Phytotoxic effects of metabolites from Alternaria euphorbiicola against its host plant Euphorbia heterophylla

A bioassay-guided fractionation of culture filtrates of the fungus Alternaria euphorbiicola, a pathogen of the weed Euphorbia heterophylla, led to the isolation of anhydromevalonolactone (1), tyrosol (2), (R)-( - )-mevalonolactone (3), and cycloglycylproline (4). When tested on the punctured leaves of the host plant, these compounds produced bleached lesions with dark brown margins at concentrations as low as 80 µM. When tested on the leaves of other relevant weeds, only cycloglycylproline showed selective activity against E. heterophylla. This is the first report on the isolation of phytotoxins from A. euphorbiicola and on the phytotoxicity of anhydromevalonolactone, (R)-( - )-mevalonolactone, and cycloglycylproline.

Intraspecific variability of Holostylis reniformis: concentration of lignans, as determined by maceration and supercritical fluid extraction (SFE-CO2), as a function of plant provenance and plant parts

Maceration and supercritical fluid extraction were used to prepare extracts from parts of plants (Holostylis reniformis) collected in two different regions of Brazil. ¹H NMR, HPLC-DAD-ESI/MS, HPLC-DAD, GC-MS, and chemometric techniques were used to analyse lignans in the extracts and showed that yields of SFE-CO2 were less than or equal to those of hexane maceration extracts. These analyses, in conjunction with the concentrations of aliphatic hydrocarbons, fatty acids and their methyl and ethyl derivatives in the extracts, also allowed the chemical composition of parts and provenance of the plant to be differentiated.

Evaluation of antiradical assays used in determining the antioxidant capacity of pure compounds and plant extracts

The efficiency of the chemiluminescence luminol method and colorimetric DPPH and ABTS methods in evaluating the antiradical capacity of pure compounds and plant extracts with antioxidant potential is compared. In case of pure compounds, the values of parameter 'n' (number of radicals quenched per molecule of antiradical) for ascorbic acid, p-hydroquinone, catechol, quercetin, and rutin are similar when measured by colorimetric assays; however, considerably lower values of n are obtained with the luminol assay. The antiradical activity of extracts from male and female individuals of Baccharis burchelli and Baccharis crispa were determined by the luminol assay and expressed using the new Trolox® percentage (%Trolox®) parameter.

Noctuidae-induced plant volatiles: current situation and prospects

Noctuids are phytophagous lepidopterans with some species causing significant damage to agriculture. The host plants, in turn, have developed defense mechanisms to cope with them, for instance chemical defenses. In this study we review the literature on plant volatiles induced by noctuids, and discuss the methodologies used to induce the production of volatiles that are usually employed in plant defense mechanisms. Future prospects involving this line of research in pest control are also discussed.

COMPARISON BETWEEN ASPHALTENES (SUB)FRACTIONS EXTRACTED FROM TWO DIFFERENT ASPHALTIC RESIDUES: CHEMICAL CHARACTERIZATION AND PHASE BEHAVIOR

Asphaltenes are blamed for various problems in the petroleum industry, especially formation of solid deposits and stabilization of water-in-oil emulsions. Many studies have been conducted to characterize chemical structures of asphaltenes and assess their phase behavior in crude oil or in model-systems of asphaltenes extracted from oil or asphaltic residues from refineries. However, due to the diversity and complexity of these structures, there is still much to be investigated. In this study, asphaltene (sub)fractions were extracted from an asphaltic residue (AR02), characterized by NMR, elemental analysis, X-ray fluorescence and MS-TOF, and compared to asphaltene subfractions obtained from another asphaltic residue (AR01) described in a previous article. The (sub)fractions obtained from the two residues were used to prepare model-systems containing 1 wt% of asphaltenes in toluene and their phase behavior was evaluated by measuring asphaltene precipitation onset using optical microscopy. The results obtained indicated minor differences between the asphaltene fractions obtained from the asphaltic residues of distinct origins, with respect to aromaticity, elemental composition (CHN), presence and content of heteroelements and average molar mass. Regarding stability, minor differences in molecule polarity appear to promote major differences in the phase behavior of each of the asphaltene fractions isolated.

Concepts in plant disease resistance

Resistance to nearly all pathogens occurs abundantly in our crops. Much of the resistance exploited by breeders is of the major gene type. Polygenic resistance, although used much less, is even more abundantly available. Many types of resistance are highly elusive, the pathogen apparently adapting very easily them. Other types of resistance, the so-called durable resistance, remain effective much longer. The elusive resistance is invariably of the monogenic type and usually of the hypersensitive type directed against specialised pathogens. Race-specificity is not the cause of elusive resistance but the consequence of it. Understanding acquired resistance may open interesting approaches to control pathogens. This is even truer for molecular techniques, which already represent an enourmously wide range of possibilities. Resistance obtained through transformation is often of the quantitative type and may be durable in most cases.

Evaluation of plant growth-promoting and bioprotecting rhizobacteria on wheat crop

Experiments were carried out under laboratory, growth chamber, and field conditions to evaluate the effect of Plant growth-promoting and bioprotecting rhizobacteria (PGPBR) seed treatment on seed pathogens, seed germination, plant growth, and grain yield of wheat (Triticum aestivum). Most of the PGPBR strongly reduced the recovery of the pathogens from infected wheat seeds. All treatments, except the chemical iprodione + thiram, significantly promoted plant growth over the nontreated control. Psudomonas putida biotype A (11) and P. agglomerans (14) showed the greatest effects. Field experiments, carried out at two locations, indicated that all treatments, except P. chlororaphis (42), significantly increased seedling emergence of wheat . In Pato Branco, PR, P. putida biotype A (11) and P. putida biotype B (44) presented the best results, both being superior to fungal biological and chemical treatments. In Passo Fundo P. putida biotype A (11) and P. putida biotype B (17 and 44) significantly improved yield over the nontreated control. Yield increases of these three PGPBR were similar to the chemical treatment iprodione + thiram. In Pato Branco, P. putida biotype A (11) and P. putida biotype B (17), as well as the chemical treatment, provided significant increase over the nontreated control. Yield increases by the PGPBR varied from 18% to 22% in Passo Fundo and from 27% to 28% in Pato Branco.

Production of policlonal antisera specific to plant viruses by rabbit oral immunization

Serological techniques are of great importance for plant virus identification and characterization. The major limiting factor for using these techniques for plant virus identification is the requirement of a good virus purified preparation to be used in immunizing animals for antiserum production. In the present study, two New Zealand rabbits were orally immunized with extracts from cowpea (Vigna unguiculata) plants systemically infected with Cowpea severe mosaic virus (CPSMV) and with extracts from papaya (Carica papaya) infected with Papaya lethal yellowing virus (PLYV). The leaf extracts were prepared in saline solution 0.15 M in the rate of 1:1 (w/v) and clarified by a centrifugation of 10,000 g for 10 min. The clarified extracts containing the viruses were orally administered to the New Zealand rabbits in two series of five daily doses of 1.0 ml each. The obtained policlonal antisera were shown to be very specific to their respective viruses in double immunodiffusion and indirect ELISA. These seem to be the first antisera specific for plant virus obtained by rabbit oral immunization. The results open up some possibilities for producing antisera to plant viruses of difficult purification. It is a simple, fast and inexpensive method for production of antisera for plant viruses when compared to the traditional techniques that involve rabbit injections with purified virus preparations.

Cultural practices and genetic resistance as factors affecting soybean stem canker and plant yield in the Cerrado

Field experiments were conducted in the 1995-96 soybean (Glycine max) growing season to evaluate the effects of cultural practices and host genetic resistance on the intensity of soybean stem canker, caused by Diaporthe phaseolorum f.sp. meridionalis (Dpm). Experiments were conducted in a commercial field severely infected in the previous (1994-95) season. In one study, minimum tillage (MT) and no-tillage (NT) cropping systems were investigated for their effects on disease development and on plant yields in cvs. FT-Cristalina (susceptible) and FT-Seriema (moderately resistant). Another study evaluated the effects of plant densities (8, 15, 21 and 36 plants/m) on disease development in cvs. FT-Cristalina, FT-101 (moderately resistant) and FT-104 (resistant). Disease incidence and severity were consistently lower in NT than in MT, and plant yields were increased by 23% and 14% in the NT system for the susceptible and moderately resistant cultivars, respectively, compared to the yields in the MT system. The Gompertz and Logistic models described well the disease progress curves in all situations. For both susceptible and moderately resistant cultivars, disease severity increased proportionately to the increase in plant densities. At the end of the season, 100% of the plants of cv. FT-Cristalina were infected by Dpm, at all plant densities. Disease levels on cv. FT-101 were intermediate while only very low disease levels were recorded on cv. FT-104. There was a consistent negative correlation between stem canker severity and yield. Some practices demonstrated potential for direct application in disease control, and could be combined considering their additive effects.

Effects of single and double infections with Potato virus X and Tobacco mosaic virus on disease development, plant growth, and virus accumulation in tomato

The tomato cv. Fukuju nº. 2 was used for studying the effect of single and double infections with Potato virus X (PVX) and Tobacco mosaic virus (TMV). Mixed infection resulted in a synergistic increase of disease severity, where more growth reduction was seen with simultaneous inoculations than with sequential inoculations at four-day intervals. At five and 12 days post-inoculation, the increased severity of the disease coincided with enhancement of virus accumulation in the rapidly expanding upper leaves. The PVX concentration in leaves nº 5 to 7 of doubly infected plants was three to six fold that of singly infected ones, as determined by DAS-ELISA. Mixed infection with the L strain led to higher enhancement of PVX than with the TMV-L11A strain. The concentration of TMV-L was lower in double infection and significantly higher than TMV-L11A in both singly and doubly infected plants. Analyses of the PVX ORF2 by Western blot and Northern hybridization revealed the pattern of accumulation of the 25 kDa protein and the RNAs, respectively, following those of the virion and coat protein. The strain TMV-L11A overcame the resistance gene in cv. GCR 237 (Tm-1). In the upper leaf nº. 8, the concentration of PVX was three times higher in plants with mixed infection than with L11A. The concentrations of the L and OM (TMV strains) in both singly and doubly infected plants were at very low levels, and the synergistic effect on PVX concentration and disease severity was not observed.

Effect of organic amendments on sclerotial germination, mycelial growth, and Sclerotium rolfsii-induced diseases

The addition of organic residues to soil is an option to control some soil-borne diseases. Benzaldehyde and powders of kudzu (Pueraria lobata), velvetbean (Mucuna deeringiana), and pine-bark (Pinus elliottii and P. taeda) added to soil could reduce certain soil-borne diseases. This study evaluated the effects of benzaldehyde and the dried powders of kudzu, velvetbean, and pine-bark as soil amendments on germination and formation of sclerotia, on mycelial growth of Sclerotium rolfsii, on plant survival, and disease incidence. The data showed that high amounts of benzaldehyde (0.4 ml kg-1 of soil) and velvetbean (100 g kg-1) inhibited S. rolfsii mycelial growth and sclerotium germination. However, low amounts of benzaldehyde (0.1 ml kg-1), kudzu (25 g kg-1), and pine-bark (25 g kg-1) stimulated mycelial growth and sclerotium germination. Kudzu (25-100 g kg-1) and velvetbean (25-100 g kg-1) inhibited the formation of sclerotia. Nevertheless, benzaldehyde at 0.2 and 0.4 ml kg-1 stimulated the formation of sclerotia. Kudzu (50 and 100 g kg-1) and pine-bark (50 g kg-1) favored the colonization of sclerotia by Trichoderma sp. The numbers of soybean (Glycine max) plants were higher and diseased plants were lower than the non-amend soil in the following treatments: kudzu (50 and 100 g kg-1), velvetbean (50 and 100 g kg-1), and pine-bark (50 g kg-1). Disease severity on tomato (Lycopersicon esculentum) plants was low in soil treated with kudzu or velvetbean (30 and 35 g kg-1) and pine-bark (35 g kg-1). Dried powders of kudzu, velvetbean, or pine-bark added to soil can reduce disease by reducing pathogen inoculum.

The use of fluorescent probes to assess viability of the plant pathogenic bacterium Clavibacter michiganensis subsp. michiganensis by flow cytometry

Determination of the viability of bacteria by the conventional plating technique is a time-consuming process. Methods based on enzyme activity or membrane integrity are much faster and may be good alternatives. Assessment of the viability of suspensions of the plant pathogenic bacterium Clavibacter michiganensis subsp. michiganensis (Cmm) using the fluorescent probes Calcein acetoxy methyl ester (Calcein AM), carboxyfluorescein diacetate (cFDA), and propidium iodide (PI) in combination with flow cytometry was evaluated. Heat-treated and viable (non-treated) Cmm cells labeled with Calcein AM, cFDA, PI, or combinations of Calcein AM and cFDA with PI, could be distinguished based on their fluorescence intensity in flow cytometry analysis. Non-treated cells showed relatively high green fluorescence levels due to staining with either Calcein AM or cFDA, whereas damaged cells (heat-treated) showed high red fluorescence levels due to staining with PI. Flow cytometry also allowed a rapid quantification of viable Cmm cells labeled with Calcein AM or cFDA and heat-treated cells labeled with PI. Therefore, the application of flow cytometry in combination with fluorescent probes appears to be a promising technique for assessing viability of Cmm cells when cells are labeled with Calcein AM or the combination of Calcein AM with PI.

Determination of herbicides residues in soil by small scale extraction

Herbicides such as trifluralin, simazine, atrazine, metribuzin and metolachlor are used in Brazilian agriculture. The efficiency of a small scale method for determination of these herbicides and two degradation products (deisopropylatrazine and deethylatrazine) in soil samples was evaluated. The compounds were extracted from soil samples (5 g) with 20 ml of ethyl acetate in a mechanical shaker for 50 min. Following the extraction, the supernatant was dried through anhydrous sodium sulphate, concentrated and analysed by high resolution gas chromatography (HRGC) with thermionic specific detection (TSD). Mean recoveries obtained from soil samples fortified at three different levels ranged from 81 to 115% with relative standard deviation (RSD) values varying from 1.2 to 12.7%. The method detection limits ranged from 0.01 to 0.06 mg kg-1. The methodology was applied using soil samples from farms located near the town of Araraquara, in the State of São Paulo, Brazil.

Flow injection visible diffuse reflectance quantitative analysis of total sulfur in biodiesel, in plant leaves and in natural waters

Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of total sulfur in the form of sulfate, precipitated in the form of barium sulfate, is presented. The method was applied to biodiesel, to plant leaves and to natural waters analysis. The analytical signal (S) correlates linearly with sulfate concentration (C) between 20 and 120 ppm, through the equation S=-1.138+0.0934 C (r = 0.9993). The experimentally observed limit of detection is about 10 ppm. The mean R.S.D. is about 3.0 %. Real samples containing sulfate were analyzed and the results obtained by the FI and by the reference batch turbidimetric method using the statistical Student's t-test and F-test were compared.