Leaf Penetration Research Articles

Foliar Iron Fertilization: A Critical Review

ABSTRACT Application of foliar iron (Fe) sprays is a common means of correcting Fe deficiency of agricultural crops. However, variable plant responses to iron sprays, ranging from no effect to defoliation, have often been described in the Fe-fertilization literature. Knowledge is still limited concerning the mechanisms of penetration of a leaf-applied, Fe-containing solution and the role of Fe in the leaf. The complex and multi-disciplinary character of the factors determining the effects of Fe sprays hinder the development of suitable foliar fertilization strategies, applicable under variable local conditions and for different plant types. This review describes some key factors involved on the process of penetration of a leaf-applied, Fe-containing solution before briefly analyzing the available foliar Fe-fertilization literature. Iron chemistry, leaf penetration, and plant-nutrition principles will be merged with the aim of clarifying the constraints, opportunities, and future perspectives of foliar Fe sprays to cure plant Fe deficiency.

Effect of temperature and photoperiod on symptoms associated with resistance toPhytophthora infestans after leaf penetration in susceptible and resistant potato cultivars

The effect of temperature and photoperiod on the expression of resistance against Phytophthora infestans in five potato cultivars with and without resistance (R) genes was investigated. Four experiments were carried out under controlled conditions in growth chambers. Two cultivars (393295.236 and 391046.22) without known R genes from the International Potato Center (CIP) in Lima, Peru, two Mexican cultivars with major R genes (Tollocan and Malinche), and a susceptible cultivar (Atlantic) were used in this study. Plants were grown for 32 days in growth chambers at two temperatures (16 and 24 C) and two photoperiods (12 and 16 h day length), then inoculated with a compatible isolate of P. infestans and incubated in a mist chamber at 18 C. The inoculation efficiency, the percentage of lesions that did not grow beyond the inoculation spot, the sporangia density, and the AUDPC were recorded. The percentage of arrested lesions decreased with temperature in the two most resistant cultivars (393295.236 and Malinche), and the AUDPC was lower at 16 than at 24 C in four of the five cultivars. The inoculation efficiency and the sporangia density were not affected by change in temperature. Sporangia density increased at 16 h photoperiod; however, the final infected leaf area was not affected. Our results demonstrate that the expression of horizontal and vertical resistance was affected by temperature; however, the relative resistance ranking among cultivars was the same in the four experiments with different temperatures and photoperiods. It is assumed that the resistance in the Mexican cultivars may be conferred by minor resistance genes and by the residual effect of defeated R genes. These results emphasize the difficulty in differentiating between horizontal and vertical resistance.

Characterisation of the feeding behaviour of western flower thrips in terms of electrical penetration graph (EPG) waveforms

Western flower thrips, Frankliniella occidentalis (Pergande) causes damage to plants when they are feeding. Also, this thrips species transmits Tomato spotted wilt virus (TSWV) during stylet penetration. We investigated the penetration behaviour (probing) of thrips on pepper leaves and on liquid diet by electrical penetration graph (EPG, DC-system) recording. In addition, we used high-magnification video observations to correlate EPG waveforms with the insect’s posture, head movements, and muscle contractions. Also, EPGs were correlated with probing on liquid diets containing radio-active tracers to distinguish and quantify ingestion waveforms. The previously described waveforms P, Q, and R were distinguished and additionally, a new waveform ‘S’ was distinguished. Waveform P could be linked with mandibular leaf penetration, waveform Q presumably with insertion of the maxillary stylets, and waveform R with ingestion of cell contents, whereas waveform S could not be correlated with any behavioural activity. Histology of the feeding damage in pepper leaves shows that thrips ingests the contents of multiple cells per probe.

The infection process of Alternaria cirsinoxia on Canada thistle ( Cirsium arvense) and host structural defence responses

The infection process of Alternaria cirsinoxia was studied on Canada thistle (Cirsium arvense) in the controlled environment and in the field. In the controlled environment, germination of conidia began at 2 h and appressoria formation at 4 h after inoculation. Approximately 75% of appressoria formed at the anticlinal wall junctions of the epidermis. Leaf penetration occurred between 6 and 24 h, most commonly in between adjoining anticlinal walls. Penetration through stomata was rare. After penetration, large, intracellular infection hyphae formed and branched within epidermal cells, ramifying throughout the leaf tissues inter- and intracellularly by 24 h. In field conditions, infection coincided with prolonged rainfall and conidia remained viable on the leaf surface for 8–9 days (d) before causing infection on leaves. A host response occurred after penetration, involving deposition of lignin and callose in the infected epidermal and mesophyll cell walls. High levels of silicon were detected in epidermal cells directly below appressoria, often appearing to form entirely silicified infected cells which were resistant to collapse after air-drying. This study shows that A. cirsinoxia has the potential for rapid invasion of the leaf tissues of Canada thistle under good moisture conditions. The implications of the host responses, in terms of defence against infection, are discussed.

Influence of Moisture and Temperature on Infection of Canada Thistle by Alternaria cirsinoxia.

Relative humidity (RH), temperature, continuous leaf wetness, and intermittent leaf wetness were evaluated for their influence on conidial germination, appressoria formation, and infection of Canada thistle by Alternaria cirsinoxia. Conidia germinated and formed appressoria at 98% RH, but required at least 100% RH, and preferably free water, to penetrate leaves. In free water, conidia germinated equally well at 10, 15, 20, 25, or 30°C. Appressoria formation and leaf penetration also occurred at all temperatures evaluated from 10 to 30°C, with the highest values at 20 to 25°C and 20°C, respectively. Conidia required 8 h of continuous leaf wetness to establish visible symptoms of infection on Canada thistle. Exposure of conidia of A. cirsinoxia to up to five intermittent leaf wetness cycles (30 min wet/30 min dry) reduced germination, appressoria formation, and leaf penetration, but conidia remained infective after all cycles. Exposure to cycles of 4 h dew/20 h dry was most detrimental to infection, compared with a 72 h dry period or cycles of 1 h dew/23 h wet or 2 h dew/22 h wet, indicating greater sensitivity of more fully germinated conidia to drying. Such nonspecific temperature requirements and survival during repeated intermittent leaf wetness periods are beneficial characteristics for a bioherbicide. However, high moisture requirements for infection may limit the potential of using A. cirsinoxia to control Canada thistle in the semi-arid prairie provinces of Canada.

Effects of Leaf Maturity, Infection Site, and Application Rate of Alternaria cirsinoxia Conidia on Infection of Canada Thistle (Cirsium arvense)

The effects of leaf maturity, infection site, and application rate of Alternaria cirsinoxia conidia on the pre- and postpenetration phases of infection of Canada thistle were studied. Leaf maturity had no effect on the germination of conidia, but appressoria formation was significantly higher on the oldest leaf than on the youngest leaf. There were no differences in the frequency of leaf penetration in the youngest and the oldest leaves, but consistently larger lesions formed on the oldest leaf at 10 days after inoculation than on the youngest leaf. Penetration of the oldest leaf was greatest at the leaf tip, compared with the midleaf area or leaf base. Increasing the application rate of A. cirsinoxia conidia (105/ml) from 200 to 800 L/ha, with either continuous leaf wetness or intermittent drying during application, resulted in increasing conidial densities on the phylloplane from 3–4 to 9–13 conidia per 1.67-mm2 field of view. Intermittent drying during application reduced germination of conidia, but leaf penetration did not differ greatly among treatments. Disease severity on whole plants at 14 days after inoculation was not affected by application rate or leaf-wetness treatment. All plants scored 5–6 on the Horsfall–Barratt rating scale, with severe infection occurring only on the older, basal leaves. Thus, the plants recovered by developing new leaves at the apical portion. These results show that A. cirsinoxia is primarily pathogenic on older, senescing leaves of Canada thistle, irrespective of the application rates tested on whole plants. This characteristic limits its potential as a bioherbicide for Canada thistle.

Scanning electron microscopy of direct host leaf penetration by urediospore-derived infection structures of Phakopsora apoda

Urediospore-derived infection structures of Phakopsora apoda, a rust fungus on kikuyu grass (Pennisetum clandestinum), penetrate the host leaf directly through the cuticle and not through the stomata. A urediospore germinates on the leaf to form a short germ tube which is delimited from a terminal appressorium by a septum. Most appressoria form at the junctions between epidermal cells. Appressoria are often sessile to the urediospores. From the base of the appressorium, a penetration peg develops, which penetrates through the host cuticle and epidermal cell wall. Penetration of the epidermal cell wall occurs approx. 6 h post inoculation. Once inside the epidermal cell, the penetration peg expands to form a penetration hypha, which traverses the epidermal cell and emerges into the intercellular space of the mesophyll tissue. A septum is formed in the intercellular portion of the penetration hypha, delimiting a primary hypha which extends further into the mesophyll, before branching to form two secondary hyphae. This penetration process appears to be very similar to that of Phakopsora pachyrhizi on soybean.

Resistance of sunflower (Helianthus annuus L.) to terminal bud attack bySclerotinia sclerotiorum (Lib.) de Bary

Resistance of sunflowers to terminal bud attack bySclerotinia sclerotiorum was studied by microscopical observations of infection processes and by genetical analyses of trials showing natural infections. Electron microscope studies showed that there were no differences in leaf morphology between susceptible and resistant genotypes, and that both were contaminated by ascospores. Only on the susceptible genotype was considerable ascospore germination observed, followed by mycelial development and leaf penetration. On the resistant genotype, there was little ascosopore germination and no further development. The genetical studies of percentage natural attack observed on eight inbred lines representing a range of reactions, and the hybrids from a factorial cross of these lines, indicated that inheritance is mainly additive, with few interactions.

Morphogenic Regulation of Pathotoxin Synthesis inCochliobolus carbonum

The fungusCochliobolus carbonumcauses leaf spot disease of maize. Highly virulent isolates of the pathogen produce a host-selective, peptide toxin that is active against susceptible genotypes of maize. Prior to infection, spores must germinate and differentiate appressoria, structures specialized for leaf penetration. Analysis of spore germination fluids by plasma desorption mass spectrometry, which allowed detection of as little as 0.5 ng toxin, revealed that spores induced to form appressoriain vitrosynthesized and released the toxin at a time coincident with maturation of appressoria. Spores incubated under conditions that did not induce appressorium formation failed to produce toxin. These observations indicate that synthesis of the host-selective toxin, which is essential for successful pathogenesis of maize byC. carbonum,is regulated by infection-related morphogenesis.

The leaf infection process and resistance to Pleiochaeta setosa in three lupin species

In field experiments in Western Australia, Lupinus albus cv. Kiev Mutant was very susceptible, L. angustifolius cv. Yorrel was susceptible, and L. luteus cv. Motiv 369 was resistant to brown spot caused by Pleiochaeta setosa. The process of leaf infection by P. setosa was examined on these 3 Lupinus species and cultivars. Field infection occurred on young plants almost exclusively on the lower side of leaves from conidia splashed from the soil. More conidia per cm2 leaf surface were deposited on Kiev Mutant than on Yorrel or Motiv 369. In humid chambers at 15�C, 94-98% of conidia germinated on all species after 24 h. On all species, appressorial formation began 6 h after inoculation, but fewer appressoria were formed on Motiv 369 (27% of germinated conidia) than on the other 2 species (average 55%) after 24 h. Leaf penetration was directly through the cuticle via appressoria with few stomata1 penetrations. Efficiency of lesion formation (expressed as the number of lesions produced per 100 conidia deposited) was greater on Kiev Mutant and Yorrel (8.3 and 7.2%) than on Motiv 369 (2.3%). More lesions per cm2 leaf area were produced on Kiev Mutant (2.4) than on Yorrel (0.7) or Motiv 369 (0.3), but average lesion size was similar in each variety. Lesions expanded from 200-250 8m at 3 days to > 500 8m radius at 16 days after inoculation. During lesion expansion, P. setosa hyphae grew 50-200 8m beyond the border of necrotic lesions on Kiev Mutant, remained at the border of lesions on Yorrel, and were 100-200 8m inside the border of lesions on Motiv 369. Lesions on the susceptible cultivars Kiev Mutant and Yorrel (but not Motiv 369) were surrounded by a large chlorotic halo up to 2 mm from the outside necrotic lesion border. More lesions per cm2 leaf area were required to cause defoliation in Motiv 369 than in Kiev Mutant and Yorrel. Brown spot resistance in Motiv 369 is expressed as a reduction in defoliation. This appears to result from reduced attachment of conidia, reduced efficiency of infection and lesion formation, restricted growth of mycelia in lesions, reduced chlorosis, and delayed leaf senescence. Fewer conidia were produced on defoliated leaves of Motiv 369 in field plots.

Factors influencing the acaricidal activity of flucycloxuron

AbstractContact activities of flucycloxuron on immature stages of the two‐spotted spider mite (Tetranychus urticae (Koch)) and the European red mite (Panonychus ulmi (Koch)) gradually decrease in the successive developmental stages. The levels of contact activity of flucycloxuron on larvae and protonymphs of T. urticae and P. ulmi are of the same order. Deutonymphs of T. urticae are less susceptible to contact activity than the similar stage of P. ulmi. In adult T. urticae, the transovarial ovicidal activity was used as an indicator for cuticular penetration. More than 90% of the maximal penetration into adult mites occurs within 8 h. Reversibility of the transovarial activity was not observed after 24 h, but did occur after a subsequent 48 h stay on untreated leaves.The ovo‐larvicidal activity of flucycloxuron on P. ulmi after treatment of apple leaves is strongly negatively influenced by leaf age, partly by lower retention of the spray liquid on the leaves. Leaf penetration was measured by application of flucycloxuron on leaf uppersides and assessment of the transovarial activity in mites (P. ulmi or T. urticae) infested on the undersides, one day after treatment. In this test system, leaf penetration was found to be strongly species dependent. Penetration was high in cucumber, moderate in French beans, cotton, roses and strawberry, but low in apple and pepper. Leaf penetration in French bean plants is drastically reduced at increasing leaf age. The overall positive effect of increase in relative air humidity on leaf penetration, is statistically highly significant (P = 0.001) for French beans and almost significant (P = 0.08) for cucumbers. With T. urticae on French bean it was found that in this test flucycloxuron needs more than one day for maximal leaf penetration.Although in apple leaves penetration from uppersides was low, penetration from undersides was much higher. The surfactants Arkopal N130, Silwet L‐77 and X2‐5309 enhance penetration from leaf undersides.

Phytotoxicity Response of Pear to Application of Abamectin-Oil Combinations

Handgun treatments of abamectin and oil applied between mid-June and late August caused distinct epidermal rings where drops of spray liquid dried on the surface of pear fruit (Pyrus communis L.). The severity of epidermal injury was related to the concentration of oil in the abamectin spray mixture (abamectin applied without oil caused no fruit damage). Of six pear cultivars tested, `Anjou' was most susceptible to injury, followed by `Cornice' and `Bartlett'. `Sensation Red Bartlett', `Bosc', and `Seckel' showed little or no phytotoxicity symptoms from abamectin and oil treatments with oil concentrations from 0.125% to 2.0% (v/v). On sensitive cultivars, the concentration of oil should not exceed 0.25% (v/v) when combined with abamectin to reduce the risk of epidermal injury. Oil at 0.25% provides for adequate leaf penetration of abamectin and results in commercially acceptable spider mite (Tetranychus urticae Koch) control. Chemical names used: avermectin B1 (abamectin).

Surface carbohydrates and cell wall structure of in vitro-induced uredospore infection structures ofUromyces viciae-fabae before and after treatment with enzymes and alkali

Uredospores ofUromyces viciae-fabae differentiate to form germ tubes, appressoria, infection hyphae and haustorial mother cells on oil-containing collodion membranes. The cell walls of these infection structures were studied with the electron microscope and with FITC-labeled lectins before and after treatment with enzymes and inorganic solvents. Binding of the FITC-labeled lectins was measured with a microscope photometer. The enzymes pronase E, laminarinase, chitinase and lipase had different effects on each infection structure. Pronase treatment uncovered the chitin of germ tubes, appressoria and haustorial mother cells, but not of substomatal vesicles and infection hyphae. A mixture of α- and β-1,3-glucanase which also contained chitinase activity dissolved germ tubes and appressoria completely, but not infection pegs, substomatal vesicles, infection hyphae and haustorial mother cells. After treatment with laminarinase or lipase, an additional layer, which is especially obvious over the substomatal vesicle, infection hypha and haustorial mother cell, bound to LCA-FITC. In the wall of the haustorial mother cell, a ring, which surrounds the presumed infection peg, had strong affinity for WGA after protease and sodium hydroxide treatment. The infection structures have a fibrillar skeleton. The main constituent seems to be chitin. This skeleton is more dense or has a higher chitin content in the walls of appressoria and haustorial mother cells. The fibrils of the skeleton extend throughout the cell wall of the germ tube and appressorium. They are embedded within amorphous material of complex chemical composition (α-1,3-glucan, β-1,3-glucan, glycoprotein). The chitin of the infection peg, substomatal vesicle, infection hypha and haustorial mother cell is covered completely with this amorphous material. These results show, that each infection structure has distinct surface and wall characteristics. They may reflect the different tasks of the infection structures during host recognition and leaf penetration.

Accumulation of host-specific toxin produced by Cochliobolus carbonum during pathogenesis of maize

During penetration and colonization of susceptible maize leaves, the foliar pathogen Cochliobolus carbonum race 1 released the cyclic tetrapeptide toxin required for genotype-specific pathogenicity. Inoculation fluids on the leaf surface and extracts of leaf tissue contained the host-specific toxin by 12 and 18 h, respectively, after inoculation. Quantities of the toxin in inoculated leaf tissue increased during the development of necrotic lesions. The following preparations did not contain detectable quantities of the host-specific toxin: extracts of leaf tissue from susceptible or resistant isolines inoculated with the weakly virulent race 2; leaf extracts of the resistant genotype inoculated with race 1; and extracts of non-germinated conidia of either race. The results indicate that the pathogen produces and releases the toxin by the time of leaf penetration and that, in the susceptible interaction, the toxin accumulates by the time defence responses in the host must be suppressed.

Ultrastructure of infection of excized leaves of celery by Septoria apiicola, causal agent of leaf spot disease

The growth of Septoria apiicola was observed by SEM on excized celery leaves and on agar medium. Initial germ tube growth was random over leaf surfaces and closely appressed to the cuticle. Leaf penetration occurred directly through the epidermis and also via stomata. After infection, hyphal growth was restricted to intercellular spaces at first but became extensive later. Limited intracellular penetration was observed when leaves were necrotic. Development of pycnidia was observed in detail in leaf tissue and on agar.

Leaf spot disease of soybean caused by Drechslera rostrata

Summary Drechslera rostrata causes a distinctive circular leaf spot on Glycine max that usually develops through lamina. Leaf penetration is direct through the epidermal cells. Leaf exudates stimulated conidial germination of the fungal pathogen. On the other hand leaf diffusates inhibited conidial germination of the fungal pathogen.

Evaluation of three techniques used to determine surfactant phytotoxicity

SummaryThree techniques were used to measure and compare the phytotoxicities of Triton X‐45 and Agral 90 (two organic surfactants) with two organosilicone surfactants (Silwet L‐77 and L‐7607), and to compare these four non‐ionic compounds with a cationic tallow amine surfactant (Hyspray). Total ion efflux and ethylene response methods were used in vivo and in vitro, while a betacyanin efflux method was an in vitro system only. The first two methods, using intact leaves, were considered to be more closely related to normal spraying conditions than the betacyanin efflux test which used explant material. However, the use of intact leaves was thought to bias the results in favour of the leaf penetration properties of the surfactants rather than their phytotoxicities. The in vitro pigment efflux method provided a simple way of ranking the surfactants in order of their potential phytotoxicities, especially with regard to effects on membrane permeability. This ranking, in increasing order of toxicity, was: Silwet L‐7607, Silwet L‐77, Agral 90, Triton X‐45 and Hyspray.

Control on Watermelon, 1988

Abstract The efficacy of several insecticides was investigated in 2 tests with small plots of watermelons grown on a sandy loam soil near Hinton, Okla. Plots in each test were 30 ft long by 6 ft wide, and each treatment was replicated 3 times. A single insecticide application was made on 1 Sep 1988 using a CO2-powered backpack sprayer. The sprayer delivered 28 gal/acre at 60 psi through 2 TX-10 hollow-cone nozzles. Rigo crop oil concentrate was added to the RH-7988 treatments at the rate of 1 qt/acre to improve leaf penetration. Efficacy was assessed by counting aphids (alate and apterous) on 15 leaves randomly selected from each plot. Counts were made on 5 Sep (4 DAT), 8 Sep (7 DAT), and 15 Sep (14 DAT). Henderson's formula was used to calculate percentage of control for each treatment.

Potential Mechanisms for Bentazon Antagonism by Haloxyfop

The antagonism of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy propanoic acid} by bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] was evaluated through studies of absorption and translocation in yellow foxtail [Setaria lutescens(Weig. ex Stuntz.) Hubb. # SETLU]. Leaf penetration of haloxyfop was reduced 37% in the presence of bentazon. Bentazon had no effect on translocation from the treated leaf. Direct chemical interactions and contact activity by bentazon do not account for the reduced uptake of haloxyfop. Experimental evidence shows the benzothiadiazione structural class of chemistry to be general antagonists of absorption for foliarly applied herbicides.

Ph 70–23: A new acaricide and insecticide interfering with chitin deposition

AbstractPH 70–23 is a new benzoylphenylurea interfering with chitin deposition. In larvae of Spodoptera littoralis, incorporation of N‐acetyl‐glucosamine into chitin was equally inhibited by PH 70–23 and diflubenzuron, the first commercially available benzoylphenylurea. In contrast to diflubenzuron, which is active only against insects and eriophyid mites, PH 70–23 has the advantage of also being highly active on spider mites. The latter activity might be partly due to leaf penetration of PH 70–23. Laboratory experiments indicate PH 70–23 to have a better ovo‐larvicidal activity than the commercial acaricides tested (cyhexatin, dicofol, fenbutatin oxide and tetradifon) against Tetranychus cinnabarinus, T. turkestani, T. urticae and Panonychus ulmi. A method in which eggs were deposited on residues of cyhexatin or fenbutatin oxide resulted in much lower activities than application of the spray liquid after egg deposition. Activities of PH 70–23, dicofol and tetradifon were hardly influenced by this difference in the test method. The direct contact activity of PH 70–23 on eggs of mites is influenced by the relative humidity and the age of the eggs. The total ovolarvicidal activity of PH 70–23 is only slightly positively influenced by the relative humidity, however. Ovicidal activity of PH 70–23 is also achieved by transovarial transmission. The compound does not influence the fertility of the mites. Comparison of a strain of T. urticae, resistant to dicofol, parathion and tetradifon, with a susceptible strain indicated absence of cross‐resistance to PH 70–23. Compared to diflubenzuron, PH 70–23 shows an interesting shift in the spectrum of insecticidal activity.