Powdery Mildew Infection Research Articles

A sense of place: transcriptomics identifies environmental signatures in Cabernet Sauvignon berry skins in the late stages of ripening

BackgroundGrape berry ripening is influenced by climate, the main component of the “terroir” of a place. Light and temperature are major factors in the vineyard that affect berry development and fruit metabolite composition.ResultsTo better understand the effect of “place” on transcript abundance during the late stages of berry ripening, Cabernet Sauvignon berries grown in Bordeaux and Reno were compared at similar sugar levels (19 to 26 °Brix (total soluble solids)). Day temperatures were warmer and night temperatures were cooler in Reno. °Brix was lower in Bordeaux berries compared to Reno at maturity levels considered optimum for harvest. RNA-Seq analysis identified 5528 differentially expressed genes between Bordeaux and Reno grape skins at 22°Brix. Weighted Gene Coexpression Network Analysis for all expressed transcripts for all four °Brix levels measured indicated that the majority (75%) of transcript expression differed significantly between the two locations. Top gene ontology categories for the common transcript sets were translation, photosynthesis, DNA metabolism and catabolism. Top gene ontology categories for the differentially expressed genes at 22°Brix involved response to stimulus, biosynthesis and response to stress. Some differentially expressed genes encoded terpene synthases, cell wall enzymes, kinases, transporters, transcription factors and photoreceptors. Most circadian clock genes had higher transcript abundance in Bordeaux. Bordeaux berries had higher transcript abundance with differentially expressed genes associated with seed dormancy, light, auxin, ethylene signaling, powdery mildew infection, phenylpropanoid, carotenoid and terpenoid metabolism, whereas Reno berries were enriched with differentially expressed genes involved in water deprivation, cold response, ABA signaling and iron homeostasis.ConclusionsTranscript abundance profiles in the berry skins at maturity were highly dynamic. RNA-Seq analysis identified a smaller (25% of total) common core set of ripening genes that appear not to depend on rootstock, vineyard management, plant age, soil and climatic conditions. Much of the gene expression differed between the two locations and could be associated with multiple differences in environmental conditions that may have affected the berries in the two locations; some of these genes may be potentially controlled in different ways by the vinegrower to adjust final berry composition and reach a desired result.

Fungal endophytic communities of two wild Rosa varieties and the role of an endophytic Seimatosporium sp. in enhancing host plant powdery mildew resistance

The aim of the study was to evaluate the possible role of endophytic fungi (EF) on Rosa powdery mildew (PM) resistance. The endophytic fungal communities of two wild Rosa varieties with different PM susceptibilities were investigated through both culture-dependent and independent methods, and the antagonistic activities of endophytes against the PM pathogen were evaluated by pot experiments. There were more OTUs recovered from the PM resistant variety than from the PM susceptible variety. Similarly, the culturable EF from the PM resistant variety (1333 isolates) was more than that from the PM susceptible variety (670 isolates). Consistent with this, the colonization rate of culturable EF of the PM resistant variety was significantly higher than that of the PM susceptible variety at each PM stage (p < 0.05). In addition, it was found that the dominant EF of both varieties were different using culture-dependent and independent methods. The α-diversity of both culturable and un-culturable EF were similar except at the early stage of PM infection. Pot experiments showed that the strain M7SB 41 (Seimatosporium sp.) from PM resistant variety significantly enhanced host plant PM resistance. The results suggested that the endophytic fungal communities of two wild Rosa varieties with different PM susceptibilities were significantly different, and the PM resistant Rosa variety harbored more EF than susceptible Rosa variety, and some EF played an important role in host plant PM resistance.

Powdery mildew (Blumeria graminis f. sp. tritici) infection and amount of key defence chemicals - cyclic hydroxamic acids - of field cultivated wheat (Triticum aestivum L.)

Cultivated wheat varieties have different degrees of resistance against powdery mildew. Cyclic hydroxamic acids are key defence chemicals of wheat. Examinations comprised the measurement of cyclic hydroxamic acid content and powdery mildew infection of three varieties (Lukullus, Lennox, Ispan) and a hybrid (Hystar) of field cultivated wheat, and the effectivity of two biological (Polyversum and Trifender) and one conventional fungicide (Solyom) on powdery mildew. Sample collection and measurement of fungus infection were carried out on three occasions: at BBCH 23-24, BBCH 32-33 and BBCH 77-83 phenological phases. Variety/hybrid and sampling time has significant effect on cyclic hydroxamic acid content, but there was no direct correlation between hydroxamic acid content and powdery mildew infection. Differences were found amongst varieties/hybrid in powdery mildew infection too. Only the hybrid, Hystar, showed considerable infection at every sampling time. The conventional chemical out of fungicides alone proved to be effective, and its effectivity lasted for five weeks.

"Macrobot": An Automated Segmentation-Based System for Powdery Mildew Disease Quantification.

Managing plant diseases is increasingly difficult due to reasons such as intensifying the field production, climatic change-driven expansion of pests, redraw and loss of effectiveness of pesticides, rapid breakdown of the disease resistance in the field, and other factors. The substantial progress in genomics of both plants and pathogens, achieved in the last decades, has the potential to counteract this negative trend, however, only when the genomic data is supported by relevant phenotypic data that allows linking the genomic information to specific traits. We have developed a set of methods and equipment and combined them into a “Macrophenomics facility.” The pipeline has been optimized for the quantification of powdery mildew infection symptoms on wheat and barley, but it can be adapted to other diseases and host plants. The Macrophenomics pipeline scores the visible powdery mildew disease symptoms, typically 5-7 days after inoculation (dai), in a highly automated manner. The system can precisely and reproducibly quantify the percentage of the infected leaf area with a theoretical throughput of up to 10000 individual samples per day, making it appropriate for phenotyping of large germplasm collections and crossing populations.

The dynamics of powdery mildew development on pumpkins

Goal. To determine the spread and development of powdery mildew on pumpkins in the Forest-Steppe of Ukraine.&#x0D; Methods of investigation. The experiments were carried out in 2016—2018 biennium in the Right-Bank Forest Steppe of Ukraine (Khmelnytsky region) on the following varieties: common pumpkins — Ukrainskyi bahatoplidnyi, hull-less — Shtyriiskyi. Assessment of severity and spread of powdery mildew was carried out by conventional methods. The records were taken by visual method at 51, 73 and 89 stages (BBCH scale). Ten plants per plot were selected and spread and severity of the disease in percentage were determined.&#x0D; Results of investigation. During the period of investigation, powdery mildew was observed on the pumpkins of both varieties annually. Its first sympthoms were noted at the 15—17 stage. According to the morphological and biometric features, the pathogen identified as Erysiphe cichoracearum (DC.) V.P. Heluta. In the varieties studied, powdery mildew was found with a non-significant difference in severity and spread. In 2016, the severity of powdery mildew on pumpkins of variety Ukrainskyi bahatoplidnyi varied in the range of 15.4—19.5%, disease spread — 45.1—49.6%, on variety Shtyriiskyi development was 13.3—17.5%, distribution — 46.2—48.1%. In 2017, we obtained the following results: the disease severity for common pumpkins was in the range 13.2—17.4%, disease spread — 42.8—46.7%, for hull-less pumpkins disease severity was 12.2—16.8%, disease spread — 41.7—45.3%. In 2018, severity of powdery mildew was higher than in previous years, accounting for 21.2—26.7% with spread 50.4—55.2% on common pumpkins, and 19.4—25.3% with spread 48.8—54.2% on hull-less pumpkins. The correlation analysis of the data showed that the closest correlation between the spread and the development of the disease was observed with the precipitation and GTC in June.&#x0D; Conclusions. Dynamics of severity of powdery mildew during 2016—2018 years on common and hull-less pumpkins were studied. At stage of full ripening, the maximum rates of spread and severity of the disease were noted, which averaged 49.2—50.5% and 19.9—21.2% over the three years, respectively. No significant difference in the powdery mildew infection between common pumpkins (variety Ukrainskyi bahatoplidnyi) and hull-less pumpkins (variety Shtyriiskyi) was found. The defining conditions for the development of powdery mildew on pumpkins are the weather conditions in June, most notably the presence of increased moisture during this period.

Effect of environmental conditions and phenology in the dispersal of secondary Erysiphe necator conidia in a vineyard

An integrated powdery mildew management strategy to identify the principal moments of secondary Erysiphe necator conidia dispersal in a vineyard based on aerobiological, phenological and meteorological data was developed. An adaptation of the physiological P-days model was conducted to obtain a descriptive equation for the prediction of the advantageous meteorological conditions for Erysiphe necator conidia dispersal in the vineyards of the Ribeiro Designation of Origin area. Moreover, a regression model was developed to predict the conidia concentration as a function of the weather and aerobiological variables with the highest influence on airborne E. necator spores. Additionally, phenological observations were conducted during the vegetative cycle of Vitis vinifera, with the aim to identify the most susceptible phenological stages to powdery mildew infection by relating them with the detected atmospheric spore concentrations. The study was carried out from 2008 to 2018 in an experimental vineyard. The E. necator spores were trapped using a Lanzoni VPPS-2000 sampler and the phenological observations were conducted following the BBCH standardized scale. The highest total fungal spore amount per season in the atmosphere of the vineyard was detected in 2013 with 4828 spores m-3, while the lowest amount was recorded in 2009 with 883 spores m-3. In general, the highest daily airborne spore concentrations were detected during the Flowering (stage 6) or in the previous and next stages, whereas the maximum total spore amount by stage was recorded during Development of Fruits (stage 7). The proposed threshold of P-days for potential secondary infections in the Ribeiro D.O. ranges from 120 to 160 P-days. The combination of aerobiological, phenological and meteorological data provides us a useful tool for the knowledge of the Erysiphe necator conidia dispersal behaviour bringing agricultural practices closer to a sustainable system.

Inferring RPW8-NLRs's evolution patterns in seed plants: case study in Vitis vinifera.

Genomic and transcriptomic studies in plants and, more in deep, in grapevine reveal that the disease-resistance RNL gene family is highly variable. RNLs (RPW8-NLRs) are a phylogenetically distinct class of nucleotide oligomerization domain (NOD)-like receptors (NLRs) identified in plants. Two RNLs, namely, the NRG1 (N Requirement Gene 1) and the ADR1 (Activated Disease Resistance 1), have been characterized; however, little is known about the RNL evolutionary history in higher plants. To trace the diversification of RNL gene subfamily, we scanned the NLR proteins of 73 plant genomes belonging to 29 taxa, revealing a noticeable diversification across species and within the same genus or botanic family together with a conspicuous expansion in important crop species. To explore the RNL variability in Vitis vinifera and gain information with respect to their structure, evolutionary diversification of five grape genomes ('Aglianico', 'Falanghina', 'Sultanina', 'Tannat', and 'Nebbiolo') has been compared to the reference genome ('Pinot Noir'). The number of RNLs ranged from 6 ('Sultanina') to 14 ('Nebbiolo'), in contrast to the 10 'Pinot Noir' RNLs. The phylogenetic study on grapevine RNLs revealed that all collapsed into NRG1-clade, rather than four. To investigate more in depth the means of intraspecific variability of grape RNL copies, a transcriptomic profiling in response to powdery mildew (PM) infection was carried out through qRT-PCRs and public databases interrogation. The RNL expression variability identified in transcriptome data sets supports the hypothesis of a functional expansion/contraction in grapevine varieties. Although no direct correlations between grapevine PM-resistance and RNL expression was identified, our work can provide good candidates for functional studies able to elucidate the putative "helper" role of RNLs in grape immune signalling.

Assessment and selection of source material for creating melon hybrids with integrated resistance to anthracnose and powdery mildew

Relevance. Melon as melon culture is cultivated in many countries of the world and is highly valued for its nutritional and dietary qualities. However, exposure to fungal diseases dramatically reduces the yield and taste of melons. Melon is affected mainly by powdery mildew and Anthracnose. In the conditions of the Bykovskaya melon breeding experimental station, the predominant type of powdery mildew is Sphaerotheca fuliginea. Evaluation and selection of the starting material with the identification of samples with complex resistance to these diseases is an important direction in the selection process, allowing to solve the problem of improving production efficiency and product quality.Methods. The aim of this work is to obtain melon varieties and hybrids with complex resistance to powdery mildew and Anthracnose. Complex stability was determined by artificial infection of melon plants in the phase of 2-3 real leaves by conventional methods.Results. 8 varieties and 10 F 1 hybrids of melon were studied for complex resistance to artificial Anthracnose and powdery mildew infection. Standard grade melon autumn was amazed powdery mildew of 81.2% with score lesion of 1.8 by Anthracnose, respectively, 93.8 per cent if the score is 2.3. The resulting hybrids were superior in stability to the standard. Hybrid x Ethiopian Farmer was amazed powdery mildew on 44% with score of 1.4. The prevalence of hybrid Original x Autumn was 54.4% powdery mildew with a score of 1.4, Anthracnose – 75% with a score of 1.8 (average for three years). The hybrid is fulfilled on economically valuable signs, has stable productivity of 17.5 t/ha, the content of dry substances in fruit juice to 17.2%. The samples and promising hybrids obtained with complex stability will be used in further breeding work.

Protective and Curative Activity of Azoxystrobin and its Mixtures against Powdery Mildew on Squash.

Squash is one of the important crops of the cucurbits family and powdery mildew causes less yield every year, Strobilurin group are common fungicides used to control powdery mildew disease. In addition, Strobilurin is more safe for humans and the environment because it is derived from a natural fungicidal source (the production of the active ingredients are achieved by wood-rotting of Strobilurus tenacellus). Strobilurin contains a group of active ingredients that control various diseases such as powdery and downy mildew on cucumber, grapes, and watermelon, early blight and late blight on tomatoes and potatoes, scab on apple and others. This study focuses on the effectiveness of protective and curative applications of Azoxystrobin as one of the active ingredients of Strobilurin group alone and mixtures against powdery mildew on squash. The induction of resistance of plants against powdery mildew by using KH2PO4 and K2HPO4, protective and curative applications. The tested compounds against powdery mildew on squash at protective method were Azoxystrobin mixture with Difenoconazole 83.3%, Azoxystrobin mixture with Tebuconazole 76.6% , Azoxystrobin alone 70.7% , Difenoconazole 62.3% , Tebuconazole 55.9%, K2HPO4 16.7% and KH2PO4 10.8%. The curative effectiveness of the tested products against powdery mildew on squash was as follows Azoxystrobin mixture with Difenoconazole 69.3% > Azoxystrobin mixture with Tebuconazole 61.2% > Azoxystrobin alone 57.6% > Difenoconazole 44.2% > Tebuconazole 42.7% > K2HPO4 12.1% > KH2PO4 7.4%. Accordingly, Azoxystrobin alone and its mixtures were most effective against powdery mildew on squash compared to Difenoconazole, Tebuconazole, K2HPO4 and KH2PO4 alone in both protective and curative applications. However the protective method was more effective compared to the curative method and the mixture of Azoxystrobin with Difenoconazole was more effective compared to all tested treatments followed by the mixture of Azoxystrobin with Tebuconazole and both treatments were slightly better or comparable to Azoxystrobin alone. In addition, the foliar application by KH2PO4 and K2hPO4 was inferior in activity to resistant powdery mildew infection under the field conditions.

Comparative proteomic analysis of cucumber powdery mildew resistance between a single-segment substitution line and its recurrent parent

Powdery mildew (PM) is considered a major cause of yield losses and reduced quality in cucumber worldwide, but the molecular basis of PM resistance remains poorly understood. A segment substitution line, namely, SSL508-28, was developed with dominant PM resistance in the genetic background of PM-susceptible cucumber inbred line D8. The substituted segment contains 860 genes. An iTRAQ-based comparative proteomic technology was used to map the proteomes of PM-inoculated and untreated (control) D8 and SSL508-28. The number of differentially regulated proteins (DRPs) in SSL508-28 was almost three times higher than that in D8. Fourteen DRPs were located in the substituted segment interval. Comparative gene expression analysis revealed that nodulin-related protein 1 (NRP1) may be a good candidate for PM resistance. Gene Ontology enrichment analysis showed that DRPs functioning in tetrapyrrole biosynthetic process, sulfur metabolic process and cell redox homeostasis were specifically enriched in the resistant line SSL508-28. DRPs categorized in the KEGG term photosynthesis increased in both lines upon PM infection, suggesting that the strategies used by cucumber may be different from those used by other crops to react to PM attacks at the initial stage. The measurement of hydrogen peroxide and superoxide anion production and net photosynthetic rate were consistent with the changes in protein abundance, suggesting that the proteomic results were reliable. There was a poor correlation between DRPs measured by iTRAQ and the corresponding gene expression changes measured by RNA-seq with the same experimental design. Taken together, these findings improve the understanding of the molecular mechanisms underlying the response of cucumber to PM infection.

A Microbial Fermentation Mixture Primes for Resistance Against Powdery Mildew in Wheat.

Since many fungal pathogens develop resistance to fungicides, novel and low-cost alternative methods to improve plant health and fitness need to be developed. An approach to improve productivity in crops is to stimulate the plant’s own defence mechanisms via priming. Therefore, we investigated if a fermentation-based elicitor could prime plant defences against powdery mildew in wheat by inducing the expression of endogenous defence-related genes. Wheat seedlings were spray-treated with a fermentation-based elicitor 8 days prior to inoculation with powdery mildew. Disease assays showed a significantly reduced number of powdery mildew pustules were formed on wheat treated with the mixed elicitor. In vitro sensitivity assays tested the ability of powdery mildew conidia to germinate on agar amended with the fermentation-based product and concluded that fungal germination and differentiation were also inhibited. Tissue samples were taken at time points pertaining to different developmental stages of powdery mildew infection. Significantly higher expression of PR genes (PR1, PR4, PR5, and PR9) was observed in the microbial fermentation mixture-treated plants compared with untreated plants. These genes are often associated with the elicitation of plant defence responses to specific biotrophic pathogens, such as powdery mildew, suggesting an elicitor-mediated response in the wheat plants tested. The product components were assessed, and the components were found to act synergistically in the microbial fermentation mixture. Therefore, this fermentation-based elicitor provides an effective method for powdery mildew control.

A Biostimulant Preparation of Brown Seaweed Ascophyllum nodosum Suppresses Powdery Mildew of Strawberry.

Strawberry, an important fruit crop, is susceptible to a large number of pathogens that reduce fruit quality and productivity. In this study, the effect of a biostimulant prepared from Ascophyllum nodosum extract (ANE) (0.1%, 0.2%, and 0.3%) was evaluated on powdery mildew progression under greenhouse and field conditions. In the greenhouse, application of 0.2% ANE showed maximum reduction in powdery mildew progression as compared to the control. Forty-eight hour post-inoculation, foliar spray of 0.2% ANE reduced spore germination by 75%. Strawberry leaves sprayed with ANE showed higher total phenolic and flavonoid content in response to powdery mildew infection. Furthermore, application of ANE elicited defense response in strawberry plants by induction of defense-related enzymes, such as phenylalanine ammonia lyase, polyphenol oxidase, and peroxidase activity. In field conditions, foliar spray of 0.2% ANE showed a reduction of 37.2% of natural incidence of powdery mildew infection as compared to the control. ANE sprayed plant also reduces the severity of powdery mildew infection under natural conditions. These results indicate that application of ANE induces the strawberry plant’s active defense against powdery mildew infection by induction of secondary metabolism and regulating the activities of defense-related enzymes.

Expression of stilbene synthase VqSTS6 from wild Chinese Vitis quinquangularis in grapevine enhances resveratrol production and powdery mildew resistance.

In grape (Vitis), stilbene phytoalexins can either be in situ synthesized or transported to the site of response during powdery mildew infection, enhancing disease resistance. Resveratrol is a phytoprotective stilbenoid compound that is synthesized by stilbene synthase (STS) in response to biotic and abiotic stresses, and is also known to have health benefits in the human diet. We have previously shown that transgenic Vitis vinifera cv. Thompson Seedless plants overexpressing a stilbene synthase gene, VqSTS6, from wild Chinese Vitis quinquangularis had a higher stilbenoid content, leading to an enhanced resistance to powdery mildew (Uncinula necator (Schw.) Burr). However, the biosynthesis and transportation in the plant tissue under powdery mildew infection are still unclear. Here, inhibitor and micro-grafting technologies were used to study the accumulation of resveratrol following powdery mildew infection. We observed that the levels of STS expression and stilbenoids increased in response to powdery mildew infection. Powdery mildew and inhibitor treatment on detached grape branches showed that resveratrol was in situ synthesized. Experiments with grafted plantlets showed that the abundance of stilbenoid compounds increased in the shoot during VqSTS6 overexpression in the root, while VqSTS6-Flag fusion was not tranported to the scions and only expressedin thetransgenic rootstocks. Compared with wild-type Thompson Seedless plants, the non-transgenic/VqSTS6 transgenic (scion/rootstock) grafted Thompson Seedless plantlets exhibited increased resistance to powdery mildew. In addition, overexpression of VqSTS6 in roots led to increased levels of stilbenoid compounds in five other European grape varieties (V. vinifera cvs. Chardonnay, Perlette, Cabernet Sauvignon, Riesling and Muscat Hamburg). In conclusion, stilbenoid compounds can be either in situ synthesized or transported to the site of powdery mildew infection, and overexpression of VqSTS6 in the root promotes stilbenoids accumulation and disease resistance in European grapevine varieties.

Leveillula lactucae-serriolae on Lactuca serriola in Jordan

Jordan contributes significantly to the Near East plant biodiversity with numerous primitive forms and species of crops and their wild relatives. Prickly lettuce (Lactuca serriola) is a common species in Jordan, where it grows in various habitats. During a survey of wild Lactuca distribution in Jordan in August 2007, plants of L. serriola with natural infections of powdery mildew were observed at a site near Shobak (Ma’an Governorate). Lactuca serriola leaf samples with powdery mildew infections were collected from two plants and the pathogen was analyzed morphologically. Characteristics of the asexual and sexual forms were obtained. Sequence analyses of the rDNA ITS region and D1/D2 domains of the 28S rDNA were used to obtain phylogenetic data, and to reach taxonomic conclusions about these specimens. Molecular determination, performed by sequencing of the ITS region, proved its identity with the type material of Leveillula lactucae-serriolae. Sequencing of the 28S rDNA region provided the first verified GenBank record of Leveillula lactucae-serriolae deposited in this public nucleotide repository. This is the first taxonomically verified record of L. lactucae-serriolae on L. serriola growing wild in Jordan, and one of the first records of the fungus in the Near East.

Grape (Vitis vinifera) VvDOF3 functions as a transcription activator and enhances powdery mildew resistance

DOF proteins are plant-specific transcription factors that play vital roles in plant development and defense responses. However, DOFs have primarily been investigated in model plants, and fairly limited research has been performed on grape (Vitis vinifera). In this study, we isolated and characterized a C2–C2 zinc finger structural DOF gene, VvDOF3, from the grape cultivar Jingxiu. The VvDOF3 protein showed nuclear localization and transcriptional activation ability, indicating that it functions as a transcription factor. The VvDOF3 gene was rapidly induced by exogenous salicylic acid (SA), jasmonic acid (JA), and powdery mildew infection. Overexpression of VvDOF3 in Arabidopsis thaliana enhanced resistance to Golovinomyces cichoracearum. Expression of the SA-responsive defense-related gene PR1 and the concentration of SA were up-regulated in transgenic Arabidopsis plants overexpressing VvDOF3. Together, these data suggest that VvDOF3 functions as a transcription factor in grape and enhances powdery mildew resistance through the SA signaling pathway.

Specific differentially expressed genes in response to powdery mildew infection in Fragaria vesca1

Specific differentially expressed genes in response to powdery mildew infection in Fragaria vesca1

Transcription factors participate in response to powdery mildew infection in Paeonia lactiflora

Herbaceous peony (Paeonia lactiflora Pall.) is a horticulturally important ornamental species that is widely cultivated in China. Biotic stress can strongly affect the quality and seed yield of herbaceous peony. Powdery mildew caused by the fungus Erysiphe polygoni is a serious biotic stress factor resulting in great losses to the peony cultivation industry. Although the molecular mechanisms underlying powdery mildew resistance have been studied extensively in various plant species, little is known about these mechanisms in P. lactiflora. In this study, we investigated the expression patterns of genes, using transcriptome profiling. During the expressed genes, we mainly focused on key TF genes that exhibited at least a log2 fold change ≥5 difference in expression level. The identified TFs genes were most belonged to the Zn-clus, C2H2, and MYB TF families. Furthermore, we examined the expression patterns of transcription factor genes in susceptible and resistant herbaceous peony varieties and identified a set of transcription factor genes that are differentially expressed in leaves in response to powdery mildew infection Based on our result, the MYB TF Pl10128 plays a critical role in defense against powdery mildew in herbaceous peony, and the AP2 TF Pl52977 is a negative regulator in response to powdery mildew of resistant variety ‘Ling Long Yu’. Taken together, this work will contribute the key transcription factors that might enhance plant immunity by controlling the expression of downstream defense-related gene.

Regulation of physiological processes in winter wheat by growth regulators in conditions of powdery mildew infection

An important way of regulating the key units of metabolism in the plant organism under the action of stressors is the use of biologically active substances with regulating properties – plant growth regulators. They affect endogenous regulatory systems, altering key metabolic pathways and thus increasing the plant's sustainability and productive potential in adverse environmental conditions. The aim of the research was to establish the possibility of regulation of physiological processes in winter wheat varieties by exogenous treatment of plants with growth regulators of synthetic (salicylic acid) and natural (Emistim C and Biolan) origin to increase their resistance to the phytopathogen Erysiphe graminis DC f. sp. tritici Em. Marchal , the causative agent of powdery mildew. The intensity of the physiological processes in plants was evaluated by the dynamics of the activity of antioxidant enzymes – ascorbate peroxidase and catalase, the release of ethylene and the integrity of the cell membranes. The objects were selected varieties of soft winter wheat, which were grown in controlled growing conditions against the background of infection by powdery mildew. The treatment of plants was carried out using aqueous salicylic acid solutions in the concentration of 10–5 M (experimentally established by us), Emistim C and Biolan (manufacturer Agrobiotech) in the concentration specified by the manufacturer at the rate of 20 mL/ha, when the development of the disease reached 5% of the total natural background of the infection in the plants during the stages of heading-beginning of flowering. Infection of winter wheat with powdery mildew leads to disruption of cell membrane integrity, increased activity of catalase and ascorbate peroxidase in leaves of the susceptible winter wheat variety. The intensification of ethylene release by leaves of the resistant variety was observed, which was caused by the hypersensitive reaction of the hormone to the effect of stress. The use of plant treatment by growth regulators contributes to maintaining the integrity of membrane structures, adaptive changes in the activity of antioxidant enzymes and regulation of the synthesis of the stress hormone ethylene in both winter wheat varieties under stress. Such changes in the physiological processes induced by plant growth regulators are accompanied by the preservation of the grain productivity of winter wheat and the increase of their resistance to the development of the disease.

Nodulation Induces Systemic Resistance of Medicago truncatula and Pisum sativum Against Erysiphe pisi and Primes for Powdery Mildew-Triggered Salicylic Acid Accumulation.

Plants encounter beneficial and detrimental microorganisms both above- and belowground and the health status of the plant depends on the composition of this pan-microbiome. Beneficial microorganisms contribute to plant nutrition or systemically or locally protect plants against pathogens, thus facilitating adaptation to a variety of environments. Induced systemic resistance, caused by root-associated microbes, manifests as aboveground resistance against necrotrophic pathogens and is mediated by jasmonic acid/ethylene-dependent signaling. By contrast, systemic acquired resistance relies on salicylic acid (SA) signaling and confers resistance against secondary infection by (hemi)biotrophic pathogens. To investigate whether symbiotic rhizobia that are ubiquitously found in natural ecosystems are able to modulate resistance against biotrophs, we tested the impact of preestablished nodulation of Medicago truncatula and pea (Pisum sativum) plants against infection by the powdery mildew fungus Erysiphe pisi. We found that root symbiosis interfered with fungal penetration of M. truncatula and reduced asexual spore formation on pea leaves independently of symbiotic nitrogen fixation. Improved resistance of nodulated plants correlated with elevated levels of free SA and SA-dependent marker gene expression upon powdery mildew infection. Our results suggest that nodulation primes the plants systemically for E. pisi-triggered SA accumulation and defense gene expression, resulting in increased resistance.

First Report of Powdery Mildew of Excoecaria cochinchinensis Caused by Pseudoidium neolycopersici in China

Excoecaria cochinchinensis Lour., a small evergreen shrub in the family Euphorbiaceae, is usually grown as a native ornamental plant in South China. In April 2019, severe powdery mildew infection was observed on E. cochinchinensis in a garden (23.9°N, 113.23°E) in Guangzhou, China. Nearly 60% of the Excoecaria plants were infected, and the foliage of infected plants turned yellow and necrotic, followed by rapid defoliation. Voucher specimens were deposited in the Herbarium of Mycology of Guangdong Institute of Traditional Chinese Medicine under accession number HMGDTCM18. White to gray rounded irregular patches, consisting of abundant mycelia and conidia of the fungus, were found on both leaf surfaces and green stems. Hyphae were septate, branched, and with moderately lobed appressoria. Conidia were solitary, borne on top of conidiophores, and were ellipsoidal, hyaline, 38 to 48 × 13 to 17 μm (mean 42 ± 3 × 15 ± 1 μm, n = 50), containing no distinct fibrosin bodies. Conidiophores were erect, unbranched, consisted of three cells, and 84 to 117 μm long (mean 106 ± 7 μm, n = 50). Chasmothecia were not observed on sample plants. The pathogenicity of this fungus was confirmed by gently pressing infected leaves onto healthy leaves and stems of three healthy seedlings in separate pots, and two noninoculated seedlings were used as a control. After maintaining at 25°C in a greenhouse for 10 days, similar disease symptoms were observed in the inoculated plants, whereas no symptoms developed on control plants. Molecular identification was conducted by extracting genomic DNA from conidia washed from infected leaves and using a Fungal DNA Kit (Omega Bio-tek, Guangzhou, China). The rDNA internal transcribed spacer region was amplified using primers ITS1/ITS4 (Glass and Donaldson 1995). The obtained sequence (GenBank accession no. MK811439) analysis by BLASTN search showed>99% similarity with Pseudoidium neolycopersici (GenBank accession nos. LC009912.1 and AB032484.1). On the basis of the morphological and molecular analyses, the fungus was identified as P. neolycopersici (Kiss et al. 2001). This pathogen has only been reported on Codiaeum variegatum, a euphorbiaceous host (Liu et al. 2015). To our knowledge, this is the first report of this fungus infecting Excoecaria. In addition, P. neolycopersici has been reported on tomato, papaya, and Physalis pubescens in China. Therefore, powdery mildew infection on E. cochinchinensis not only poses a potential threat to health and beauty of this ornamental plant but may also serve as a reservoir of the pathogen that could allow spread to other economically important hosts.