Untreated Leaf Research Articles

Effects of Deoxynivalenol on Content of Chloroplast Pigments in Barley Leaf Tissues

To understand further the role of deoxynivalenol (DON) in development of Fusarium head blight (FHB), we investigated effects of the toxin on uninfected barley tissues. Leaf segments, 1 to 1.2 cm long, partially stripped of epidermis were floated with exposed mesophyll in contact with DON solutions. In initial experiments with the leaf segments incubated in light, DON at 30 to 90 ppm turned portions of stripped tissues white after 48 to 96 h. The bleaching effect was greatly enhanced by addition of 1 to 10 mM Ca(2+), so that DON at 10 to 30 ppm turned virtually all stripped tissues white within 48 h. Content of chlorophylls a and b and of total carotenoid pigment was reduced. Loss of electrolytes and uptake of Evans blue indicated that DON had a toxic effect, damaging plasmalemmas in treated tissues before chloroplasts began to lose pigment. When incubated in the dark, leaf segments also lost electrolytes, indicating DON was toxic although the tissues remained green. Thus, loss of chlorophyll in light was due to photobleaching and was a secondary effect of DON, not required for toxicity. In contrast to bleaching effects, some DON treatments that were not toxic kept tissues green without bleaching or other signs of injury, indicating senescence was delayed compared with slow yellowing of untreated leaf segments. Cycloheximide, which like DON, inhibits protein synthesis, also bleached some tissues and delayed senescence of others. Thus, the effects of DON probably relate to its ability to inhibit protein synthesis. With respect to FHB, the results suggest DON may have multiple roles in host cells of infected head tissues, including delayed senescence in early stages of infection and contributing to bleaching and death of cells in later stages.

Mechanical and thermal characterization of epoxy composites reinforced with random and quasi-unidirectional untreated Phormium tenax leaf fibers

The present work investigates tensile and flexural behavior of untreated New Zealand flax ( Phormium tenax) fiber reinforced epoxy composites. Two series of laminates were produced using the same reinforcement content (20 wt%), arranged either as short fibers or quasi-unidirectional ones. Composites reinforced using quasi-unidirectional fibers showed higher modulus and strength both in tensile and flexural loading, when compared to neat epoxy resin. Short fiber composites, although still superior to epoxy resin both for tensile and flexural moduli, proved inferior in strength, especially as concerns tensile strength. These results have been supported by scanning electron microscopy (SEM), which allowed characterizing fiber–matrix interface, and by acoustic emission (AE) analysis, which enabled investigating failure mechanisms. In addition, thermal behavior of both untreated phormium fibers and composites has been studied by thermogravimetric analysis (TGA), revealing the thermal stability of composites to be higher than for phormium fibers and epoxy matrix alone.

Diaphorina citri(Hemiptera: Psyllidae) Infection and Dissemination of the Entomopathogenic FungusIsaria fumosorosea(Hypocreales: Cordycipitaceae) Under Laboratory Conditions

ABSTRACT The infectivity and horizontal transfer of Isaria fumosorosea Wize among Diaphorina citri Kuwayama was measured using a detached leaf bioassay in which blastospores were sprayed on citrus leaf sections or yellow plastic tags (artificial attractant surface). Four leaf sections or three leaf sections and one yellow tag were placed together in a Petri dish chamber. One to four of the leaf sections or the yellow tag was sprayed with I. fumosorosea (1.2–1.7×103 blastospores/mm2). After treatments dried, a single adult psyllid was released into each chamber. Mortality due to I. fumosorosea for the adult psyllid was observed 4.9 ± 0.21–6.1 ± 0.37 d following exposure to the pathogen. The rate of colonization by I. fumosorosea on adults in chambers with untreated leaf sections and one treated yellow tag was as effective in inducing mortality as in chambers with one treated leaf section at 8 days post application. Under high humidity, I. fumosorosea blastospores readily produced hyphae on the surface of l...

The response of rice straw varieties to urea treatment

Sixteen rice straw varieties comprising 6 single-crop and 10 double-crop varieties were treated with 40 g/l urea solution (50 g straw per 200 ml of solution) for 21 days at 27 °C and total and insoluble ash, crude protein, neutral detergent fibre and in vitro digestibility (IVD) were measured after samples were dried at 60 °C to constant weight. The mean IVD values across treatments for the single-crop varieties were 0.500, 0.480, 0.418 and 0.499 for all fractions (whole straw, stem, leaf sheath, and leaf blade), corresponding values for the double-crop varieties were higher, 0.560, 0.598, 0.542 and 0.627, respectively. The untreated IVD values across varieties were 0.496, 0.497, 0.404 and 0.462 for whole straw, stem, leaf sheath, and leaf blade; and for urea treated, 0.564, 0.581, 0.556 and 0.665, respectively. Urea treatment caused a decrease in neutral detergent fibre exclusive of residual ash (NDFom) and in increase in IVD of all fractions ( P<0.001). Single-crop fractions were all lower in IVD ( P<0.001), and all fractions except whole straw were higher in NDFom ( P<0.05) than double-crop varieties. Based on criterion variables selected from step-wise discriminant analysis, single- and double-crop varieties clustered separately before but together after urea treatment which may be important in selecting genetic varieties. Regression analysis showed, in general, fractions with a lower IVD intercept responded better to urea treatment evaluated by relatively higher regression coefficients of 0.39, 0.67, 0.79 and 0.80, respectively for whole straw, stem, leaf sheath, and leaf blade. The effect of the untreated stem, leaf sheath, and leaf blade IVD on the IVD of untreated and urea-treated whole straw was described by single and multiple regressions where the most important fraction was the leaf blade IVD for urea-treated whole straw IVD and the leaf sheath IVD for the untreated whole straw IVD. Multiple regressions, although they had higher R 2, did not show any fraction to be more important than found in the simple regressions. It is concluded that although urea-treatment may result in a better response in poorer quality straws, rice straw varieties with a high leaf sheath IVD would improve the quality and utilisation of whole straw without urea treatment whereas high leaf blade IVD would improve the quality and utilisation of whole straw with urea treatment.

Studies on application of teak leaf powders for the removal of color from synthetic and industrial effluents

Batch studies were conducted to investigate the potential of untreated teak leaf powder (TLP) to remove color from synthetic and industrial effluents. Langmuir and Freundlich isotherms were used to analyze the equilibrium data. Langmuir isotherm was found to be the best-fitting isotherm. The monolayer adsorption capacity was found to be 99.1, 145.2, 188.7 and 207.9 mg methylene blue/g TLP at 293, 303, 313 and 323 K, respectively. It was also found from the thermodynamic analysis that the adsorption of methylene blue onto TLP was spontaneous, chemisorption and exothermic in nature. The color of the effluent was quantified in terms of the area under absorbance spectrum. Percentage color, COD and total dissolved solids (TDS) removed from a diluted effluent (10% effluent by vol.) were found to be 57.41, 45.95 and 49.46, respectively. The monolayer capacity was calculated in terms of TDS and was found to be 219 mg/g.

A Novel Burdock Fructooligosaccharide Induces Changes in the Production of Salicylates, Activates Defence Enzymes and Induces Systemic Acquired Resistance to Colletotrichum orbiculare in Cucumber Seedlings

AbstractThe ability of burdock fructooligosaccharide (BFO), a type of linear fructooligosaccharide extracted and isolated from the roots of Arctium lappa, to induce systemic acquired resistance (SAR) was studied in cucumber seedlings. BFO strongly induced changes in salicylic acid (SA) and SA‐glucoside (SAG) in BFO‐treated leaves, and similar changes of SA and SAG were also found in untreated leaves of the same seedling. The level of SA in the first leaves sprayed with BFO (5.0 g/l) increased by 3.6 times after 24 h and then gradually declined from 48 to 96 h and finally decreased to a nadir at 120 h. The SAG level increased by 2.1 times at 24 h and then continued to increase to about 10.0 times as much as that in control from 96 to 120 h. The levels of SA in the untreated leaves of the same seedling only increased by 1.6–1.9 times during the period of 24–72 h followed by a decrease at 120 h, while SAG increased by 1.1 times at 24 h but steadily continued to increase to its maximum from 24 to 120 h. In summary, the patterns of expression of SA and SAG in the untreated leaf were similar to that of the treated leaf of the same seedling, while the pattern of expression of SAG was quite different from that of SA both in the treated and untreated leaves. Pretreatment with BFO reduced the lesions caused by Colletotrichum orbiculare by 56.8%. Additionally, the amount of lignin and the activities of some defensive enzymes including peroxidase, superoxide dismutase, polyphenoloxidase and β‐1,3‐glucanase significantly increased in the first leaves pretreated with BFO and followed with C. orbiculare inoculation. These results demonstrate that BFO can enhance the contents of endogenous SA, the resistance against C. orbiculare, and the activities of defensive enzymes of cucumber seedlings.

Direct analysis of Stevia leaves for diterpene glycosides by desorption electrospray ionization mass spectrometry

The analysis of Stevia leaves has been demonstrated without any sample preparation using desorption electrospray ionization (DESI) mass spectrometry. Direct rapid analysis was achieved using minimal amounts of sample ( approximately 0.15 cm x 0.15 cm leaf fragment). Characteristic constituents of the Stevia plant are observed in both the positive and negative ion modes including a series of diterpene 'sweet' glycosides. The presence of the glycosides was confirmed via tandem mass spectrometry analysis using collision-induced dissociation and further supported by exact mass measurements using an LTQ-Orbitrap. The analysis of both untreated and hexane-extracted dry leaves proved that DESI can be successfully used to analyze untreated leaf fragments as identical profiles were obtained from both types of samples. Characterization and semi-quantitative determination of the glycosides was achieved based on the glycoside profile within the full mass spectrum. In addition, the presence of characteristic glycosides in an all-natural commercial Stevia dietary supplement was confirmed. This study provides an example of the application of DESI to direct screening of plant materials, in this case diterpene glycosides.

Foliar fertilization of peach ( Prunus persica (L.) Batsch) with different iron formulations: Effects on re-greening, iron concentration and mineral composition in treated and untreated leaf surfaces

A trial to assess the effects of applying several Fe-containing formulations on Fe-deficient (chlorotic) peach leaves was carried out under field conditions. Solutions consisting of an Fe-containing compound (FeSO 4·7H 2O, Fe(III)–citrate, Fe(III)–EDTA, Fe(III)–DTPA or Fe(III)–IDHA) and one of five different surfactant treatments (no surfactant, an organo-silicon, an ethoxylated oil, a non-ionic alkyl polyglucoside and a household detergent) were applied to one half of the leaf via dipping, first at the beginning of the trial and then after 4 weeks. The re-greening of treated and untreated leaf areas was estimated with a SPAD apparatus, on a weekly basis, during 8 weeks. At the end of the experimental period, leaves were detached, and tissue Fe, N, P, K, Ca, Mg, Mn, Zn and Cu concentrations were determined in Fe-treated and untreated leaf areas. Treatment with Fe-containing solutions always resulted in leaf chlorophyll (Chl) increases, which however significantly depended on the Fe-source, the surfactant-type and the combination between both formulation components. Untreated leaf zones experienced a Chl increase only in some cases, and this depended on the type of surfactant used. Iron application significantly increased the Fe concentration of treated and untreated leaf areas, especially with some formulations. Foliar treatment with Fe-containing solutions induced significant changes in the concentration of several nutrients as compared to those found in Fe-deficient peach leaves, with changes being similar in treated and untreated leaf areas, although in some elements the extent of the changes was of a different magnitude in both materials. This indicates that some leaf mineral composition changes typical of chlorotic leaves are dependent on leaf Fe concentration rather than on leaf Chl levels. Results obtained are relevant to help understand the factors involved in the penetration and bioavailability of leaf-applied Fe, and to assess the potential of foliar Fe fertilization to control Fe deficiency in fruit trees.

Effects of process variables on kinetics of methylene blue sorption onto untreated guava (Psidium guajava) leaf powder: Statistical analysis

The sorption of methylene blue onto untreated guava leaf powder has been studied. The kinetics of sorption of methylene blue is described by pseudo-second-order model. Effects of initial dye concentration, solution temperature, and adsorbent dosage have been studied. The pseudo-second-order rate constant has been correlated as a function of the system variables. Statistical tools like Student's t-test, F-test, ANOVA and lack of fit have been employed to determine the significance of each coefficient that appeared in the model. Model adequacy has been checked by residual distribution. The proposed model explains 95.1% of the total variation in the response.

Effects of kaolin particle film on Myzus persicae (Hemiptera: Aphididae) behaviour and performance

The emergence of resistance mechanisms to, and revocation of, many insecticides used in the control of the polyphagus aphid pest, Myzus persicae (Sulzer), has increased the pressure to develop novel approaches for the control of the pest in many crops. Kaolin-based particle films provide a physical barrier against insect pests and show considerable potential for controlling M. persicae. We conducted a series of laboratory experiments to investigate the mode of action of kaolin against aphids. The material appeared to have no direct effect on M. persicae; spraying adult aphids with aqueous kaolin suspension had no significant impact on their subsequent survival or reproduction on untreated plants. Similarly, when aphids were placed on kaolin-treated host-plants (Brassica oleracea), their performance (survival, growth rate and reproduction) was not significantly different from aphids on untreated plants. However, when M. persicae were given a choice between kaolin-treated and untreated (or water solvent-treated) leaf areas, both adults and nymphs exhibited a significant preference for non-kaolin-treated host-plant material. Rejection of kaolin-treated plant material occurred very rapidly (within 20 min) and this behavioural effect may be related to the efficacy of kaolin in controlling aphids under field conditions.

Retention and rainfastness of mancozeb as affected by physicochemical characteristics of adaxial apple leaf surface after enhanced UV-B radiation

It is not clear so far whether alteration of leaf micromorphology and surface wax chemistry due to the impact of environmental factors, such as UV-B radiation, affects retention and rainfastness of applied pesticide solutions. In this study; UV-B treated and untreated adaxial leaf surfaces of apple seedlings (Malus domestica Borkh.) were characterized in terms of chemical composition, micromorphological fine structure, hydrophobicity, and wettability. Furthermore, the retention and rainfastness of applied fungicide mancozeb were studied. The samples were examined 0, 24 and 48 h after ultraviolet (UV)-B radiation (0.022 kW m− 2 for 150 min) The total wax mass, recovered from the adaxial leaf surface, amounted from 0.38 μ g cm− 2 (control) up to 0.49 μ g cm− 2 (24 h). Chemical composition of surface wax altered, whereas the contact angle of applied water droplets on leaf surface of UV-B treated plants did not change significantly compared to the control. The alteration of surface wax quantity and quality significantly affected retention of a.i.; it increased at a sampling time of 24 h after UV-B irradiation, whereas rainfastness of the fungicide spray solution was not significantly influenced.

Physiological basis for antagonism induced by mixtures of quizalofop‐ethyl and bromoxynil in maize (Zea mays)

SummaryIn this study, the physiological basis for antagonism induced by mixtures of quizalofop‐ethyl and bromoxynil was investigated in maize seedlings. In sequential applications, antagonism was observed when bromoxynil was applied before quizalofop‐ethyl or in a mixture with quizalofop‐ethyl, but was minimal when bromoxynil was applied afterwards. The degree of antagonism differed with application rates of bromoxynil and with the timing of the treatment. When test herbicides were applied locally to the second leaf, the inhibition of photosystem II (PS‐II) in the herbicide‐treated leaf was higher with the mixture than with bromoxynil or quizalofop‐ethyl alone. Subsequent growth of the untreated third leaf inhibited by quizalofop‐ethyl alone then recovered, depending on the dose of bromoxynil. There was no evidence that bromoxynil affected absorption of quizalofop‐ethyl. In local applications at different positions on the second leaf, antagonism was only observed when quizalofop‐ethyl was applied to the distal part of the leaf and bromoxynil applied to the proximal part. The antagonism of bromoxynil + quizalofop‐ethyl did not occur at the level of acetyl CoA carboxylase and Hill reaction, as revealed by in vitro assays. These results suggest that bromoxynil inhibits the phloem transport of quizalofop‐ethyl and thus antagonises its whole‐plant activity in maize.

Fungicide and Clay Treatments for Control of Powdery Mildew Influence Wine Grape Microflora

There is very little information on the interaction of wine grape microflora with fungicides used to control grape diseases. The objective of this study was to determine how fungicides used in a standard grape pest management program and an experimental clay being developed for control of powdery mildew affect grape microflora. Grape leaves and fruit were surveyed for bacteria, fungi and yeast six times over the growing season in 2000 after treatment with clay or fungicides. In 2001 only clay was studied for control of powdery mildew in `Chancellor' grapes. The total number of propagules present on untreated leaf and fruit tissue were 76% bacteria, 14% yeast, and 9% fungi. Fungicides used for grape disease control significantly reduced epiphytic fungi (P &lt; 0.0001), bacteria (P = 0.03), and yeast (P = 0.0001) on grape berries and epiphytic fungi (P &lt; 0.0001), and yeast (P = 0.03) on leaves. The clay treatment had no detectable effect on grape microflora because no significant differences were recorded between clay or untreated grape berries or leaves on any of the sampling dates. Over the growing season the fungicide spray program reduced incidence and severity of powdery mildew better than clay. Clay controlled powdery mildew on `Chancellor' fruit in 2000 and 2001.

Effect of Copper Hydroxide on Slug Feeding

Abstract Kocide® 2000 (53.8% copper hydroxide) and Kocide® 4.5 LF (37.5% copper hydroxide) were examined for their effectiveness at reducing slug feeding using rates found on the Kocide® label. The marsh slug, Deroceras laeve (Müller), was given a choice among two untreated lettuce leaf plugs, one untreated leaf plug and one leaf plug treated with Kocide® 2000 at the rate of 4600 ppm Cu(OH)2 (3.0 tbsp/gal), and one untreated leaf plug and one leaf plug treated with Kocide® 2000 at the rate of 9200 ppm Cu(OH)2 (6.0 tbsp/gal). In a follow-up trial, D. laeve were exposed to Kocide® 4.5 LF at rates of 3100 ppm Cu(OH)2 (1.33 pt/A) and 6200 ppm Cu(OH)2 (2.66 pt/A). A second species, the three-banded slug, Lehmannia valentiana (Férussac), was presented with one untreated lettuce leaf plug and three treated leaf plugs using Kocide® 2000 at the rates of 3100, 6300, and 9400 ppm Cu(OH)2 (2.0, 4.0, and 6.0 tbsp/gal). In each study, D. laeve and L. valentiana showed a preference for the untreated lettuce, indicating that Kocide® 2000 and Kocide® 4.5 LF effectively reduce feeding in these common pest species.

Control of Alternaria Spot Disease on Loquat (Eriobotrya japonica Lindl.) Using Detached Fruits and Leaf-disk Assay

Treatments with four types of new, slightly toxic and non-residual fungicides and two preparations of Trichoderma harzianum were applied against Alternaria alternata, causal organism of Alternaria leaf and fruit spot disease of loquat. Preventive and curative effects of the above-mentioned treatments were bioassessed by measuring lesion diameter of A. alternata and its sporulation density on detached loquat fruits and leaf discs. Results indicated that preventive and curative effects of the treatment with difenoconazole (Score®) and cyprodinil+flodioxonil (Switch®) applied at a rate of 0.35% (V/V) and 0.20% (W/V), respectively, significantly reduced the lesion diameter of A. alternata on treated fruits and leaf discs compared to the untreated control fruits and leaf discs. Also, application of the above-mentioned fungicides at the same rates completely inhibited the sporulation of A. alternata at preventive and curative treatment with Switch® and at curative treatment with Score® on treated leaf discs compared to the untreated control organs. Conidia of T. harzianum (strain Th2) formulated in invert emulsion and applied at a concentration of 1.3X108 conidia/ml of the preparation, significantly suppressed lesion diameter of A. alternata and its sporulation density on treated fruits compared to treatment with conidial suspension of T. harzianum in sterile distilled water, and the control (blank formulation of invert emulsion or sterile distilled water only). These results should be confirmed under field conditions before large scale application.

Use of carbon‐11 in Populus shows that exogenous jasmonic acid increases biosynthesis of isoprene from recently fixed carbon

ABSTRACTA new approach for pulse labelling of plants using the short‐lived positron emitting radioisotope carbon‐11 (half‐life: 20.4 min) as 11CO2 is reported together with its application to measuring [11C]isoprene emissions from intact leaves capturing information associated with: (1) rate of emission; (2) the relative contribution of recently fixed carbon to isoprene biosynthesis; and (3) the transit time for tracer movement through the leaf and biochemical pathways associated with isoprene biosynthesis. This approach was applied to study the response of certain Populus species to exogenous treatments of jasmonic acid (JA), a plant hormone implicated in signal transduction linked to defence response against herbivory. Twelve hours after treatment of single intact leaves of aspen (Populus tremuloides) with a 1 m m JA spray, isoprene emissions from those leaves increased 1.5 times the controls from 35.4 ± 2.2 to 53.1 ± 4.8 nmol m−2 s−1. [11C]Isoprene emissions from the same leaves, reflecting the isoprene that was derived from recently fixed carbon, increased much more, to 2.2 times the controls. This increase coincided with a change in emitted [11C]isoprene from 0.31 to 0.68% of 11C fixed in the leaf tissue, while the tracer transit time remained constant at 12.5 min. These results suggest that JA had no effect on enzyme kinetics involved in isoprene biosynthesis, but did impact the source of recent carbon feeding that pathway. Studies with poplar (Populus nigra clone NC 5271) showed similar trends in systemic emissions (from an untreated leaf on the same plant).

Identification of pathogen-responsive regions in the promoter of a pepper lipid transfer protein gene (CALTPI) and the enhanced resistance of the CALTPI transgenic Arabidopsis against pathogen and environmental stresses

The 5' flanking region of the CALTPI gene, which encodes a basic lipid transfer protein, was isolated and characterized from the genomic DNA of Capsicum annuum. Four different regions of the promoter sequence of the CALTPI gene were fused to the beta-glucuronidase (GUS) coding region. In an Agrobacterium-mediated transient expression assay, the transcriptional activations of the promoter deletions were examined in tobacco leaves after infection with Pseudomonas syringae pv. tabaci, and treatment with ethylene and salicylic acid. The -808 bp region of the CALTPI gene promoter sequence exhibited full promoter activity. The W-box and ERE-box elements, which are essential for induction by all signals, were localized in the region between -555 bp and -391 bp upstream of the translation initiation site. A CALTPI transgene was then introduced under the control of the 35S promoter into the Arabidopsis ecotype Col-0. Transgenic Arabidopsis lines expressing the CALTPI gene developed rapidly compared to the wild-type plants, indicating that CALTPI may be involved in plant development. Overexpression of the CALTPI gene enhanced the resistance against infection by P. syringae pv. tomato and Botrytis cinerea. The transgenic plants expressing the CALTPI gene also showed high levels of tolerance to NaCl and drought stresses at various vegetative growth stages. No transcription of the PR-1, PR-2, PR-5, thionin, and RD29A genes was observed in untreated leaf tissues of the transgenic plants. The enhanced resistance to pathogen and environmental stresses in transgenic Arabidopsis correlated with the enhanced expression of the CALTPI gene.

Transcriptional response of sugarcane roots to methyl jasmonate

The effect of methyl jasmonate treatment on gene expression in sugarcane roots signalling between roots and shoots was studied. A collection of 829 ESTs were obtained from sugarcane roots treated with the defence-regulator methyl jasmonate (MJ) treatment. A subset of 747 of these were combined with 4793 sugarcane ESTs obtained from stem tissues in a cDNA microarray and experiments undertaken to identify genes that were induced in roots 24–120 h following treatment with MJ. Two data analysis systems ( t-statistic and tRMA) were used to analyse the microarray results and these methods identified a common set of 21 ESTs corresponding to transcripts significantly induced by MJ in roots and 23 that were reduced in expression following MJ treatment. The induction of six transcripts identified in the microarray analysis was tested and confirmed using northern blotting. Homologues of genes encoding lipoxygenase and PR-10 proteins were induced 8–24 h after MJ treatment while the other four selected transcripts were induced at later time points. Following treatment of roots with MJ, the lipoxygenase homologue, but not the PR-10 homologue, was induced in untreated stem and leaf tissues. The PR-10 homologue and a PR-1 homologue, but not the lipoxygenase homologue, were induced in untreated tissues after the application of SA to roots. Repeated foliar application of MJ had no apparent effects on plant growth and was demonstrated to increase lipoxygenase transcripts in roots, but did not increase transcript levels of other genes tested. These results lay a foundation for further studies of induced pest and disease resistance in sugarcane roots.

Ancymidol-enhanced hyperhydric malformation in relation to gibberellin and oxidative stress in liquid-cultured Narcissus leaves

The growth retardant ancymidol inhibited gibberellin biosynthesis and enhanced hyperhydric malformation of Narcissus leaf sections cultured in liquid medium. Superoxide dismutase activities were examined by spectrophotometry and native polyacrylamide gel analysis, and gibberellin and hydrogen peroxide levels were determined spectrophotometrically in either hyperhydric or non-hyperhydric leaf sections. In ancymidol-treated hyperhydric leaf sections, superoxide dismutase activity and hydrogen peroxide levels were higher during the initial culture period, when hyperhydric malformation occurred, than in control untreated leaf sections. At a later stage, when the meristematic centers started to form on ancymidol-enhanced hyperhydric leaf sections, superoxide dismutase activity, hydrogen peroxide, and gibberellin levels were significantly lower in hyperhydric leaf sections than in non-treated leaf sections. The changes in superoxide dismutase activities, hydrogen peroxide, and gibberellin levels appeared to be related to hyperhydric malformation and meristematic center initiation.

The Effect of Leaf Wax Extracts from the Leaves of Eight Azalea Genotypes (Rhododendron spp.) on Feeding and Oviposition by Azalea Lace Bug [Stephanitis pyrioides (Scott)

Azalea Lace Bug (ALB) is a significant pest on azalea species. ALB feeding injury causes a stippled appearance on the leaves of susceptible genotypes from late spring until leaf drop. To determine whether leaf surface lipids are a factor in determining resistance or susceptibility to ALB, epicuticular leaf wax was extracted from the leaves of eight azalea genotypes, half with resistance and half susceptible to ALB. Leaf wax from each genotype was extracted and re-suspended in an 2 ethanol: 1 water solution for application to all entries in a full diallel manner, including a control of solution only. Each treatment included three replications. The leaf wax solution was applied to each replication (single leaf) by painting the solution on one side of the midrib, on both abaxial and adaxial surfaces. By applying solution to one side of the leaf, the untreated leaf surface served as a control. Each leaf and two female ALB were placed in separate 50-mL sealed tubes at 24 °C and 12-hour daylength for 48 hours, at which time the number of live adults, frass spots, and eggs were counted. Frass and egg data were recorded separately for treated and untreated sides of each leaf. The application of leaf wax solution had an impact on the level of frass and egg deposition by ALB in all genotypes. The effect was most pronounced when solution of resistant genotypes was placed on susceptible genotypes, resulting in lower numbers of frass spots and eggs. The solution alone had little effect on frass or egg numbers. This research acknowledges that a major constituent of an azalea's resistance or susceptibility to ALB is via epicuticular wax components.