A Comparison of Two Approaches for Modelling Cassava (Manihot esculenta Crantz.) Crop Growth

Two approaches for modelling the growth and development of cassava,Manihot esculenta Crantz, are described and evaluated. The twomodels differ only in the hypotheses accounting for storageroot growth. In model 1, assimilate allocation to storage rootsis governed by the combined Chanter's (1976: Mathematical modelsin mushroom research and production. PhD Thesis, Universityof Sussex, UK) growth equation; and in model 2 the spill-overhypothesis for assimilate allocation to storage root governsstorage root growth. In both models, canopy photosynthesis generatesthe carbon substrate required for all growth processes. Thegrowth rates of leaves, stems and storage roots are definedby growth equations subject to substrate saturation kinetics.A key feature of both models is that the growth demands of thestem, fibrous roots and storage roots are related to leaf demandrates. Allocation to stems and branches was modelled by meansof a modified logistic growth equation which includes all theparameters and variables (number of nodes, internode lengths,stem density, stem modulus of elasticity and branch tensilestrength) that define the limits of the load bearing capacityof the shoot's supportive structures. The correlation coefficientsfor determination of yield prediction for the models werer =0.898,P =0.0385 (model 1) and r =0.954, P =0.0117 (model 2). For agrowth season of 290 d (after which leaf area index equals zeroand crop growth ceases), both models simulate the sigmoidaltransition from the lag to exponential phase of crop growth.Both models are equally well corroborated by observed data;however, model 1 has greater explanatory power. Copyright 2000Annals of Botany Company Allocation, simulation, model, crop growth, cassava, Manihot esculenta Crantz.     

Transfer of Mass and Energy in a Cassava Community (Manihot esculenta Crantz cv. Cubana) 2. CO2 Exchange in a Savanna Climate

The energy balance approach was applied to calculate the CO₂flux above and within a cassava community, growing during asavanna wet season. Data of the response of CO₂ exchange todiurnal changes in the savanna environment were integrated toa growth analysis of the cassava crop. The carbon budget of the entire community was calculated atdifferent development stages. Results indicate that CO₂ uptakein cassava appears to follow a linear net radiation responsecurve, dependent on crop age. The maximum net CO₂ uptake decreasedfrom 0.195 MJ m^–2 day^–1 at maximum leaf area development(August) to 0.028 MJ m^–1 day-1 2 months later. These ratesrepresent 41 and 19 per cent gross assimilation. Data of energy conversion efficiency show that at a maximumleaf area development, the crop fixed 2.2 and 0.9 per cent Rtas gross (_g) and net photosynthesis (n) respectively. As theseason proceeded,n decreased to 0.1, whereas g decreased to0.7, which indicates that dry matter lost by respiration isone of the determining factors in the seasonal trend of efficiencychanges. The comparison of growth characteristics calculated for cv.Cubana, growing during consecutive years in the same experimentalsite, indicate that yearly variability in dry matter accumulationis due to the wide range of environmental conditions presentduring the savanna wet season. Operational factors acting depressivelyon the cassava carbon budget and affecting dry matter productionwere also analysed. Manihot esculenta Crantz, cassava, microclimate, carbon budget, carbon dioxide fluxes     

An Assessment of Genetic Diversity Within a Collection of Cassava (Manihot esculenta Crantz) Germplasm Using Molecular Markers

Cassava (Manihot esculenta Crantz) cDNA clones were used todetect restriction fragment length polymorphisms in a collectionof Manihot germplasm maintained as in vitro plants at ORSTOM,Montpellier. The collection consisted of mostly African cultivarsof M. esculenta, together with a few M. glaziovii Mueller vonArgau and M. caerulescens Pohl, and some interspecific hybridsbetween M. esculenta and M. glaziovii. The clones revealed significantlevels of polymorphism both within and between the species;sufficient to construct dendrograms indicating the genetic diversitywithin the collection.Copyright 1993, 1999 Academic Press Cassava, Manihot esculenta (Crantz), restriction fragment length polymorphisms, RFLPs, genetic diversity     

Somatic Embryogenesis in Cassava: The Anatomy and Morphology of the Regeneration Process

Anatomical and morphological studies demonstrated that somaticembryos developed similarly on mature seed and clonal leaf explantsof cassava (Manihot esculenta Crantz) cultured for 20–24d on Murashige and Skoog (MS2) basal medium supplemented with4.0 mg l^–1 2,4-D (Stage 1) before transfer to MS2 basalmedium supplemented with 0–01 mg l^–1 2,4-D and 0–1mg l^–1 6-benzylaminopurine (Stage II medium). Within 7d of inoculation onto Stage I medium, cell divisions occurredin the adaxial tissues of cotyledon-piece and leaf-lobe explants,and associated with this was the development of embryogeneticprotusions and ridges on the adaxial surface. Foliose structuresand somatic embryo initials developed from these tissues oncotyledon, embryonic axis and leaf-lobe explants and, when cultureswere transferred to Stage II medium, further somatic embryodevelopment occurred. Somatic embryos apparently originatedfrom groups of cells and were identified by the presence ofa closed root axis, a shoot axis and cotyledons of similar shapeand venation to those of zygotic embryos. Somatic embryos hadno vascular connection with parental cultures. Manihot esculenta, cassava, somatic embryogenesis, tissue culture, anatomy, morphology, morphogenesis     

Differences in the Interacting Effects of Light and Temperature on Growth of Four Species in the Vegetative Phase

A comparative study, employing the concepts of growth analysis,has been made of the varying responses in the early vegetativephase of Gossypium hirsutum, Helianthus annuus, Phaseolus vulgaris,and Zea mays to combinations of light intensity (1.08, 2.16,3.24, 4.32, and 5.4 x 10⁴ lx—photoperiod 14 h) and constantdiurnal air temperatures (10, 15, 20, 25, 30, and 35 °C).Depending on the combination of treatments, the temperatureof the internal tissues departed from air temperature by 6.9to 1.4 °C: so only the internal temperatures are cited here. For each species there are complex interactions between theeffects of light and temperature on the net assimilation rate,the leaf-area ratio, and the relative growth-rates of plantweight and leaf area. The magnitude of the changes induced bythe two factors vary both with the growth component and thespecies. The temperature responses are maximal up to 20–5°C while at the highest temperatures they may be negative.The temperature coefficients for leaf-area ratio are consistentlyless than those of the other three components: here betweenspecies the coefficients over 10–20 °C vary by a factorof 9.6, 5.4, and 5.1 for the rates of gain in plant weight andleaf area and the net assimilation rate, while the orderingwithin each growth component is species dependent. Under conditions of optimal temperature the relative growth-rateand net assimilation rate progressively increase, accordingto the species, up to either 4.32 or 5.4x 10⁴ lx. The leaf-arearatio is always largest at the lowest intensity. The level oflight at which the rate of gain in leaf area reaches a maximumranges from 2.16x 10⁴ lx for Phaseolus to between 4.32 and 5.40x10⁴ lx for Gossypium. The highest relative growth-rate and net assimilation rate ofHelianthus exceed those of Zea substantially. Indeed the maximalassimilation rate for Helianthus of 2.10 g dm^–2 week^–1is the highest ever recorded under field or controlled conditions.Possible reasons for this reversal of the photosynthetic potentialsof the two species observed by previous workers are discussed.     

Transfer of Mass and Energy in a Cassava (Manihot esculenta Crantz cv. Cubana) Community 1. Microclimate and Water Vapour Exchange in a Savanna Climate

The energy balance approach was used to evaluate the transferprocesses which occur between a cassava community, growing duringa savanna wet season, and its environment. Crop performanceunder these conditions was also analysed. During this season, the soil profile remained near saturation,hence net radiation absorbed by the cassava crop during typicallow radiation days, was mainly dissipated as latent heat (78–86per cent); a process which depends on the growth stage and onthe foliage cover of the canopy. However, the seasonal rootenvironment, with a sufficient water supply, contrasted withthe extremely variable shoot environment, because the dailyflux density of short wave radiation input reached values similarto those reported for typical dry season days. On these days,cassava responded to environmental stress mainly by a reductionin transpiration. At the end of the wet season soil water content markedly decreased,an additional stress factor on the roots, which produced a notablereduction of cassava leaf area index. Therefore, the moderatechanges in energy partitioning determined by morphological andphysiological adaptive responses of cassava, produce a hindrancein the equilibrium between water vapour transfer and the surroundingsavanna environment. Manihot esculenta Crantz, cassava, microclimate, energy balance, heat fluxes     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.     

Effect of Temperature on Growth of Crotalaria juncea L. and Crotalaria sericea Retz.

Growth performances of Crotalaria juncea L. and C. sericea Retz.have been compared at two controlled temperatures, 16–20°C, and 28–32 °C, with respect to increase ind. wt and leaf area, relative growth rate, leaf area ratio,specific leaf area, leaf weight ratio, net assimilation rate,the ratio of mean relative growth rate to mean relative rateof leaf area increase () and shoot/root ratios. Both the speciesgrew better at the higher temperature; however the relativegrowth rate was more affected by temperature in C. sericea thanin C. juncea. Further, it was observed to be more dependenton net assimilation rate than on the leaf area ratio. Crotalaria juncea L., Crotalaria sericea Retz., relative growth rate, leaf area ratio, specific leaf area, leaf weight ratio, leaf area increase, net assimilation rate, shoot/root ratio     

A Rapid Non-destructive Method for the Estimation of Leaf Areas in Cassava

A rapid and non-destructive method of estimating leaf areaswas required for detailed study of new cassava varieties. Theoutlines of leaves were traced in the field and leaf areas wereobtained with a planimeter. Variety Caricass 2 was chosen fordetailed study and 50 leaves of each lobe number (three to ninelobes per leaf) were measured. The length and width were recordedfor all lobes and correlations were made with leaf areas. Alllobe lengths and length x width were highly correlated withleaf area. It is therefore necessary to measure the length ofonly one lobe to get an estimate of leaf area. Comparisons ofleaves with five and seven lobes from Caricass 1, Caricass 3and a local variety showed that these varieties could be measuredin the same way and that the regression coefficient for Caricass2, Caricass 3 and the local variety were not significantly different.A common regression coefficient could be used to estimate leafarea on all three varieties. Manihot esculenta Crantz, cassava, root crop, leaf area     

Photosynthetic Characteristics of Cassava (Manihot esculenta Crantz), a C3 Species with Chlorenchymatous Bundle Sheath Cells

Cultivars of cassava, Manihot esculenta Crantz, were studiedto determine the mechanism of photosynthetic carbon assimilationin this species. The results, contrary to recent reports, indicatethat cassava is a C₃ plant based on a number of physiologicaland biochemical photosynthetic characteristics. The CO₂ compensationpoints among 10 cassava cultivars ranged from 55 to 62 µlliter^–1, which was typical for C₃ plants including castorbean, a member of the same family (Euphorbiaceae). The initialproducts of photosynthesis in cassava are C₃-like; the activitiesof several key C₄ enzymes in cassava are low and similar tothose of C₃ plants. Data on the rates of photosynthesis perunit of leaf area and the photosynthetic response of cassavato CO₂ is also consistent with C₃ photosynthesis. Cassava hasa distinctive chlorenchymatous vascular bundle sheath locatedbelow a single layer of palisade cells. Unlike C₃-C₄ intermediatesand C₄ species, the bundle sheaths of cassava are not surroundedby mesophyll cells. The bundle sheath cells which occur at highfrequency in cassava may function in both photosynthesis andtransport of photosynthates in the leaf. (Received July 31, 1990; Accepted September 25, 1990)     

The effect of the cassava green mite Mononychellus tanajoa on the growth and yield of cassava Manihot esculenta in a seasonally dry area in Kenya

The effect of the cassava green mite Mononychellus tanajoa on the growth and yield of cassava Manihot esculenta was studied over a 10-month period in two field trials near Lake Victoria in Kenya. One plot was maintained free of mites by means of acaricide, while the other was artificially infested.The highest population density of M. tanajoa occurred during the dry season. A maximum leaf area index (LAI) of about 2 was reached at the onset of the dry season. The total leaf area of mite infested plants was reduced compared with uninfested plants during the dry spell. During the following rainy season infested plants recovered and attained the same leaf area as uninfested plants. A multiple regression model predicting the leaf area showed that 58% of the seasonal variation could be explained by plant age, soil water, and leaf injury.The net growth rate of infested plants was lower than that of uninfested plants. Maximum values of 21 (infested plants) and 49 (uninfested plants) g m^-2 week^-1 were attained at the onset of the second rainy season. No difference was found between uninfested and infested plants with respect to net assimilation rates per unit leaf area during the dry season. The net assimilation rates reached a maximum almost at the same time as the growth rates, but the infested plants peaked slightly earlier and at a lower level than the uninfested plants. M. tanajoa did not affect the relative allocation of dry matter into stems and storage roots, but the absolute allocation of dry matter declined with increasing mite injury. Thus, after 10 months the dry matter of infested plants was reduced by 29% and 21% for storage roots and stems, respectively, compared with the uninfested plants.     

Somatic Embryogenesis from Clonal Leaf Tissues of Cassava

Leaf lobes were isolated from palmate leaves of clonal cassava(Manihot esculenta Crantz) material growing in vitro or in glasshouseconditions and subjected to a two-stage culture procedure involvingincubation on Murashige and Skoog (MS2) basal medium supplementedwith 2–12 mg l^–1 2,4-D for 20 d (Stage I) beforetransfer to MS2 basal medium supplemented with 0.01 mg l^–12,4-D and 0.1 mg l^–1 6-benzylamino purine (BAP) (StageII medium). Embryogenetic tissues, foliose structures and somatic embryosdeveloped from leaf lobes at all Stage I 2,4-D concentrations,except on those explants isolated from shoot-tip cultures incubatedon MS2 basal medium supplemented with 0.1 mg l^–1 NAA and1.0 mg l^–1 BAP. Leaf lobes isolated directly from glasshouse plants showed optimalembryogenetic competence when subjected to a Stage I cultureperiod of 17 d, although foliose structure initiation was optimalwith shorter Stage I durations. Leaf lobes of 2–4 mm lengthand those isolated from phyllotaxic leaf numbers 4 and 5 showedthe greatest embryogenetic competence. Manihot esculenta, cassava, somatic embryogenesis, tissue culture, morphogenetic competence     

Accumulation of Hydroxycoumarins During Post-harvest Deterioration of Tuberous Roots of Cassava (Manihot esculenta Crantz)

The use of the root crop Cassava (Manihot esculenta Crantz)is constrained by its rapid deterioration after harvest. Chemicaland spectroscopic examination revealed the accumulation of fourhydroxycoumarins (esculin, esculetin, scopolin and scopoletin),compounds derived from the phenylpropanoid pathway, during thetime course of post-harvest deterioration. Fluorescence-microscopyrevealed their localization in the apoplast of the parenchyma.Scopoletin and scopolin showed the most dramatic increases inconcentration, peaking by day 2 after harvesting. A smallersecondary peak of scopoletin tended to be more pronounced incultivars showing lower susceptibility to deterioration. Evidencefor the metabolism of scopoletin to an insoluble coloured productby means of a peroxidase is presented. This product may be thecause of the discolouration of the vascular tissue during storage.Copyright 2000 Annals of Botany Company Cassava, hydroxycoumarins, Manihot esculenta, peroxidases, post-harvest physiological deterioration, wound response     

Sink Activity Estimation by Sink Size and Dry Matter Increase During the Ripening Stage of Barley (Hordeum vu/gare) and Rice (Oryza sativa)

During the ripening stage of barley and rice, the sink activitywas defined as the dry matter increase per units sink size,leaf area and time, as follows: NAR = A.SinkW+NAR', where NAR is the net assimilation rate (g d.wt dm^–2d^–1);A is the sink activity [g d.wt g^–1d.wt (ear) dm^–2d^–1]; Sink W is ear wt per plant at heading (g d.wt);and NAR' is net assimilation rate excluding the assimilate ofsink organ (g d.wt dm^–2 d^–1). Plant material with 16 combinations of mutually different sink(ear) and source (leaf) size were produced at heading for eachcrop: parts of each leaf and ear were removed to produce fourgrades in barley, and also a part of each leaf was removed producingfour grades for four rice varieties showing different ear size.NAR and NAR' were determined during 26 and 21 d in barley andrice after heading, respectively. Sink activity (A), representedas the assimilation rate induced by the sink organ, was estimatedfrom the relationship between SinkW and NAR using the previousequation. The sink activity was significantly higher in ricewith a value of 0–0.028 g d.wt g^–1 d.wt (ear) dm^–2d^–1 vs. 0–0.0017 in barley, suggesting that therelative role of leaves for grain filling is considerably higherin rice than in barley. The sink activity obtained in the studymight be introduced into a model to predict the yields of barleyand rice. Hordeum vulgare L, barley, Oryza saliva L, rice, dry matter, NAR, sink, source, sink activity, model     

Physiological and Ecological Studies in the Analysis of Plant Environment: XII. The Role of the Light Factor in Limiting Growth

Previous investigations in southern England on twenty-two herbaceousspecies have demonstrated that for widely spaced plants thediurnal solar radiation limits the net assimilation rate ofall species and restricts the relative growth rate of many.In examining how far these limitations apply to other environmentsit is now shown that in the subtropics and tropics the levelsof net assimilation rate and relative growth rate can greatlyexceed those so far recorded for cool temperate regions, andthese differences are attributed to the higher insolation andtemperatures. From a variety of evidence it is concluded that as the distancebetween plants is reduced 8O the net assimilation rate is progressivelydiminished even in regions of high insolation through the enhancedmutual shading. In consequence levels of light which may besupra-optimal for relatively isolated individuals may yet limitthe dry-matter production of a dense population. There is anoptimal ratio of leaf area to ground surface (leaf-area index)for the maximal exploitation of the incoming radiation in carbonfixation by the population and this optimum will vary with thespecies and the light intensity. Where other environmental factorsare favourable, light may limit dry-matter production everywhere. On an annual basis dry-matter production will be dependent ontwo components—the length of the ‘growing season’and the period over which the leaf-area index remains optimal.In the tropics the highest annual rate of production so farrecorded is 7⁸ tonnes/hect. produced by Saccharum officinarumandin north-east Europe 23.5 tonnes by Fagus sylvatica. Over shortperiods the rate of dry-matter production can attain 3⁸g./m.²/dayand the utilization of solar energy can be as high as 4.2 percent., or 9.5 per cent, for the range 4, 000–7, 000 A. Although information on the productivity of natural communitiesis still ex-ceedingly scanty, an attempt has been made to interpretthe general pattern in terms of the length of the growing season,the level of solar radiation, the magni-tude of the leaf-areaindex of the whole community, and the period over which theleaf canopy remains green. It is postulated that in any regionthe vegetation reaches a dynamic equilibrium when there is themaximum exploitation of the incoming radiation to produce thegreatest production of dry matter.     

Variation in Photosynthesis and Enzyme Activity in Cenchrus ciliaris L.

Populations of Cenchrus ciliaris differ significantly in relativegrowth-rate (R), net assimilation rate (E), and leaf-area ratio(F). Differences in R were related to differences in E ratherthan in F. The populations also differed in the rate of apparentphotosynthesis of individual leaves as measured by infra-redgas analysis. Warburg and ^l4CO₂ techniques. Temperature andlight-response measurements revealed optimum temperature forphotosynthesis of 35 °C and the rate in most populationscontinued to increase up to the highest levels of irradianceemployed (200 W m²). The relative order of the populations wassimilar in all methods of analysis, but there was no relationshipevident between leaf photosynthesis and E derived from growthanalysis. The activity of the enzyme PEP carboxylase, expressedin terms of unit leaf area, was correlated with photosyntheticrate of the leaf. Activities of PEP carboxylase and of proteinsynthesis in vitro expressed on a basis of soluble protein contentwere correlated with E, but no such relationship was found forthe enzymes acid phosphatase and alanine--ketoglutarate aminotransferase.     

Growth Analysis of Sweet Pepper (Capsicum annuum L.): 2. Interacting Effects of Irradiance, Temperature and Plant Age in Controlled Conditions

A growth analysis was carried out with sweet pepper plants grownin a phytotron. Irradiance conditions were: 0.84 or 3.25 MJm^–2 in 8 h, 1.67 MJ m^–2 in 16 h and 2.51 MJ m^–2in 24 h. Temperatures applied were 25 or 21 °C during thephotoperiod in combination with 25, 21 and 17 or 21, 17 and13 °C respectively during the nyctoperiod. Highest values for leaf area and total dry weight were foundwhen applying 1.67 MJ m^–2 in 16 h, followed by 3.25 MJm^–2 in 8 h, irrespective of the temperature regime. Continuousirradiance ultimately resulted in leaf drop. A reduction inthe day temperature decreased leaf area and total dry weight.At a day temperature of 25 °C the dry weight increased withdecreasing night temperature when applying 3.25 MJ m^–2in 8 h. At a day temperature of 21 °C leaf area and dryweight were reduced when 17 or 13 °C were applied duringa 16 h nyctoperiod. Values for relative growth rate, net assimilation rate, leafarea ratio and leaf weight ratio strongly decreased with advancingplant age. The effects of irradiance treatment on RGR and NARwere analogous to those on total dry weight while the reversepattern was observed for the LAR. A decrease in day temperaturedecreased the RGR. The effects of night temperature exhibitedstrong interactions with day temperature and photoperiod. Theinfluence of temperature on RGR was largely mediated throughchanges in the LAR. The latter parameter was highly correlatedwith the specific leaf weight. Capsicum annuum L., sweet pepper, growth analysis, irradiance, temperature, plant age     

Studies in the Nutrition of Apple Rootstocks: II. Effects of Concentration of Iron in the Nutrient Solution on Growth and Chlorophyll Content

Rooted one-year shoots were grown for one season by sprayingtheir roots with nutrient solution. Iron supplied as Fe-EDTAat four concentrations resulted in plants which were respectively(a) severely chlorotic, (b) mildly chlorotic, (c) dark greenand healthy (controls), and (d) dark green but with slight reductionin growth. Severely deficient plants showed 40–70 per cent reductionsin growth as measured by fresh weight, shoot length, diameterincrease, leaf area, net assimilation and relative growth-rates.Dry weights were reduced 70–80 per cent and of the totaldry-weight increment a greater proportion remained in the leaves,which had a lower dry weight and higher water content per unitarea. However, because the initial old stem formed a greaterproportion of the total dry weight, the leaf area ratio remainedabout 11 per cent lower than in the controls. Severely deficientplants had, per unit of chlorophyll, a higher dry-weight increaseand net assimilation rate than the controls. Mild deficiency caused 10–20 per cent reductions in growthand net assimilation rate; the leaf area ratio was normal. Possible mechanisms of the effects of low iron supply are discussed,while the small growth reduction at the highest Fe-EDTA concentrationis attributed to chelate toxicity     

Nitrogen Uptake and Plant Growth I. Effect of Nitrogen Removal on Growth of Polygonum cuspidatum

Polygonun cuspidatum was grown hydroponically to examine theeffect of nitrogen removal from the nutrient solution upon plantgrowth and the partitioning of dry matter and nitrogen amongorgans. Nitrogen removal reduced the growth rate mainly dueto the reduced growth of leaf area. Accelerated root growthwas observed only in plants which earlier had received highlevels of nitrogen. Nitrogen removal caused almost exclusiveallocation of available nitrogen to root growth. Nitrogen fluxfrom the shoot to the root occurred in plants which had receivedlow nitrogen. Not only was net assimilation rate (NAR) littleaffected by nitrogen removal, but it also was not correlatedwith the concentration of leaf nitrogen on an area basis. Light-saturatedCO₂ exchange rate (CER) was highly correlated with the concentrationof leaf nitrogen. Nitrogen use efficiency (NUE) in CER (CERdivided by leaf nitrogen) remained constant against leaf nitrogen,indicating efficient use of nitrogen under light saturation,while NUE in terms of NAR decreased with higher concentrationof leaf nitrogen. Polygonum cuspidatum Sieb. et Zuce., CO₂ exchange rate, growth analysis, leaf nitrogen, net assimilation rate, nitrogen use efficiency, partitioning of dry matter and nitrogen     

Growth Responses of Two Solanum Species to Contrasting Temperatures and Irradiance Levels: Relations to Photosynthesis, Dark Respiration and Chlorophyll Fluorescence

Potato production in the tropical lowlands during the rainyseason is constrained by high temperature and low irradiance.This study examined the effect of these two variables on drymatter production and allocation, using plant growth, leaf anatomy,gas exchange and chlorophyll fluorescence measurements. Plantsof two clones, Solanum goniocalyx cv. Garhuash Huayro (GH) andDTO-33, a heat tolerant clone of S. tuberosum x S. phureja,were grown in growth chambers at 33/25 °C or 20/10 °Cday/night temperature. At each temperature, plants were grownin either 12 h high irradiance (430–450 µmol m^–2s^–1 PAR) or 12 h low irradiance (250–280 µmolm^–2 s^–1) both with a 6–h photoperiod extensionof 6 µmol m^–2 s^–1. Plants were harvested after10 d (initial harvest) and after 20 d (final harvest). By theend of the study DTO-33 had produced more dry matter and hadtuberized, whereas GH had a greater leaf area ratio (LAR) andspecific leaf area (SLA). The highest relative growth rate (RGR)was at low temperature and low irradiance, possibly due to acombination of thin leaves with a large surface area. At thehigh temperature, low irradiance had the opposite effect, producingthe lowest net assimilation rate (NAR) and lowest RGR. Bothtuber number and weight were markedly reduced by high temperature.Low irradiance, in combination with high temperature, producedvirtually no tubers. Stomatal density, which was greater onGH than in DTO-33, was increased at high temperature. When measuredat 30 °C both clones, especially DTO-33, showed heat-adaptationin terms of ability to maintain a high rate of net photosynthesisat 30 °C. Plants grown at high irr-adiance and low temperaturehad the lowest net photosynthetic rate at 30 °C. Concurrentmeasurements of chlorophyll fluorescence indicated that onlythe initial (O) fluorescence parameter was affected. The dataconfirm the field observation that reduction in potato growthat high temperature can be aggravated by lower irradiance. Thisreduction is associated with a reduced leaf area and NAR. Growth analysis, heat adaptation, light