Genotypic Differences in the Temperature Responses of Tropical Crops: I. GERMINATION CHARACTERISTICS 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.I. Germination characteristics of groundnut (Arachis hypogaeaL.) and pearl millet (Pennisetum typhoides S. & H.).—J.exp. Bot. 39: 1121–1128. The germination at constant temperature of several genotypesof groundnut and pearl millet was investigated between 0?C and50?C on a thermal gradient plate. Large differences in bothgermination rate and percentage germination were observed inboth species. Base temperatures vary from 8–11.5?C and 8–13.5?Cin groundnut and millet, respectively and optimum temperaturesfrom about 29–36.5?C in both. Maximum temperatures forgermination ranged from 41–47?C. The results are discussedin terms of adaptation to high soil temperature and crop establishmentin the semi-arid tropics. Key words: Temperature, germination, millet, groundnut     

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.): 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.     

Leaf Growth in Cotton (Gossypium hirsutum L.) 1. Growth in Area of Main-stem and Sympodial Leaves

A model is presented for growth of individual and successivemain-stem leaves of cotton, based on a series of indoor experimentsand data sets from the literature. Three variable parametersare used to describe individual leaf growth: relative growthrate of meristematic tissue (R¹), relative rate of approachof final area (R₂) and a ‘position parameter’ (t_0.5)which governs the transition from meristematic to extensiongrowth. Final area of a leaf does not occur in the model asa deterministic quantity but it is a result of the processesduring growth. The model generates successive mainstem leavesand sympodial leaves as an integrated system. Assimilate shortagesoccurring in the plant operate on R₁ leading to the characteristicchange of final leaf area along the mainstem. Gossypium hirsutumL., cotton, leaf growth, relative growth rate, meristematic tissue, extension growth, mathematical model     

Influence of Saturation Deficit on Leaf Production and Expafision in Stands of Groundnut-{Arachis hypogaea L.) Grown Without Irrigation

The response of leaf area expansion to atmospheric saturationdeficit (SD) and soil moisture deficit was examined in termsof leaf water potential (₁) and turgor potential (_p), as partof a wider study of the effects of SD on groundnut growth. Standsof plants were grown at four levels of SD and without irrigationin controlled environment glasshouses. A fifth stand was grownat low SD on soil kept irrigated to field capacity. Large saturation deficits accelerated the depletion of soilmoisture reserves in the unirrigated stands and greatly reducedleaf area index, particularly in the driest treatment. Leafnumber per plant and leaf size both decreased as SD increased,but the effect on leaf size was greater than on number. SD hadless effect than soil water deficit on leaf production. Turgorpotential and leaf extension rate (R) were both reduced at highsaturation deficits and R was linearly related to _p between0900 and 1600 h. However, leaf extension rate and turgor potentialwere poorly correlated between 0400 and 0700 h in the driesttreatment. Arachis hypogaea L., groundnut, saturation deficit, leaf growth, canopy development     

Response to Saturation Deficit of Leaf Extension in a Stand of Pearl Millet (Pennisetum typhoides S. & H.)II: II. DEPENDENCE ON LEAF WATER STATUS AND IRRADIANCE

This paper describes how the dominant relation between leafextension and temperature in pearl millet is modified by atmosphericsaturation vapour pressure deficit (SD) and irradiance. Standsof plants were grown at two levels of SD and soil moisture content.Leaf extension, water potential (₁) and stomatal conductancewere all reduced at high SD, ₁ was more closely related to transpirationrate than to SD itself. Leaf extension rate (R) was poorly correlatedwith ₁, even after correction for temperature differences, owingto variation in solute potential between leaves. However, Rin individual leaves was linearly related to turgor potential,except after periods of low irradiance. The thermal time conceptwas modified to incorporate turgor potential and used to showthat the ‘turgor thermal rate of extension’ decreasedsharply at low irradiances, presumably due to assimilate shortage. Key words: Extension, Saturation deficit, Millet     

An Association between Flowering and Reduced Stomatal Sensitivity to Water Stress in Pearl Millet [Pennisetum americanum (L.) Leeke]

Stomatal sensitivity to water stress was investigated in pearlmillet [Pennisetum americanum (L.) Leeke] in relation to stageof plant development, leaf water status and ABA content by samplingplants at midday. For the same leaf water potential (), droughtedplants with emerged panicles were found to have a greater leafconductance (g_L), indicative of greater stomatal opening, thanplants sampled prior to panicle emergence. The difference betweensuch flowering (F) and non-flowering (NF) plants in at stomatalclosure was estimated to be at least 0.6 MPa. This differencewas considered unlikely to be the result of differential bulkleaf osmotic adjustment, and for most samples from both F andNF plants, bulk leaf turgor potential (_p) was estimated to bezero. Stomatal closure in NF plants was associated in two genotypes(BJ 104 and line 112) with higher leaf ABA levels. Differencesin ABA levels between F and NF plants were, however, smalleror absent in genotypes Serere 39 and B282. These genotypes wereat lower than BJ 104 and line 112 when sampled and showed smallerdifferences between F and NF plants in conductance. Lower ABA levels in F plants are ascribed either to effectsof leaf ageing or to effects of flowering on ABA content ofthe leaf. Significant differences in g_L in the absence of differencesin ABA content are taken to imply changes in stomatal sensitivityto the hormone or in its access to the stomatal complex. Pennisetum americanum (L.) Leeke, pearl millet, flowering, stomata, water stress, abscisic acid     

Heat Shock Proteins of Sorghum [Sorghum bicolor (L.) Moench] and Pearl Millet [Pennisetum glaucum (L.) R.Br.] Cultivars with Differing Heat Tolerance at Seedling Establishment Stage

The production of heat shock proteins was compared in sorghumand pearl millet genotypes differing in seedling establishmentcharacteristics under heat stress. Two major heat shock proteins(hsps) of apparent mol. wt. 65 kD and 62 kD were seen in allthe genotypes of sorghum tested when the incubation temperatureof the 40 h seedlings was altered from 35 ?C to 45 ?C for 2h. Under identical conditions, pearl millet genotypes showedmore hsps and the apparent mol. wt. of these ranged from 30–70kD. The hsp bands were more prominent in whole seedlings androots as compared to plumules. Differences in the productionof hsps were seen in sorghum and pearl millet genotypes withcontrasting heat tolerance at seedling establishment stage butthe significance of these needs to be studied further. Key words: Heat shock proteins, sorghum, genotypic differences     

The Influence of Temperature and Soil Water Deficit on the Development and Morphology of Groundnut (Arachis hypogaea L.)

The rate/temperature relation of several developmental processesin groundnut was examined in a suite of temperature-controlledglasshouses maintained at mean air temperatures of 19, 22, 25,28 and 31 °C. The sensitivity of the various processes tosoil water deficit was also examined. When the relation between rate and temperature was linear, measurementswere analysed in terms of thermal time (°Cd) and an extrapolatedbase temperature (T_b) at which the rate was zero. T_b was conservative(10 °C) for leaf appearance, branching, flowering, peggingand podding. A higher value of T_b for seedling emergence (16°C) was probably an artifact caused by soil pathogens. Leafappearance and branching were more sensitive to soil water deficitthan the other processes examined. Key words: Temperature, Soil water deficit, Development, Groundnut     

Leaf Growth in Cotton (Gossypium hirsutum L.) 2. The Influence of Temperature, Light, Water Stress and Root Restriction on the Growth and Initiation of Leaves

The rate parameters R₁, R₂, I/LI and I/t_0.5, which characterizethe growth in area of successive main-stem leaves, probablyall have the same temperature response. Temperature thereforeonly operates on the time scale. Water stress reduces both therelative growth rate and the advance of developmental age, thelatter however to a lesser extent than the former. The effectof root restriction is explained as resulting from mineral shortage. Gossypium hirsutum L., cotton, leaf growth, leaf initiation, relative growth rate, temperature, light, water stress, root restriction     

Stomatal Responses of Pearl Millet (Pennisetum americanum (L.) Leeke) Genotypes, in Relation to Abscisic Acid and Water Stress

Stomatal responses to water stress and to applied (±)-abscisicacid (ABA) were examined in genotypes of pearl millet (Pennisetumamericanum (L.) Leeke) known to differ in amounts of endogenousABA accumulating during drought. In both a pot and a field experiment,Serere 39, a genotype with a high capacity to accumulate ABA,showed a higher stomatal sensitivity to water stress than didthe ‘low’ ABA accumulator, BJ 104. In the fieldexperiment, a third genotype, B282, accumulating least amountsof ABA, also had the lowest stomatal sensitivity to water stress. There were no significant differences between these genotypesin stomatal response to applied (±)-ABA, or in the relationshipsbetween leaf conductance and levels of endogenous ABA. It isconcluded that the differences in accumulation of endogenousABA by these genotypes of pearl millet are of functional significance,and that endogenous ABA generated during a water stress whichdevelops over days or weeks mediates stomatal responses to suchstress.     

The role of apical development around the time of leaf initiation in determining leaf width at maturity in wheat seedlings (Triticum aestivum L.) with impeded roots

High soil resistance to root penetration (measured as penetrometerresistance, R_s slows down leaf growth and reduces mature leafsize in wheat seedlings {Triticum aestivum L.). Underlying changesin the kinetics of cell partitioning and expansion and in thesize and organization of mature cells were reported in companionpapers (Beemster and Masle, 1996; Beemster et al., 1996). Inthe present study, the relationships between apex growth, primordiuminitiation and expansion were analysed for plants grown at contrastingR_s, focusing on a leaf whose whole development proceeded afterthe onset of root impedance (leaf 5). High R_s reduced the rates of apex and leaf development, butdid not appear to have immediate effects on the pattern of developmentof the newly initiated phytomers. During an initial short period,the rate of development of a leaf primordium and associatednode were related to plastochronic age, according to similarrelationships (slopes) at the two R_s. Effects on developmentalpatterns were first detected on phytomer radial expansion duringplastochron 2. The ontogenetic pattern of leaf elongation wasaffected later, during the next few plastochrons preceding leafemergence (‘post-primordial stage’). It is concludedthat a reduction in the number of formative divisions and inthe number of proliferative cells along the intercalary mer-istemreported earlier (Beemster and Masle, 1996; Beemster et al.,1996) is not related to the size of the apical dome at leafinitiation nor to the size and number of meristematic cellsinitially recruited to the leaf primordium, which were all unaffectedby R_s. Rather they are generated at the primordial and post-primordialstages. Key words: Wheat, apex development, leaf primodium development, mature leaf width, root impedance     

Effects of Photoperiod and Maturity Genes on Plant Growth, Partitioning, Radiation Use Efficiency, and Yield in Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of four isolines of soyabean [Glycine max(L.) Merrill]‘Clark’, viz‘L71-920’ (maturity genecomplemente₁e₂e₃ ), ‘L80-5914’ (E₁e₂e₃), ‘Clark’(e₁E₂E₃), and ‘L65-3366’ (E₁E₂E₃), were grown inshort (12.25 h d ^{- 1}natural light) and long days (12.25 h d^{- 1}natural light supplemented with 2.75 h d ^{- 1}low-irradianceartificial light) from first flowering to maturity in a polythenetunnel maintained at 30/24°C (day/night). Whereas therewere few differences among the isolines grown in short days,in long days the dominant alleles increased crop duration, biomassand seed yield substantially. Increases in biological and economicyield were not solely a consequence of longer crop duration:the dominant alleles also increased crop growth rate and radiationuse efficiency in long days (from 1.3 g MJ ^{- 1}total radiationine₁e₂e₃ to 2.8 g MJ ^{- 1}inE₁E₂E₃ ). Greater radiation use efficiencyresulted from a relatively longer leaf area duration, betterdistribution and orientation of a larger mass of leaves withinthe canopy, and smaller partitioning of assimilates to reproductivestructures. The work reveals the substantial effects of thethree lociE₁ / e₁, E₂/ e₂and E₃/e₃ on the response of plantgrowth, as well as development, to environment. Their relevanceto crop adaptation is discussed. Copyright 2000 Annals of BotanyCompany Glycine max(L.) Merrill, soyabean, maturity genes, flowering, phenology, growth, yield     

Water-Stress and Leaf Growth in Field-grown Crops of Potato (Solanum tuberosum L.)

The appearance and growth of individual leaves were examinedin crops of potato (Solanum tuberosum L.) grown either fullyirrigated or droughted from plant emergence. The rate of appearance of leaves was increased and the durationof growth decreased in leaves of the droughted crop in 1986but not in 1987. In droughted crops, leaf growth rate was correlatedwith afternoon measurements of leaf water potential (₁) andturgor (P), being reduced in comparison with that in irrigatedcrops when ₁ and P were less than –0.28 and 0.5 MPa respectively.Leaf growth was highly correlated to soil moisture deficit (SMD)and declined rapidly when the SMD was greater than 16 mm. Key words: Solanum tuberosum, leaf growth, leaf appearance, drought, irrigation     

Solute Accumulation and Growth in Plants of Pearl Millet (Pennisetum americanum [L.] Leeke) Exposed to Abscisic Acid or Water Stress

Henson, I. E. 1985. Solute accumulation and growth in plantsof pearl millet (Pennisetum americanum [L.] Leeke) exposed toabscisic acid or water stress.—J. exp. Bot. 36: 1889–1899.Experiments were conducted to investigate whether abscisic acid(ABA) elicits the accumulation of solutes and lowering of osmotic(solute) potential (₂) which occurs in leaves of pearl millet(Pennisetum americanum [L.] Leeke) exposed to water stress.When (?)–ABA was injected into the base of the shoot of15–d–old plants, ₂ of the fifth leaf was reducedsignificantly below controls 27–72 h after treatment.The reductions, however, were small (< 0.10 MPa) and wereaccompanied by a significant inhibition of shoot growth. Incontrast, no significant reduction in ₂ or in growth occurredwhen the hormone was introduced directly into leaf five viaits mid–rib. ABA concentrations in leaf five were highshortly after direct injection, but declined to control levelswithin 48 h. Injecting ABA into the shoot base resulted in lowerleaf five ABA concentrations. Hence, the ABA concentration inthe leaf was not the most critical factor for its effect on₂. ABA also reduced ₂ of shoots when applied to seedlings 48h or 72 h after sowing via the roots. As with older plants,the effects of ABA on ₂ were small ( 0–2 MPa) and wereaccompanied by inhibition of shoot growth. A water stress treatmentand an ABA treatment were compared. Although both treatmentsresulted in a similar degree of growth inhibition, the stresstreatment was much more effective than was ABA in reducing ₂. Key words: Pennisetum americanum [L.], pearl millet, abscisic acid, water stress, osmotic     

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     

Nitrate Effects on Pre-emergence Growth and Emergence Percentage of Wheat (Triticum aestivum L.) from Different Sowing Depths

The effects of a range of applied nitrate (NO₃^–) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO₃^– concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO₃^– concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO₃^– concentration of 0 to 1·0 mol m^–3then decreased only slightly with further increases in appliedNO₃^– of about 5·0 mol m^–3. Root and shoot growth, NO₃^– accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m^–3 NO₃^– at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO₃^– butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m^–3 NO₃^– than with zero NO₃^–.Root dry wt. was unaffected by NO₃^–. Nitrate concentrationand NRA in root and shoot were always low without NO₃^–.At 1·0 and 10 mol m3 NO₃^–, NO₃^– accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO₃^– concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO₃^–. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO₃^–was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence     

Changes in Respiratory Potential of Dormant and Non-dormant Galium aparine L. (cleavers) Seeds during Dry Storage

Hilton, J. R. and Thomas, J. A. 1987. Changes in respiratorypotential of dormant and non-dormant Galium aparine L. (cleavers)seeds during dry storage.—J. exp. Bot. 38: 1484–1490. Pre-germinative rates of O₂ uptake of two collections of Galiumaparine L. seed were compared throughout a 9 month period ofdry storage at 4 °C, 23 °C and at ambient (frost-protected)temperatures. Uptake of O₂ by the dormant seeds was generallyhigher than that of the less dormant seeds except when freshly-harvested.Moreover, changes in the O₂ consumption of seeds stored at ambienttemperatures could be associated with periods of germinationand seedling emergence in the field. The results are discussedin relation to changes in respiratory metabolism during dormancybreakage.     

Development of the Fifth Leaf is Indicative for Whole Plant Performance at Low Temperature in Tomato

In the search for early-detectable selection criteria for growthat low temperature conditions in tomato, first the initiationand growth of individual leaves was analysed. Scanning electronmicroscopy revealed that the first four primordia had alreadydeveloped during the germination period at 25°C. The primordiumof the fifth leaf, however, was initiated after the transferof seedlings to the experimental conditions. The increase inlength of the first three leaves, and to a lesser extent ofthe fourth leaf, was considerably smaller in comparison withthat of later formed leaves. Moreover, the morphology of thefirst three to four leaves was deviant, whereas the others showedthe normal compound leaf architecture. All these results indicatedthat the fifth leaf was the earliest formed leaf with growthcharacteristics that might reflect the growth potential of thewhole plant. Development of the fifth leaf was tested as a marker for wholeplant growth. At three temperature, 18, 15 and 12°C, growthresponses of the fifth leaf were similar to that of whole plantsin four tomato genotypes: Line A, Line B, Premier and MXXIV-13.Significant differences in relative growth rate of dry weightof whole plants and fifth leaves (RGR_W)and of leaf area of thefifth leaves (RGR_LA between two fast growing and two slow growinggenotypes were found. No genotype by temperature interactionfor RGR_W and RGR_LA was found, indicating that the effect oftemperature decrease was similar for the four genotypes. The structure of the mature fifth leaf of one fast and one slowgrowing genotype, Line A and MXXIV-13, was analysed. For bothgenotypes, leaves were small and thick at low temperature, 12°C.The total number of epidermis and palisade parenchyma cellsper leaf was smaller but the size of the cells developed at12°C was larger than at 18°C. Consequently, the slowgrowth at 12°C was due to a low rate of cell division. Atboth temperatures, the fifth leaf to MXXIV-13 was smaller comparedto that of line A. Since the size of the cells were similar,the smaller leaf size was due to lower number of leaf cells. The results confirm the suitability of the growth, especiallyexpressed as RGR_LA , of the fifth leaf as a nondestructive marketfor vegetative development of tomato at low temperature. Growthdifferences between genotypes were mainly reflected by differencesin cell number of leaves, which might be correlated with geneticallydetermined differences in cell number of leaf primordia.Copyright1993, 1999 Academic Press Lycopersicon esculentum Mill. genotypes, plant growth, selection criteria, low temperature, leaf initiation, leaf development, RGR, leaf structure, cell expansion