Genotypic Differences in the Temperature Responses of Tropical Crops: II. SEEDLING EMERGENCE AND LEAF GROWTH OF GROUNDNUT (ARACHIS HYPOGAEA L.) AND PEARL MILLET (PENNISETUM TYPHOIDES S. & H.)

Mohamed, H. A., Clark, J. A. and Ong, C. K. 1988. Genotypicdifferences in the temperature responses of tropical crops.II. Seedling emergence and leaf growth of groundnut (Arachishypogaea L.) and pearl millet (Pennisetum typhoides S. &H.).—J. exp. Bot. 39: 1129-1135. Measurements of seedling emergence and leaf growth of five milletand seven groundnut genotypes were made at soil temperaturesranging from 7 to 27?C. The rate of seedling emergence (R_e)varied greatly between millet genotypes but R_e was remarkablysimilar in groundnut genotypes. In pearl millet there is a strongcorrelation between the rate of germination and the rate ofleaf production, hourly leaf extension and seedling emergence.The results are discussed in terms of the thermal time requirementsof various processes. Key words: Temperature, emergence, groundnut, millet     

Genotypic Differences in the Temperature Responses of Tropical Crops: III. LIGHT INTERCEPTION AND DRY MATTER PRODUCTION OF PEARL MILLET (PENNISETUM TYPHOIDES S. & H.)

Mohamed, H. A., Clark, J. A. and Ong, C. K. 1988. Genotypicdifferences in the temperature responses of tropical crops.III. Light interception and dry matter production of pearl millet(Pennisetum typhoides S. & H.).—J. exp. Bot. 39: 1137–1143. Leaf area development, light interception and dry matter productionof four contrasting pearl millet cultivars were investigatedat mean air temperatures of 19.5, 21, 26 and 31?C. Growth wasslowest as 19.5?C and fastest at 31?C. The canopies of the cultivarsvaried considerably with regard to their light transmissioncoefficients (K₁), from 0.47 for Sanio to 0.23 for Oasis andin their mean efficiency of energy conversion (e), from 1.0to 2.7 g MJ^–1. The ranking of the cultivars in these respectsis consistent with those for germination and early establishmentand early establishment reported in the preceding papers. Key words: Light, dry matter production, millet     

Time, Temperature and Germination of Pearl Millet (Pennisetum typhoides S. & H.): II. ALTERNATING TEMPERATURE

Methods of analysing the response of germination to constanttemperature are extended to alternating temperatures. The analysisis illustrated for seeds of pearl millet (Pennisetum typhoidesS. & H.) germinated on a thermal gradient plate in pairsof alternating temperatures ranging from 15?C to 47?C. Alternatingtemperatures had a small but systematic effect on germinationrate such that below 42 ?C, alternations in temperature hadno effect on the maximum fraction of seeds which germinatedin the population, but increases in temperature amplitude fromzero to ?8 ?C caused a small but systematic increase in therate of germination.     

Time, Temperature and Germination of Pearl Millet (Pennisetum typhoides S. & H.): I. CONSTANT TEMPERATURE

The germination of pearl millet (Pennisetum typhoides S. &H.) seeds was investigated at constant temperatures between12 ?C and 47 ?C on a thermal gradient plate. The rate of germination increased linearly with temperaturefrom a base T_b to a sharply defined optimum T_o beyond whichthe rate decreased linearly with temperature, reaching zeroat T_m. The linearity of the response both above and below T_oallowed time and temperature to be combined in a thermal timeat which a specified fraction of the seeds germinated. Withinthe population T_b and T_m were constant.     

Time, Temperature and Germination of Pearl Millet (Pennisetum typhoides S. & H.): III. INHIBITION OF GERMINATION BY SHORT EXPOSURE TO HIGH TEMPERATURE

Seeds of pearl millet were germinated on wet filter paper attemperatures up to 50 ?C. In one experiment, the temperaturewas held at 50 ?C during imbibition and was then lowered to32 ?C or 25 ?C. Germination rate and the maximum fraction ofseeds germinating (G_m) both decreased as the time of exposureto 50 ?C increased. In contrast, exposure to 50 ?C after imbibitionfor 8 h slowed germination but did not significantly reduceG_m. When the ‘high’ temperature imposed after imbibitionwas reduced from 50 ?C to 45 ?C, there was a small reductionin the rate of germination but not in G_m. The responses haveimplications for the optimum time of sowing in the tropics whenmaximum daytime soil temperature at the depth of sowing is inthe range of 45–50 ?C. Key words: Pennisetum typhoides, Temperature, Germination     

Response to Temperature in a Stand of Pearl Millet: VI. LIGHT INTERCEPTION AND DRY MATTER PRODUCTION

Stands of pearl millet were grown in glasshouses in which meanair temperature was controlled to 19, 22, 25, 28 and 31 ?C withan amplitude of ?5 ?C. During the main growth period, leaf areaindex increased at a constant rate which was proportional tomean temperature above a base of 10 ?C. The warmest stand, therefore,intercepted more radiation before anthesis but the transmissioncoefficient was independent of temperature (K 0.3). Based ondry weight at final harvest, the efficiency of conversion forintercepted radiation ranged from about 2.1–2.4 g MJ^–1consistent with field experience. Combining this informationwith figures for the duration of growth in relation to temperaturesuggests that growth rate should be maximal at 25–27 ?Cand total dry weight at 20–22 ?C. Key words: Temperature, Pearl millet, Growth rate, Light     

The Influence of Temperature on Seed Germination Rate in Grain Legumes: III. A COMPARISON OF FIVE FABA BEAN GENOTYPES AT CONSTANT TEMPERATURES USING A NEW SCREENING METHOD

Ellis, R. H., Simon, G. and Covell, S. 1987. The influence oftemperature on seed germination rate in grain legumes. III.A comparison of five faba bean genotypes at constant temperaturesusing a new screening method.—J. exp. Bot. 38: 1033–1043. A screening procedure which requires information on the progressof germination at only four temperatures was able to definethe response of the rate of seed germination to sub- and supra-optimaltemperatures for whole seed populations of each of five fababean (Vicia faba L.) genotypes. In one population of the cultivarSutton the models for sub- and supra-optimal temperatures derivedfrom the screen satisfactorily explained observations from anearlier separate investigation at a wider range of temperatures.Two discrete groups of genotypes were identified. Within eachgroup the base temperature T_b did not differ significantly:for the landraces Lebanese Local Large and Syrian Local Largethe value was estimated to be –7·5°C and forthe landrace Lebanese Local Small and the cultivars Sutton andAquadulce it was –4·0°C. The optimum temperaturefor the 50th percentile [T_o(50), at which temperature the rateof germination is maximal] also varied between these two groupsof genotypes, being 20·5–21·5°C forthe first group and 24·5–26·0°C forthe second. In several temperature regimes some of the viableseeds within a seed population failed to germinate. Nevertheless,even at temperatures where a substantial proportion of the seedsfailed to germinate the models defined by the screening methodpredicted the germination times of those seeds which did germinate. Key words: Faba bean, seed gemination rate, temperature     

Quantal Response of Fruit and Seed Germination Rate in Quercus robur L. and Castanea sativa Mill, to Constant Temperatures and Photon Dose

A linear relationship between constant temperatures in the sub-optimaltemperature range and germination rate is shown in both Quercusrobur L and Castanea sativa Mill germinated under nominal darkconditions. The mean base temperature was interpolated for Qrobur as 0 8 ? or 2-4 ?, depending on seed lot provenance, andfor C. sativa as 1 -4? The optimum temperature for germinationin Q. robur was about 20? compared with around 28 ? in C. sativaOver the sub-optimal temperature range the distribution of thermaltimes was log-normal for each population studied their spreadvarying both between Q robur seed lots and between species However,in C. sativa germinated close to the mean base temperature,the distribution in thermal times was reduced Thermal timesto germination were decreased in Q. robur and C sativa by approximately0 3 and 0-5 log-units, respectively, when the pericarp was removed,i.e in the seeds, but the sensitivity of the response remainedrelatively unaltered In both species the germination rate was the same when nominaldark or safe green light conditions were employed during thegermination test. However, at 21 ? Q robur exhibited the highirradiance reaction (HIR) at photon doses above 30mmol m^–2d^–1. HIR first affected the germination rate by an inhibitionof radicle extension The sensitivity of the response to thermaltime was reduced as photon dose increased. This photo-inhibitionwas exacerbated at supra-optimal temperatures. In contrast,C. sativa germination rate at 26 ? was little influenced bylight at a photon dose of 752 mmol m^–2 d^–1 Key words: Seed germination rate, temperature, thermal time, light, photon dose     

The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. in Flowing Solution Culture: I. GROWTH

Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. in flowing solution culture. I. Growth.—J.exp. Bot. 38: 42–52 Oilseed rape (Brassica napus L. cv. Bien venu) was grown for49 d in flowing nutrient solution at pH 6?0 with root temperaturedecrementally reduced from 20?C to 5?C; and then exposed todifferent root temperatures (3, 5, 7, 9, 11, 13,17 or 25?C)held constant for 14 d. The air temperature was 20/15?C day/nightand nitrogen was supplied automatically to maintain 10 mmolm^–3 NH₄NO₃ in solution. Total dry matter production wasexponential with time and similar at all root temperatures givinga specific growth rate of 0?0784 g g^–1 d^–1. Partitioningof dry matter was influenced by root temperature; shoot: rootratios increased during treatment at 17?C and 25?C but decreasedafter 5 d at 3?C and 5?C. The ratio of shoot specific growthrate: root specific growth rate increased with the ratio ofwater soluble carbohydrates (shoot: root). Concentrations ofwater soluble carbohydrates in shoot and root were inverselyrelated to root temperature; at 3, 5 and 7?C they increasedin stem + petioles throughout treatment, coinciding with a decreasein the weight of tissue water per unit dry matter. These resultssuggest that the accumulation of soluble carbohydrates at lowtemperature is the result of metabolic imbalance and of osmoticadjustment to water stress. Key words: Brassica napus, oilseed rape, root temperature, specific growth rate     

The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. cv. Bien venu in Flowing Solution Culture: II. UPTAKE FROM SOLUTIONS CONTAINING NH4NO3

Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. CV. Bien venu in flowing solution culture.II. Uptake from solutions containing NH₄NO₃.—J. exp. Bot.38: 53–66 The effects of root temperature on uptake and assimilation ofNH₄⁺ and NO₃^– by oilseed rape (Brassica napus L. CV. Bienvenu) were examined. Plants were grown for 49 d in flowing nutrientsolution at pH 6?0 with root temperature decrementally reducedfrom 20?C to 5?C; and then exposed to different root temperatures(3, 5, 7, 9, 11, 13, 17 or 25?C) held constant for 14 d. Theair temperature was 20/15?C day/night and nitrogen was suppliedautomatically to maintain 10 mmol m^–3 NH₄NO₃ in solution.Total uptake of nitrogen over 14 d increased threefold between3–13?C but was constant above 13?C. Net uptake of NH₄⁺exceeded that of NO₃^– at all temperatures except 17?C,and represented 47–65% of the total uptake of nitrogen.Unit absorption rates of NH₄⁺ and of 1?5–2?7 for NO₃^–suggested that NO₃^– absorption was more sensitive thanNH₄⁺ absorption to temperature. Rates of absorption were relativelystable at 3?C and 5?C compared with those at 17?C and 25?C whichincreased sharply after 10 d. Tissue concentration of N in theshoot, expressed on a fresh weight basis, was independent ofroot temperature throughout, but doubled between 3–25?Cwhen expressed on a dry weight basis. The apparent proportionof net uptake of NO₃^– that was assimilated was inverselyrelated to root temperature. The results are used to examinethe relation between unit absorption rate adn shoot:root ratioin the context of short and long term responses to change ofroot temperature Key words: Brassica napus, oilseed rape, root temperature, nitrogen uptake     

The Interactive Effects of Phytochrome, Nitrate and Thiourea on the Germination Response to Alternating Temperatures in Seeds of Ranunculus sceleratus L.: A Quantal Approach

Probert, R. J., Gajjar, K. H. and Haslam, I. K. 1987. The interactiveeffects of phytochrome, nitrate and thiourea on the germinationresponse to alternating temperatures in seeds of Ranunculussceleratus L.: A quantal approach.—J. exp. Bot. 38: 1012–1025. The interactive effects of phytochrome, potassium nitrate andthiourea on the germination response to alternating temperaturesin achenes (seeds) of Ranunculus sceleratus L. were studied.Using thermogradient bars, high levels of germination were recordedover a broad range of alternating temperatures providing seedsreceived daily irradiations. Reduced germination in temperaturecycles with a relatively long warm phase was related to thelevel of the active form of phytochrome (Pfr). Dose-responseexperiments to red light (R) and temperature shifts showed thatthe actions of Pfr and alternating temperatures were interdependent.Maximum germination was recorded when intermittent pulses ofR were combined with daily 4 h temperature shifts from 16°Cto 26°C. Whilst probit analysis showed that potassium nitrateand thiourea both increased population sensitivity to temperatureshifts, thiourea was a more potent stimulant. Although the effectof both chemicals was dependent on phytochrome photo-equilibriumthe threshold level of Pfr required for thiourea action wasclearly much lower than that required for nitrate action. Thioureapotentiated a response to daily temperature shifts even whenPfr was at a low, normally inhibitory level. These results indicatedifferent mechanisms of action for potassium nitrate and thioureain relation to phytochrome controlled seed germination. Key words: Phytochrome, nitrate, thiourea, alternating temperatures, germination     

Light Actions in the Germination of Cocklebur Seeds: III. EFFECTS OF PRE-TREATMENT TEMPERATURE ON GERMINATION RESPONSES TO FAR-RED LIGHT AND ON DARK GERMINATION IN THE RED LIGHT-REQUIRING UPPER SEEDS

Esashi, Y., Oota, H., Saitoh, H. and Kodama, H. 1985. Lightactions in the germination of cocklebur seeds. III. Effectsof pre-treatment temperature on germination responses to far-redlight and on dark germination in the red light-requiring upperseeds.—J. exp. Bot. 36: 1465-1477. Red light (R) responsiveness in R-requiring upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds changed in differentpatterns during a soaking period at different temperatures.At temperatures above 23°C, the responsiveness increasedand then decreased. At lower temperatures (3–18°C),however, it continued to increase throughout an experimentalperiod. The lower temperatures caused germination in the subsequentdark at 33°C, regained the R responsiveness and acquiredthe dark germinability when subsequently exposed to 8°C,to an extent proportional to the duration of the chilling. Far-red (FR) was inhibitory to germination in an earlier soakingperiod at lower temperatures, but its effect gradually decresed,and finally turned promotive. The negative FR response was repeatedlycontrolled by the following R irradiation. However, the positiveFR response was enhanced by an immediate R irradiation, andFR/R reversibility occurred after the second FR. In contrastto the R responsiveness and dark germinability, the positivegermination response to FR was not induced by soaking at 3°C,in which the growth of the axial tissue as a photoreceptivesite did not occur at all. Similarly, it was not manifestedwhen the seeds soaked at 33°C were subsequently subjectedto 8°C. Key words: Cocklebur seeds, dark germination, far-red light, low temperature, red light, seed germination, Xanthium pennsylvanicum     

Response to Temperature in a Stand of Pearl Millet (Pennisetum typhoides S. & H.): VIII. ROOT GROWTH

P J. Gregory. 1986. Response to temperature in a stand of pearlmillet (Pennisetum typhoides S. & H.). VIII. Root growth—J.exp. Bot. 37: 379–388. Two experiments were made in controlled glasshouscs to investigatethe growth of roots of pearl millet at different air and soiltemperatures. The experimental plants were grown in columnsof soil within stands of millet for 3 to 4 weeks and destructivelysampled at regular intervals to estimate the length of individualroot axes and of the root system. The length of individual rootaxes increased exponentially with time and at any particulartime the rate of extension was faster the higher the soil temperature.Clear ontogenctic effects on the rates of elongation were detected,with each succeeding axis elongating faster than its predecessor.Total root length was longer the higher the soil temperature(at a particular air temperature) and increased exponentiallywith time and with thermal time assessed from temperatures measuredat 2·0 cm depth. Whereas length at a particular timehad a 10-fold range, length at a particular thermal time hadonly a 3-fold range. Mean irradiance differed between the twoexperiments and as a means of exploring the importance of carbohydrateresources for root extension, relations between root length,leaf area and the amount of radiation intercepted were sought. Root length and leaf area were linearly related for all temperaturetreatments in both years as were root length and interceptedradiation. However, whilst the former relation was the samein both years, the latter was different. Root dry weight andintercepted radiation were also linearly related with the samerelation for both years so that the root length: weight ratiosdiffered between years because of factors not controlled inthese experiments. The results show the close relation between root and shoot growthand that thermal time together with the amount of radiationintercepted by the leaves might be used as the basis for quantifyingthe effects of temperature on root growth. Key words: Pearl millet, temperature, thermal time, root extension, root growth     

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Controlled environment experiments were performed to determinethe effects of temperature and water potential on germination,radicle elongation and emergence of mungbean (Vigna radiata(L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15–45°C) and water potentials (0 to –2.2 MPa) on germinationand radicle elongation rates were studied using an osmoticumtechnique, in which seeds were held against a semi-permeablemembrane sac containing a polyethylene glycol solution. Linearrelationships were established between median germination time(Gt₅₀) and water potential at different temperatures, and betweenreciprocal Gt₅₀ (germination rate) and temperature at differentwater potentials. Germination occurred at potentials as lowas –2.2 MPa at favourable temperatures (30–40 °C),but was fastest at 40 °C when water was not limiting, withan estimated base temperature (T_b) of about 10 °C. Subsequentradicle elongation, however, was restricted to a slightly narrowertemperature range and was fastest at 35 °C. The conceptof thermal time was used to develop an equation to model thecombined effects of water potential and temperature on germination.Predictions made using this model were compared with the actualgermination obtained in a related series of experiments in columnsof soil. Some differences observed suggested the additionalimportance of the seed/soil/water contact zone in influencingseed germination in soil. Seedling emergence appeared to reflectfurther the radicle elongation results by occurring within anarrower range of temperatures and water potentials than germination.Emergence had an estimated T_b of 12.6 °C and was fastestat 35 °C. A soil matric potential of not less than about–0.5 MPa at sowing was required to obtain 50% or moreseedling emergence. Key words: Germination, temperature, water potential     

Germination Strategy of a Woodland Grass: Milium effusum L.

Caryopses of Millum effusum L. were collected from wild plantsin south-east England Laboratory tests established that germination immediately followingharvest occurred relatively slowly at a narrow range of temperatures;optima occurred at 16 °C in the first weeks of experimentsand subsequently at 21 °C, at which the highest proportionof germination occurred Levels of germination increased aftercaryopses had been stored at 25 °C over anhydrous calciumchloride, when tests were done at fluctuating temperatures;or after chilling treatments at 2 °C, or high temperature(26 and 31 °C) conditioning treatments of imbibed seed Freshlyharvested caryopses displayed an inverse relationship betweentemperature and time taken to germinate resulting from variationsin the speed at which after-ripening processes were completedat different temperatures These responses were used to construct a model representativeof all populations of M effusum throughout its natural range.The results suggested that a coherent and plausible interpretationof the responses could be arrived at by suggesting that adaptationto local conditions depends largely on phenotypic plasticityarising from interactions between the germination characterand a variety of differing climatic conditions Millum effusum L wood millet, germination, temperature response     

Light and temperature control of germination in Agropyron smithii seeds

In darkness, A. smithii seeds germinated poorly at constanttemperatures but well at alternating temperatures. Prolongedperiods on the high part of the temperature cycles reduced germination;the higher the temperature the shorter was the period requiredon the high part of the temperature cycles for optimum germination.Continuous, unfiltered, incandescent illumination and intermittentfar red at 15?–25?C alternation also inhibited germination;the inhibitory effects were similar to those caused by the highintensity reaction. Far red inhibited germination when appliedafter 1 and 2 complete 15?–25?C cycles in darkness butnot after 3 cycles. Less than 20% of the seeds were under phytochromecontrol at constant 20?C. When red light was applied directlyafter far red that was applied in intermittent cycles at 15?–25?C,however, 50% of the seeds caused to germinate by the alternatingtemperature were shown to be controlled by the reversible phytochromereaction. The induced high-temperature dormancy was overcome by gibberellicacid (GA₃) plus kinetin. The hormonal treatment was much moreeffective than light for breaking dormancy. Inhibition fromprolonged illumination was alleviated or eliminated by GA₃+kinetin.The failure of red light to promote good germination at 20?Cwas also overcome with GA₃+kinetin; effects of light plus thehormone treatments were more than additive. These data suggestthat optimum alternating temperatures facilitate a proper balanceand interaction of hormones, enzymes, substrates and possiblypreexistent P_fr so that the germination of A. smithii seedscan proceed without benefit of a light treatment. (Received July 7, 1976; )     

The Influence of Temperature on Seed Germination Rate in Grain Legumes: II. INTRASPECIFIC VARIATION IN CHICKPEA (Cicer arietinum L.) AT CONSTANT TEMPERATURES

Positive linear relationships were shown between constant temperaturesand the rates of progress of germination to different percentiles,G, for single populations of each of five genotypes of chickpea(Cicer anetinum L.). The base temperature, T_b, at which therate of germination is zero, was 0·0°C for all germinationpercentiles of all genotypes. The optimum temperature, T_o(G),at which rate of germination is most rapid, varied between thefive genotypes and also between percentiles within at leastone population. Over the sub-optimal temperature range, i.e.from T_b to T_o(G), the distribution of thermal times within eachpopulation was normal. Consequently a single equation was appliedto describe the influence of sub-optimal temperatures on rateof germination of all seeds within each population of each genotype.The precision with which optimum temperature, T_b(G), could bedefined varied between populations. In each of three genotypesthere was a negative linear relationship between temperatureabove T_b(G) and rate of germination. For all seeds within anyof these three populations thermal time at supra-optimal temperatureswas constant. Variation in the time taken to germinate at supra-optimaltemperatures was a consequence of normal variation in the ceilingtemperature, T_o(G)—the temperature at or above which rateof progress to germination percentile G is zero. A new approachto defining the response of seed germination rate to temperatureis proposed for use in germplasm screening programmes. In two populations final percentage germination was influencedby temperature. The optimum constant temperature for maximumfinal germination was between 10°C and 15°C in thesepopulations; approximately 15°C cooler than the optimumtemperature for rate of germination. It is suggested that laboratorytests of chickpea germination should be carried out at temperaturesbetween 10°C and 15°C. Key words: Chickpea, seed germination rate, temperature     

Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Seed conditioning and germination in witchweed (Striga asiatica(L.) Kuntze) were temperature-dependent. With higher conditioningtemperatures, shorter conditioning time was required for germinationwith terminal dl-strigol (strigol) treatment at 30 °C. Maximumgermination (80–100%) was obtained by conditioning inwater at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively,and terminally treating with 10^–6 M strigol at 30 °C.Seeds conditioned in 10^–8 M strigol instead of water germinatedmuch less with the same terminal strigol treatment. Generally,conditioning was slower when seeds were conditioned in strigolrather than water. The reduction in germination rate by pretreatmentin strigol or pretreatment at low temperatures could be overcomeby increasing the terminal strigol concentration in the germinationtest. Conditioned seeds did not germinate at 10 and 15 °Cwith a terminal 10^–6 M strigol treatment but yielded closeto maximum germination at 25, 30 and 35 °C with the sameterminal strigol treatment. To obtain maximum germination, boththe minimum conditioning temperature and the minimum germinationtemperature for conditioned seeds were 20 °C. Factors suchas conditioning time, and strigol concentration and temperatureduring conditioning and/or germination determine whether seedsremain in the conditioning phase or shift to a germination phase. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica, temperature, weed control     

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

The onset of germination of faba bean seeds at constant temperaturewas progressively delayed as that temperature diverged froman optimum of 25.5 ?C. At temperatures below 10 ?C, or above28 ?C, the maximum germination percentage fell to below 90%.There was no germination at 39 ?C. Positive and negative linearrelationships were established between the constant temperaturesand the rates of progress of germination to different percentiles,at sub-optimal and supra-optimal temperatures, respectively.Like germination rates, base temperature (T_b) declined from3.71 to –0.83 ?C as the percentile value increased from10% to 80%. Caution was urged in extrapolating beyond the experimentaldata set. Differences in the ceiling temperature (T_c) with percentilecould not be discerned. Cumulative germination progress curves at each temperature weremodelled by the Weibull, logistic, and cumulative normal distributionfunctions. Cardinal temperatures (T_b and T_c) calculated fromthese data reasonably approximated the actual data. The Weibullfunction demonstrated a good approximation at all percentilelevels, while the logistic and cumulative normal distributionfunctions, as a result of their inherent symmetry, deviatedat the extreme percentiles. It was concluded that the Weibullfunction not only accurately modelled cumulative germinationbut could also be used in the calculation of cardinal temperatures. Key words: Seed germination rate, cardinal temperatures, faba bean, Weibull function, probit and logic scales     

Effect of Cultivar, Temperature and Seed Size on the Germination and Emergence of Soya Beans (Glycine max (L.) Merr.)

The rapid and uniform establishment of soya bean [Glycine max(L.) Merr.] stands is conducive to higher yields. This studywas undertaken to determine the effects of cultivar, temperature,and seed size on the rate of germination and emergence. No cultivar effect on the germination rate was observed. However,in an emergence study from a sand-soil-peat mixture, cultivardifferences in emergence rates were noted(‘Chippewa 64’> ‘Wayne’ > ‘Amsoy 71’). In anotheremergence study (sand media) the cvs ‘Calland’ and‘Williams’ emerged faster than the cv. 'Wayne or‘Wells’. Time required for 50 per cent germination decreased (18.8–4.0days) as the temperature increased from 10 to 30 °C (5 °Cincrements). Emergence (50 per cent) from a sand-soil-peat mixturewas more rapid (19.8–6.3 days) as the simulated plantingdate (growth chamber set to simulate field temperatures) wasdelayed from 16 April to 15 June with an intermediate date of16 May. In addition, time required for 50 per cent emergence of thecultivars from sand decreased (793–76 h) as the temperaturewas increased from 10 to 30 °C with no decrease from 30to 35 °C. Seed size effects were apparent, with the very small seed germinatingslower than the three larger seed sizes. In the emergence studieswith both the sand and sand-soil-peat mixture there was a generaltrend toward more rapid emergence with the smaller seeds. However,the absolute differences were small. Significant cultivar x temperature interactions were observedfor the germination and emergence rates. In most cases the cultivarsmerged in terms of germination and emergence rates at temperaturesbetween 10 and 20 °C and at the higher temperatures thecultivar rankings were different from those observed at temperaturesbelow the merging point. Glycine max (L.) Merr, soya bean, seed germination, establishment of seedlings