Response to Temperature in a Stand of Pearl Millet: 9. EXPANSION PROCESSES

Effects of temperature on the size of the leaf canopy, the stemsand the panicles were investigated for stands of pearl milletin controlled-environment glasshouses. Expansion of each structurewas examined in terms of a duration and a mean rate. The duration(t) for vegetative structures responded to temperature as anormal developmental period, in that l/t increased linearlywith rise in temperature between a base (10 °C) and an optimum(30 to 35 °C). The rate for these structures also increasedlinearly with temperature between a similar base and optimum.Effects of temperature on rate compensated for those on duration,such that the leaf area index and height of the canopy werelittle affected by temperature. The panicles responded slightlydifferently in that length increased with rise in temperatureby about 2% per degree. For all structures, rate, duration andsize were little influenced by unsystematic differences betweentreatments in the rate of dry matter production. Key words: Pearl millet, temperature, expansion, thermal time     

Relationship between Plant Weight and Growing Period for Vegetable Crops in the United Kingdom

A generalized equation is derived that relates total dry matterproduction to time from emergence for crops grown in the fieldwith adequate water and nutrients. It is: w+K₁lnw+W₀=K₂t where w is the plant dry weight in t ha^–1, t is time indays after emergence, K₂ and K₁ are constants and W₀ equals–(w₀+K₁lnw₀) where w₀ is the value of w at the start ofthe growing period. The increases in the dry matter of 18 different types of vegetablecrop were measured at intervals during growth in the field.In every case the data fitted the equation very satisfactorilywith K₁ set equal to 1 t ha^–1. The fitted values of K₂were similar for many crops; those of W₀ varied considerablybut were always similar to the values calculated from the individualseed weight and the plant population. Good fits were also obtainedwhen time in days was replaced with cumulative evaporation froman open water surface. It is concluded that the growth-time curves of many differentvegetable crops can be described by the same simple equationand that the variation between curves can be largely attributedto differences in seed weight and plant population.     

The Effect of Temperature on Growth and Development of Echinochloa Millets

Accumulation of dry weight and leaf plus stem area were measuredin Echinochloa utilis and E. frumentacea grown at temperatureregimes from 15/10°C to 33/28°C (day/night). Tilleringand height were recorded in addition to leaf number which wassubsequently used as a developmental index. In both species shoot dry weight increased with temperatureup to 33/28°C; the increase in relative growth rate (RGR)was negligible above 27/22°C. Below 27/22°C the RGRof E. frumentacea decreased sharply and at 15/10°C it madeno effective growth. At low temperatures the RGR of E. frumentaceawas lower than that of E. utilis due to slow leaf area expansion,and in particular smaller individual leaves. E. frumentaceatillered more than E. utilis. Plant development was retardedat low temperatures but was not as responsive to temperatureas dry weight and leaf area. The different responses to temperatureof the two species were described in equations suitable forinclusion in predictive growth models. Echinochloa spp., millet, growth, development, temperature, relative growth rate     

A Comparison of the Growth of the C4 Grass Spartina anglica with the C3 Grass Lolium perenne at Different Temperatures

Dunn, R., Thomas, S. M., Keys, A. J. and Long, S. P. 1987. Acomparison of the growth of the C₄ grass Spartina anglica withthe C₃ grass Lolium perenne at different temperatures.—J.exp. Bot. 38: 433–441. S. anglica is one of the few C₄ species which occurs naturallyin cool temperate zones. It is known to attain photosyntheticrates which equal or exceed those of C₃ grasses over the temperaturerange typical of the spring and summer in cool temperate climates.This study examines whether S. anglica can also attain comparablegrowth rates at these temperatures. Seedlings of S. anglicaand L. perenne cv. S23 were grown in controlled environmentsat 10,15,20 and 25 °C. Quantitative growth analysis wasconducted by taking frequent harvests to determine the progressionsof leaf area and plant weight of individual plants with time.Quadratic regressions were found to describe these progressionswell. Instantaneous derived growth parameters were calculatedfrom the fitted regressions. Both absolute and relative growthrates of S. anglica were significantly lower than for L. perenne,this being largely attributable to a lower ratio of leaf areaproduction per unit of plant dry weight. Although the amountof dry matter invested into leaves was similar, the leaf areaper unit of leaf dry weight was lower in S. anglica. In comparisonto L. perenne, the rate of dry matter accumulation per unitof leaf area (ULR) was higher in S. anglica at 25 °C andinitially equal at 10 °C. Prolonged exposure to 10 °Csteadily reduced ULR in S. anglica which approached zero at80 d. Although growth in S. anglica is reduced more by low temperaturethan it is in L. perenne, by comparison to other C₄ speciesthe assimilatory capacity of S. anglica is more tolerant oflow temperature exposure. Key words: C4 photosynthesis, temperature, quantitative growth analysis     

Growth and Partitioning in Pascopyrum smithii (C3) and Bouteloua gracilis(C4) as Influenced by Carbon Dioxide and Temperature

This study investigated how CO₂and temperature affect dry weight(d.wt) accumulation, total nonstructural carbohydrate (TNC)concentration, and partitioning of C and N among organs of twoimportant grasses of the shortgrass steppe,Pascopyrum smithiiRydb. (C₃) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C₄).Treatment combinations comprised two temperatures (20 and 35°C)at two concentrations of CO₂(380 and 750 µmol mol^-1),and two additional temperatures of 25 and 30°C at 750 µmolmol^-1CO₂. Plants were maintained under favourable nutrient andsoil moisture and harvested following 21, 35, and 49d of treatment.CO₂-induced growth enhancements were greatest at temperaturesconsidered favourable for growth of these grasses. Comparedto growth at 380 µmol mol^-1CO₂, final d.wt of CO₂-enrichedP.smithiiincreased 84% at 20°C, but only 4% at 35°C. Finald.wt ofB. graciliswas unaffected by CO₂at 20°C, but wasenhanced by 28% at 35°C. Root:shoot ratios remained relativelyconstant across CO₂levels, but increased inP. smithiiwith reductionin temperature. These partitioning results were adequately explainedby the theory of balanced root and shoot activity. Favourablegrowth temperatures led to CO₂-induced accumulations of TNCin leaves of both species, and in stems ofP. smithii, whichgenerally reflected responses of above-ground d.wt partitioningto CO₂. However, CO₂-induced decreases in plant tissue N concentrationswere more evident forP. smithii. Roots of CO₂-enrichedP. smithiihadgreater total N content at 20°C, an allocation of N below-groundthat may be an especially important adaptation for C₃plants.Tissue N contents ofB. graciliswere unaffected by CO₂. Resultssuggest CO₂enrichment may lead to reduced N requirements forgrowth in C₃plants and lower shoot N concentration, especiallyat favourable growth temperatures. Acclimation to CO₂; blue grama; Bouteloua gracilis ; carbohydrate; climate change; global change; grass; growth; growth temperature optima; nitrogen; N uptake; Pascopyrum smithii; western wheatgrass     

Regeneration of Ribulose 1,5-bisphosphate and Ribulose 1,5-bisphosphate carboxylase/oxygenase Activity Associated with Lack of Oxygen Inhibition of Photosynthesis at Low Temperature

The nature of the lack of oxygen inhibition of C₃-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO²), 21 kPa p(O₂), balance N₂) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O₂). At 20°C, lowering p(O₂) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O₂) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O₂). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O₂) suggestingthat RuBP regeneration was reduced at low p(O₂) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O₂) was 24% higherthan at 21 kPa p(O₂). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O₂). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase     

Temperature-dependent consumption and gut-residence time in the opossum shrimp Mysis relicta

Maximum daily consumption was estimated for Mysis relicta fedad libitum rations of Daphnia pulex at 4,10,15 and 18°C.Gut-residence time was also evaluated for M.relicta fed clado-ceranprey at 4, 10 and 157deg;C. Mean daily consumption (g dry weightof Daphnia g^–1 dry weight of Mysis day^–1) rangedfrom 6% at 4%C to 12% at 10°. At 18°C, Mysis feedingrate declined to 9% day1. Mean, weight-adjusted consumptionrates exhibited a ‘dome-shaped’ response in relationto water temperature. Consumption rate was highest at 10°Cand lowest at 4°C. Estimated Q₁₀ was more sensitive from4 to 10°C (Q₁₀= 3) than from 10 to 15°C (Q₁₀=1.2). Gut-residencetime for Mysis was inversely related to water temperature, implyingthat evacuation rate increases linearly with water temperature.Feeding and gut-evacuation rates become disassociated at watertemperatures >10°C. As water temperature increased above1°C, relative evacuation rate increased, whereas feedingrate declined. It is postulated that at higher water temperatures,disassociated feeding and gut-evacuation rates reduce the scopefor growth of vertically migrating Mysis and impose a physiologicalconstraint that isolates Mysis from warm, epilimnetic waterduring thermal stratification. ¹Present address: Center for Aquatic Ecology, Illinois NaturalHistory Survey, Sam Parr Biological Station, 6401 Meacham Road,Kinmundy, IL 62854, USA     

The Growth and Development of Maize (Zea mays L.) at Five Temperatures

The objectives of this work were to measure growth and developmentrates over a range of temperatures and to identify processeswhich may limit vegetative yield of maize (Zea mays L.). Twosingle cross Corn Belt Dent maize hybrids were grown from sowingin a diurnal temperature regime of 16/6 °C day/night andin constant temperature environments of 16, 20, 24 and 28 °C.The 16/6 °C environment was close to the minimum for sustainedgrowth and 28 °C was near the optimum. Entire plants wereharvested at stages with 4, 6, 7 and 8 mature leaves in alltemperature treatments except 20 °C in which the final twoharvests were carried out at 9 and 10 mature leaves. Mean totalleaf number varied between 19.5 and 16.0 with the maximum occurringat 16/6 °C. Although harvests were carried out at comparableleaf numbers, and hence at similar developmental stages, thetime interval between sowing and harvest decreased considerablyas temperatures increased. The relative rates of dry weight and leaf area accumulationwith time increased with a Q₁₀ of 2.4 between 16 and 28 °C,while leaf appearance rate increased with a Q₁₀ of 2.9 overthe same range; both rates were highest at 28 °C. Althoughdry matter partitioning to the shoots increased with temperature,the area of individual leaves varied in a systematic patternwhich resulted in maximum leaf area, leaf area duration andconsequently dry weight being realized at 20 °C for anygiven stage of development. Zea mays, corn, low temperature stress, temperature response, growth, development     

Temperature Effects on Rice at Elevated CO2 Concentration

The continuing increase in atmospheric carbon dioxide concentration([CO₂]) and projections of possible future increases in globalairtemperatures have stimulated interest in the effects of theseclimate variables on agriculturally important food crops. Thisstudywas conducted to determine the effects of [CO₂] and temperatureon rice (Oryza sativa L., cv. IR–30). Rice plants weregrownseason-long in outdoor, naturally sunlit, controlled-environment,plant growth chambers in temperature regimes ranging from 25/18/21°Cto 37/30/34°C (daytime dry bulb air temperature/night-timedry bulb air temperature/paddy water temperature)and [CO₂] of660 µmol CO₂ mol1 air. An ambient chamber was maintainedat a [CO₂] of 330 µmol mol^–1 and temperature regimesof 28/21/25°C. Carbon dioxide enrichment at 28/21/25°Cincreased both biomass accumulation and tillering and increasedgrain yield by 60%. In the 660 µmol mol^–1 [CO₂]treatment, grain yield decreased from 10.4 to 1.0 Mg ha^–1with increasing temperature from 28/21/25°C to the 37/30/34°Ctemperature treatment. Across this temperature range, the numberof panicles plant^–1 nearly doubled while the number ofseeds panicle^–1 declined sharply. These results indicatethat while future increases in atmospheric [CO₂] are likelyto be beneficial to rice growth and yield, potentially largenegative effects on rice yield are possible if air temperaturesalso rise. Key words: Oryza sativa, CO₂, temperature, growth, yield     

Evidence for Essential Maintenance Respiration of Leaves of Xanthium Strumarium at High Temperature

Mesophyll resistance to photosynthetic carboxylation (r'_m) wasused as a criterion for leaf integrity. It was measured, at25 °C, in the light, before and after periods of high temperature(3 h at 38 °C) in the dark. During the high temperatureperiods, respiration (R_D) of attached leaves of Xanthium strumariumwas suppressed from 27%-36% by either low [O₂] (1.04% or 0.21%v.v.) or high [CO₂] (840 µl 1^–1) in the ambientair. Neither treatment affected rates of R_D or photo-respirationduring the second period at 25 °C. There was no significant increase of r'_m when R_D was not suppressedduring the high temperature treatment. When R_D was suppressedat high temperatures, r'_m increased from about 3s cm^–1before, to about 26 s cm^–1 after the high temperaturetreatment. The increase depended upon the degree of suppression. It is concluded that increased R_D at high temperature in Xanthiumleaves is partly the result of an increase of energy demandingmaintenance. The subsequent rate of carbon dioxide fixationis reduced when this increase of maintenance-induced respirationis inhibited.     

Chlorophyll Deficiency Caused by a Specific Blockage of the C5-Pathway in Seedlings of Virescent Mutant Rice

Temperature-sensitive mutants of rice, designated virescent(v₁, v₂ and v₃), develop chlorophyll-deficient leaves at a restrictivetemperature (20°C) but develop nearly normal green leavesat a permissive temperature (30°C). Analysis of the chlorophyllbiosynthetic pathway in the virescent mutants indicated thatthe chlorophyll deficiency at the restrictive temperature wasdue to specific blockage of the C₅-pathway. Northern analysissuggested that the chlorophyll deficiency in the virescent mutantswas caused by specific inhibition of the expression of chloroplasttRNA^Glu. (Received October 22, 1993; Accepted January 25, 1994)     

Fruit Number in Relation to Pollen Production and Viability in Groundnut Exposed to Short Episodes of Heat Stress

Hot days and warm nights are important environmental factorslimiting fruit yields of groundnuts in the semi-arid tropics.The objective of the present research was to quantify the effectsof short episodes of heat stress on pollen production and viability,and fruit yield. Plants of cultivar ‘ICGV 86015’were grown at a day/night temperature of 28/22 °C from sowinguntil 9 d after flowering. Cohorts of plants were then exposedto a factorial combination of four day (28, 34, 42 and 48 °C)and two night (22 and 28 °C) temperatures for 6 d. Thereafter,all plants were maintained at 28/22 °C until final harvest9 d later. Number of flowers per plant (FN), the proportionof flowers setting pegs (fruit-set), the number of pegs andpods per plant (reproductive number, RN_t), pollen productionper flower and pollen viability were determined during the 6d stress period. There were strong negative linear relationsbetween day temperature over the range of 28 to 48 °C andFN (slope, -1.1 °C^-1), fruit-set (-2.8% °C^-1), RN_t(-0.90°C^-1), and pollen production (-390 °C^-1) and viability(-1.9% °C^-1). Warmer night temperature (28 vs. 22 °C)had no effect on FN, but reduced fruit-set (31 to 19%), RN_t(8to 5), and pollen production (4389 to 2800) and viability (49to 40%). There were no significant interactions between dayand night temperature. Reduced fruit-set was a consequence offewer pollen grains and reduced pollen viability. The thresholdday temperature for pollen production and viability was 34 °Cand there were strong negative linear relations between bothpollen production and pollen viability and accumulated temperature>34 °C. Copyright 1999 Annals of Botany Company Arachis hypogaea L., fruit-set, groundnut, heat-stress, peanut, pollen viability, pollen production, temperature.     

Chilling Damage to Photosynthesis in Young Zea mays: I. EFFECTS OF LIGHT AND TEMPERATURE VARIATION ON PHOTOSYNTHETIC CO2 ASSIMILATION

Carbon dioxide and water vapour exchanges of the second leafof Zea mays in controlled environment cuvettes were measuredin an open gas-exchange system, during and following subjectionto low temperature stress. Photosynthetic CO2 assimilation (Fc)decreased markedly with decrease in leaf temperature so thatFc at 5 °C was c. 7% of Fc at 20 °C. Fc continued todecline if leaf temperature was maintained at 5 °C, andwhen returned to 20 °C the leaf could not regain its previousFc. This chill-induced reduction in the capacity of the leafto assimilate CO2 was proportional to the duration of the chilland increased with water vapour pressure deficit and photonflux density (I_n). Six hours at 5 °C decreased Fc on returnto 20 °C, relative to Fc prior to treatment, by c. 10% indarkness and by c. 50% in a photon flux density approachingfull-sunlight (I_p = 1.5 mmol m^–2 s^–1). The degreeof reduction in Fc following chill treatment showed an almostlinear dependence on both the length and temperature of thechill. Chill treatments resulted in a decrease in both stomataland mesophyll conductances. Examination of the responses ofF_c to light and CO₂ concentration suggested that chill damageto the capacity for CO₂ assimilation resulted from effects onboth the light and CO₂ limited processes within photosynthesis. Key words: Chilling, Photosynthesis, Zea mays, Light-temperature interaction     

Stomatal Behaviour and Water Relations of Chilled Phaseolus vulgaris L. and Pisum sativum L.

Leaf diffusion resistance interpreted as stomatal resistance,leaf water potential (_w), solute potential (_s) and leaf turgorpotential (_p) of the chilling sensitive species Phaseolus vulgariswere determined during chilling at 4 °C in the light. Bothchill-hardened and non-hardened plants were used. For comparison,the chilling resistant species Pisum sativum was also used. The results for chilled P. sativum were similar to those obtainedfor chill-hardened P. vulgaris plants receiving a chilling treatment.In both cases a reduction in stomatal aperture and the maintenanceof a positive leaf turgor were the responses to chilling. Leavesof chilled but non-hardened P. vulgaris plants were found tomaintain open stomata throughout the chilling treatment despitea severe wilt developing after 7 h at 4 °C. This was incontrast to the chill-resistant P. sativum. which showed a rapidclosing and subsequent re-opening of the stomata to a new reducedaperture. During the first 12 h of chilling _wof P. vulgaris leaves changedfrom –0.47 MPa to –1.24 MPa. On more prolonged chilling_w tended to return to pre-chilling values. In addition. _p decreasedfrom 0.42 MPa to zero after only 9 h of chilling, and remainedat this value for the remainder of the chilling period, _s, changedrapidly from –0.89 MPa to –1.35 MPa in the first7.5 h, and after 9 h. _w and _s, were equal, i.e. zero _p. In contrast,the chilling resistant plant P. sativum maintained a positive_p throughout the chilling period, and there was little differencebetween values of _w, and _s in control and chilled leaves. Key words: Chilling, Stomata, ater relations, Phaseolus vulgaris, Pisum sativum     

The Effects of Temperature and Form of Nitrogen Supply on the Relative Contribution of Root Uptake and Remobilization in Supplying Nitrogen for Laminae Regrowth of Lolium perenne L.

Plants of Lolium perenne L. cv. S23 were grown in sand culturesupplied with either ammonium (NH₄⁺) or nitrate (NO₃^–)in an otherwise complete nutrient solution at 12°C or 20°C.Three weeks after germination, plants were clipped weekly tosimulate grazing. After 10 weeks growth all nitrogen (N) wassupplied enriched with ¹⁵N to quantify the effects of form ofN supply and temperature on the relative ability of currentroot uptake and remobilization to supply N for laminae regrowth. The form of N supply had no effect on the dry matter partitioning,while at 20°C more dry weight was allocated to laminae regrowthand less to the remaining plant material. The current root uptakeof N, which subsequently appeared in the laminae regrowth, wassimilar for plants supplied with NH₄⁺ or NO₃^–, and bothwere equally reduced at the lower temperature of growth. Remobilizationof N to laminae regrowth was greater for plants receiving NH₄⁺than NO₃^–; remobilization with either form of N supplywas reduced at the lower temperature of growth. Remobilizationwas reduced to a lesser extent at 12°C than current rootuptake. It was concluded that remobilization became relativelymore important in supplying N for regrowth of laminae at lowertemperatures. Key words: Lolium perenne, ammonium, nitrate, temperature, remobilization     

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     

Growth of White Clover, Dependent on N2 Fixation, in Elevated CO2 and Temperature

Clonal plants of white clover (Trifolium repens L ), whollydependent on N₂ fixation, were grown for 6 weeks in controlledenvironments providing either (C680 regime) 23/18 °C day/nighttemperatures and a CO₂, concentration of 680 µmol mol^–1,or (C340 regime) 20/15 °C day/night temperatures and a CO₂,concentration of 340 µmol mol^–1 During the firsthalf of the experimental period the C680 plants grew fasterthan their C340 counterparts so that by week 3 they were twicethe weight this 2 1 superiority in weight persisted until theend of the experiment The faster initial growth of the C680plants was based on an approx 70 % increase in leaf numbersand an approx 30 % increase in their individual area Initially,specific leaf area (cm2 g^–1 leaf) was lower in C680 thanin C340 leaves but became similar in the latter half of theexperiment Shoot organ weights, including petioles and stolons,reflected the C680 plant's better growth in terms of photosyntheticsurface Throughout, C680 plants invested less of their weightin root than C340 plants and this disparity increased with timeAcetylene reduction assays showed that nitrogenase activityper unit nodule weight was the same in both C680 and C340 plantsBoth groups of plants invested about the same fraction of totalweight in nodules Nitrogen contents of plant tissues were similarirrespective of growth regime, but C680 expanded leaves containedslightly less nitrogen and their stolons slightly more nitrogenthan their C340 counterparts However, C680 leaves containedmore non-structural carbohydrate Young, unshaded C680 leavespossessed larger palisade cells, packed more tightly withinthe leaf, than equivalent C340 leaves The reason for the C680regime's loss of superiority in relative growth rate duringthe second half of the experiment was not clear, but more accumulationof non-structural carbohydrate, constriction of root growthand increased self-shading appear to be the most likely causes Trifolium repens, white clover, elevated CO₂, elevated temperature, growth, N₂ fixation, leaf structure     

Thermodormancy Release of Celery Seed by Gibberellins, 6-Benzylaminopurine, and Ethephon Applied in Organic Solvent to Dry Seeds

The emergence of celery (Apium graveolens L. cv. Utah 52–70)seeds was promoted by growth regulators when exposed to hightemperatures during the germination period. The growth regulatorswere applied to dry seeds prior to sowing, by means of the organicsolvent dichloromethane (DCM). A mixture of gibberellins A₄and A₇ (GA_4/7) strongly enhanced emergence at a high day-timetemperature of 35°C alternating with night temperaturesof 20°C and 25°C; however, emergence was very poor whenthe night temperature was raised to 30°C. Under the latterregime, only mixtures of GA_4/7 with 6-benzylaminopurine (BA)or with 2-chlorophosphonic acid (ethephon) promoted seed emergence.However, BA and ethephon applied separately or in combinationwere much less effective in enhancing seed emergence withoutthe addition of GA_4/7, under all the temperature regimes.     

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