Hyperspectral mapping of the response of grapevine cultivars to Plasmopara viticola infection at the tissue scale.

Resistance of grapevine to Plasmopara viticola is associated with the hypersensitive reaction, accumulation of stilbenoids, and formation of callose depositions. Spectral characterization of infected leaf tissue of cvs 'Regent' and 'Solaris' with resistance genes Rpv 3-1 and Rpv 10 and Rpv 3-3, respectively, suggested that resistance is not dependent on large-scale necrotization of host tissue. Reactions of the resistant cultivars and a reference susceptible to P. viticola were studied using hyperspectral imaging (range 400-1000 nm) at the tissue level and microscopic techniques. Resistance of both cultivars was incomplete and allowed pathogen reproduction. Spectral vegetation indices characterized the host response to pathogen invasion; the vitality of infected and necrotic leaf tissue differed significantly. Resistance depended on local accumulation of polyphenols in response to haustorium formation and was more effective for cv. 'Solaris'. Although hypersensitive reaction of some cells prevented colonization of palisade parenchyma, resistance was not associated with extensive necrotization of tissue, and the biotrophic pathogen survived localized death of penetrated host cells. Hyperspectral imaging was suitable to characterize and differentiate the resistance reactions of grapevine cultivars by mapping of the cellular response to pathogen attack on the tissue level and yields useful information on host-pathogen interactions.

Pathogenesis of Plasmopara viticola Depending on Resistance Mediated by Rpv3_1, and Rpv10 and Rpv3_3, and by the Vitality of Leaf Tissue.

Grapevine cultivars vary in their resistance to Plasmopara viticola, causal agent of downy mildew. Genes from various Vitis species confer pathogen resistance (Rpv), resulting in reduced compatibility of the host-pathogen interaction and partial disease resistance that may become apparent at different stages of pathogenesis. This study describes the pathogenesis of P. viticola on the partially resistant cultivars Regent (Rpv3-1) and Solaris (Rpv3-3, Rpv10) as compared with the susceptible cultivar Mueller-Thurgau using various microscopic techniques, visual disease rating as well as qPCR. Host plant resistance had no effect on the initial steps of pathogenesis outside the host plant cells (zoospore attachment, formation of substomatal vesicle) and became detectable only after the formation of primary haustoria. The restricted compatibility resulted in reductions in haustorium size and in the number of secondary haustoria and was associated with callose depositions around haustoria and stomatal guard cells, collapsed mesophyll cells (hypersensitive reaction), and additional production of an amorphous substance in the intercellular space of cultivar Solaris. Resistance mechanisms reduced the efficiency of P. viticola haustoria and largely restricted tissue colonization to the spongy parenchyma; resistance of cultivar Solaris having thicker leaves was more effective than that of cultivar Regent. Despite of the effects of resistance genes, P. viticola was able to complete its life cycle by forming sporangiophores with sporangia through the stomata on both resistant cultivars indicating partial resistance. Differences in the pathogenesis on detached and attached grapevine leaves highlighted the impact of host tissue vitality on both resistance and susceptibility to the biotrophic pathogen.

Mycotoxins in soil and environment.

Mycotoxins are secondary metabolites produced by specific fungi that have harmful effects on animals and humans. Worldwide more than 300 different mycotoxins are already known, frequently with concentrations in harvest products exceeding acceptable limits. Nevertheless, although these compounds have extensively been studied in food and feed, only little is known about their occurrence and fate in soil and agro-environmental matrices, such as manure, sewage sludge, drainage water and sediments. Therefore, the aim of this review was to (i) resume available methods for quantifying mycotoxins in soil, (ii) describe the occurrence and quantities of mycotoxins in soil and related agro-environmental matrices, and (iii) discuss the environmental fate of these target compounds with specific focus on their leaching potential into groundwater. The safest and most reliable method for mycotoxin quantification relies on mass spectrometry, while the extraction method and solvent composition differ depending on the compound under investigation. Mycotoxin levels detected in soils to date were in the µg range, reaching maximum amounts of 72.1 µg kg-1 for zearalenone, 32.1 µg kg-1 for deoxynivalenol, 23.7 µg kg-1 for ochratoxin A, 6.7 µg kg-1 for nivalenol, and 5.5 µg kg-1 for aflatoxin. Different compartments in the agroecosystem (cereals, corn, rice, water, manure, sewage sludge) each contained at least one mycotoxin. Mycotoxin retention in soils is controlled by texture, with significant adsorption of the compounds to clays but leaching potentials in sandy soils. We did not find any reports detecting mycotoxins in sediments, although there are increasing reports of mycotoxins in freshwater samples. Overall, it appears that soils and sediments are still underrepresented in research on potential environmental contamination with mycotoxins.

Development of a LC-MS/MS Method for the Simultaneous Determination of the Mycotoxins Deoxynivalenol (DON) and Zearalenone (ZEA) in Soil Matrix.

Mycotoxins, toxins of fungal origin, can directly or indirectly contaminate food and feed and are poisonous to livestock and humans. While a large amount is known about their occurrence in crops, food, and feeds, little is known about mycotoxin amounts in soil. However, soil is known as a major fungal habitat and a potential sink for mycotoxins in the environment. Furthermore, there is neither a reliable detection nor an extraction method for mycotoxins testing in different soil textures or for potential deficits due to aging processes. Therefore, the aim of the present study was to present a reliable extraction and detection method for the simultaneous quantification of the most common mycotoxins, deoxynivalenol (DON) and zearalenone (ZEA), via liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method was validated with six different samples with different textures and different soil organic matter (SOM). Deuterated standards were used to overcome possible matrix effects. This extraction method could eliminate potential aging processes. The recovery rate was always >80% for DON and >82% for ZEA. The quantification limits were 1 ng per g soil for DON and 0.5 ng per g soil for ZEA.