Thermal Time Requirements Research Articles

Modelling development of broccoli (Brassica oleracea L. var. italica) from transplanting to head initiation

SummaryA model is suggested to predict head initiation in broccoli. Head initiation is defined as the time when the apex diameter reaches 0.6 mm and predictions are made from observations of air temperature. The model is constructed from three years of field experiments with three cultivars and four plantings per year. No juvenile phase after transplanting could be estimated and the model consists only of a head induction phase starting at transplanting. The rate of head induction is modelled by a piecewise linear temperature response function with a base, optimum, and maximum temperature. At optimum temperature the duration of the head induction phase is shortest. The estimates for base, optimum, and maximum temperature are 9.98C, 16.18C and 22.38C, respectively. The estimates for cultivar dependent thermal time requirements are 49 day-degrees, 55 day-degrees, and 38 day-degrees for cvs Caravel, Shogun and Emperor, respectively. The three cultivars were anticipated to have the same cardinal temperatures for head induction. The model of the head induction phases can account for 68% of the variation in the observed durations from transplanting to head initiation. A model of leaf appearance is used to standardize transplant size to four visible leaves at planting. The leaf appearance rate is described by a linear relationship to number of leaves and air temperature and the model can account for 89% of the variation in time from transplanting to appearance of a certain number of leaves. The temperature response of leaf appearance rate had a base temperature of about 2 to 38C, depending on cultivar, and showed no indications of having a temperature optimum below 208C. The leaf appearance rate at 158C range from 0.2 leaves per day for plants with four visible leaves to 0.4 leaves per day for plants with 14 visible leaves.

Controlled-temperature effects on cotton growth and development

The growth and development of cotton was studied on cotton plants grown in pots in growth rooms under constant day/night temperature (C) and varying temperature regimes throughout the day and/or night (V) The V-treatments had a common mean temperature of 22°C. The objectives were to determine the thermal requirements of three cultivars and to observe the extent of genotype×thermal environment interactions throughout the entire growth period.Vegetative growth was found to be almost exclusively time and temperature dependent, varietal differences being largely insignificant. Plant material was found to accumulate four times faster under the warmest C-regime, which was 7°C warmer than the coolest. The C-treatments caused variation in the number and size of lateral shoots and leaves, causing leaf area to be larger at the squaring stage in cool environments but at maturity in warm regimes. Relatively cool nights lowered the position of the first floral or fruiting branch, whereas warm days shortened flowering intervals and thus promoted earliness. However, the effect of temperature in altering the position of the first floral branch seems to be less important than its effect on the shedding of early squares.The effects of fluctuating temperature (V) on vegetative growth and earliness were similar to those from constant temperature environments. Growth and development rates were low in the low minimum V-regimes, especially when the maximum temperature was also low. Temperature variation affected vegetative growth to a greater extent in the early than in the later stages of development. At squaring, leaf area and dry weight were lowest under the regime with the highest minimum and maximum temperatures. Later on, only leaf area at flowering and total dry weight at maturity significantly differed between treatments. High maximum or minimum temperatures produced effects similar to a higher or lower mean temperature, respectively. The low minimum raised the node number of the first floral or fruiting branch, whereas in the case of boll dry weight it acted in the same way as a further drop in temperature, decreasing the weight, regardless of the maximum temperature. Boll period was affected mainly by the temperature variation itself rather by than the type of variation.The inverse of time to a certain stage and the corresponding mean temperature were linearly related and allowed threshold temperatures (T0) and thermal time requirements to be estimated. T0=12°C, except for the initial stage, when it was lower. A cotton growing season cooler on average by only 1°C will considerably delay maturity.

Thermal time requirements for the development of green pea ( Pisum sativum L.)

The purpose of this investigation was to quantify, for crop modelling purposes, temperature response functions of various developmental stages of several green pea ( Pisum sativum L.) cultivars. Cardinal temperatures, namely the base ( T b), optimum ( T m) and maximum temperature ( T x), for various developmental stages, were also determined. Below T b and above T x, development rates were zero and at T m development proceeded at the maximum rate. Developmental stages were monitored in both controlled environments and field trials. No significant differences were found between cultivars regarding optimum temperatures for 50% germination. A T b of 0°C, T m of 29°C and T x of 40°C for germination represents a good summary of the results. For the emergence, vegetative and reproductive stages, a T b of 3°C, T m of 28°C and T x value of 38°C are appropriate. In the field, the crops required approximately 100°C d for emergence, 260°C d to reach the four-leaf stage, 380°C d till the seven-leaf stage and 730°C d to reach the 14-leaf stage. Thermal time requirements from sowing to flowering ranged from 770°C d to 890°C d for different cultivars, and from sowing to maturity (tenderometer reading of 130) from 1370°C d to 1450°C d.

Pearl Millet Phenology and Growth in Relation to Thermal Time under Arid Environment

AbstractPearl millet (Pennisetum glaucum L.R.Br.) hybrid MH 179 was grown under two moisture regimes viz., optimal moisture and rainfed conditions. The field experiment was continued for three consecutive rainy seasons to quantify the pearl millet development with thermal time. The possible influence of variation in natural sowing date on the relationships between crop development and thermal time have been described. At cardinal temperatures of 10°C (base temperature below which pearl millet development ceases), 33°C (optimal temperature for development) and 45°C (maximum temperature at and above which no development takes place), the crop required 1490–1794°Cd thermal time to reach physiological maturity. The thermal time requirement for different developmental stages was influenced by the sowing time and moisture availability during the growing season of the crop.The leaf tip appearance on the main shoot of pearl millet in relation to thermal time was almost linear under both moisture conditions requiring about 44–50°Cd ± 2.6 °Cd leaf−1, till the appearance of the flag (last) leaf. However, leaf tip appearance on primary tillers was slightly slower and required 53‐58°Cd ± 4.7°Cd for each new leaf. Appearance of first primary tiller was later (at 320°Cd after emergence) under the rainfed condition as compared to the crop under the optimal moisture (at 250°Cd).Thereafter, the tiller appearance in relation to thermal time under both moisture conditions was at a linear rate of about 53‐56°Cd ± 9.5°Cd tiller−1.Effect of microclimatic variations, canopy temperature, radiation and photoperiod on the phenology‐thermal time relationships have been discussed under both the moisture conditions.

Effects of constant and fluctuating temperature on time to budburst in Betula pubescens and its relation to bud respiration

Effects of fluctuating and constant temperatures on budburst time, and respiration in winter buds were studied in Betula pubescens Ehrh. Dormant seedlings were chilled at 0°C for 4 months and then allowed to sprout in long days (LD, 24 h) at constant temperatures of 6, 9, 12, 15, 18 and 21°C, and at diurnally fluctuating temperatures (12/12 h, LD 24 h) with means of 9, 12, 15 and 18°C. No difference in thermal time requirements for budburst was found between plants receiving constant and fluctuating temperatures. The base temperature for thermal time accumulation was estimated to 1°C. Respiration in post-dormant (dormancy fully released) excised winter buds from an adult tree increased exponentially with temperature and was 20 times as high at 30°C than at 0°C. However, respiration in buds without scales was 30% higher at 0°C, and it was 2.7 times higher at 24°C than in intact buds. Thus, the tight bud scales probably constrain respiration and growth and are likely to delay budburst in spring. Arrhenius plots of the respiration data were biphasic with breaks at 13–15°C. However, this phase transition is unlikely to be associated with chilling sensitivity since the present species is hardy and adapted to a boreal climate.

Transplanted maize (Zea mays) for grain production in southern England. I. Effects of planting date, transplant age at planting and cultivar on grain yield

Agroclimatic conditions in the UK are not ideally suited to maize (Zea mays L.) as a grain crop. An alternative growing technique to direct-seeded maize was investigated at Reading University over three growing seasons, using four cultivars (Bastion, Ace, Anko and Mirna) of different FAO maturity ratings. In the main trials conducted in 1989 and 1990, seedlings were raised for 15–45 days in a glasshouse and planted in the field between early May and mid-June, at 10 plants/m2. On each planting date, maize kernels of the same cultivars were also sown in the field. At the end of each growing season, transplanted and direct-seeded crops were assessed for grain maturity and grain yield components. Averaged over year and cultivar, transplants matured significantly earlier than direct-seeded maize and tended to give higher grain yields. Their grain dry weights (86% DM) averaged 7·0 t/ha in a preliminary study in 1988, 9·0 t/ha in 1989 and 6·1 t/ha in 1990, whereas those of direct-seeded maize averaged 4·0, 8·0 and 3·0 t/ha, respectively. The highest grain weights resulted from May plantings using 15-day-old seedlings of the late cv. Mirna, and from June plantings using 30-day-old seedlings. Yield benefits from transplanting were not significant in 1989, suggesting that in a very warm season transplants may not necessarily outyield direct-seeded crops. Differences in grain weight between transplanted and direct-seeded maize are discussed with respect to grain moisture content, 1000-grain weight, ear length, and number of grains and grain rows per ear; and applications of maize transplanting for cropping systems are outlined. It is concluded that suitable combinations of cultivar, transplant age at planting and planting date can meet the thermal time requirement for a grain harvest in southern England.

Thermal time and ecological strategies ‐ a unifying hypothesis

SummaryRates of embryogenesis and of development and growth in several nematodes are linearly related to temperature over a considerable range. On this basis, published data on the thermal time requirements are compared for a tropical and a temperate species of plant parasitic nematode Meloidogyne javanica and M. hapla respectively, the two being closely related and morphologically and biologically similar. M. hapla has a lower base temperature (Tb) and a higher thermal constant (S) than M. javanica with the relative values being almost inversed. Consequently, above their respective Tb values the slope of the relationship between rate of development and temperature was greater for the tropical species than that for the temperate species. A mathematical exploration of the relationship between Tb and S was made assuming that, over a narrow range, Tb×S was a constant. With this assumption, for any given average environmental temperature (Te) the optimum base temperature for minimum developmental duration was Te/2, and the temperature at which the duration of development was equal for the otherwise identical species was shown to be the sum of their base temperatures. The practical effect of the differences in Tb and S was to give M. hapla, the temperate species, a shorter life cycle and hence a competitive advantage at temperatures below 21ÅC and M. javanica, the tropical species, the advantage above that temperature. It is argued that a negative correlation between Tb and S is likely to be widespread, and provides a mechanism for regulating the distributions of related, competing organisms. Support for the hypothesis that the value of S tends to decrease as Tb increases is derived from data on the embryogenesis of an animal parasitic nematode Haemonchus contortus and from seed germination studies. Contrary results and exceptions are also briefly discussed. The observed interaction between Tb and S may be fundamental to many poikilothermic organisms and plants and provides an explanation for tropical species generally having higher Tb values than temperate ones. The ecological implications of different values of Tb and of S, including their relationship with organisms which are “r” or “K” strategists are briefly discussed.

Climatic risk for sweet corn production in Canterbury, New Zealand

Abstract The risk of sweet corn (Zea mays L.) crops failing to reach harvest maturity as a result of climatic variability among seasons was quantified for four locations on the east coast of New Zealand's South Island. Results of field experiments in the region showed that three representative cultivars had thermal time requirements from planting to maturity ranging from 1215 to 1320 °C days above a base temperature of 6°C. In simulations, crop success or failure was estimated for combinations of five hypothetical cultivar maturities and four planting dates spanning the ranges likely to be used in the region. Calculations used temperature records that ranged from 17 to 25 seasons depending on location. A crop was judged to fail if either its thermal time requirement was not met by 30 April or it was frosted before the requirement was met. Allowance was made for the fact that some “failed” crops were sufficiently close to maturity to be harvested successfully. Risk was negligible at Blenheim, the most nort...

Leaf Emergence and Leaf Duration Related to Thermal Time Calculations in Ceres‐Maize

AbstractIn the CERES‐Maize model, maize (Zea mays L.) leaf initiation and appearance are modeled using thermal time derived from air temperature. Prior to the elevation of the culm apex, soil temperature, which is calculated by the model from air temperature, is used to calculate thermal time. No provision is made for response differences in leaf appearance rate due to cultivar or daylength. This research compares predicted with actual leaf development for up to 10 hybrids in five experiments for 4 yr. It also compares calculated versus measured soil temperatures in 1 yr. Thermal time requirements for appearance of leaf tips and collars and for duration of leaf expansion were determined using thermal time equations from the CERES‐Maize model. Thermal time values per leaf were stable within experiments, but varied substantially among years and hybrids. Although the CERES‐Maize model predicts leaf tip appearance moderately well, the rate of leaf development appears to differ among hybrids and may be sensitive to daylength and temperature extremes that are not considered by the model. Improvements are also needed in the model prediction of soil temperature.

Predicted changes in the synchrony of larval emergence and budburst under climatic warming.

The impact of climatic warming on the synchrony of insect and plant phenologies was modelled in the case of winter moth (Operophtera brumata) and Sitka spruce (Picea sitchensis) in the Scottish uplands. The emergence of winter moth larvae was predicted with a thermal time requirement model and the budburst of Sitka spruce was predicted from a previously published model (Cannell and Smith 1983) based on winter chilling and thermal time. The date of emergence of winter moth larvae was predicted to occur earlier under climatic warming but the date of budburst of Sitka spruce was not greatly changed, resulting in decreased synchrony between larval emergence and budburst. The general question of how a change of climate might affect phenological synchrony and insect abundance is discussed.

Thermal time assessment of suitable areas for navy bean (Phaseolus vulgaris) production in the UK

SummaryIn field trials at eight sites throughout the UK the mean thermal time requirement for navy beans from sowing to harvest for a standard cultivar, Marcus, was 2069 Ontario Heat Units (OHU). Low level plastic covers increased the range of warm environments at one site and gave a mean thermal time required of 2098 OHU.Analysis of daily air temperatures from six weather stations throughout the UK over a 29 year period, showed a 14 day possible planting period on the south coast of England, but gave a high probability of crop failure in Scotland.Maps of England and Wales indicating the probability of achieving 2000 OHU were produced from 5 km grid point temperatures. Less than 2% of the land had more than a 60% chance of receiving 2000 OHU under the present climate, however this area increased to 70% with a mean temperature rise of 1.5°C. Although 2000 OHU is often used as the thermal time requirement of navy beans, these trials showed that it may be more accurate to use the higher figure of 2087 OHU from sowing to harvest, and restrict the use of 2000 OHU to the period between emergence and harvest. When the map was redrawn using 2087 OHU and current climate, no parts of England and Wales showed a reasonable chance of growing the present cultivars of navy beans.

Manipulation of bolting and flowering in celery (Apium graveolensL. var.dulce). II. Juvenility

SummaryAfter germination, a juvenile phase of development was apparent in cvs New Dwarf White and Celebrity. During this incompetent phase, plants were not induced flower even when subjected to chilling at 5°C for nine weeks. Juvenility ended and the plants became competent to perceive chilling as a vernalization stimulus when they had initiated 17 leaves including leaf primordia in cv. New Dwarf White and between 17 and 20 leaves in cv. Celebrity. After phase transition, the level of competence was not affected by plant age. The rate of leaf initiation in cv. New Dwarf White during juvenile and competent vegetative growth related linearly to temperature, increasing between 3 and 22.8°C and then declining over the range 22.8 to 37.4°C. The first 17 leaves of celery cv. New Dwarf White had longer plastochrons of 43° Cd (>3°C) each than subsequently initiated leaves with 29° Cd for each leaf. The thermal time requirement for completion of juvenile development after radicle emergence was 731° Cd> 3°C. In cv....

Heat tolerance for yield and its components in different wheat cultivars

Twenty one diverse, standard and experimental cultivars of common spring wheat (Triticum aestivum L.) were tested for the effect of heat stress on phenology, yield and its components by growing the materials for 2 years under full irrigation during the hot summer (offseason), and the cool winter (normal) conditions. Heat tolerance was estimated for each variable by the ‘heat susceptibility index’ (S) which scales the reduction in cultivar performance from cool to hot conditions relative to the respective mean reduction over all cultivars. Genotypes differed significantly in S for yield and its components. The ranking of cultivars in S over the 2 years was consistent for yield, kernels per spike and kernel weight, but not for spike number. Of the three yield components, the greatest genotypic variation in S was expressed for kernels per spike. However, S for yield could not be simply attributed to S in a unique component across all cultivars. On the other hand, a general linear model regression of summer yield on its components revealed that the most important yield component affecting yield variation among cultivars under heat stress was kernel number per spike. Kernel number per spike was positively associated across cultivars with longer duration and greater stabilty of thermal time requirement from emergence to ‘double ridge’. It is therefore concluded that kernel number per spike under heat stress is a reasonable estimate of heat tolerance in yield of wheat and that this tolerance is operative already during the first 2 to 3 weeks of growth.

Germination and elongation of the hypocotyl and radicle of kenaf (Hibiscus cannabinus) in response to temperature

Abstract Temperature controls pre-emergent development of seedlings, and is generally the prime determinant of the duration from sowing to seedling emergence. This study was conducted to examine seed germination and the elongation of the hypocotyl and radicle of kenaf (Hibiscus cannabinus L.) under constant temperature conditions, and to provide the temperature parameters necessary to model the processes of seedling emergence. Seed of kenaf, cv. Guatemala-4, were germinated in incubators at 8 constant temperatures (15, 20, 25, 30, 35, 40, 43 and 45°C). The numbers of germinated seeds and lengths of the hypocotyl and radicle were measured over time in each temperature regime. Final germination percentage was unaffected by temperatures in the range 15–35°C, but declined sharply at the higher temperatures. The optimum (To) and maximum temperatures (Tm) for rate of seed germination, which was defined as the inverse of the half-time of germination, were 35°C and 45°C, respectively. Values of To and Tm for the lag and linear phases of hypocotyl elongation were about 31°C and 43°C, respectively. Similar values for To and Tm were calculated for elongation of the radicle. Above a base temperature (Tb) of 10°C, the thermal time requirement for 50% seed germination was 8.2°C d, the lag phase of hypocotyl elongation required 17.0°C d, and linear hypocotyl elongation required 0.45°C d mm−1. It is proposed that the emergence of kenaf seedlings can be modelled from a specified sowing depth by the summation of the thermal time required for germination and the lag and linear phases of hypocotyl elongation.

Use of the Weibull Function to Calculate Cardinal Temperatures in Faba Bean

The major objective of this paper is to demonstrate not only that the Weibull function accurately models cumulative germination, but also that it can be used to calculate cardinal temperatures and thus thermal time requirement for the germination of seeds, in this case faba bean

Thermal Time Requirements for Phenological Development of Peanut

AbstractTemperature is a major environmental factor that determines the rate of plant development. Relation of thermal time to phenological development of peanut would provide a better understanding of this crop's response to temperature. Thermal time measured in day‐degrees (°Cd) was used to determine peanut (Arachis hypogaea L.) phenological development of a Spanish botanical‐type culitvar, Pronto, and a Virginia botanical‐type breeding line, OK‐FH15. Peanuts were grown under field conditions, on a Teller sandy loam (fineloamy, mixed, thermic, Udic Argiustoll) in 1985, 1986, and 1987. Irrigation plus rainfall ranged from 840 mm in 1985 to 400 mm in 1987. At 12 d after planting (DAP) when >80% emergence had occurred, 136 ± 18 °Cd had accumulated. Pronto produced more mainstem nodes (vegetative stage) than did OK‐FH15. Regression analyses indicated that both vegetative and reproductive development were highly correlated with °Cd for both genotypes. Incipient flowering (R1) began at 313 and 360 °Cd in 1985 and 1986, respectively. At 50% R1 in 1987, 410 and 498 °Cd had accumulated for Pronto and OK‐FH15, respectively. Both vegetative and reproductive stage development were slower with less water. Although attainment of a high reproductive stage value (7 to 9) does not indicate a high yield per se, it does indicate the degree of crop maturity. Seasonal accumulation of °Cd in 1985, 1986, and 1987 was 1456,1672, and 1473, respectively. Crop yields (pods) for the fullirrigation treatment were 312, 325, and 288 g m−2 for Pronto and 358, 405, and 308 g m−2 for OK‐FH15 in 1985, 1986, and 1987, respectively. Knowledge of °Cd accumulated can provide an estimate of harvest date as well as crop development stage.

Date of Budburst of Fifteen Tree Species in Britain Following Climatic Warming

(1) The thermal times (T) (day 'C > 5 'C since 1 January) to vegetative budburst were measured on fifteen woody perennials in Britain after different durations of chilling (C) (number of days < 5 'C since 1 November). (2) Late-flushing species, like Fagus sylvatica, had high values of T, even after 145 chill days, and T increased greatly with decreased chilling. Early-flushing species, like Crataegus monogyna, had small values of T, which did not increase much until there were fewer than 80-100 chill days. (3) Relationships of the form T= a + b exp (r C) were fitted for each species, which were then classified into five groups. Past meteorological records were then used to estimate the mean dates of budburst of each group of species at Edinburgh (26 m altitude) and Braemar (339 m) with 0-3 'C uniform climatic warming. (4) Climatic warming did not markedly shift the date of budburst of any group of species at Edinburgh, so they flushed in warmer conditions and failed to exploit the earlier springs. However, at Braemar, the species with small thermal time and chilling requirements, like C. monogyna, flushed much earlier following climatic warming.

Threshold Temperature and Minimum Thermal Time Requirements for the Complete Life Cycle of Meloidogyne Hapla From Northern Europe

The base threshold temperature for the development of a population of Meloidogyne hapla from a glasshouse in Finland was estimated as 8.25°. The thermal time requirement above this base for development from juvenile to the first juvenile of the second generation was about 553 day°. Two field populations from northern Europe had similar thermal requirements. In some experiments there was an indication that the rate of egg hatch had slowed at the lowest temperature used (17°), possibly because of a slight diapause. Tomato was a better host than cabbage, but the thermal requirements of the M. hapla were similar on both.

Genotypic Differences in the Temperature Responses of Tropical Crops

In greenhouse trials, seedling emergence and leaf growth of 5 pearl millet [P. americanum] and 7 groundnut cultivars were measured at soil temp. of 7-27°C. Rate of seedling emergence varied greatly between pearl millet cultivars, but was very similar in all groundnut cultivars. In pearl millet there were strong correlations between germination rate and leaf production rate, hourly leaf extension and seedling emergence. The thermal time requirements of various processes are discussed

The winter development, reproduction and lifespan of viviparae of Sitobion avenae (F.) (Hemiptera: Aphididae) on wheat in England

AbstractViviparae of Sitobion avenae (F.) in clip-cages on winter wheat in field plots in southern England were monitored throughout the 1980–81 winter to determine characteristics of development, reproduction and lifespan under winter conditions. Rate-temperature relationships for development and reproduction were well described by straight lines when temperatures were measured above 3°C. A simple thermal-time scale could therefore be used for both processes. The parental morph and the time of year modified thermal-time requirements for the production of an adult's first 20 nymphs but did not affect those for development. For both alatae and apterae, nymph production per day-degree was greater than at higher temperatures and the relationship between reproductive rate and age was different. The minimum temperature experienced by the aphids was −7°C; survival was good, with little low temperature mortality. Total fecundity of apterae was usually greater than at higher temperatures, though some apterae and alatae that were deposited in October had low fecundity, possibly because they were insufficiently acclimatized at the onset of cold winter weather. Overwintering alatae had lower development rates, reproductive rates and total fecundity than apterae and did not survive as long, but were restless as young adults and appeared ready to migrate. Oviparae were produced from late September to mid-October but not after this, suggesting that the clone used could ‘switch off’ sexual morph production in winter.