scholarly journals Calculating "Hydrothermal time" to quantify seed germination of tall fescue

2016 ◽  
Vol 78 ◽  
pp. 163-168 ◽  
Author(s):  
S. Sharifiamina ◽  
D.J. Moot ◽  
M. Bloomberg
Keyword(s):  
Water Potential ◽  
Tall Fescue ◽  
Festuca Arundinacea ◽  
Germination Rate ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Effects Of Temperature ◽  
Moisture Conditions ◽  
Base Water Potential ◽  
Moderate Stress

The objective of this study was to quantify the combined effects of temperature and moisture on germination of tall fescue seed. Seeds were incubated for up to 50 days at a range of constant temperatures (5-35ºC) and germinated at five water potentials (0, -0.18, -0.37, -0.63 and -0.95 MPa). The maximum final germination percentages were 94 to 98 at 15-30ºC when water was not limited (0 MPa). Germination rate increased linearly from 5 to 27.5ºC, and then decreased linearly from 27.5 to 32.5ºC. Extrapolation of the sub-optimal temperatures identified a base temperature of 3.5 ± 0.5ºC and an optimum temperature of 27.5ºC. More negative water potential indicative of drier conditions, delayed germination and reduced germination rate. The average base water potential was -0.95 MPa at the suboptimal range of temperatures. An optimum range of germination (80-100%) occurred when temperatures were between 10 and 30ºC and water potential was between 0 to -0.37 MPa (moderate stress). These results provide a matrix of soil temperature and moisture conditions that are expected to result in successful germination and therefore provide the maximum opportunity for emergence of tall fescue seedlings. Keywords: Festuca arundinacea, 'Finesse Q', hydrothermal time

Hydropriming accelerates seed germination of Medicago sativa under stressful conditions: A thermal and hydrotime model approach

2017 ◽  
Author(s):  
Rong Li ◽  
Dandan Min ◽  
Lijun Chen ◽  
Chunyang Chen ◽  
Xiaowen Hu
Keyword(s):  
Water Potential ◽  
Germination Rate ◽  
High Water ◽  
Nacl Stress ◽  
Base Temperature ◽  
Severe Water Stress ◽  
Hydrotime Model ◽  
Response To Temperature ◽  
Base Water Potential ◽  
Temperature Water

This study determined the effects of priming on germination in response to temperature, water potential and NaCl. Thermal and hydrotime models were utilized to evaluate changes in parameters of the model after priming. Priming reduced the amount of thermal time in both cultivars, but slightly increased the base temperature for germination from 1.0 to 3.5°C in “Longdong”. Priming significantly increased germination rate at high water potential but had no effect at low water potential. Further, priming reduced the hydrotime constant but made the median base water potential value slightly more positive in both cultivars. Thus, priming increased germination rate in water but decrease it under severe water stress. Germination rate was significantly increased in both cultivars under salinity (NaCl) stress. Moreover, priming improved seedling growth in response to temperature, water and salinity stress in both cultivars.

Ecological aspects of seed dormancy loss

1998 ◽  
Vol 8 (2) ◽  
pp. 183-192 ◽  
Author(s):  
Phil S. Allen ◽  
Susan E. Meyer
Keyword(s):  
Water Potential ◽  
Seed Dormancy ◽  
Laboratory Data ◽  
Simulation Models ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Seed Biology ◽  
Seed Population ◽  
Germination Timing ◽  
Base Water Potential

AbstractAdvances in seed biology include progress in understanding the ecological significance of seed dormancy mechanisms. This knowledge is being used to make more accurate predictions of germination timing in the field. For several wild species whose seedlings establish in spring, seed populations show relevant variation that can be correlated with habitat conditions. Populations from severe winter sites, where the major risk to seedlings is frost, tend to have long chilling requirements or to germinate very slowly at low temperatures. Populations from warmer sites, where the major risk is drought, are non-dormant and germinate very rapidly under these same conditions. Seed populations from intermediate sites exhibit variation in dormancy levels, both among and within plants, which spreads germination across a considerable time period. For grasses that undergo dry after-ripening, seed dormancy loss can be successfully modelled using hydrothermal time. Dormancy loss for a seed population is associated with a progressive downward shift in the mean base water potential, i.e., the water potential below which half of the seeds will not germinate. Other parameters (hydrothermal time requirement, base temperature and standard deviation of base water potentials) tend to be constant through time. Simulation models for predicting dormancy loss in the field can be created by combining measurements of seed zone temperatures with equations that describe changes in mean base water potential as a function of temperature. Successful validation of these and other models demonstrates that equations based on laboratory data can be used to predict dormancy loss under widely fluctuating field conditions. Future progress may allow prediction of germination timing based on knowledge of intrinsic dormancy characteristics of a seed population and long-term weather patterns in the field.

scholarly journals Using hydrothermal time concepts to model seed germination response to temperature, dormancy loss, and priming effects in Elymus elymoides

2000 ◽  
Vol 10 (3) ◽  
pp. 213-223 ◽  
Author(s):  
Susan E. Meyer ◽  
Susan B. Debaene-Gill ◽  
Phil S. Allen
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Time Course ◽  
Germination Rate ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Time Model ◽  
Priming Effects ◽  
Elymus Elymoides ◽  
Temperature Regimes

AbstractHydrothermal time (HTT) describes progress toward seed germination under various combinations of incubation water potential ( ) and temperature (T). To examine changes in HTT parameters during dormancy loss, seeds from two populations of the bunchgrass Elymus elymoides were incubated under seven temperature regimes following dry storage at 10, 20 and 30°C for intervals from 0 to 16 weeks. Fully after-ripened seeds were primed for 1 week at a range of s. Data on germination rate during priming were used to obtain a HTT equation for each seed population, while data obtained following transfer to water were used to calculate HTT accumulation during priming. HTT equations accurately predicted germination time course curves if mean base water potential, b(50), was allowed to vary with temperature. b(50) values increased linearly with temperature, explaining why germination rate does not increase with temperature in this species. b(50) showed a linear decrease as a function of thermal time in storage. Slopes for the T × b(50) relationship did not change during after-ripening. This thermal after-ripening time model was characterized by a single base temperature and a constant slope across temperatures for each collection. Because the difference between initial and final b(50)s was uniform across tempera-tures, the thermal after-ripening requirement was also a constant. When seeds were primed for 1 week at −4 to −20 MPa, accumulation of HTT was a uniform 20% of the total HTT requirement. When primed at 0 to −4 MPa, HTT accumulation decreased linearly with decreasing priming potential, and a hydrothermal priming time model using a constant minimum priming potential adequately described priming effects. Use of these simple HTT relationships will facilitate modelling of germination phenology in the field.

Relationship between accumulated hydrothermal time during seed priming and subsequent seed germination rates

1994 ◽  
Vol 4 (2) ◽  
pp. 63-69 ◽  
Author(s):  
Kent J. Bradford ◽  
Anthony M. Haigh
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Seed Priming ◽  
Threshold Temperature ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Time Model ◽  
Radicle Emergence ◽  
The Times ◽  
Base Water Potential

AbstractSeed germination rates are sensitive to both temperature (T) and water potential (ψ). The times to germination of seeds imbibed at suboptimal T and/or reduced ψ are inversely proportional to the amounts by which T exceeds a base temperature (Tb) and ψ exceeds a base water potential (ψb). Germination rates across a range of suboptimal T and ψ can be normalized on the basis of the hydrothermal time accumulated in excess of these thresholds. However, seeds can also progress metabolically toward germination even at T or ψ too low to allow radicle emergence to occur. Seeds preimbibed at low ψ and dried back, or primed, germinate more rapidly upon subsequent reimbibition. We show here that the increase in germination rates of tomato (Lycopersicon esculentum Mill.) seeds resulting from seed priming is linearly related to the hydrothermal time accumulated during the priming treatment. The threshold temperature (Tmin = 7.05°C) and water potential (ψmin = −2.50 MPa) for metabolic advancement were considerably lower than the corresponding thresholds for radicle emergence of the same seed lot (Tb = 11°C; ψb = −0.71 MPa), allowing the accumulation of hydrothermal priming time that is subsequently expressed as more rapid germination when T or ψ increase. The hydrothermal time model can now be applied to quantify and analyse germination rates of seeds across the entire range of suboptimal T and ψ at which metabolic progress toward radicle emergence is possible.

scholarly journals Germination response of Hylocereus setaceus (Salm-Dyck ex DC: ) Ralf Bauer (Cactaceae) seeds to temperature and reduced water potentials

2010 ◽  
Vol 70 (1) ◽  
pp. 135-144 ◽  
Author(s):  
E. Simão ◽  
M. Takaki ◽  
VJM. Cardoso
Keyword(s):  
Water Potential ◽  
Germination Rate ◽  
Base Temperature ◽  
Temperature Range ◽  
Water Potentials ◽  
Germination Response ◽  
Wide Range ◽  
Optimum Interval ◽  
Time Courses ◽  
Base Water Potential

The germination response of Hylocereus setaceus seeds to isothermic incubation at different water potentials was analysed by using the thermal time and hydrotime models, aiming to describe some germination parameters of the population and to test the validity of the models to describe the response of the seeds to temperature and water potential. Hylocereus setaceus seeds germinated relatively well in a wide range of temperatures and the germination was rate limited from 11 to 20 °C interval and beyond 30 °C until 40 °C, in which the germination rate respectively shifts positively and negatively with temperature. The minimum or base temperature (Tb) for the germination of H. setaceus was 7 °C, and the ceiling temperature varied nearly from 43.5 to 59 °C depending on the percent fraction, with median set on 49.8 °C. The number of degrees day necessary for 50% of the seeds to germinate in the infra-optimum temperature range was 39.3 °C day, whereas at the supra-optimum interval the value of θ = 77 was assumed to be constant throughout. Germination was sensitive to decreasing values of ψ in the medium, and both the germinability and the germination rate shift negatively with the reduction of ψ, but the rate of reduction changed with temperature. The values of base water potential (ψb) shift to zero with increasing temperatures and such variation reflects in the relatively greater effect of low ψ on germination in supra optimum range of T. In general, the model described better the germination time courses at lower than at higher water potentials. The analysis also suggest that Tb may not be independent of ψ and that ψb(g) may change as a function of temperature at the infra-otimum temperature range.

scholarly journals A hydrothermal after-ripening time model for seed dormancy loss in Bromus tectorum L.

2006 ◽  
Vol 16 (1) ◽  
pp. 17-28 ◽  
Author(s):  
Necia B. Bair ◽  
Susan E. Meyer ◽  
Phil S. Allen
Keyword(s):  
Water Potential ◽  
Time Course ◽  
Bromus Tectorum ◽  
Base Temperature ◽  
Time Model ◽  
Seed Collection ◽  
Ripening Time ◽  
Water Potentials ◽  
Ripening Rate ◽  
Base Water Potential

After-ripening, the loss of dormancy under dry conditions, is associated with a decrease in mean base water potential for germination ofBromus tectorumL. seeds. After-ripening rate is a linear function of temperature above a base temperature, so that dormancy loss can be quantified using a thermal after-ripening time (TAR) model. To incorporate storage water potential into TAR, we created a hydrothermal after-ripening time (HTAR) model. Seeds from twoB. tectorumpopulations were stored under controlled temperatures (20 or 30 °C) and water potentials (−400 to −40 MPa). Subsamples were periodically removed from each storage treatment and incubated at 15 or 25 °C to determine germination time courses. Dormancy status (mean base water potential) was calculated from each time course using hydrothermal time equations developed for each seed collection. Seeds stored at −400 MPa did not after-ripen. At water potentials from −400 to −150 MPa, the rate of after-ripening increased approximately linearly with increasing water potential. Between −150 and −80 MPa, there was no further increase in after-ripening rate, while at −40 MPa seeds did not after-ripen and showed loss of vigour. These results suggest that the concept of critical water potential thresholds, previously shown to be associated with metabolic activity and desiccation damage in partially hydrated seeds, is also relevant to the process of after-ripening. The HTAR model generally improved field predictions of dormancy loss when the soil was very dry. Reduced after-ripening rate under such conditions provides an ecologically relevant explanation of how seeds prolong dormancy at high summer soil temperatures.

Temperature- and moisture-dependent models of seed germination and shoot elongation in green and redroot pigweed (Amaranthus powellii, A. retroflexus)

Weed Science ◽  
1997 ◽  
Vol 45 (4) ◽  
pp. 488-496 ◽  
Author(s):  
Joseph O. E. Oryokot ◽  
Stephen D. Murphy ◽  
A. Gordon Thomas ◽  
Clarence J. Swanton
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Weed Management ◽  
Germination Rate ◽  
Shoot Elongation ◽  
Thermal Time ◽  
Base Temperature ◽  
Mathematical Function ◽  
Redroot Pigweed ◽  
Mean Temperature

To predict weed emergence and help farmers make weed management decisions, we constructed a mathematical model of seed germination for green and redroot pigweed based on temperature and water potential (moisture) and expressing cumulative germination in terms of thermal time (degree days). Empirical observations indicated green pigweed germinated at a lower base temperature than redroot pigweed but the germination rate of redroot pigweed is much faster as mean temperature increases. Moisture limitation delayed seed germination until 23.8 C (green pigweed) or 27.9 (redroot pigweed); thereafter, germination was independent of water potential as mean temperatures approached germination optima. Our germination model, based on a cumulative normal distribution function, accounted for 80 to 95% of the variation in seed germination and accurately predicted that redroot pigweed would have a faster germination rate than green pigweed. However, the model predicted that redroot pigweed would germinate before green pigweed (in thermal time) and was generally less accurate during the early period of seed germination. The model also predicted that moisture limitation would increase, rather than delay, seed germination. These errors were related to the mathematical function chosen and analyses used, but an explicit interaction term for water potential and temperature is also needed to produce an accurate model. We also tested the effect of mean temperature on shoot elongation (emergence) and described the relationship by a linear model. Base temperatures for shoot elongation were higher than for seed germination. Shoot elongation began at 15.6 and 14.4 C for green and redroot pigweed, respectively; they increased linearly with temperature until the optimum of 27.9 C was reached. Elongation was dependent on completion of the rate-limiting step of radicle emergence and was sensitive to temperature but not moisture; hence, elongation was sensitive to a much smaller temperature range. Beyond mathematical changes, we are testing our model in the field and need to link it to ecophysiological, genetic, and spatially explicit population processes for it to be useful in decision support for weed management.

INFLUENCE OF WATER STRESS CONDITIONING ON PHOTOSYNTHETIC WATER STRESS RESPONSE OF SWITCHGRASS (PANICUM VIRGATUM L.) AND TALL FESCUE (FESTUCA ARUNDINACEA SCHREB.)

2001 ◽  
Vol 49 (1) ◽  
pp. 15-24 ◽  
Author(s):  
Z. Kiss ◽  
D. D. Wolf
Keyword(s):  
Water Stress ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Tall Fescue ◽  
Festuca Arundinacea ◽  
Panicum Virgatum ◽  
Leaf Water ◽  
Panicum Virgatum L ◽  
Influence Of Water ◽  
Stress Cycles

The objective of this study was to investigate the influence of water stress conditioning on the photosynthesis response of switchgrass (Panicum virgatum L.) and tall fescue (Festuca arundinacea Schreb.) to moisture deficiency. Tillers of the two species were grown in the same, controlled, environment and were subjected to three conditioning water stress cycles, or were kept well watered. After drought conditioning all plants were subjected to moisture deficiency while photosynthesis and leaf water potential were monitored. Measurements were taken between –0.8 and –4.0 MPa and the rate of water stress was 0.49 MPa/day. The conditioning of switchgrass produced a 26% reduction in the photosynthesis rate during drought, while that of tall fescue produced a 57% reduction in photosynthesis. Both species maintained elongation and photosynthesis down to lower leaf water potentials after drought conditioning than before conditioning. The conditioning water stress cycles decreased the leaf conductance, mesophyll resistance and transpiration of tall fescue plants after rewatering. The leaf water potential of conditioned switchgrass plants was lower upon rewatering after three conditioning water stress cycles than the leaf water potential of non-conditioned plants, while the leaf conductance, mesophyll resistance and transpiration of conditioned and non-conditioned tillers were equal. These data indicate an improvement in the drought tolerance of tall fescue and switchgrass plants, emphasize the importance of knowing the previous water stress history of the plants in moisture deficiency experiments, and help to choose proper irrigation management for switchgrass and tall fescue.

scholarly journals A Correlative Study of Sunflower Seed Vigor Components as Related to Genetic Background

Plants ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 386
Author(s):  
Marine Saux ◽  
Benoît Bleys ◽  
Thierry André ◽  
Christophe Bailly ◽  
Hayat El-Maarouf-Bouteau
Keyword(s):  
Genetic Background ◽  
Sunflower Seed ◽  
Selection Process ◽  
Germination Rate ◽  
Seed Vigor ◽  
Base Temperature ◽  
Crop Selection ◽  
Important Trait ◽  
Base Water Potential

Seed vigor is an important trait that determines seed performance in the field, which corresponds to seed germination rate and seedling establishment. Previous works brought helpful equations to calculate several parameters allowing vigor characterization. In this work we used base water potential (Ψb), base temperature (Tb) and seed lot (Ki) constants to characterize the vigor of 44 sunflower seed lots. Contrasting responses to water or temperature stress and storage potential were recorded within this population, the most interesting being the opposite responses between Ψb and Ki. The genotypes that were resistant to water stress presented low ability for storage and vice versa. Furthermore, Ψb and Ki presented narrow ranges while Tb showed important variability within the 44 genotypes. The analysis of the whole dataset showed that these constants are not correlated to each other or to the seed size, suggesting that genetic background is the most important determining factor in seed performance. Consequently, vigor characterization of genotypes is needed in the crop selection process in order to optimize agricultural productivity.

Weather, Physiology and Seasonality of Tea (Camellia sinensis) Yields in Malawi

1979 ◽  
Vol 15 (4) ◽  
pp. 321-330 ◽  
Author(s):  
G. R. Squire
Keyword(s):  
Water Potential ◽  
Air Temperature ◽  
Shoot Growth ◽  
Narrow Range ◽  
Field Measurements ◽  
Base Temperature ◽  
Saturation Deficit ◽  
Mean Temperature ◽  
Effects Of Temperature ◽  
Independent Effects

SUMMARYField measurements with a pressure chamber showed that the water potential of tea shoots was more closely related to the atmospheric saturation deficit than to the amount of water in the soil. Records for shoot growth and weather then revealed that, within a narrow range of mean temperature, the weekly rate of shoot extension was inversely related to mean saturation deficit measured at 1400 h. During periods when saturation deficit did not rise above 20 mbar, the rate of shoot extension varied linearly with mean temperature above a base temperature of 12.5–13.0°C. These correlations suggested that seasonality of shoot growth in tea can be explained largely by the independent effects of temperature and humidity. The effect of mean air temperature on the rate of shoot extension was confirmed in a glasshouse built over an established crop.

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