No abstract

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.

Resistance of grapevine to Plasmopara viticola is associated to 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 & Rpv 3-3, respectively, suggested that resistance is not depending 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 to 1000 nm) at 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 tissue level and yields useful information on host-pathogen interactions.

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.