (Sesamum indicum L.) Cultivars: Estimating the Cardinal Temperatures

Seed fatty acid composition can influence seed quality, followed by seed germination and optimal seedling establishment. Therefore, to find out the role of seed fatty acids in changing the cardinal temperatures of six sesame cultivars germinated at different temperatures (10, 15, 20, 25, 30, 35, 40, and 45 °C) and water potentials (0, −0.2, −0.4, −0.6, −0.8, −1, and −1.2 MPa), an experiment was conducted. The dent-like, beta, and segmented models were used to analyze the data. The results showed that different cultivars at optimal temperatures show different reactions to environmental conditions; for example, the germination rate in Halil and Dashtestan2 cultivars followed the dent-like model, Darab1, Oltan, and Yellow-White followed the beta model, and Naz followed the segmented model. Based on the results, the average temperature in all water potentials of the base, sub-optimal, supra-optimum, and ceiling was determined as 12.6, 33.3, 38, and 43.9 °C, respectively, once the superior dent-like model was used. Using the superior beta model, the average temperatures in the base, optimum, and ceiling were 8.5, 31.2, and 50.5 °C. In contrast, when the segmented superior model was used, they were determined to be 7.6, 34, and 44.1 °C, respectively. According to the results, it can be stated that the Halil cultivar with more oleic acid and less linoleic acid has a higher base temperature and is more adapted to high temperatures for later cultivations. The Naz cultivar with a long biological clock is suitable for earlier cultivations. The ceiling temperature of these cultivars was also affected by the osmotic potential and decreased significantly with the increase in osmotic levels. Dashtestan2 cultivar with a high germination rate could be chosen for cultivation in water and high-temperature stress areas.

Physiological and Germination Responses of Muskmelon (Cucumis melo L.) Seeds to Varying Osmotic Potentials and Cardinal Temperatures via a Hydrothermal Time Model.

Climatic changes have a direct negative impact on the growth, development, and productivity of crops. The water potential (ψ) and temperature (T) are important limiting factors that influence the rate of seed germination and growth indices. To examine how the germination of seed responds to changes in water potential and temperature, the hydrotime model and hydrothermal model (HTT) have been employed. The HTT calculates the concept of germination time across temperatures, between Tb-To, with alteration, and between Tb-Tc, in supra-optimal ranges. The seeds of Cucumis melo L. were germinated in the laboratory for a hydro-thermal time experiment. Seeds were sown in Petri dishes containing a double-layered filter paper at different osmotic potentials (0, -0.2, -0.4, -0.6, and -0.8 MPa) by providing PEG 6000 (drought stress enhancer) at different temperatures (15, 20, 25, 30, and 35 °C). The controlled replicate was treated with 10 mL of distilled water and the rest with 10 mL of PEG solution. Results indicated that the seed vigor index (SVI-II) was highest at 15 °C with 0 MPa and lowest at 30 °C with -0.2 MPa. However, the highest activity was shown at 15 °C by catalase (CAT) and guaiacol peroxidase (GPX) at (-0.6 MPa), while the lowest values of CAT and GPX were recorded for control at 35 °C with -0.8 MPa at 35 °C, respectively. Germination energy was positively correlated with germination index (GI), germination percentage (G%), germination rate index, seed vigor index-I (SVI-I), mean moisture content (MMC), and root shoot ratio (RSR) and had a negative correlation with mean germination rate, percent moisture content of shoot and root, CAT, superoxide dismutase, peroxidase ascorbate peroxidase, and GPX. In conclusion, thermal and hydrotime models correctly predicted muskmelon germination time in response to varying water potential and temperature. The agronomic attributes were found to be maximum at 30 °C and minimum at 15 °C.