Highlights What are the main findings? Hyperspectral imaging is suitable to spectrally separate whitish disease symptoms caused by biotroph pathogens on leaves of apple and grapevine. Plant species, leaf side, variability of symptoms and their interactions are key factors that influence the spectral reflectance of affected tissue and its potential for disease differentiation. What are the implications of the main findings? In remote sensing, spectral similarity of whitish symptoms facilitates disease detection, though it impedes their differentiation. In proximal sensing, more detailed spectral information and higher spatial resolution enable the differentiation of whitish disease symptoms.Highlights What are the main findings? Hyperspectral imaging is suitable to spectrally separate whitish disease symptoms caused by biotroph pathogens on leaves of apple and grapevine. Plant species, leaf side, variability of symptoms and their interactions are key factors that influence the spectral reflectance of affected tissue and its potential for disease differentiation. What are the implications of the main findings? In remote sensing, spectral similarity of whitish symptoms facilitates disease detection, though it impedes their differentiation. In proximal sensing, more detailed spectral information and higher spatial resolution enable the differentiation of whitish disease symptoms.Abstract Diseases like downy mildew (DM) and powdery mildew (PM) are characterized by whitish symptoms on leaves of many plant species. Hyperspectral imaging (HSI) has been successfully used for the detection and identification of various diseases associated with different symptoms. Proximal HSI (400-1000 nm) was tested under controlled conditions for its potential to differentiate among whitish disease symptoms on leaves of apple and grapevine due to DM, PM, and a non-melanized mutant of apple scab at the leaf and tissue (microscopic) level. Spectral traits were analyzed by using difference spectra and spectral ratios, spectral vegetation indices like NDVI, and average brightness and half NIR increase introduced here and were confirmed by supervised spectral angle mapper classification. Although similar, spectral signatures of whitish symptoms were significantly different and could be used for spectral separation of diseases; differences were greater on the tissue level than on the leaf level. However, disease detection and differentiation were affected by spectral differences between plant species, leaf sides, the variability of symptoms in space and time, and the integrity of superficial pathogen structures. In the case of similar disease symptoms, additional spectral information on the effects of pathogens on plant metabolism, e.g., leaf water patterns, supports spectral differentiation of leaf diseases.

Downy mildew, caused by Plasmopara viticola, leads to significant reductions in grape yield and quality. Copper-based compounds are used for control, which can have ecotoxicological impact on the environment. Biocontrol agents and biostimulants show an environmentally-friendly alternative for pesticide reduction. However, understanding of the modes of action is needed to achieve maximum efficacy against pathogens. Previous work has demonstrated the successful application of a synergistic complex of a copper- and chitosan-tolerant Trichoderma isolate and chitosan, resulting in the reduction of downy mildew on grapevine. For a better understanding of the tri-trophic interaction between the synergistic complex, grapevine and P. viticola, the induced resistance by T. koningiopsis and chitosan has to be further characterized. The indirect mode of action of the complex was verified in greenhouse experiments. Moreover, pathogen-related gene expression analysis showed an increased expression in different grapevine cultivars when both agents were applied simultaneously. Similarly, studies of reactive oxygen species accumulation after treatment with agents showed an oxidative burst in resistant cultivars. Since haustoria are a key structure of P. viticola, haustoria number after agent treatment was studied. An inhibitory effect on haustoria formation was observed. This study contributes to a better understanding of the multipurpose properties of the synergistic complex against P. viticola and improves the use of a promising tool with simultaneous copper reduction.

The length of incubation period, i.e., the time between first contact of host and pathogen and the appearance of symptoms, varies among diseases and depends on environmental conditions. Cercospora beticola is the most important fungal pathogen in sugar beet production worldwide, as Cercospora leaf spot (CLS) reduces the leaf area contributing to yield formation. Using sugar beet cultivars differing in CLS resistance, a single infection period of C. beticola resulted in minor differences in the incubation period among host genotypes and among individual plants of cultivars, greater differences among leaves within plants, and substantial variation within individual leaves. Under greenhouse conditions not suitable for secondary infections, the first CLS lesions appeared 10 days after inoculation; however, the number of leaf spots and CLS severity further increased significantly for another 7 to 17 days. A geographic information system approach enabled the tracking of colony appearance and growth of all CLSs on inoculated leaves for up to 27 days. Asymptomatic colonization of leaves was associated with thick hyphae which switched to thin hyphae or melanization after lesion appearance. The lifestyle of C. beticola—intercellular tissue colonization, triggering of necrotic host reaction—is discussed considering the experimental results as well as literature resources.

The water status of plants is affected by abiotic and biotic environmental factors and influences the growth and yield formation of crops. Assessment of the leaf water content (LWC) of grapevine using hyperspectral imaging (1000–2500 nm) was investigated under controlled conditions for its potential to study the effects of the downy mildew pathogen Plasmopara viticola on LWC of host tissue in compatible and incompatible interactions. A calibration curve was established for the relationship between LWC and the Normalized Difference Leaf Water Index (NDLWI1937) that uses spectral information from the water absorption band and NIR for normalization. LWC was significantly lower for abaxial than for adaxial leaf sides, irrespective of grapevine genotype and health status. Reflecting details of leaf anatomy, vascular tissue exhibited effects reverse to intercostal areas. Effects of P. viticola on LWC coincided with the appearance of first sporangia on the abaxial side and increased during further pathogenesis. Continuous water loss ultimately resulted in tissue death, which progressed from the margins into central leaf areas. Tiny spots of brown leaf tissue related to the reaction of partial resistant cultivars could be monitored only at the sensor’s highest spatial resolution. Proximal sensing enabled an unprecedented spatial resolution of leaf water content in host–pathogen interactions and confirmed that resistance reactions may produce a combination of dead and still-living cells that enable the development of biotrophic P. viticola.

Effects of Venturia inaequalis on water relations of apple leaves were studied under controlled conditions without limitation of water supply to elucidate their impact on the non-haustorial biotrophy of this pathogen. Leaf water relations, namely leaf water content and transpiration, were spatially resolved by hyperspectral imaging and thermography; non-imaging techniques-gravimetry, a pressure chamber, and porometry-were used for calibration and validation. Reduced stomatal transpiration 3-4 d after inoculation coincided with a transient increase of water potential. Perforation of the plant cuticle by protruding conidiophores subsequently increased cuticular transpiration even before visible symptoms occurred. With sufficient water supply, cuticular transpiration remained at elevated levels for several weeks. Infections did not affect the leaf water content before scab lesions became visible. Only hyperspectral imaging was suitable to demonstrate that a decreased leaf water content was strictly limited to sites of emerging conidiophores and that cuticle porosity increased with sporulation. Microscopy confirmed marginal cuticle injury; although perforated, it tightly surrounded the base of conidiophores throughout sporulation and restricted water loss. The role of sustained redirection of water flow to the pathogen's hyphae in the subcuticular space above epidermal cells, to facilitate the acquisition and uptake of nutrients by V. inaequalis, is discussed.

Microscopic evidence demonstrated a strictly biotrophic lifestyle of the scab fungus Venturia inaequalis on growing apple leaves and characterised its hemibiotrophy as the combination of biotrophy and saprotrophy not described before. The pathogen–host interface was characterised by the formation of knob-like structures of the fungal stroma appressed to epidermal cells as early as 1 day after host penetration, very thin fan-shaped cells covering large parts of the host cell lumen, and enzymatic cuticle penetration from the subcuticular space limited to the protruding conidiophores. The V. inaequalis cell wall had numerous orifices, facilitating intimate contact with the host tissue. Pathogen-induced modifications of host cells included partial degradation of the cell wall, transition of epidermal cells into transfer cells, modification of epidermal pit fields to manipulate the flow of nutrients and other compounds, and formation of globular protuberances of mesophyll cells without contact with the pathogen. The non-haustorial biotrophy was characterised by enlarged areas of intimate contact with host cells, often mediated by a matrix between the pathogen and plant structures. The new microscopic evidence and information on the pathogens’ biochemistry and secretome from the literature gave rise to a model of the lifestyle of V. inaequalis, lacking a necrotrophic stage that covers and explains its holomorphic development.

Venturia inaequalis is the ascomycetous pathogen causing apple scabs and forms dark-pigmented spores and partially melanised infection structures. Although melanin is considered to be essential for the infection of host tissue, a spontaneously occurring melanin-deficient mutant was isolated from an abaxial side of an apple leaf and can be cultivated in vitro as well as in vivo. The morphology and development of the melanin-deficient-isolate SW01 on leaves of susceptible apple plants were compared to that of the corresponding wild-type isolate HS1. White conidia of SW01 were often wrinkled when dry and significantly increased their volume in suspension. Germination and formation of germtubes and appressoria were not impaired; however, the lack of melanisation of the appressorial ring structure at the interface with the plant cuticle significantly reduced the infection success of SW01. The colonisation of leaf tissue by non-melanised subcuticular hyphae was not affected until the initiation of conidiogenesis. Non-melanised conidiophores penetrated the plant cuticle from inside less successfully than the wild type, and the release of white conidia from less solid conidiophores above the cuticle was less frequent. Melanin in the outer cell wall of V. inaequalis was not required for the survival of conidia under ambient temperature or at −20 °C storage conditions, however, promoted the tolerance of the pathogen to copper and synthetic fungicides affecting the stability and function of the fungal cell wall, plasma membrane, respiration (QoIs) and enzyme secretion, but had no effect on the sensitivity to sulphur and SDHIs. The roles of melanin in different steps of the V. inaequalis life cycle and the epidemiology of apple scabs are discussed.

Plasmopara viticola, causal agent of downy mildew and one of the most severe grapevine diseases, is commonly controlled by multiple fungicide applications, primarily based on copper compounds in organic viticulture. Biostimulants and biocontrol agents could make a major contribution to pesticide reduction. A synergistic biocontrol and biostimulating complex consisting of Trichoderma sp. and chitosan was investigated to achieve copper fungicide reduction in the control of P. viticola. To ensure complex efficacy, the interactions and effects of all agents need to be investigated at the tri-trophic level of grapevine, downy mildew, and biocontrol and biostimulating complex. To guarantee the compatibility of Trichoderma sp. and chitosan, the chitosan tolerance of different copper-tolerant Trichoderma isolates was investigated in mycelial growth and germination tests. A T. koningiopsis isolate proved to be highly chitosan-tolerant was identified for further studies. The timing of spray application with T. koningiopsis and various chitosans was evaluated for efficacy against P. viticola. In the period 0 to 1 day before inoculation with the pathogen, the formation of the sporangia number was significantly reduced by the tested agents. To further describe the mode of action and efficacy of T. koningiopsis and chitosan against P. viticola, the application of single agents on upper and lower grapevine leaves inoculated with the pathogen in comparison to resistance inducers and copper fungicide were tested. Moreover, the combination of T. koningiopsis with different chitosans and a reduced copper rate was investigated on the respective leaf sides of greenhouse plants. Both, a direct and indirect mode of action against downy mildew was demonstrated. Regardless of the treated leaf side, sporulation of downy mildew was clearly inhibited compared to the untreated control. Moreover, microscopic images showed successful establishment of T. koningiopsis and uniform distribution of chitosan on leaves. The tested biocontrol and biostimulating complex might show a promising combatting tool against P. viticola while simultaneously reducing copper rate.

Fungal infections trigger defense or signaling responses in plants, leading to various changes in plant metabolites. The changes in metabolites, for example chlorophyll or flavonoids, have long been detectable using time-consuming destructive analytical methods including high-performance liquid chromatography or photometric determination. Recent plant phenotyping studies have revealed that hyperspectral imaging (HSI) in the UV-range can be used to link spectral changes with changes in plant metabolites. To compare established destructive analytical methods with new non-destructive hyperspectral measurements, the interaction between sugar beet leaves and the pathogens Cercospora beticola, which causes Cercospora leaf spot disease (CLS), and Uromyces betae, which causes sugar beet rust (BR), was investigated. With the help of destructive analyses, we showed that both diseases have different effects on chlorophylls, carotenoids, flavonoids, and several phenols. Non-destructive hyperspectral measurements in the UV-range revealed different effects of CLS and BR on plant metabolites resulting in distinct reflectance patterns. Both diseases resulted in specific spectral changes that allowed differentiation between the two diseases. Machine learning algorithms enabled the differentiation between the symptom classes and recognition of the two sugar beet diseases. Feature importance analysis identified specific wavelengths important to the classification, highlighting the utility of the UV-range. The study demonstrates that HSI in the UV-range is a promising, non-destructive tool to investigate the influence of plant diseases on plant physiology and biochemistry.

The cuticle is a protective layer covering aerial plant organs. We studied the function of waxes for the establishment of the cuticular barrier in barley (Hordeum vulgare). The barley eceriferum mutants cer-za.227 and cer-ye.267 display reduced wax loads, but the genes affected, and the consequences of the wax changes for the barrier function remained unknown. Cuticular waxes and permeabilities were measured in cer-za.227 and cer-ye.267. The mutant loci were isolated by bulked segregant RNA sequencing. New cer-za alleles were generated by genome editing. The CER-ZA protein was characterized after expression in yeast and Arabidopsis cer4-3. Cer-za.227 carries a mutation in HORVU5Hr1G089230 encoding acyl-CoA reductase (FAR1). The cer-ye.267 mutation is located to HORVU4Hr1G063420 encoding β-ketoacyl-CoA synthase (KAS1) and is allelic to cer-zh.54. The amounts of intracuticular waxes were strongly decreased in cer-ye.267. The cuticular water loss and permeability of cer-za.227 were similar to wild-type (WT), but were increased in cer-ye.267. Removal of epicuticular waxes revealed that intracuticular, but not epicuticular waxes are required to regulate cuticular transpiration. The differential decrease in intracuticular waxes between cer-za.227 and cer-ye.267, and the removal of epicuticular waxes indicate that the cuticular barrier function mostly depends on the presence of intracuticular waxes.

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.

The biotrophic basidiomycete Phakopsora pachyrhizi is the causal agent of Asian soybean rust (ASR), which has become a serious soybean disease in South America. Control of this disease is mainly based on fungicide applications, with demethylation inhibitors (DMIs), quinone outside inhibitors (QoIs) and succinate dehydrogenase inhibitors (SDHIs) representing a large market. DMIs have been the key component for ASR-control for many years. This ongoing selection pressure has led to an adaptation of P. pachyrhizi resulting in a continuous shift of the population towards reduced sensitivity. The objective of the present study was to characterize the resistance of P. pachyrhizi to DMIs and the underlying mutations in the target gene (CYP51), using single spore isolates for the first time. The fungal populations from which these isolates were obtained, originated from infected soybean leaves from South America. Sequence analyses of the CYP51-gene confirmed three newly identified mutations (V130A, I145V, F154Y), occurring in one allele in combination with previously described mutations. A total of nine mutations were observed in CYP51 of P. pachyrhizi (F120L, V130A, Y131F/H, K142R, I145V/F, F154Y, I475T), present in different combinations. Their locations in the enzyme were shown by CYP51-protein modeling. The newly identified mutation combinations F120L + V130A + Y131F, F120L + Y131H + I145V and F120L + Y131H + F154Y are associated with different sensitivities to DMIs. The sensitivity studies also demonstrated incomplete cross-resistance of P. pachyrhizi to DMIs caused by different mutation combinations. Furthermore, using an isolate mixture (defined population), it could be shown that different DMIs select different mutation combinations. P. pachyrhizi produces dikaryotic uredospores, and moreover, this study confirmed that each spore contains a total of 6 CYP51-copies.

BACKGROUND Copper-containing fungicides are applied broadly in organic viticulture against downy mildew caused by Plasmopara viticola. Although long-term application of copper-based fungicides is associated with ecotoxic effects on the environment, their use in viticulture is required until sustainable alternatives are available. Trichoderma spp. might be a promising approach to fungicide reduction while promoting plant growth and development and displaying biocontrol activity. This study aims to examine the tolerance and compatibility of Trichoderma spp. to copper fungicides. This work contributes to the development of a spray application consisting of a copper-tolerant Trichoderma sp. combined with a downscaled copper fungicide rate against P. viticola. RESULTS Trichoderma spp. isolated from grapevine wood in vineyards were identified and used for tolerance screening in various concentrations of copper fungicides. Copper hydroxide was identified as being highly compatible with Trichoderma. Two Trichoderma candidates, T. koningiopsis and T. harzianum, showed high copper tolerance in mycelial growth and germination tests, and were adapted to 2.85 g Cu L-1 of the selected fungicide. Microscopic investigations showed the attachment of copper compounds to fungal cell walls and copper uptake within the cytoplasm. In the case of high tolerance, large-scale copper uptake was prevented. CONCLUSION Our findings identified two highly copper-tolerant Trichoderma isolates with natural adaptation to the vineyard ecosystem, which could be further tested as biostimulants and biocontrol agents, combined with a reduced fungicide rate for sustainable plant protection. (c) 2022 Society of Chemical Industry.

The generation of single spore isolates is usually the first approach to characterize plant fungal pathogens with respect to their specific resistance mechanisms to fungicides. The isolation procedure can be time-consuming and can carry the risk of contamination, but for fungal species with saprophytic growth (e.g., Zymoseptoria tritici) it is simple to perform in most cases. However, for biotrophic fungi such as Phakopsora pachyrhizi the situation is more difficult. This may be the reason why all published studies on fungicide resistance mechanisms of this fungus have been conducted with populations or monouredinial isolates. Monouredinial isolates, in contrast to single spore isolates, are generated from several spores of one uredinium, and thus, it is not ensured that these isolates are clones and therefore genetically identical. Since only dikaryotic uredospores of P. pachyrhizi have been found in the field so far, the mechanisms of fungicide resistance are more complex than for other pathogens. Therefore, the use of clones as a tool for further characterization is mandatory. We established a reliable method to generate single spore isolates of P. pachyrhizi and demonstrated that the isolates are clonal. For this verification, single spore isolates were used in detached leaf tests (DLTs) and treated with two demethylation inhibitors (DMIs) with different selection pattern. These isolates had different frequency values of three relevant mutations in CYP51. Additionally, a population was included in the DLT that represented a mixture of isolates with the respective CYP51 mutations under the detection limit (< 5%). In contrast to the population in which target site mutations were selected after DMI treatments in an expected manner, the single spore isolates showed no change in their mutation frequencies on untreated or treated leaves. This indicates that these isolates are genetically identical and thus valuable for further elucidation of the complex resistance mechanisms, especially against DMIs, in this fungal species.

In recent studies, the potential of hyperspectral sensors for the analysis of plant-pathogen interactions was expanded to the ultraviolet range (UV; 200-380 nm) to monitor stress processes in plants. A hyperspectral imaging set-up was established to highlight the influence of early plant-pathogen interactions on secondary plant metabolites. In this study, the plant-pathogen interactions of three different barley lines inoculated with Blumeria graminis f. sp. hordei (Bgh, powdery mildew) were investigated. One susceptible genotype (cv. Ingrid, wild type) and two resistant genotypes (Pallas 01, Mla1- and Mla12-based resistance and Pallas 22, mlo5-based resistance) were used. During the first 5 days after inoculation (dai) the plant reflectance patterns were recorded and plant metabolites relevant in host-pathogen interactions were studied in parallel. Hyperspectral measurements in the UV range revealed that a differentiation between barley genotypes inoculated with Bgh is possible, and distinct reflectance patterns were recorded for each genotype. The extracted and analysed pigments and flavonoids correlated with the spectral data recorded. A classification of noninoculated and inoculated samples with deep learning revealed that a high performance can be achieved with self-attention networks. The subsequent feature importance identified wavelengths as the most important for the classification, and these were linked to pigments and flavonoids. Hyperspectral imaging in the UV range allows the characterization of different resistance reactions, can be linked to changes in secondary plant metabolites, and has the advantage of being a non-invasive method. It therefore enables a greater understanding of plant reactions to biotic stress, as well as resistance reactions.

This work established a hyperspectral library of important foliar diseases of wheat induced by different fungal pathogens, representing a time series from infection to symptom appearance for the purpose of detecting spectral changes. The data were generated under controlled conditions at the leaf scale. The transition from healthy to diseased leaf tissue was assessed, and spectral shifts were identified and used in combination with histological investigations to define developmental stages in pathogenesis for each disease. The spectral signatures of each plant disease that indicate a specific developmental stage during pathogenesis, defined as turning points, were combined into a spectral library. Machine learning analysis methods were applied and compared to test the potential of this library to detect and quantify foliar diseases in hyperspectral images. All evaluated classifiers had high accuracy (≤99%) for the detection and identification of both biotrophic and necrotrophic fungi. The potential of applying spectral analysis methods in combination with a spectral library for the detection and identification of plant diseases is demonstrated. Further evaluation and development of these algorithms should contribute to a robust detection and identification system for plant diseases at different developmental stages and the promotion and development of site-specific management techniques for plant diseases under field conditions.

As biorationals, plant oils offer numerous advantages such as being natural products, with low ecotoxicological side effects, and high biodegradability. In particular, drying glyceride plant oils, which are rich in unsaturated fatty acids, might be promising candidates for a more sustainable approach in the discussion about plant protection and the environment. Based on this, we tested the protective and curative efficacy of an oil-in-water-emulsion preparation using drying plant oils (linseed oil, tung oil) and a semi-drying plant oil (rapeseed oil) separately and in different mixtures. Plant oils were tested in greenhouse experiments (in vivo) on green beans (Phaseolus vulgaris L.) against bean rust (Uromyces appendiculatus). We observed that a 2% oil concentration showed no or very low phytotoxic effects on green beans. Both tested drying oils showed a protective control ranging from 53–100% for linseed oil and 32–100% for tung oil. Longer time intervals of 6 days before inoculation (6dbi) were less effective than shorter intervals of 2dbi. Curative efficacies were lower with a maximum of 51% for both oils when applied 4 days past inoculation (4dpi) with the fungus. Furthermore, the results showed no systemic effects. These results underline the potential of drying plant oils as biorationals in sustainable plant protection strategies.

Previous plant phenotyping studies have focused on the visible (VIS, 400–700 nm), near-infrared (NIR, 700–1000 nm) and short-wave infrared (SWIR, 1000–2500 nm) range. The ultraviolet range (UV, 200–380 nm) has not yet been used in plant phenotyping even though a number of plant molecules like flavones and phenol feature absorption maxima in this range. In this study an imaging UV line scanner in the range of 250–430 nm is introduced to investigate crop plants for plant phenotyping. Observing plants in the UV-range can provide information about important changes of plant substances. To record reliable and reproducible time series results, measurement conditions were defined that exclude phototoxic effects of UV-illumination in the plant tissue. The measurement quality of the UV-camera has been assessed by comparing it to a non-imaging UV-spectrometer by measuring six different plant-based substances. Given the findings of these preliminary studies, an experiment has been defined and performed monitoring the stress response of barley leaves to salt stress. The aim was to visualize the effects of abiotic stress within the UV-range to provide new insights into the stress response of plants. Our study demonstrated the first use of a hyperspectral sensor in the UV-range for stress detection in plant phenotyping.

Waxes are components of the cuticle covering the aerial organs of plants. Accumulation of waxes has previously been associated with protection against water loss, therefore contributing to drought tolerance. However, not much information is known about the function of individual wax components during water deficit. We studied the role of wax ester synthesis during drought. The wax ester load on Arabidopsis leaves and stems was increased during water deficiency. Expression of three genes, WSD1, WSD6 and WSD7 of the wax ester synthase/diacylglycerol acyltransferase (WS/DGAT or WSD) family was induced during drought, salt stress and abscisic acid treatment. WSD1 has previously been identified as the major wax ester synthase of stems. wsd1 mutants have shown reduced wax ester coverage on leaves and stems during normal or drought condition, while wax ester loads of wsd6, wsd7 and of the wsd6wsd7 double mutant were unchanged. The growth and relative water content of wsd1 plants were compromised during drought, while leaf water loss of wsd1 was increased. Enzyme assays with recombinant proteins expressed in insect cells revealed that WSD6 and WSD7 contain wax ester synthase activity, albeit with different substrate specificity compared with WSD1. WSD6 and WSD7 localize to the endoplasmic reticulum (ER)/Golgi. These results demonstrated that WSD1 is involved in the accumulation of wax esters during drought, while WSD6 and WSD7 might play other specific roles in wax ester metabolism during stress.

Hyperspectral imaging has proved its potential for evaluating complex plant-pathogen interactions. However, a closer link of the spectral signatures and genotypic characteristics remains elusive. Here, we show relation between gene expression profiles and specific wavebands from reflectance during three barley-powdery mildew interactions. Significant synergistic effects between the hyperspectral signal and the corresponding gene activities has been shown using the linear discriminant analysis (LDA). Combining the data sets of hyperspectral signatures and gene expression profiles allowed a more precise differentiation of the three investigated barley-Bgh interactions independent from the time after inoculation. This shows significant synergistic effects between the hyperspectral signal and the corresponding gene activities. To analyze this coherency between spectral reflectance and seven different gene expression profiles, relevant wavelength bands and reflectance intensities for each gene were computed using the Relief algorithm. Instancing, xylanase activity was indicated by relevant wavelengths around 710 nm, which are characterized by leaf and cell structures. HvRuBisCO activity underlines relevant wavebands in the green and red range, elucidating the coherency of RuBisCO to the photosynthesis apparatus and in the NIR range due to the influence of RuBisCO on barley leaf cell development. These findings provide the first insights to links between gene expression and spectral reflectance that can be used for an efficient non-invasive phenotyping of plant resistance and enables new insights into plant-pathogen interactions.