Powdery Mildew Pathogen Research Articles

Occurrence and epidemiological consequences of Erysiphe neolycopersici on tomato plants in Mauritius

Leveillula taurica has until recently been believed to be the causal pathogen of powdery mildew of tomatoes in Mauritius. However, in the year 2022, another powdery mildew species was detected on tomatoes under culture in various tomato growing localities of the island. Based on morphological comparison and molecular analysis, its identity was confirmed as Erysiphe neolycopersici (anam. Pseudoidium neolycopersici). This species has a worldwide distribution causing severe epidemics mainly on greenhouse tomatoes. There is evidence of the rapid spread of this pathogen during 2022–2023 causing serious infection of all tomato cultivars in greenhouse culture in Mauritius. The origin of these infections and its epidemiological consequences are discussed.

A fungal plant pathogen overcomes mlo-mediated broad-spectrum disease resistance by rapid gene loss.

Hosts and pathogens typically engage in a coevolutionary arms race. This also applies to phytopathogenic powdery mildew fungi, which can rapidly overcome plant resistance and perform host jumps. Using experimental evolution, we show that the powdery mildew pathogen Blumeria hordei is capable of breaking the agriculturally important broad-spectrum resistance conditioned by barley loss-of-function mlo mutants. Partial mlo virulence of evolved B. hordei isolates is correlated with a distinctive pattern of adaptive mutations, including small-sized (c. 8-40 kb) deletions, of which one is linked to the de novo insertion of a transposable element. Occurrence of the mutations is associated with a transcriptional induction of effector protein-encoding genes that is absent in mlo-avirulent isolates on mlo mutant plants. The detected mutational spectrum comprises the same loci in at least two independently isolated mlo-virulent isolates, indicating convergent multigenic evolution. The mutational events emerged in part early (within the first five asexual generations) during experimental evolution, likely generating a founder population in which incipient mlo virulence was later stabilized by additional events. This work highlights the rapid dynamic genome evolution of an obligate biotrophic plant pathogen with a transposon-enriched genome.

Fine mapping and identification of candidate genes associated with powdery mildew resistance in melon (Cucumis melo L.).

Powdery mildew (PM), a common disease of many major crop species, including melon (Cucumis melo L.), affects plant growth and fruit quality and seriously reduces production. Using a combined morphological and molecular approach, we attribute the PM pathogen that naturally occurs in melon to Podosphaera xanthii, and specifically to physiological race 1. An investigation into the genetic basis of PM resistance in melon using the resistant accession 'PI 164637' and susceptible counterpart 'HDZ' reveals dominant inheritance of PM resistance at the seedling stage, supported by F2 and backcross population segregation ratios. Adult plant assessments indicate a major gene with an additive effect for PM resistance. Bulk segregant analysis coupled with high-throughput sequencing identified a significant quantitative trait locus on chromosome 6 that is associated with PM resistance. Genetic mapping narrowed down the candidate region to 63.5kb using InDel molecular markers, harboring 12 candidate genes. The marker chr06_indel_5 047 127 demonstrated high accuracy in screening PM resistance in an F2 segregating population and 30 inbred lines as natural populations. Functional annotation and expression analysis of candidate genes revealed that MYB transcription factor MELO3C006700, GATA transcription factor MELO3C028829 and heparanase-like protein MELO3C006697 are promising candidate genes for PM resistance in melon. The genetic architecture underlying this resistance in melon offers valuable insights for breeding programs, and the identified markers, especially chr06_indel_5 047 127, may enable practical applications for marker-assisted selection in developing PM-resistant melon varieties.

Powdery mildew pathogen [Erysiphe necator (Schw.) Burrill.] induced physiological and biochemical alterations in leaf tissue of grapevines (Vitis spp.)

Grapevine serves as a host for an array of pathogenic agents, among which powdery mildew (PM), a fungal disease, stands as a major threat under changing climate and erratic weather patterns. The study aimed to examine the physiological, biochemical responses and microscopic examinations of diverse grapevine genotypes including the 42 Vitis species to powdery mildew infection caused by Erysiphe necator (Schw.) Burrill. Significant reductions were observed in leaf gas exchange parameters like net photosynthetic rate (33.09 %) and transpiration rate (32.36 %) in the infected leaves of susceptible genotypes compared to resistant and moderate genotype groups. Susceptible genotypes had higher intercellular CO2 concentration (4.01 %). Chlorophyll fluorescence analysis revealed a decrease in the maximum quantum efficiency of photosystem-II in PM-infected leaves across the genotype groups. Furthermore, PM infection led to a decrease in chlorophyll content, particularly in susceptible plants, along with a notable reduction in total chlorophyll (25.86 %) and total carotenoids (3.58 %) contents. The ascorbic acid/dehydroascorbic ascorbic acid ratio was observed to be increased by 50 % in the susceptible genotypes due to PM infection. The higher potassium content was registered in healthy leaves of resistant genotypes compared to PM infection stage. This clearly demonstrated the genotype-specific ability to withstand biotic stress. Antioxidant enzyme activities, including glutathione reductase (1.27-fold), polyphenol oxidase (1.15-fold), phenylalanine ammonia-lyase (1.02-fold) and peroxidase (1.21-fold), were enhanced in PM infected plants, suggesting the activation of different defence mechanisms against oxidative stress induced due to pathogen. Scanning electron microscopy revealed prominent differences in fungal hyphae growth between susceptible and resistant genotypes, which showed restricted tissue growth and host cell necrosis.

Identification and characterization of the causal agent of powdery mildew on native salmonberry and thimbleberry plants in British Columbia

Salmonberry (Rubus spectabilis) and thimbleberry (Rubus nutkanus) are important native berry plants for Indigenous communities and restoration sites in the coastal region of British Columbia (BC). Compared to cultivated berry plants, information on the diseases impacting native berry plant species is limited. In late August 2022, powdery mildew symptoms and signs were observed on field plots of salmonberry and thimbleberry plants at the Agassiz Research and Development Centre, BC. The disease symptoms progressed until the end of September. The morphology of conidiophores and conidia when examined under a compound and scanning electron microscope showed they matched with those of Podosphaera aphanis. DNA from diseased foliage was subjected to PCR amplification with primers representing the internal transcribed spacer (ITS) region of rDNA followed by sequencing. The corresponding sequences from both hosts showed >99% similarity to P. aphanis in GenBank and grouped with several accessions of P. aphanis following phylogenetic analysis. In artificially inoculated trials conducted in the greenhouse, powdery mildew symptoms developed within 3−4 weeks post-inoculation and P. aphanis isolates from salmonberry and thimbleberry were cross-pathogenic to each host. To our knowledge, this is the first study characterizing the powdery mildew pathogen infecting salmonberry and thimbleberry and demonstrating cross-pathogenicity to both hosts. The outcomes from this study provide insight into the biology of the powdery mildew pathogen infecting native Rubus spp.

Morphological and molecular characterization of Neoerysiphe galeopsidis causing powdery mildew on Lagopsis supina in central China

Lagopsis supina (Xia Zhi Cao) is a widely distributed and cultivated herbal plant that has been extensively used as a traditional Chinese medicine, Tibetan medicine and Mongolian medicine for disease treatments for centuries. While the bioactive compounds of L. supina are extensively studied, the fungal pathogens of this plant are still obscure. In 2021, powdery mildew signs and symptoms were observed on leaves of L. supina in Xinxiang City, Henan Province, China. However, the causal pathogen had not been identified. Therefore, morphological characteristics and molecular analysis was applied to identify the powdery mildew pathogen. The sequence of the internal transcribed spacer (ITS) region of the fungus was obtained and showed 99.83% identity with the previously reported Neoerysiphe galeopsidis. The virulence of this phytopathogen on L. supina was confirmed by utilizing Koch’s postulates. Therefore, we identified the causal pathogen as N. galeopsidis. Based on biological and molecular characterization, this is the first comprehensive report of powdery mildew caused by N. galeopsidis on L. supina in central China. The occurrence of powdery mildew disease on L. supina may detract from the plant’s medical and ornamental value. The identification and confirmation of N. galeopsidis on L. supina expands the knowledge of this causal agent and will support efforts towards future control and management of powdery mildews.

Evaluation of the genotypes of the Kazakh-Siberian nursery (KASIB) in the conditions of the Novosibirsk region

The paper presents the results of evaluation of the KASIB-22 nursery soft wheat samples resistance to the main wheat pathogens. The research material was 44 wheat samples obtained from different regions of Russia and Kazakhstan within the framework of the KASIB shuttle breeding program (A.I. Barayev Research and Production Centre for Grain Farming, Omsk State Agrarian University, ICiG SB RAS, Karabalyk AES, Karaganda AES, North-Kazakhstan AES, FSBSI "Omsk ASC", HE SAU of the Northern Trans-Urals, Aktyubinsk AES, Kurgan Research Institute of Agriculture, Pavlodar AES, agrokomplex "Kurgansemena", Samara Research Institute of Agriculture, Chelyabinsk Research Institute of Agriculture). The following breeding lines were identified as highly productive and possessing high and medium resistance to brown rust, powdery mildew and loose smut: Line Pt-311 (Kurgan Research Institute of Agriculture), Lutescens 1462, Lutescens 1486, Line1616ae14 (Samara Research Institute of Agriculture), Lutescens 1356 (ICiG SB RAS). The yield of the selected samples averaged 42.1–51.2 c/ha. Genotypes Novosibirskaya 41, Line 435/12 and Lutescens 1364 are of interest for selection for quality. The gluten content of the nursery genotypes ranged from 24.1 (Line 23/07 in 2022) to 38.0% (variety Astana 2 in 2021), protein ranged from 13.4 (variety Tertia in 2022) to 19.5% (Lutescens 1364 in 2022). Each of the selected lines is of practical value for breeding, and the samples from the KASIB-22 nursery allow to expand the genetic diversity of spring soft wheat by selecting the most resistant forms to local populations of powdery mildew, leaf rust and loose smut pathogens.

First Report of Powdery Mildew caused by Erysiphe astragali on Sphaerophysa salsula.

Sphaerophysa salsula (Pall.) DC., also known as Yang Liao Pao, belongs to the Leguminosae family and is the only existing species in the Sphaerophysa genus. S. salsula is tolerance to cold, high salt, and alkaline soil, it is widely cultivated in China as a forage crop, and used as a Chinese folk medicine to treat hypertension (Ma et al., 2002). In 2023, signs and symptoms similar to powdery mildew were found on S. salsula planted in Tumd left (40.515°N, 110.424°E), Baotou City, Inner Mongolia Autonomous Region, China. The white powdery substance covered 90% of the leaf area, and the infected plants showed weak growth and senescence. More than 80% of plants (n=200) had these powdery mildew-like symptoms. Hyphal appressoria are solitary, conidiophores have few branches and septa. Conidia are cylindrical to clavate, 25-32 μm long and 8-15 μm wide (n=30), conidia form single subapical germ tubes, straight to curved-sinuous, with swollen apex or distinctly lobed conidial appressorium. Based on these morphological characteristics, the fungus was tentatively identified as an Erysiphe sp. (Schmidt and Braun 2020). Fungal structures were isolated from diseased leaves, and genomic DNA of the pathogen was extracted using the method described by Zhu et al. (2022). The internal transcribed spacer (ITS) region was amplified by PCR using the primers PMITS1/PMITS2 (Cunnington et al. 2003) and the amplicon sequenced by Invitrogen (Shanghai, China). The powdery mildew strain, named as KMD (GenBank accession no.: PP267067), showed an identity of 100% (645/645bp) with Erysiphe astragali, a powdery mildew reported on Astragalus glycyphyllos in Golestan, Iran (GenBank: OP806834) and identity of 99.6% (643/645bp) with Erysiphe astragali (GenBank: MW142495), a powdery mildew reported on A. scaberrimus in Inner Mongolia, China (Sun et al. 2023). Pathogenicity tests were conducted by brushing the conidia from infected S. salsula leaves onto leaves of four healthy plants, while four control plants were brushed in the same manner. All the treated plants were placed in separate growth chambers maintained at 19°C and 65% humidity, with a 16 h light/8 h dark photoperiod. Nine days after inoculation, the treated plants showed powdery mildew symptoms, while the control plants remained asymptomatic. The same results were obtained for two repeated pathogenicity experiments. The powdery mildew fungus was reisolated and identified as E. astragali based on morphological and molecular analysis, thereby fulfilling Koch's postulates. No report on the occurrence of powdery mildew on S. salsula plants has been found previously. The occurrence of this destructive powdery mildew may adversely affect the cultivation of S. salsula. Identifying the pathogen of powdery mildew will support future efforts to control and manage powdery mildew on S. salsula.

First Report of Powdery Mildew on Berchemia floribunda Caused by Erysiphe berchemiae in China.

The genus Berchemia (family Rhamnaceae), a group of climbing plants, is mainly distributed in Asia, Africa, and South America. Berchemia plants are widely used in traditional medicine in some Asian countries (Inoshiri et al. 1987). For example, in Japan, B. racemosa (synonym B. floribunda) is used for the treatment of gallstones, liver diseases, neuralgia, and stomach cramps, and in China, B. floribunda is used for the treatment of rheumatism and lumbago. In August 2022, typical powdery mildew symptoms were observed on wild B. floribunda plants in Huaxi District, Guiyang, Guizhou Province, China. The incidence was approximately 60% among 100 B. floribunda plants observed outdoors. White colonies almost entirely covered on both adaxial and abaxial surfaces of all leaves on symptomatic plants. Infected leaves appeared curled or chlorotic, infection occasionally leading to defoliation. To describe the pathogen morphologically, fungal samples were collected from two individual B. floribunda plants and microscopically characterized. In these samples, hyphae were flexuous to straight, branched, septate, 3-6 μm wide, with lobed hyphal appressoria. Conidiophores were erect, flexuous to straight, and 50-160 µm long (n = 30). Foot cells were subcylindrical to slightly curved-sinuous at the base, 20-40 µm long (n = 30), followed by 2-3 shorter cells. Conidia formed singly, occasionally 2-3 in a chain. Conidia were ellipsoid to ovoid, 20-42 × 12-18 µm (n = 50), without fibrosin bodies. Chasmothecia were not found. For molecular identification, the ribosomal DNA internal transcribed spacers (ITSs) of the two fungal samples were amplified and sequenced using the ITS1/ITS4 primer pair (White et al. 1990). The obtained 649-bp ITS sequences (GenBank accession nos. OR414364 and OR414365, respectively) shared 100% identity, and they showed 99.52% identity with the ITS sequence (GenBank accession no. LC009934) of Erysiphe berchemiae. Phylogenetic analysis grouped OR414364 and OR414365 in a clade with LC009934. Based on morphological and molecular characteristics, the powdery mildew fungus from B. floribunda was identified as E. berchemiae (Braun and Cook 2012). The voucher specimen (accession no. GZNU-BFEE/0820/2022) were deposited at the School of Life Sciences, Guizhou Normal University. Pathogenicity was assessed by gently pressing naturally diseased leaves of B. floribunda onto leaves of three healthy potted 1-year-old B. floribunda plants. Three non-inoculated healthy plants were used as controls. The plants were incubated in a greenhouse at 25 ± 2°C, 80% relative humidity. Similar powdery mildew symptoms were observed on the inoculated plants 9 days after inoculation, whereas the control plants remained symptomless. The reisolated fungus from inoculated leaves was morphologically identical to that observed on the original diseased leaves, and the ITS sequence of the reisolated fungus shared 100% identity with OR414364 and OR414365, fulfilling Koch's postulates. E. berchemiae has previously been described as a powdery mildew pathogen on B. yunnanensis (Chen et al. 1987) and B. kulingensis (Chen 1993) in China and B. racemosa (synonym B. floribunda) in Japan (Braun and Cook 2012; Takamatsu et al. 2015), but this is the first report of E. berchemiae causing disease of B. floribunda in China. This work suggests that E. berchemiae is an important pathogen of Berchemia plants, at least for some species in the genus Berchemia.

Effects of microclimate on disease prevalence across an urbanization gradient.

Increased temperatures associated with urbanization (the "urban heat island" effect) have been shown to impact a wide range of traits across diverse taxa. At the same time, climatic conditions vary at fine spatial scales within habitats due to factors including shade from shrubs, trees, and built structures. Patches of shade may function as microclimate refugia that allow species to occur in habitats where high temperatures and/or exposure to ultraviolet radiation would otherwise be prohibitive. However, the importance of shaded microhabitats for interactions between species across urbanized landscapes remains poorly understood. Weedy plants and their foliar pathogens are a tractable system for studying how multiple scales of climatic variation influence infection prevalence. Powdery mildew pathogens are particularly well suited to this work, as these fungi can be visibly diagnosed on leaf surfaces. We studied the effects of shaded microclimates on rates of powdery mildew infection on Plantago host species in (1) "pandemic pivot" surveys in which undergraduate students recorded shade and infection status of thousands of plants along road verges in urban and suburban residential neighborhoods, (2) monthly surveys of plant populations in 22 parks along an urbanization gradient, and (3) a manipulative field experiment directly testing the effects of shade on the growth and transmission of powdery mildew. Together, our field survey results show strong positive effects of shade on mildew infection in wild Plantago populations across urban, suburban, and rural habitats. Our experiment suggests that this relationship is causal, where microclimate conditions associated with shade promote pathogen growth. Overall, infection prevalence increased with urbanization despite a negative association between urbanization and tree cover at the landscape scale. These findings highlight the importance of taking microclimate heterogeneity into account when establishing links between macroclimate or land use context and prevalence of disease.

Deciphering the Genomic Landscape and Virulence Mechanisms of the Wheat Powdery Mildew Pathogen Blumeria graminis f. sp. tritici Wtn1: Insights from Integrated Genome Assembly and Conidial Transcriptomics.

A high-quality genome sequence from an Indian isolate of Blumeria graminis f. sp. tritici Wtn1, a persistent threat in wheat farming, was obtained using a hybrid method. The assembly of over 9.24 million DNA-sequence reads resulted in 93 contigs, totaling a 140.61 Mb genome size, potentially encoding 8480 genes. Notably, more than 73.80% of the genome, spanning approximately 102.14 Mb, comprises retro-elements, LTR elements, and P elements, influencing evolution and adaptation significantly. The phylogenomic analysis placed B. graminis f. sp. tritici Wtn1 in a distinct monocot-infecting clade. A total of 583 tRNA anticodon sequences were identified from the whole genome of the native virulent strain B. graminis f. sp. tritici, which comprises distinct genome features with high counts of tRNA anticodons for leucine (70), cysteine (61), alanine (58), and arginine (45), with only two stop codons (Opal and Ochre) present and the absence of the Amber stop codon. Comparative InterProScan analysis unveiled "shared and unique" proteins in B. graminis f. sp. tritici Wtn1. Identified were 7707 protein-encoding genes, annotated to different categories such as 805 effectors, 156 CAZymes, 6102 orthologous proteins, and 3180 distinct protein families (PFAMs). Among the effectors, genes like Avra10, Avrk1, Bcg-7, BEC1005, CSEP0105, CSEP0162, BEC1016, BEC1040, and HopI1 closely linked to pathogenesis and virulence were recognized. Transcriptome analysis highlighted abundant proteins associated with RNA processing and modification, post-translational modification, protein turnover, chaperones, and signal transduction. Examining the Environmental Information Processing Pathways in B. graminis f. sp. tritici Wtn1 revealed 393 genes across 33 signal transduction pathways. The key pathways included yeast MAPK signaling (53 genes), mTOR signaling (38 genes), PI3K-Akt signaling (23 genes), and AMPK signaling (21 genes). Additionally, pathways like FoxO, Phosphatidylinositol, the two-component system, and Ras signaling showed significant gene representation, each with 15-16 genes, key SNPs, and Indels in specific chromosomes highlighting their relevance to environmental responses and pathotype evolution. The SNP and InDel analysis resulted in about 3.56 million variants, including 3.45 million SNPs, 5050 insertions, and 5651 deletions within the whole genome of B. graminis f. sp. tritici Wtn1. These comprehensive genome and transcriptome datasets serve as crucial resources for understanding the pathogenicity, virulence effectors, retro-elements, and evolutionary origins of B. graminis f. sp. tritici Wtn1, aiding in developing robust strategies for the effective management of wheat powdery mildew.

Occurrence of Powdery Mildew Caused by Erysiphe corylacearum on Hazelnuts in Israel

Hazelnut (Corylus avellana L) is an emerging crop in Israel, primarily cultivated as a host plant to establish truffle plantations through symbiosis with ectomycorrhizal fungi. A significant damage and yield reduction is caused by the prevalent occurrence of powdery mildew in hazelnut trees (Sezer et al., 2017). Until recently, Phyllactinia guttata was considered the primary pathogen in Western Asia, the Caucasus region, and Europe (Abasova et al. 2018; Arzanlou et al. 2018; Mezzalama et al. 2021). However, in the last years, a new destructive species Erysiphe corylacearum has been identified as the pathogen of powdery mildew on hazelnuts in these regions (Meparishvili et al. 2019; Mezzalama et al. 2021; Kalmár et al. 2022; Zajc et al. 2023). In May 2022, powdery mildew symptoms were observed on hazelnut plants in the Ein-Zivan truffle plantation, gardens of Merom-Golan, and the adjacent garden of the packing house Pri-Beresheet in the northern Golan region of Israel. Symptoms were observed on the abaxial and adaxial leaf surfaces, fruits, and husks. Disease incidence and severity ranged between 30-70% and 5-90%, respectively. Disease severity was significantly greater on the leaves of the offshoots compared to those on the tree canopy. Morphological characterization of leaf samples from ten different trees showed the following characteristics: hyphal appressoria were lobed, solitary, 1–4 μm in diameter; mycelium was amphigenous, hyaline, and septate; conidiophores vertically elevated from the mycelium 50– 80 μm long. Conidia (n= 30) on conidiophores were hyaline, ellipsoid to ovoid, 24 – 34 μm long and 15.5 – 23 μm wide. Chasmothecia in several maturation degrees appeared in October on both sides of the leaves. They were spherical (n= 30) 86 – 125 μm in diameter, with 7 - 14 aseptate straight appendages, 67 - 96 μm long, 4.9 - 7.1 μm wide, dichotomous branched at the end 42 - 56 μm wide. In each chasmothecia, there were 3-5 asci (n=30) with a width of 38 – 43 μm and a length of 48–64 μm of oval-ellipsoid shape. Asci contained 4-8 ascospores (n=30), 18 - 26 μm long and 11 - 15.5 μm wide. A pathogenicity test was conducted to fulfill Koсh’s postulates. Both detached leaves and plants of C. avellana were artificially infected by brushing conidia from infected leaves. Inoculated leaves in Petri dishes on 2% water agar (n= 5), and plants (n= 5) were incubated under 25°C and 12-h photoperiod/day. Untreated leaves and plants served as control. Typical symptoms appeared on the upper surface of the leaves within 7-10 days after inoculation. No symptoms were found on untreated control plants or detached leaves. The fungus isolated from the inoculated leaves was morphologically identical to the original isolates from natural diseased plants. DNA was extracted and the rDNA internal transcribed spacer region of five isolates originated from leaves of the tree canopy and offshoots was amplified using primers ITS1 and ITS4, and sequenced. BLAST analysis of 595 bp fragments (all identical and represented by isolate Cora1, GenBank Accession No. OR752437) showed 99% identity to ITS rDNA sequences of E. corylacearum from Georgia (MK157199) and 100% identity to isolates from Azerbaijan, Turkey and Italy (LC270863, KY082910 and MW045425, respectively) and only 83% similarity to P. guttata (accession number AB080558). To the best of my knowledge this is the first report on E. corylacearum causing powdery mildew in Israel. Future control measures to manage the disease on hazelnuts in truffle plantations in Israel should be considered.

High-Copy Transposons from a Pathogen Give Rise to a Conserved sRNA Family with a Novel Host Immunity Target.

Small RNAs (sRNAs) are involved in gene silencing in multiple ways, including through cross-kingdom transfers from parasites to their hosts. Little is known about the evolutionary mechanisms enabling eukaryotic microbes to evolve functional mimics of host small regulatory RNAs. Here, we describe the identification and functional characterization of SINE_sRNA1, an sRNA family derived from highly abundant short interspersed nuclear element (SINE) retrotransposons in the genome of the wheat powdery mildew pathogen. SINE_sRNA1 is encoded by a sequence motif that is conserved in multiple SINE families and corresponds to a functional plant microRNA (miRNA) mimic targeting Tae_AP1, a wheat gene encoding an aspartic protease only found in monocots. Tae_AP1 has a novel function enhancing both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), thereby contributing to the cross activation of plant defenses. We conclude that SINE_sRNA1 and Tae_AP1 are functional innovations, suggesting the contribution of transposons to the evolutionary arms race between a parasite and its host. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A diverse panel of 755 bread wheat accessions harbors untapped genetic diversity in landraces and reveals novel genetic regions conferring powdery mildew resistance

Key message A bread wheat panel reveals rich genetic diversity in Turkish, Pakistani and Iranian landraces and novel resistance loci to diverse powdery mildew isolates via subsetting approaches in association studies.Wheat breeding for disease resistance relies on the availability and use of diverse genetic resources. More than 800,000 wheat accessions are globally conserved in gene banks, but they are mostly uncharacterized for the presence of resistance genes and their potential for agriculture. Based on the selective reduction of previously assembled collections for allele mining for disease resistance, we assembled a trait-customized panel of 755 geographically diverse bread wheat accessions with a focus on landraces, called the LandracePLUS panel. Population structure analysis of this panel based on the TaBW35K SNP array revealed an increased genetic diversity compared to 632 landraces genotyped in an earlier study and 17 high-quality sequenced wheat accessions. The additional genetic diversity found here mostly originated from Turkish, Iranian and Pakistani landraces. We characterized the LandracePLUS panel for resistance to ten diverse isolates of the fungal pathogen powdery mildew. Performing genome-wide association studies and dividing the panel further by a targeted subsetting approach for accessions of distinct geographical origin, we detected several known and already cloned genes, including the Pm2a gene. In addition, we identified 22 putatively novel powdery mildew resistance loci that represent useful sources for resistance breeding and for research on the mildew-wheat pathosystem. Our study shows the value of assembling trait-customized collections and utilizing a diverse range of pathogen races to detect novel loci. It further highlights the importance of integrating landraces of different geographical origins into future diversity studies.

Bioactive carbohydrate from potato peels: A sweet inducer that mediate resistance against powdery mildew disease of cucumber through phytohormonal alterations

Large volumes of nutritive wastes are generated by food industries, which can be used in the production of bioactive compounds of commercial values. The waste generated by potato chips industries contains high quantities of insoluble starch, high concentrations of total suspended solids and chemical oxygen demand, or environmental issues. In this study, the starch extracted from the potato peels was subjected to bioconversion of isomaltose-oligosaccharide by enzymatic method and further eluted isomatlose by liquid chromatography-mass spectrometry. The structural elucidation of isomaltose was confirmed by 1H NMR and 13C NMR spectroscopy. The purified isomaltose displayed excellent in vitro antifungal action against Erysiphe cichoracearum and Fusarium oxysporum at concentrations 1.0 and 2.5 mg/ml, respectively. Notably, cucumber-seeds primed with isomaltose (2.5 and 5.0 mg/mL) concentrations recorded a significant improvement of germination (91.5 and 89 %) and vigor (2210.93 and 2015.7) over the untreated control. Subsequently, the isomaltose-primed cucumber plants challenged with powdery mildew pathogen showed enhanced protection of 63% in comparison with pathogen alone-induced plants. This enhanced growth parameters and induced resistance in cucumber may be fairly contributed by the upregulation of phytohormone levels in primed plants observed in this study. Taken together, this study is unique in the use of bioactive isomaltose from potato peels, which could enable us to minimize the agro-industrial wastes and most importantly could help to develop new formulations for sustainable crop protection strategies.

Taxonomy, Phylogeny, and Host Expansion of Powdery Mildew Fungi Parasitic to Veronica Species

Powdery mildew is a prevalent fungal disease that affects various Veronica spp. (Plantaginaceae), caused by species in the genera Podosphaera and Golovinomyces (Erysiphales). There have been recent taxonomic changes in these groups and ongoing disease occurrence on a range of Veronica species previously unrecognized as hosts; however, the pathogen found in Korea remains unidentified. This study aimed to identify the causative agent of powdery mildew on Veronica spp. in Korea through molecular phylogenetic analysis of internal transcribed spacer (ITS) and large subunit (LSU) sequences of rDNA and morphological examination. Our study identified Golovinomyces bolayi as the sole pathogen affecting all nine Veronica species in Korea and confirmed that G. cichoracearum s. str., which was previously identified as the pathogen, was not the causal agent. These results expand the known host range of G. bolayi, including the addition of five Veronica species in Korea: V. hederifolia, V. kiusiana var. glabrifolia, V. longifolia, V. polita, and V. serpyllifolia. Notably, V. kiusiana has been added as a new global host of powdery mildew. These findings substantially enhance our understanding of the taxonomy of powdery mildew pathogens on Veronica species and provide valuable insights into their evolutionary host expansion.

Multiplex gene editing reveals cucumber MILDEW RESISTANCE LOCUS O family roles in powdery mildew resistance.

Powdery mildew (PM) is one of the most widespread and prevalent diseases that affects a wide range of crops. In cucumber (Cucumis sativus L.), previous forward genetic studies have identified MILDEW RESISTANCE LOCUS O 8 (CsMLO8) as necessary but alone insufficient for cucumber PM resistance (PMR) and suggested the involvement of other members of the CsMLO family. However, the function of other CsMLO family members in cucumber remains largely unknown. Here, we developed a highly efficient multiplex gene editing system in cucumber to generate a series of Csmlo mutants from all the 13 family members. Systematic analysis of these mutants revealed growth effects of these CsMLO family members on development and PMR. Importantly, we obtained the Csmlo1/8/11 triple mutant with complete resistance to PM. Transcriptome and proteome analysis of PM-resistant Csmlo mutants suggested that the kinesin-like calmodulin-binding protein (KCBP)-interacting Ca2+-binding protein (CsKIC), calmodulin-like protein 28 (CsCML28), and Ca2+-dependent protein kinase 11 (CsCPK11)-mediated calcium signaling pathway is involved in PMR. CsMLO8 interacted directly with CsKIC, and the simultaneous silencing of both genes resulted in a phenotype that resembled the silencing of CsKIC alone. Silencing CsCML28 and CsCPK11 increased susceptibility to PM, whereas overexpressing CsCPK11 through genetic transformation enhanced cucumber's PMR, demonstrating their positive regulatory roles in PMR. Given the importance of PMR for cucurbit crops, this research provides unprecedented insights into the function of the proteins encoded by the CsMLO gene family as well as the plant defense response to PM pathogen.

AEGILOPS AS A SOURCE OF TRAITS FOR RESISTANCE AGAINST MAJOR FOLIAR PATHOGENS FOR THE BREEDING OF WINTER SOFT WHEAT

The article presents the results of research on the resistance to foliar diseases of individual species of the genus Aegilops and amphidiploids, whose parental forms are the genera Aegilops and Triticum. A comparison of plants from the genus Aegilops and Triticum aestivum species for resistance to powdery mildew, leaf septoria, and brown rust pathogens was conducted. The study was carried out during the 2021/2022–2022/2023 growing seasons at the collection nursery of the Institute of Agriculture of the National Academy of Agrarian Sciences of Ukraine. The assessment of resistance was conducted using commonly accepted methodologies, with calculations of the significance coefficient of deviation of resistance indicators. As a result, it was found that some species and amphidiploids exhibited higher resistance compared to T. aestivum, indicating the potential of the genus Aegilops in enhancing the genetic diversity and resistance of soft wheat to powdery mildew, septoria leaf spon, and brown rust. Certain species and amphidiploids were identified as promising sources of resistance to the pathogens of the studied diseases, which could contribute to their utilization in breeding programs aimed at improving yield and reducing losses from foliar disease infections. The conclusions of the study open up new possibilities for breeding programs in agriculture and promote further research in this direction.

Breeding value and homeostaticity of the spike performance and its constituents in medium tall winter bread wheat (Triticum aestivum L.) accessions in relation to resistance to the pathogens of powdery mildew (Blumeria graminis (DC.)...

Identification of sources of group resistance in winter bread to the pathogens B. graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal and S. tritici Rob. et Desm. and of high performance of the spike and its constituents is a necessary and relevant step towards the creation of comprehensively valuable and adaptable genotypes. The paper presents the results of evaluation of the breeding value and homeostaticity of the spike performance and its constituents in medium tall winter bread wheat in relation to resistance to powdery mildew and Septoria leaf blotch. New sources of consistently high group resistance to the powdery mildew and Septoria leaf blotch pathogens have been identified: Kyivska 17, Zorianka, Sicheslava, and Svitiaz (UKR). We have selected accessions with high performance of the spike and its constituents in combination with high breeding value and homeostaticity of these characteristics: the kernel weight per spike (Kyivska 17 (Sc = 1.8; Hom = 21.9) (UKR)); the kernel number per spike (Svitohliad (Sc = 37.8; Hom = 554.1), Stritenska (Sc = 36.4; Hom = 452.5), Svitiaz (Sc = 35.8; Hom = 451.8), MIP Lada (Sc = 33.6; Hom = 572.7) (UKR), and Manella (Sc = 33.1; Hom = 460.8) (NLD)); and the thousand kernel weight (Kyivska 17 (Sc = 42.9; Hom = 1053.7), Sicheslava (Sc = 42.6; Hom = 873.2) (UKR), and Turanus (Sc = 41.3; Hom = 707.5) (AUT)). It was found that the percentage of accessions with high homeostaticity of the thousand kernel weight, the kernel number per spike and the kernel weight per spike was 63.6%, 31.8%, and 22.7%, respectively. In the medium tall winter bread wheat accessions, there were strong positive correlations between the breeding value of the kernel weight per spike and resistance to Septoria leaf blotch (r = 0.77, P < 0.01) and between the kernel number per spike and resistance to powdery mildew (r = 0.71, P < 0.01). Significant positive correlations were observed between the breeding value of the thousand kernel weight and resistance to Septoria leaf blotch (r = 0.61, P < 0.01), between the homeostaticity of the thousand kernel weight and resistance to Septoria leaf blotch (r = 0.51, P < 0.01) and between the breeding value of the kernel number per spike and resistance to Septoria leaf blotch (r = 0.56, P < 0.01). The selected sources of high group resistance to powdery mildew and Septoria leaf blotch, high performance of the spike and its constituents in combination with the breeding value and homeostaticity of these traits are valuable starting materials to create highly promising winter bread wheat cultivars, which would be adaptable to limiting biotic factors.

CsPM5.2, a phosphate transporter protein-like gene, promotes powdery mildew resistance in cucumber.

Powdery mildew (PM) is one of the most serious fungal diseases affecting cucumbers (Cucumis sativus L.). The mechanism of PM resistance in cucumber is intricate and remains fragmentary as it is controlled by several genes. In this study, we detected the major-effect Quantitative Trait Locus (QTL), PM5.2, involved in PM resistance by QTL mapping. Through fine mapping, the dominant PM resistance gene, CsPM5.2, was cloned and its function was confirmed by transgenic complementation and natural variation identification. In cultivar 9930, a dysfunctional CsPM5.2 mutant resulted from a single nucleotide polymorphism in the coding region and endowed susceptibility to PM. CsPM5.2 encodes a phosphate transporter-like protein PHO1; H3. The expression of CsPM5.2 is ubiquitous and induced by the PM pathogen. In cucumber, both CsPM5.2 and Cspm5.1 (Csmlo1) are required for PM resistance. Transcriptome analysis suggested that the salicylic acid (SA) pathway may play an important role in CsPM5.2-mediated PM resistance. Our findings help parse the mechanisms of PM resistance and provide strategies for breeding PM-resistant cucumber cultivars.