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1.
An electronic differentiator was designed to display directly,in units of mm h–1, the extension rate of leaves measuredwith displacement transducers. The differentiator calculatesthe mean extension rate occurring over predetermined time intervalsof 0·25 or 1·0 h and discriminates rates of 0·01mm hr–1. It reduces considerably the work needed to determinemean extension rates from chart records of transducer outputvoltage and improves the accuracy of calculated extension rates.  相似文献   

2.
THOMAS  H. 《Annals of botany》1983,51(3):363-371
Lolium temulentum seedlings were grown on a nutrient mediumcontaining NH4NO2 at 0, 0·1, 0·5, 1·0 and4·3 mmoll–1 as the sole N source. Relative andabsolute extension rates, maximal leaf size, duration of extensiongrowth, rate of leaf appearance and plastochron index were determinedfrom the parameters of Richards functions fitted to lengthsof laminae measured at intervals after sowing. The final lengthof leaf I was relatively insensitive to N whereas mean relativeextension rate was increased and duration of growth decreasedwith increasing NH4NO2 concentration. Leaves 2 and 3 enlargedprogressively with N at concentrations up to 1·0 mmoll–1but were unresponsive thereafter. There was no significant correlationbetween final length and mean relative extension rate for leaves1 to 3. Leaves 4 to 6 continued to show increasing length beyond1·0 mmoll–1 N and final length was significantlycorrelated with mean relative extension rate. Increasing N increasedthe rate of leaf appearance by decreasing the duration of leafextension and plastochron. These results are discussed in relationto the control of leaf and N turnover. Lolium temulentum, rye grass, leaf extension, nitrogen, Richards function, growth analysis  相似文献   

3.
The objective of this experiment was to determine how diurnalvariations in rates of leaf extension of wheat plants in anirrigated field crop were related to temperatures and carbohydrateconcentrations of the extension zone. Leaves 3, 4. 5 of themain shoot were studied as each emerged from the encirclingsheath. The carbohydrates in the extension zone of the emergingleaf were analysed by converting them to glucose-6-phosphateand then measuring the reduction of NADP in the presence ofglucose-6-phosphate dehydrogenase. Average hexose concentrations(glucose and fructose) increased each day from 4 up to 5 mgg–1 fr. wt. and sucrose from 3 up to 7 mg g–1 fr.wt. with the maximum in mid-afternoon; there were no differencesamong the three leaves. Concentrations of fructans were constantthroughout the day for leaves 3 and 4 but showed a mid-afternoonrise in leaf 5. The average concentrations of fructans in theextension zones increased from 0 to 5 to 11 mg g–1 fr.wt. for leaves 3, 4, and 5 respectively and was consistent withthe conclusion that there was an increasing over-supply of carbohydratesfor growth of the shoot as the plant increased in size. Ratesof leaf extension were correlated with temperature but not withhexose concentrations. We concluded that the supply of carbohydratesdid not limit the growth of leaves under field conditions buttheir utilization in leaf growth was limited by temperature.The rates of leaf extension increased exponentially with temperatureand the relationship was described by the Arrhenius equation.The Q10 at 15 °C for leaf extension was 2.7 for leaves 4and 5 and 3.2 for leaf 3.  相似文献   

4.
The growing part of a wheat leaf (the extension zone) is loocatedat the leaf base and following from this it was proposed thatthe absolute leaf extension rate (Ler) can be partitioned intotwo components: the length of the extension zone (Lez) and therelative extension rate of that extension zone (Rez). Rez isan appropriate measure of the efficiency of leaf growth forcomparing different leaves. This model of a wheat leaf was thenused to investigate whether differences in growth rates betweensuccessive leaves on wheat plants were due to differences inhexose sugar or protein concentrations within the extensionzone. Measurements were done in an irrigated field crop suppliedwith 0, 3, 10, or 30 kg N ha–1 per week. The mean values of Ler at 15 °C increased with leaf numberand with nitrogen supply as did values for Lez. In contrastRez at 15 °C declined from 0.9 d–1 for the first leavesto 0.3 d–1 for the flag leaf. Nitrogen supply had littleeffect on Rez. A separate measure of the efficiency of leafgrowth, the responsiveness of Ler to temperature (measured asthe slope of the temperature response curve), also decreasedwith leaf number by the same order as Rez and was similarlyunaffected by nitrogen supply. The protein concentrations in the extension zones of the firstleaves were around 40 mg g–1 fr. wt. and this declinedto approximately 20 mg g–1 fr. wt for leaves emergingafter tillers emerged and remained low thereafter. Protein concentrationswere not correlated with the external supply of nitrogen. Hexosesugar concentrations followed a reverse pattern of increasingin the later order leaves and these also increased as nitrogensupply decreased. Both Rez and the responsiveness of Ler to temperature were positivelycorrelated with the protein concentration, the relationshipin each case being described by a rectangular hyperbola equation(P < 0.01), and negatively correlated with hexose concentrations.It was concluded that internal competition between growing pointsfor reduced nitrogen caused the observed effects. However, differencesin protein concentrations may not simply reflect differencesin enzyme concentrations; rather these differences may indicatechanges in some other character such as cell numbers.  相似文献   

5.
L. C. HO   《Annals of botany》1979,43(4):437-448
Simultaneous measurement of export from leaves and import tofruits were made on tomato plants reduced to one fully expandedleaf and one fruit. Experimental leaves were exposed to sixlight flux densities (0.5–100 W m–2) for 24 h whilerapidly growing fruits were kept in the dark at 22 °C. The rates of export of assimilate from these leaves varied from70 to 120 mg C leaf–1 day–1 corresponding with ratesof carbon fixation from 3 to 290 mg C leaf–1 day–1.Export from leaves with the lowest carbon fixation rates weremaintained by a loss of up to one-sixth of their initial carbon.In contrast, leaves with the highest carbon fixation rates exportedonly half the newly fixed carbon. The rates of import of assimilate to similar-sized fruits (c.16 cm3) were between 80 and 110 mg C fr–1 day–1but differed from the export rates of the source leaves. Thespecific growth rates and the specific respiration rates ofthe fruits were related to their initial carbon content at thebeginning of the experiment. Thus, over 24 h, the rate of importwas predetermined by the developmental stage of the fruit unalteredby the rate of current carbon fixation in the source leaf. Translocationof assimilate was regulated by sink demand under both source-and sink-limiting conditions in this short-term situation. The dynamic relationship between assimilate production in leavesand its utilization in fruits is discussed together with therole of sucrose concentration in these organs in regulatingtransport. Lycopersicon esculentumL, tomato assimilate translocation, source-sink relationships  相似文献   

6.
The leaf extension rate of millet plants was measured with auxanometersin temperature-controlled glasshouses. Temperature was the dominantenvironmental factor governing the rate of leaf extension. Theobserved linear relation between extension rate and meristemtemperature had a base temperature of 10 ?C and a less clearlydefined optimum of about 30–32 ?C. Leaf growth was expressed as extension per unit thermal time,mm (?C h)–1, to examine the influence of saturation deficit,irradiance and ontogeny at different temperatures. Leaf extensionwas independent of saturation deficit below 3.0 kPA. Irradiance,ranging from 4–16 MJ m–2 d–1, had a greaterinfluence on the first five leaves than the subsequent onesbut there was a large effect of leaf position. The results arediscussed in relation to the growth of crop leaves in a tropicalclimate. Key words: Leaf extension, Millet, Temperature  相似文献   

7.
Leaf extension rates of young maize plants were measured inthe field. Large diurnal fluctuations of air temperature fromabout 5—35°C caused extension rates to vary from 0·4mm h–1– 3·6 mm h–1. When the temperatureof the shoot apical meristem was kept at 30–34°C,extension rates remained constant, despite diurnal fluctuationsof air temperature. Leaf water potentials () above –8 or –9 bars hadlittle apparent effect on extension rate. It was concluded that gradients within leaves could account for this.  相似文献   

8.
Net photosynthesis rate (Pn), stomatal conductance to CO2 andresidual conductance to CO2 were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO2 and O2 levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (Vmes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm2 of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. Pn per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm–2 h–1 and32·32±1·61 mg dm–2 h–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in Pn per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in Vmes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin Pn per unit leaf area was studied. Key words: Photosynthesis, structure, wheat  相似文献   

9.
The crop growth rates and structures of three temperate foragegrasses Lolium perenne cv. S24, L. perenne cv. Reveille andFestuca arundinacea cv. S170, were examined in the field duringa summer growth period. The growth rates of the varieties wereremarkably similar at 7 g DM m–2 day–1. The angularstructures of the varieties were different and they varied duringthe experiment. However, these differences did not seem to affectcrop growth rates. Nevertheless, a decrease in the efficiencyof light energy conversion of approximately 24 per cent wasobserved after a change to a more prostrate form of canopy dueto lodging. There appeared to be an inverse relationship betweenthe number of tillers per unit ground area and the weight ofan individual stem. There were large numbers of relatively lighttillers in S24 whereas S1 70 had fewer but heavier tillers.Furthermore, S24 had many small leaves per unit ground areacompared with SI70 which had fewer longer leaves per groundarea and a slower rate of leaf appearance. There were diurnalchanges in the rates of leaf extension for all the varieties.The mean daily extension rates declined as the canopies developed.  相似文献   

10.
Lolium temulentum plants were grown at 20 °C, under an 8-hdaylength, in a controlled-environment chamber, and the kineticsof leaf expansion were observed by measuring the movement ofan optical grid attached to the fourth leaf. The leaf emerged23–24 d after sowing and was fully expanded 9–10d later. Extension rate was maximal between the second and fifthdays after emergence and declined markedly thereafter. Duringthe rapid growth phase the rate of elongation exhibited a distinctdiurnal rhythm, fluctuating between 1.9 to 2.3 mm h–1in the light period, and 1.3 to 1.7 mm h–1 in the dark.A circadian oscillation with a period of about 27 h was observedin leaves elongating in continuous darkness. When plants weretransferred to 5 °C soon after emergence of the fourth leafthere was an immediate reduction in rate of growth to about22 per cent of the rate at 20 °C: the Q10 for the mean elongationrate in the range 20–5 °C was 3.7. When plants weretransferred from 20 to 2 °C at fourth leaf emergence, meanextension rate declined to less than 5 per cent, correspondingto a Q10 in the range 5–2 °C of more than 300. Furthermore,growth at 2 °C was confined almost entirely to the darkphase of the photoperiod cycle. The responsive tissue was shownto be a small area of expanding leafless than 1.5 cm above theshoot apex and the possible mechanisms underlying low temperatureeffects in this region are discussed. Lolium temulentum L., leaf growth, auxanometer, low temperature, diurnal rhythm  相似文献   

11.
VOS  J; BIEMOND  H 《Annals of botany》1992,70(1):27-35
Potatoes (Solanum tuberosum L) were planted in pots in a temperature-controlledglasshouse to collect data on the rate of leaf apearance, leafexpansion, apical lateral branching and active life spans ofleaves The treatments consisted of three rates of nitrogen supply,i e the NI treatment with 2 5 g N per pot and the N2 and N3treatments with 8 and 16 g N per pot, respectively The rate of leaf appearance was 0·53 leaves d–1(one leaf per 28 °C d) and was negligibly affected by nitrogensupply The rate of leaf expansion was related to leaf numberand nitrogen supply The areas of mature leaves increased withleaf number on the main stem to reach a maximum for leaf numbers12–14, and declined for higher leaf numbers Leaves onapical lateral branches declined in mature area with increasein leaf number The expansion rate of leaves was the dominantfactor that determined the mature leaf area, irrespective ofleaf number and nitrogen treatment The smallest leaves wereobserved at the lowest rate of nitrogen supply Nitrogen promotedapical branching and hence the total number of leaves that appearedon a plant The proportion of total leaf area contributed byleaves on apical branches increased with time and nitrogen supply Active life span, i e the period of time between leaf appearanceand yellowing of the leaf, showed a similar relation to leafnumber as mature leaf area, at least in qualitative terms Leavesof the N3 treatment showed systematically longer life spansthan leaves of the NI and N2 treatment in the order of 3 weeksThe number of main stem leaves was not affected by nitrogensupply Potato, Solanum tuberosum L, leaf development, leaf extension, plant structure, nitrogen nutrition  相似文献   

12.
CO2-exchange rates (CER) of the sixth and the flag leaves oftwo spring-wheat varieties, Kolibri and Famos, were comparedusing an open-circuit infrared gas analysing system. Measurementswere repeated every two weeks starting when leaf blades werefully expanded. Single plants were grown in a controlled environmenthaving a photopuiod of 15 h and a day/night temperature of 24/19°C(H), 18/13 °C (M), and 12/7 °C (L) respectively untilapprox. 2 weeks after anthesis and at 18/13 °C until maturity.The photosynthetic photon-flux density (PPFD) at the top ofthe plants was 500 µE m–2 sec–1. During themeasurements PPFD was gradually reduced from 2000 to 0 µEm–2 sec–1 whereas the temperature was maintainedat the respctive growth-temperatures during the light period.The CER of the sixth leaf declined fairly similarly for bothvarieties, except for Kolibri where a faster decline was observedduring the first two weeks after full leaf expansion. The CERof the flag leaf declined more slowly than that of the sixthleaf. With the flag leaf of Famos, the decline was nearly linear,whereas with Kolibri it was very slow during the first few weeksbut rapid as the leaves further senesced. This pattern becamemore pronounced as the growth temperature decreased. The declinein relation to leaf age was much smaller at low PPFD than athigh PPFD during the same period. At full leaf expansion Kolibrireached higher maximum CER than Famos except at H. As the PPFDwas reduced the difference became smaller and at very low PPFDsuch as 50 µE m–2 sec–1 was reversed for thesixth leaf. Under optimum growth conditions maximum values ofCER were greater than 50mg CO2 dm–2h–1 and PPFDfor light saturation was close to 2000 µE m–2 sec–1.A comparison between the actual CER and a fitted curve widelyused, PN=(a+b/l)–1–DR, showed that the goodnessof fit strongly depends on cultivar, treatment and leaf ageas well as on the number and the level of PPFD from which datafor calculations are taken. Triticum aestivum, L., wheat, photosynthesis, photon-flux density, light response, carbon, dioxide exchange  相似文献   

13.
The potential for leaf extension of plants of Lolium perennecv S24 growing in small artificial communities under naturalconditions was measured as the plants progressed from the vegetativeto the reproductive state In two consecutive years, 1975 and 1976, ‘simulated swards’were sown in autumn and overwintered in an open, unheated glasshouseIndividual swards from the batch sown in 1975 were brought into a growth room on two occasions in spring 1976 to measuretheir potential for leaf extension at a range of temperatures(5–20 °C) Individual swards from the batch sown inautumn 1976 were brought in to the growth room on 15 occasionsbetween November 1976 and May 1977 and their potential for leafextension was measured at a single temperature of 15 °CFrequent dissections were made in both years to describe changesin the developing apex. The potential for leaf extension at 15 °C decreased fromc 17 mm day–1 in November to c 10 mm day–1 in mid-winter.In January, the potential rapidly increased threefold to reach30mm day–1 by mid February The increase began coincidentwith the earliest stages of floral initiation and was completedby the time of double-ridge formation Spring-grown vegetativeplants, however, showed potential rates of < 20 mm day–1at 15 °C The results are discussed in relation to reproductive developmentand to changes in the carbohydrate strategy of the plants inearly spring Lolium perenne L perennial ryegrass, leaf extension, temperature response  相似文献   

14.
The main objective of this study was to determine the relationshipbetween the relative rate of growth of emerging wheat leavesand the hexose sugar concentration of the extension zone. Shortperiods of intense shading (to 20 or 5% of full sun for up to14 d) were used to decrease hexose concentrations. Shading decreased hexose concentrations to a fraction of thatof controls and also resulted in thin and narrow leaves thatwere less in dry weight than control leaves of the same length.Shading did however increase the length of the zone of extendingtissue at the leaf base by 30%. The effect of hexose concentrations on the relative rate ofleaf growth was evaluated by determining the ratio between growthrates of shaded and control leaves. This ratio declined as hexoseconcentrations declined and the relationship was described bya rectangular hyperbola (r > 0.95, P < 0.01). Combineddata from many leaves on the main shoot and its tillers fromtwo irrigated wheat crops all conformed to the same relationship.The hexose concentrations where the ratio of growth rates washalf the maximum rate were 0.42 mg g–1 fr. wt. for extensiongrowth and 1.74 mg g–1 fr. wt. for dry weight growth.These values were significantly (P < 0.01) different. These results were compared with data from emerging leaves offield crops and it was concluded that hexose concentrationshad not limited leaf growth rates, the lowest values recordedbeing 2.5–3.0 mg g–1 fr. wt. It was further suggestedas unlikely that leaf growth rates of wheat crops in the fieldwould be limited by hexose concentrations.  相似文献   

15.
Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO3 by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO3 at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d–1, or constant external concentrations ([NO3)of 3, 10, 20, and 100 mmol m–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d-1, although growth was notlimited by N supply at RAR =0.18 d-1. Growth rates showed littlechange with [NO3–] between 10–100 mmol m–3(RGR=0·15 –0·16 d-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO3, accumulation of NO3 in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO3 from 1 mol m–3 solutions were assessed relativeto the growth-related requirement for NO3, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d–1 , but decreased thereafter to a theoretical minimumvalue at RGR  相似文献   

16.
Measurements of the growth of sainfoin and lucerne were madein the field after cutting on 31 May 1977. Sainfoin reacheda total above-ground dry weight of 408 g m–2 over thegrowing period of 48 days compared with 598 g m–2 in lucerne.Final leaf area indices (LAIs) were 2.8 in sainfoin and 6.1in lucerne. The specific leaf areas (SLAs) for sainfoin wereapproximately half those of lucerne throughout the regrowthperiod. The maximum rates of leaf appearance were 0.12 leavesper day in sainfoin and 0.85 leaves per day in lucerne. Themaximum mean rate of plant extension growth for lucerne of 2.12mm h–1 occurred during the night, whereas, in sainfointhe maximum rate of 1.72 mm h–1 occurred during the day. Measurements of extinction coefficients for PAR ranged from0.45 to 0.89 in sainfoin and from 0 42 to 0.57 in lucerne. Asthe lucerne crop increased in size leaf water potentials andsolute potentials became more negative. In sainfoin leaf waterpotentials remained remarkably high throughout the growth period,solute potentials decreased and turgor potentials increased.The stomatal conductances of the two species were similar. The photosynthetic capacities and rates of dark respirationper unit leaf area in both species were similar. The rate ofcanopy ‘gross’ photosynthesis at 295 W m–2was always greater in lucerne than in sainfoin. This was largelya matter of differences between the species in LAI, althoughat higher LAIs the more erect structure of lucerne leads toa better utilization of photosynthetically active radiation. Onobrychis vicifolia Scop, sainfoin, Medicago sativa L., lucerne, photosynthesis, water relations, temperature, canopy structure  相似文献   

17.
The present study deals with structure and functioning of threeareas of Himalayan oak forest. Low- and mid-altitude oaks, namelyQuercus leucotrichophora, and Quercus floribunda, form predominantevergreen forests in Central and Western Himalaya. The totaltree basal cover ranged between 33·89 m2 ha–1 (Q.floribunda site) to 36·83 m2 ha–1 (Q. leucotrichophorasite). The density ranged between 570 and 760 individuals ha–1.Allometric equations relating biomass of different tree componentsto GBH (girth at breast height) were significant with the exceptionof leaf biomass in Q. leucotrichophora and Rhododendron arboreum.Total vegetation biomass (29·40–467·0 tha–1) was distributed as 377·1 t ha–1 intrees, 5·40 t ha–1 in shrubs and 1·23 tha–1 in herbs. Total forest floor biomass ranged between4·6 and 6·2 t ha–1. Of the total annuallitter fall (4·7–4·8 t ha–1), 77·5% was contributed by leaf litter, 17·8 % by wood litterand 4·7 % by miscellaneous litter. Turnover rate of treelitter varied from 0·66 to 0·70. Net primary productionof total vegetation ranged between 15·9 and 20·6t ha–1 yr–1, of which the contribution of trees,shrubs and herbs was 81·2 %, 8·6 % and 10·2%, respectively. A compartment model of dry matter on the basisof mean data across sites was developed to show dry matter storageand flow of dry matter within the system. Quercus leucotrichophora forest, Q. floribunda forest, Q. lanuginosa forest, biomass, litter fall, net primary production, compartmental transfer  相似文献   

18.
The present study deals with structure and function of fourareas of Himalayan chir pine forest. Tree layer was monospecificon all sites with varied density and basal cover in the rangeof 540–1630 individuals per ha and 25·0–47·2m2ha–1, respectively. Shrubs having low density were sparselydistributed. All allometric equations relating to biomass ofdifferent components, to circumference at breast height (cbh)were significant, with the exception of that for cone biomass.Total vegetation biomass (115–236 t ha–1) was distributedas 113–283 t ha–1 in trees. 0·56–0·82t ha–1 in shrubs and 1·63–2·57 t ha–1in herbs. Total forest floor biomass including herbaceous litterranged between 9·6 and 13·6 t ha–1. Of thetotal annual litter fall (4·26–7·38 t ha–1),60·3–75·1 per cent was distributed in leaflitter and 24·9–39·7 per cent in wood litter.Turnover rate of tree litter varied from 0·45 to 0·53,whereas rates for shrubs and herbs were assumed to 1. Net primaryproduction of total vegetation ranged between 9·91 and21·2 t ha–1 year–1, of which the contributionof trees, shrubs and herbs was 76·5– 88·1per cent 0·6–1·8 per cent and 11·3–21·5per cent, respectively. A compartment model of dry matter onthe basis of mean data across sites was developed to show drymatter storage and flow of dry matter within the ecosystem. Pinus roxburghii forest, biomass, litter fall, net primary production, compartmental transfer  相似文献   

19.
BERGQUIST  R. R. 《Annals of botany》1974,38(1):213-221
Three fungicide rates, 4·48, 2.24, and 1.12 kg peT ha,and four spray intervals, 5, 7, 10, and14-day intervals, were investigated for the control of Phytophthoraleaf blight of taro in a subtropical field environment in Hawaii.The fungicide rate was studied in two separate locations onthe windward sides of the island of Kauai. The fungicide utilizedin these experiments was a co-ordination product of zinc ionand manganese ethylene bisdithiocarbamate (Dithane M-45, 80per cent WP). In the lower rainfall location, there was no differencedue to different fungicide rates while in the wetter location,the 4·48 kg per ha rate gave better control than the1·12 kg per ha rate. There was no significant differencebetween the 5, 7, and IO-day spray intervals butwhen compared with the 14-day interval, the 5-day interval wassuperior. Periods of increased rainfall were reflected in thefollowing week by increased lesion counts. Present data indicatethat rainfall is a major factor to consider as a basis for predictingdisease was occurrences and may be utilized for planning intervalof fungicide application. The amount of disease was a functionof initial disease levels, rainfall, temperature, relative humidity,fungicide rate, and spray interval between fungicide applications.Applications of fungicide at weekly intervals when weekly rainfallaccumulation exceeded 1 cm per week and/or when lesion countsexceeded more than one per plant gave substantial disease control.Thus, once these parameters of disease have been established,fungicide application could be governed conveniently by monitoringrainfall and disease incidence to achieve practical Phytophthowraleaf blight control. The 2·24 and 4·48 kg ha-1rates gave significant yield increases over the 1·12and check (no fungicide) treatments where Phytophthora leafblight occurred in epidemic proportions.  相似文献   

20.
We grew water hyacinth [Eichhornia crassipes (Mart.) Solms]for 60 days in a greenhouse under natural light and in a controlledenvironment room at 31/25?C day/night temperatures and 90, 320and 750/µEm–2sec–1. We then determined maximumphotosynthetic rates in 21% and 1% oxygen, stomatal diffusionresistances, contents of chlorophyll and soluble protein, andthe size and density of the photosynthetic units (PSU) in representativeleaves from the four treatments. In air containing 21% oxygen,maximum photosynthetic rates were 14, 27 and 29 mg CO2 dm–2hr–1for plants grown in artificial light at 90, 320 and 750µEm–2sec–1,respectively. Plants grown in natural light (maximum of 2000µEm–2sec–1) had maximum photosynthetic ratesof 34 mg CO2 dm–2hr–1. In all treatments, photosyntheticrates in 1% oxygen were about 50% greater than rates in normalair, indicating the presence of photorespiration in water hyacinth.There was no apparent relationship between maximum photosyntheticrate per unit leaf area and stomatal conductance, chlorophyllcontent per unit area, or PSU density per unit area. However,the higher maximum photosynthetic rates were associated withgreater mesophyll conductances, specific leaf weights and proteincontents per unit area. When plants grown at 90µEm–2sec–1for 120 days were transferred to 750µEm–2sec–1for 5 days, only young leaves that were just beginning to expandat the time of transfer exhibited adaptation to the higher irradiance.The 40% increase in light-saturated photosynthetic rate in theseyoung leaves was associated with increases in mesophyll conductance,soluble protein content per unit area, and specific leaf weight. 1 Mississippi Agricultural and Forestry Experiment Station cooperating. (Received July 19, 1978; )  相似文献   

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