Tolerance of Spinach (Spinacia oleracea) Plants to Partial Defoliation

Vegetables in the tropics are grown continuously throughout the year due to the favorable climate. Unfortunately, leafy vegetables are often damaged because of slugs and snails. These mollusks and other herbivores cause different levels of defoliation to plants which can significantly impact their growth, production, and quality of the harvested product. A study was carried out in order to artificially simulate the effect of a loss in foliar area caused by these pests. The impact of severe artificial defoliation in spinach plants (Spinacia oleracea) was evaluated in Tunja, Colombia. Under greenhouse conditions and after transplanting, the plants had 75% of their leaf area removed. This procedure was repeated weekly on newly emerging leaves while a control group of plants was left intact. 71 days after transplanting, the plants were harvested, and the leaf area and dry weight of the plants were measured with which some allometric variables were calculated to express growth. Variables such as the number of leaves, plant height, total dry weight, relative growth ratio, leaf weight ratio (LWR), and root to shoot ratio (R:S) were unaffected by defoliation while leaf area, leaf area ratio (LAR), and specific leaf area (SLA) were reduced with the partial removal of the leaf area. The partial defoliation resulted in an increased partial biomass of the leaves. These results suggest that spinach plants have a moderate tolerance to partial defoliation.

     

土壤水分有效性对梨枣叶片光合参数和抗旱性的影响

利用自动称量和补水系统,对三年生梨枣树进行适宜水分、轻度和重度干旱三种土壤水分处理(土壤含水量分别为田间持水量的75%±5%、60%±5%和45%±5%),旨在探究不同土壤水分对梨枣叶片光合参数和抗旱性的影响。结果表明:(1)轻度干旱对梨枣叶片的光合参数没有显著影响,但重度干旱引起净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、胞间CO2浓度(Ci)和光能利用率(LUE)明显降低,而水分利用效率(WUE)和气孔限制值(Ls)增加。(2)轻度干旱对梨枣叶片丙二醛(MDA)含量影响不大,过氧化氢酶(CAT)活性则显著上升;而重度干旱下MDA含量显著上升,同时超氧化物歧化酶(SOD)和过氧化物酶(POD)活性以及抗坏血酸(ASA)和还原型谷胱甘肽(GSH)含量明显升高,但仍不能消除重度干旱对梨枣叶片膜系统造成的严重伤害。因此,轻度干旱并未引发梨枣叶片显著的生物学胁迫,而在重度干旱条件下梨枣叶片的光合能力和膜系统均受到严重影响。     

Tolerance of Faba Bean Plants (<Emphasis Type="Italic">Vicia faba</Emphasis>) to Partial Defoliation

Throughout the development of plants, certain biotic and abiotic phenomena can occur which reduce not only the photosynthetic area, but also the growth, depending on the stage of plant development. Responses by plants to defoliation depend on species, the timing of agricultural practices and the intensity level of defoliation. An experiment was carried out in Tunja, Colombia under greenhouse conditions, in order to evaluate the tolerance of faba bean plants (Vicia faba) to partial defoliation. Every week material was removed along each newly emerged leaflet to simulate 50% defoliation. Another group was grown with the entire leaf area to function as a control. As a result of partial defoliation, the specific leaf area, absolute growth rate, relative growth rate and total biomass were reduced, but the leaf weight ratio was increased. In addition, the pattern of dry matter partitioning was altered so that the amount of biomass accumulated was reduced in the roots, but increased in the leaves. Additionally, the partially defoliated plants showed the ability to partly restore the removed leaf area. In this way it could be inferred that the plants of Vicia faba present a moderate capacity to tolerate early defoliation during the vegetative phase.     

The influence of citrus rootstocks on the relationship between the mite Brevipalpus phoenicis and citrus leprosis disease

BACKGROUND: Leprosis is one of the most serious citrus plant diseases. Leprosis‐affected plants, especially sweet orange [Citrus sinensis (L.) Osbeck], which is the most widely cultivated citrus fruit worldwide, show reduced photosynthetic capacity and severe defoliation. The aim was to evaluate the relationship between the Brevipalpus phoenicis (Geijskes) vector mite and citrus leprosis disease in Pera sweet orange plants grafted on different rootstocks. Data were analysed using numerical classification and conventional statistical analysis (ANOVA). RESULTS: Both viruliferous and non‐viruliferous B. phoenicis populations increased in number on plants maintained at low soil water content. Among the evaluated rootstocks, Sunki mandarin proved least favourable for mite population increase. Furthermore, the viruliferous mite population increased more rapidly than the non‐viruliferous mite population. CONCLUSION: The Cleopatra rootstock showed low variability in leaf nitrogen content, low mite number and low leprosis severity, thereby producing the most favourable results. Under appropriate moisture conditions, the Sunki rootstock produced the best results, showing the least severe leprosis. Rangpur lime rootstock grown in soil with varying water content showed the greatest variation in foliar nitrogen content, mite number and severity of leprosis and is considered to be the most difficult rootstock to manage. Copyright © 2012 Society of Chemical Industry     

Effects of EPTC, fluorodifen and monuron on transpiration and photosynthetic oxygen output in Eupatorium odoratum plants

The influence of foliar sprays of EPTC, fluorodifen and monuron on transpiration and photosynthetic oxygen output of Eupatorium odoratum plants is demonstrated. Foliar sprays with 100 ppm EPTC or monuron led to a significant decrease in transpiration for a continuous period of 14 days. Treatment with 100 ppm fluorodifen led to a noticeable increase in transpiration during the first eight days. All three herbicides significantly reduced photosynthetic oxygen output from the Eupaiorium plants. EPTC and monuron however, gave greatest effect. Reduction in transpiration from the plants was due to stomatal closure while reduction in photosynthetic oxygen output was due to both stomatal closure and probably also inhibition of the Hill reaction.     

Influence of magnesium on physiological responses of wheat infected by Pyricularia oryzae

Although magnesium (Mg) is considered an essential element for wheat growth, its importance for disease control has often been overlooked, and the physiological features of diseased plants mediated by Mg remain elusive. In this study, the effect of three Mg concentrations (0·25, 2·5 and 4 mm ) on wheat resistance to leaf blast (Pyricularia oryzae), leaf gas exchange, invertase activity, cellular damage and foliar concentration of photosynthetic pigments and nutrients was investigated. Foliar Mg increased from 1·9 to 3·9 g kg^?1, whereas calcium (Ca) decreased from 7·8 to 4·9 g kg^?1 as the applied Mg increased from 0·25 to 4 mm . Blast severity increased from 11·3 to 39·6% as the applied Mg increased from 0·25 to 4 mm . Photosynthesis, stomatal conductance, transpiration and photosynthetic pigment concentrations decreased in inoculated plants compared to non‐inoculated plants regardless of the Mg concentration; however, the reductions were more pronounced for plants grown with 4 mm Mg than those grown with 0·25 mm Mg. On the other hand, a higher internal CO₂ concentration, invertase activity and malondialdehyde concentration was recorded in inoculated plants grown with 4 mm Mg compared to those grown with 0·25 mm Mg. In conclusion, reduced Ca uptake may partially explain the increased susceptibility of wheat to leaf blast with the highest Mg concentration. Mg‐induced susceptibility to leaf blast appeared responsible for the photosynthetic impairments. These were most probably due to biochemical constraints because plants grown with the highest Mg concentration suffered extensive cellular damage and degradation of photosynthetic pigments as a result of high disease severity.     

Barley yield losses due to defoliation of upper three leaves either healthy or infected at boot stage by <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis>

This paper evaluates, in the greenhouse and under natural conditions, barley yield losses due to defoliation treatments of the upper three leaves either healthy or infected at the boot stage by Pyrenophora teres f. teres. Defoliation was assumed as a loss of a similar leaf area caused by net blotch disease severity of 100%. Contribution to grain yield was defined herein as a difference between defoliation treatments and a treatment where plants lost all their upper three leaves. In contrast, yield losses referred to differences in yield between defoliations and the control. In the greenhouse, removal of the antepenultimate leaf did not affect any yield component. For main stems, defoliating upper three leaves reduced grain yield by 30% and this was mainly due to flag leaf removal. These losses were similar to those induced by net blotch disease under natural conditions, but were of 42% for all tillers. Grain yield losses due to disease severity were not equivalent to the defoliation effect of a similar healthy leaf area. On the other hand and for a significant contribution to grain yield, flag leaf was dependent on the presence of the other two leaves. Inoculation and defoliation of 21 cultivars induced similar grain yield losses of 32%. However, biotic stress reduced by 40% the contribution of their upper three leaves. Under field conditions, yield losses were not significant until barley plants lost more than one upper leaf and flag leaf contribution was equivalent to that of the remaining leaves. Characteristic roots, defined as leaf coefficients for plant performance, were 0.13, 0.06 and 0.01 for the flag, penultimate and antepenultimate leaves, respectively. Because antepenultimate leaves become trivial at the boot stage, we propose that coefficients of the remaining leaves should be used when modelling yield losses due to barley foliar diseases.     

Fruit Quality and Yield in Partially Defoliated Strawberry Plants in the Tropical Highlands

The partial loss or reduction of leaf area is a wide-spread occurrence in the plant life cycle, caused e.g. by herbivory, stress or pathogen attack. The objective of the study was to evaluate the effect of partial defoliation on fruit production and quality in strawberry (Fragaria ×ananassa Duch. cv. Chandler). Plants were grown in a greenhouse in Tunja, Colombia, in hydroponics with an aerated nutrient solution. As leaves emerged, one or two leaflets were removed from each compound leaf, to attain 38 % and 67 % reduction of leaf area. Control plants grew intact, without defoliation. Fruit yield and fruit quality characteristics were evaluated for each plant. The pH, total soluble solids, ratio of total soluble solids to fruit juice acidity, fruit yield, fruit mass and size, and the ratio of leaf area/fruit yield were reduced drastically in defoliated plants. Leaf area reduction in excess of 38 % adversely affected physical and chemical characteristics of strawberry fruit, which did not meet marketing criteria.     

Photosynthesis and sugar concentration are impaired by the defective active silicon uptake in rice plants infected with Bipolaris oryzae

The effect of soluble silicon (Si) on photosynthetic parameters and soluble sugar concentrations was determined in leaves of rice cv. Oochikara and mutant plants of Oochikara defective in active Si uptake [low silicon 1 (lsi1)]. Plants were grown in hydroponic culture amended with 0 (?Si) or 2 mm Si (+Si), under either low or high photon flux density (PFD) and with or without inoculation with Bipolaris oryzae, the causal agent of brown spot of rice. Leaf Si concentration increased by 141 and 435% in +Si cv. Oochikara and by 119 and 251% in +Si lsi1 mutant plants under high and low PFD, respectively, compared with ?Si plants. Plant biomass accumulation was improved by Si regardless of PFD, especially plants for cv. Oochikara. Brown spot severity was highest in ?Si plants for cv. Oochikara and lsi1 mutant plants under low PFD. In the presence of Si, disease severity in plants grown under both low and high PFD was reduced, except for lsi1 mutant plants under high PFD. Plant inoculation reduced the photosynthetic parameters measured regardless of plant material or Si supply. A decrease of net carbon assimilation rate (A) of inoculated plants under low PFD compared with non‐inoculated plants was associated with damage in the photosynthetic apparatus, except for +Si cv. Oochikara in which stomatal restriction [low water vapour conductance (g_s)] contributed to A reduction. Under high PFD, damage to the photosynthetic apparatus of inoculated plants was the main reason for the reduction in A for +Si and ?Si lsi1 mutant plants. In addition, for ?Si cv. Oochikara, a reduction in g_s contributed to reduced A. However, for +Si cv. Oochikara, g_s was the limiting factor for A. Inoculated plants of +Si cv. Oochikara had higher A values than +Si lsi1 mutant plants, regardless of environmental conditions. Soluble sugars were not detected in leaf tissues of plants under low PFD. For high PFD, Si improved the hexose concentration in non‐inoculated plants at 144 h after inoculation (hai) for lsi1 mutant plants and from 96 hai onwards for cv. Oochikara compared with ?Si plants. However, plant inoculation reduced hexose concentration compared with non‐inoculated plants, mainly in +Si plants, regardless of plant material. Sucrose concentration increased in leaves of cv. Oochikara in the presence of Si whether inoculated or not. For +Si lsi1 mutant plants, sucrose concentration increased only at 48 hai compared with ?Si plants, whether inoculated or not. The results of this study show that a minimum Si concentration is needed in leaf tissues of rice plants to avoid the negative impact of B. oryzae infection on photosynthesis and sugar concentration. High leaf Si concentration resulted in an increased soluble sugar concentration and together, but in independent ways, soluble sugar and Si reduced brown spot severity of rice.     

Impact of Cuscuta australis infection on the photosynthesis of the invasive host,Mikania micrantha,under drought condition

Cuscuta species (dodders) are widespread stem holoparasites that depend on host plants for their entire mineral and water and most carbohydrate requirements. Dodders negatively affect host photosynthesis but precise information on their impact on hosts in the presence of environmental stress factors (i.e. drought) is little known. In a pot experiment, the leaf traits, gas exchange and chlorophyll a fluorescence of the invasive climber, Mikania micrantha, parasitized by Cuscuta australis, were investigated in order to study variations of host photosynthesis in response to parasitism and drought. The results showed that the concomitant presence of C. australis infection and drought significantly impacted the leaf traits (i.e. increased leaf dry mass content), gas exchange (i.e. decreased stomatal conductance and transpiration rates and increased water‐use efficiency) and quantum yield of chlorophyll a fluorescence of M. micrantha. The presence of a single stress factor (C. australis infection or drought), however, only significantly affected the leaf traits and gas exchange of M. micrantha. These results suggested that the combined additive effects of C. australis parasitism and drought significantly suppressed the photosynthesis of M. micrantha in relation to both stomatal and non‐stomatal limitation of host photosynthesis. This study provides insights into Cuscuta–host interactions under drought conditions in the tropics.     

Morphological and physiological responses of the invasive weed Isatis tinctoria to contrasting light, soil-nitrogen and water

We evaluated the morphological and physiological responses to contrasting above- and below-ground resources for the invasive weed, Isatis tinctoria L. (dyer's woad). Plants were grown under low and high levels of light [shade (50% of ambient) and full sun], soil water (50 and 100 mL day⁻¹), and soil nitrogen (N) (0 and 20 mg N kg⁻¹ soil) in 8 L pots in 63 day glasshouse experiments conducted during winter and spring. Soil-N enrichment did not increase any of the growth variables (shoot and root dry mass, shoot:root ratio, leaf area, and specific leaf area) or physiological variables (stomatal conductance and ¹³C discrimination) in either experiment. The absence of plasticity in response to changes in soil-N supply suggests that I. tinctoria may survive and persist in nutrient-poor conditions by having low-N requirements, low-N productivity, or both. In contrast, plants compensated for shaded conditions by altering leaf area, specific leaf area, and shoot:root ratio to improve light capture. We discuss the potential mechanisms whereby response to these variable resources may be associated with a series of adaptations that favour the ability to tolerate and colonize harsh, nutrient-poor conditions, as well as invade shaded and undisturbed sites.     

Response of photosynthesis and chlorophyll a fluorescence in leaf scald‐infected rice under influence of rhizobacteria and silicon fertilizer

Leaf scald caused by Monographella albescens reduces the photosynthetic area, causing yield losses in rice. This study investigated the efficacy of the rhizobacteria Burkholderia pyrrocinia (BRM‐32113) and Pseudomonas fluorescens (BRM‐32111), combined with silicon (Si) fertilization, to reduce lesion size and the area under the disease progress curve (AUDPC), as well as to minimize the negative effects on gas exchange, chlorophyll a fluorescence, chlorophyll content and the activity of oxidative stress enzymes. The experiment used a completely randomized design with four replications and seven treatments. Compared with plants only fertilized with Si, plants fertilized with Si and treated with BRM‐32113 showed reductions of 22% in scald lesion expansion and 37% in AUDPC, a 27% increase in the rate of CO₂ assimilation (A), a 33% decrease in the internal CO₂ concentration (C_i), and a 40% increase in ascorbate peroxidase activity. It was therefore concluded that the combination of BRM‐32113 with Si fertilization reduces the severity of leaf scald, protecting the photosynthetic apparatus, thus representing a sustainable method of reducing the loss of income caused by leaf scald in rice.     

Ecophysiological characteristics of five weeds and a wheat crop in the Indo‐Gangetic Plains,India

The objective of this research was to compare selected ecophysiological parameters for a wheat crop found in the Indo‐Gangetic Plains of India and its five dominant weeds. The dominant and regionally ubiquitous weeds in the wheat field that was selected for the study were Anagallis arvensis, Chenopodium album, Melilotus albus, Phalaris minor and Rumex dentatus. Taller weeds, such as C. album and P. minor, constituted one group along with the crop, with a low photosynthetic rate, specific leaf area, leaf nitrogen mass basis, chlorophyll content, photosynthetic nitrogen‐use efficiency and leaf area ratio, in comparison to shorter weeds, such as A. arvensis, M. albus and R. dentatus, which formed another group with a high photosynthetic rate, specific leaf area, leaf nitrogen mass basis, chlorophyll content, photosynthetic nitrogen‐use efficiency and leaf area ratio. Interspecific variations in the photosynthetic rate were driven mainly by variability in the specific leaf area and leaf nitrogen content. The taller weeds and the crop had a low specific leaf area later in the season, whereas the smaller weeds had a relatively high specific leaf area, which might be an adaptation to the shaded environment below the canopy. The result indicates that any weed management in the wheat fields of the Indo‐Gangetic Plains will need two different approaches because of the different strategies followed by the two weed groups that were identified in the present study.     

Modelling short-term effects of sulphur dioxide. 1. A model for the flux of SO2 into leaves and effects on leaf photosynthesis

A model for the flux of atmospheric SO₂ into leaves and the effects of SO₂ metabolites (S(IV) compounds) on leaf photosynthesis and stomatal resistance is presented. The S(IV) balance in the leaf is determined by the rate of SO₂ uptake and S(IV) removal by oxidation to sulphate. Toxic S(IV) compounds reduce the rate of photosynthesis and induce stomatal closure as a result of feed back control of stomatal resistance by photosynthesis. Other proposed mechanisms, like effects through a pH reduction, are not likely to play a role in short-term effects of realistic SO₂ concentrations. The model contains two key parameters which describe biochemical characteristics: a time coefficient for S(IV) oxidation and a parameter describing the sensitivity of photosynthesis for S(IV).Simulation results demonstrate the potential of plants to avoid extremely toxic concentrations of S(IV) in the leaf by three mechanisms: (i) rapid oxidation of S(IV) to less toxic sulphate, (ii) relatively high resistance to SO₂ uptake and (iii) feed back control between photosynthesis and stomatal resistance. S(IV) concentrations in the leaf and SO₂ concentrations in the stomatal cavities in stable situations are less than 1% of concentrations which build up without these mechanisms. Leaf thickness appears to be an important factor determining the susceptibility of plants to air pollutants. Thin leaves should be more sensitive than thicker leaves. It is concluded that effects of SO₂ on photosynthesis should be related to the uptake per unit of leaf volume instead of the commonly used flux per unit leaf area. The model accurately described the time course of photosynthetic reduction during a short fumigation period and subsequent recovery period.Samenvatting Een model wordt gepresenteerd waarmee de flux van SO₂ vanuit de lucht in het blad en de effecten van SO₂-metabolieten op de bladfotosynthese en stomataire geleidbaarheid kan worden gesimuleerd. De S(IV)-balans in het blad wordt bepaald door de SO₂ opnamesnelheid, en de snelheid van S(IV)-verwerking door met name oxidatie tot sulfaat. Toxische S(IV)-componenten reduceren de fotosynthese en veroorzaken daardoor stomataire sluiting. Andere in de literatuur beschreven mechanismen voor de effecten van SO₂, zoals effecten door een daling van de pH, spelen geen rol op de korte termijn. Het model bevat twee parameters die de biochemische karakteristieken beschrijven: de tijdconstante voor S(IV)-oxidatie en een parameter die de gevoeligheid van de fotosynthese voor S(IV) beschrijft.De simulatieresultaten laten zien dat de plant extreem toxische concentraties in het blad kan voorkomen door: (i) de snelle oxidatie van S(IV) tot sulfaat, (ii) de relatief hoge weerstand voor SO₂-opname en (iii) de stomataire sluiting die een gevolg is van een gereduceerde fotosynthese. S(IV)-concentraties in het blad en SO₂-concentraties in de stomataire holten zijn kleiner dan 1% van de concentratie die zou ontstaan als deze mechanismen niet zouden werken. Bladdikte blijkt de gevoeligheid van planten voor SO₂ in sterke mate te bepalen. De effecten van SO₂ op de fotosynthese dienen te worden gerelateerd aan de opnamesnelheid per eenheid bladvolume, in plaats van bladoppervlak. Het model simuleert de reductie in fotosynthese gedurende een korte begassingsperiode en een herstelperiode nauwkeurig.     

Biochemical and physiological responses to long‐term Citrus tristeza virus infection in Mexican lime plants

Reactions that occur when a plant is subjected to Citrus tristeza virus (CTV) infection often result in triggering of numerous defence mechanisms to fight the infection. The reactions vary according to virus strain, host genotype, time of exposure to the infection and environmental conditions. To date, no study has examined in detail the consequences of 10‐year exposure to CTV infection on the biochemical and physiological status of susceptible Mexican lime plants (Citrus aurantifolia). To understand the reaction of such plants, changes in nutrient status, total proteins, enzyme activity involved in scavenging of reactive oxygen species, photosynthetic and transpiration rates, chlorophyll content, membrane permeability and water content were analysed in plants infected with different CTV isolates and in healthy plants. The activity of superoxide dismutase and polyphenol oxidase significantly decreased in the infected leaves, and membrane permeability was lower in the infected plants. Macro‐ and micronutrient elements were significantly changed: concentrations of leaf nitrogen, zinc, magnesium and iron were elevated but potassium concentration depressed in comparison to noninfected control leaves. Levels of other analysed nutrient elements, enzymes, photosynthesis and stomatal conductance, chlorophyll content and relative water content were unchanged. Clear physiological changes were found among infected and noninfected control plants but none between plants infected with different CTV isolates. The data suggest that some of the defence mechanisms investigated here were suppressed due to the continuous and long‐term pressure of biotic stress.     

干旱胁迫对不同抗旱类型芜菁苗期生理特性的影响

以干旱敏感型芜菁(WJC106)和抗旱型芜菁(WJC129)为试验材料,采用盆栽自然干旱方法,研究干旱胁迫对不同抗旱类型芜菁苗期丙二醛含量、相对电导率、抗氧化酶活性、渗透调节物质、光合荧光以及叶片气孔形态特征的影响。结果表明：干旱胁迫显著增加芜菁苗期丙二醛含量和相对电导率,WJC106的增幅分别为59.71%和27.05%,WJC129分别为54.52%和20.06%,其细胞膜受损程度较大。WJC129有较强的调节能力,在干旱胁迫下其抗氧化酶活性和渗透调节物质的含量显著高于WJC106。干旱胁迫下WJC106和WJC129脯氨酸增幅分别为85.22%和88.97%,可溶性蛋白增幅分别为32.51%和58.26%,脯氨酸和可溶性蛋白起主要渗透调节作用。干旱胁迫除对芜菁有效光量子产量影响不明显之外,对叶绿素含量、光合及荧光参数均造成负面影响,其中WJC106受影响较大,WUE下降了71.5%,而WJC129光合及荧光各项指标相对比较稳定,WUE反而增加了18.2%。干旱胁迫使两个不同抗旱类型的芜菁苗期叶片气孔变小,保卫细胞变薄,气孔开度和气孔张开率显著减小。在干旱胁迫下,抗旱型芜菁的气孔开...     

叶片被毛对干旱区短命植物狭果鹤虱生理生态特征的影响

以荒漠短命植物狭果鹤虱为研究对象,通过野外控制实验,研究叶片被毛(leaf hairs)对狭果鹤虱生理生态特征的影响。结果表明:对于叶片有被毛的植物,模拟凝结水能显著提高叶厚、叶重、叶片水势、净光合速率、气孔导度以及地上生物量(干重),而对根径、根长与地下生物量(干重)表现出较小的效应;对于人工去除叶片被毛的植物,模拟凝结水对其根长、根径、叶厚、叶重、叶片水势、净光合速率、气孔导度、地上与地下生物量的影响不大。由此可知,被毛的存在能显著增加狭果鹤虱叶片吸附凝结水的量,同时也能增强其对干旱环境的适应能力。     

THE BASIS OF THE DIFFERENTIAL PHYTOTOXICITY OF 4-HYDROXY-3,5-DI-IODOBENZONITRlLE*

Summary. Entry of ioxynil-¹⁴C into portions of leaves was greater with mustard than with barley or pea and was unrelated to stomatal density. Measurement of ioxynil content of sprayed plants showed that by increasing the concentration of ioxynil and adding a surfactant, almost as much ioxynil could be made to enter barley as entered mustard from a lower concentration without surfactant. Auto radiographs showed that a limited amount of ¹⁴C was translocated to a small extent in plants following localized application of ioxynil-¹⁴C. An experiment comparing leaf removal by cutting with destruction of equivalent leaf areas by ioxynil treatment suggested a greater translocated effect of ioxynil with mustard than with pea or barley. Les principes de la phytotoxicité différentielle du 4-hydroxy-3,5-di-iodobetZonitrile II. Absorption et migration     

Fusion of sensor data for the detection and differentiation of plant diseases in cucumber

The development of plant diseases is associated with biophysical and biochemical changes in host plants. Various sensor methods have been used and assessed as alternative diagnostic tools under greenhouse conditions. Changes in photosynthetic activity, spectral reflectance and transpiration rate of diseased leaves, inoculated with Cucumber mosaic virus (CMV), Cucumber green mottle mosaic virus (CGMMV), and the powdery mildew fungus Sphaerotheca fuliginea were assessed by the use of non‐invasive sensors during disease development. Spatiotemporal changes in leaf temperature related to transpiration were visualized by digital infrared thermography. The maximum temperature difference within a leaf was an appropriate parameter to differentiate between healthy and diseased plants. The photosynthetic activity of healthy and diseased cucumber plants varied as measured by chlorophyll fluorescence and compared to the actual chlorophyll content. Hyperspectral imaging data were analysed using spectral vegetation indices. The results from this study confirm that each pathogen has a characteristic influence on the physiology and vitality of cucumber plants, which can be measured by a combination of non‐invasive sensors. Whereas thermography and chlorophyll fluorescence are unspecific indicators for plant diseases, hyperspectral imaging offers the potential for an identification of plant diseases. In a sensor data fusion approach, an early detection of each pathogen was possible by discriminant analysis. Although it still needs to be validated under real conditions, the combination of information from different sensors seems to be a promising tool.