Biological control of wheat powdery mildew disease by the termite-associated fungus Aspergillus chevalieri BYST01 and potential role of secondary metabolites

BACKGROUND

Wheat powdery mildew, caused by the biotrophic pathogen Blumeria graminis f. sp. tritici (Bgt) is a serious fungal disease. Natural metabolites produced by microorganisms are beneficial biological control agents to inhibit Bgt. In the present study, we investigated the effects of Aspergillus chevalieri BYST01 on wheat powdery mildew.

RESULTS

A strain isolated from the termite was identified as A. chevalieri BYST01 by morphological characteristics and phylogenetic analysis. The fermentation broth of BYST01 showed good biocontrol effect on the Bgt in vivo with the control efficiencies of 81.59% and 71.34% under the protective and therapeutic tests, respectively. Four known metabolites, including the main compound physcion (30 mg/L), were isolated from the fermentation broth of BYST01 extracted with ethyl acetate. Importantly, under a concentration of 0.1 mM, physcion repressed conidial germination of Bgt with an inhibition rate of 77.04% in vitro and showed important control efficiencies of 80.36% and 74.64% in vivo under the protective and therapeutic tests, respectively. Hence, the BYST01 showed important potential as a microbial cell factory for the high yield of the green natural fungicide physcion. Finally, the biosynthetic gene clusters responsible for physicon production in BYST01 was predicted by analyzing a chromosome-scale genome obtained using a combination of Illumina, PacBio, and Hi-C sequencing technologies.

CONCLUSION

Aspergillus chevalieri BYST01 and its main metabolite physcion had a significant control effect on wheat powdery mildew. The biosynthesis pathway of physcion in BYST01 was predicted. © 2023 Society of Chemical Industry.

Structure-Based Discovery of New Succinate Dehydrogenase Inhibitors via Scaffold Hopping Strategy

Scaffold hopping strategy has become one of the most successful methods in the process of molecular design. Seeking to develop novel succinate dehydrogenase inhibitors (SDHIs), we employed a scaffold hopping strategy to design compounds featuring geminate dichloralkenes (gem-dichloralkenes) fragment. After stepwise modifications, a series of N-cyclopropyl-dichloralkenes-pyrazole-carboxamide derivatives was synthesized. Among them, compounds G28 (IC50 = 26.00 nM) and G40 (IC50 = 27.00 nM) were identified as the best inhibitory activity against porcine SDH, with IC50 values reaching the nanomolar range, outperforming the lead compound pydiflumetofen. Additionally, the greenhouse assay indicated that compounds G37 (EC90 = 0.031 mg/L) and G34 (EC90 = 1.67 mg/L) displayed extremely high activities against wheat powdery mildew (WPM) and cucumber powdery mildew (CPM), respectively. Computational results further revealed that the gem-dichloralkene fragment and fluorine substituted pyrazole form an extra hydrophobic interaction and dipolar-dipolar interaction with SDH. In summary, our study provides a novel gem-dichloralkene scaffold with outstanding fungicidal properties, obtained through scaffold hopping, that holds great potential for future research on PM control.

Haplotype Analysis Sheds Light on the Genetic Evolution of the Powdery Mildew Resistance Locus Pm60 in Triticum Species

Wheat powdery mildew (Blumeria graminis f. sp. tritici, Bgt, recently clarified as B. graminis s. str.), is one of the most destructive diseases of wheat. Pm60 is a nucleotide-binding leucine-rich repeat (NLR) gene that confers race-specific resistance to Bgt. Allelic variants (Pm60, Pm60a, and Pm60b) were found in Triticum urartu and T. dicoccoides, the wild progenitors of wheat. In the present study, we studied the diversity of the Pm60 locus in a large set of wheat germplasm and found 20 tetraploid wheats harboring the Pm60 alleles, which correspond to three novel haplotypes (HapI-HapIII). HapI (Pm60 allele) and HapII (Pm60a allele) were present in domesticated tetraploid wheats, whereas HapIII (Pm60a allele) was identified in wild tetraploid T. araraticum. A sequence comparison of HapII and HapIII revealed that they differed by three SNPs and a GCC deletion. Results of the phylogenetic analysis revealed that HapII was more closely related to the functional haplotype MlIW172. Infection tests showed that HapII-carrying lines display a partial resistance response to Bgt#GH, while HapI was susceptible. Our results provide insights into the genetic evolution of the Pm60 locus and potential valuable alleles for powdery mildew resistance breeding.

Antagonistic Activity and Mechanism of Bacillus subtilis XZ16-1 Suppression of Wheat Powdery Mildew and Growth Promotion of Wheat

Wheat powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most serious wheat diseases in the world. Biological control is considered an environmentally safe approach to control plant diseases. Here, to develop effective biocontrol agents for controlling wheat powdery mildew, antagonistic strain XZ16-1 was isolated and identified as Bacillus subtilis based on the morphological, biochemical, and physiological characteristics and 16S rDNA sequence. The culture filtrate of B. subtilis XZ16-1 and its extracts had a significant inhibitory effect on the spore germination of Bgt. Moreover, the therapeutic and prevention efficacy of the 100% culture filtrate on wheat powdery mildew reached 81.18 and 83.72%, respectively, which was better than that of chemical fungicide triadimefon. Further antimicrobial mechanism analysis showed that the XZ16-1 culture filtrate could inhibit the development of powdery mildew spores by disrupting the cell membrane integrity, causing reductions in the mitochondrial membrane potential, and inducing the accumulation of reactive oxygen species in the spores. Biochemical detection indicated that XZ16-1 could solubilize phosphate, fix nitrogen, and produce hydrolases, lipopeptides, siderophores, and indole-3-acetic acid. Defense-related enzymes activated in wheat seedlings treated with the culture filtrate indicated that disease resistance was induced in wheat to resist pathogens. Furthermore, a 10⁶ CFU/ml suspension of XZ16-1 increased the height, root length, fresh weight, and dry weight of wheat seedlings by 77.13, 63.46, 76.73, and 19.16%, respectively, and showed good growth-promotion properties. This study investigates the antagonistic activity and reveals the action mechanism of XZ16-1, which can provide an effective microbial agent for controlling wheat powdery mildew.

Identification of the powdery mildew resistance gene in wheat breeding line Yannong 99102-06188 via bulked segregant exome capture sequencing

Powdery mildew of wheat (Triticum aestivum), caused by Blumeria graminis f.sp. tritici (Bgt), is a destructive disease that seriously threatens the yield and quality of its host. Identifying resistance genes is the most attractive and effective strategy for developing disease-resistant cultivars and controlling this disease. In this study, a wheat breeding line Yannong 99102-06188 (YN99102), an elite derivative line from the same breeding process as the famous wheat cultivar Yannong 999, showed high resistance to powdery mildew at the whole growth stages. Genetic analysis was carried out using Bgt isolate E09 and a population of YN99102 crossed with a susceptible parent Jinhe 13-205 (JH13-205). The result indicated that a single recessive gene, tentatively designated pmYN99102, conferred seedling resistance to the Bgt isolate E09. Using bulked segregant exome capture sequencing (BSE-Seq), pmYN99102 was physically located to a ~33.7 Mb (691.0-724.7 Mb) interval on the chromosome arm 2BL, and this interval was further locked in a 1.5 cM genetic interval using molecular markers, which was aligned to a 9.0 Mb physical interval (699.2-708.2 Mb). Based on the analysis of physical location, origin, resistant spectrum, and inherited pattern, pmYN99102 differed from those of the reported powdery mildew (Pm) resistance genes on 2BL, suggesting pmYN99102 is most likely a new Pm gene/allele in the targeted interval. To transfer pmYN99102 to different genetic backgrounds using marker-assisted selection (MAS), 18 closely linked markers were tested for their availability in different genetic backgrounds for MAS, and all markers expect for YTU103-97 can be used in MAS for tracking pmYN99102 when it transferred into those susceptible cultivars.

Large-scale mutational analysis of wheat powdery mildew resistance gene Pm21

Wheat powdery mildew is a devastating disease leading to severe yield loss. The powdery mildew resistance gene Pm21, encoding a nucleotide-binding leucine-rich repeat receptor (NLR) protein, confers broad-spectrum resistance to powdery mildew and has great potential for controlling this disease. In this study, a large-scale mutagenesis was conducted on wheat cultivar (cv.) Yangmai 18 carrying Pm21. As a result, a total of 113 independent mutant lines susceptible to powdery mildew were obtained, among which, only one lost the whole Pm21 locus and the other 112 harbored one- (107) or two-base (5) mutations in the encoding region of Pm21. From the 107 susceptible mutants containing one-base change, we found that 25 resulted in premature stop codons leading to truncated proteins and 82 led to amino acid changes involving in 59 functional sites. We determined the mutations per one hundred amino acids (MPHA) indexes of different domains, motifs, and non-domain and non-motif regions of PM21 protein and found that the loss-of-function mutations occurred in a tendentious means. We also observed a new mutation hotspot that was closely linked to RNBS-D motif of the NB-ARC domain and relatively conserved in different NLRs of wheat crops. In addition, we crossed all the susceptible mutants with Yangmai 18 carrying wild-type Pm21, subsequently phenotyped their F₁ plants and revealed that the variant E44K in the coiled-coil (CC) domain could lead to dominant-negative effect. This study revealed key functional sites of PM21 and their distribution characteristics, which would contribute to understanding the relationship of resistance and structure of Pm21-encoded NLR.

Genetically Dissecting the Novel Powdery Mildew Resistance Gene in Wheat Breeding Line PBDH1607

Powdery mildew is one of the most destructive diseases in wheat production. Identifying novel resistance genes and deploying them in new cultivars is the most effective approach to minimize wheat losses caused by powdery mildew. In this study, wheat breeding line PBDH1607 showed high resistance to powdery mildew at both the seedling and adult plant stages. Genetic analysis of the seedling data demonstrated that the resistance was controlled by a single dominant gene, tentatively designated PmPBDH. The ΔSNP index based on bulked segregant RNA sequencing indicated that PmPBDH was associated with an interval of about 30.8 Mb (713.5 to 744.3 Mb) on chromosome arm 4AL. Using newly developed markers, we mapped PmPBDH to a 3.2-cM interval covering 7.1 Mb (719,055,516 to 726,215,121 bp). This interval differed from those of Pm61 (717,963,176 to 719,260,469 bp), MlIW30 (732,769,506 to 732,790,522 bp), and MlNSF10 (729,275,816 to 731,365,462 bp) reported on the same chromosome arm. PmPBDH also differed from Pm61, MlIW30, and MlNSF10 by its response spectrum, origin, or inheritance mode, suggesting that PmPBDH should be a new Pm gene. In the candidate interval, five genes were found to be associated with PmPBDH via time course gene expression analysis, and thus they are candidate genes of PmPBDH. Six closely linked markers, including two kompetitive allele-specific PCR markers, were confirmed to be applicable for tracking PmPBDH in marker-assisted breeding.

The Quantitative Analyses for the Effects of Two Wheat Varieties With Different Resistance Levels on the Fungicide Control Efficacies to Powdery Mildew

Effective strategies to reduce the occurrence of wheat powdery mildew include the use of resistant varieties and application of fungicides. However, most studies rarely focus on the quantitative value of fungicide reduction using resistant varieties. To explore how the fungicides performed on different resistant wheat varieties to powdery mildew, field experiments were conducted during wheat growing seasons in 2018/19 and 2019/20 to investigate the control efficacies of enostroburin⋅epoxiconazole 18% SC and triadimefon 20% EC to wheat powdery mildew on a highly resistant wheat variety ("Baofeng104") and a highly susceptible wheat variety ("Jingshuang16"). The analyses of variance on control efficacies showed that the control efficacies of enostroburin⋅epoxiconazole 18% SC to wheat powdery mildew were mostly significantly higher than triadimefon 20% EC under the same conditions (i.e., varieties, dosages). However, both fungicide and variety resistance made variabilities in the mildew disease index and played a significant role in mildew management. Particularly, the variety resistance made the greatest contribution in mildew-reducing, and the disease index could significantly be reduced on the highly resistant variety even in the absence of fungicide treatment. The control efficacies to mildew on the highly susceptible variety mainly depended on the high efficiency of fungicides whereas the highly resistant variety were mainly by virtue of variety resistance through the comparative analyses of linear regression models. Furthermore, the random-coefficient regression models and quantile models quantificationally expounded that the relationships between active ingredient dosage and disease index or control efficacy varied from the effects of variety, fungicide, and year, particular from variety. Thus, a dosage reference table of enostroburin⋅epoxiconazole 18% SC or triadimefon 20% EC for different resistant wheat varieties were provided; it would be helpful for users to formulate an appropriate dosage of fungicide on mildew management in the field and avoid overusing or superfluous application. Further study needs to consider the effects of fungicide reduction on wheat yields, only then the maximum-economic benefits on mildew management can be determined.

Hyperspectral Monitoring of Powdery Mildew Disease Severity in Wheat Based on Machine Learning

Powdery mildew has a negative impact on wheat growth and restricts yield formation. Therefore, accurate monitoring of the disease is of great significance for the prevention and control of powdery mildew to protect world food security. The canopy spectral reflectance was obtained using a ground feature hyperspectrometer during the flowering and filling periods of wheat, and then the Savitzky-Golay method was used to smooth the measured spectral data, and as original reflectivity (OR). Firstly, the OR was spectrally transformed using the mean centralization (MC), multivariate scattering correction (MSC), and standard normal variate transform (SNV) methods. Secondly, the feature bands of above four transformed spectral data were extracted through a combination of the Competitive Adaptive Reweighted Sampling (CARS) and Successive Projections Algorithm (SPA) algorithms. Finally, partial least square regression (PLSR), support vector regression (SVR), and random forest regression (RFR) were used to construct an optimal monitoring model for wheat powdery mildew disease index (mean disease index, mDI). The results showed that after Pearson correlation, two-band optimization combinations and machine learning method modeling comparisons, the comprehensive performance of the MC spectrum data was the best, and it was a better method for pretreating disease spectrum data. The transformed spectral data combined with the CARS-SPA algorithm was able to extract the characteristic bands more effectively. The number of bands screened was more than the number of bands extracted by the OR data, and the band positions were more evenly distributed. In comparison of different machine learning modeling methods, the RFR model performed the best (coefficient of determination, R ² = 0.741-0.852), while the SVR and PLSR models performed similarly (R ² = 0.733-0.836). Taken together, the estimation accuracy of spectral data transformation using the MC method combined with the RFR model (MC-RFR) was the highest, the model R ² was 0.849-0.852, and the root mean square error (RMSE) and the mean absolute error (MAE) ranged from 2.084 to 2.177 and 1.684 to 1.777, respectively. Compared with the OR combined with the RFR model (OR-RFR), the R ² increased by 14.39%, and the R ² of RMSE and MAE decreased by 23.9 and 27.87%. Also, the monitoring accuracy of flowering stage is better than that of grain filling stage, which is due to the relative stability of canopy structure in flowering stage. It can be seen that without changing the shape of the spectral curve, and that the use of MC to preprocess spectral data, the use of CARS and SPA algorithms to extract characteristic bands, and the use of RFR modeling methods to enhance the synergy between multiple variables, and the established model (MC-CARS-SPA-RFR) can better extract the covariant relationship between the canopy spectrum and the disease, thereby improving the monitoring accuracy of wheat powdery mildew. The research results of this study provide ideas and methods for realizing high-precision remote sensing monitoring of crop disease status.

Introgression of the Powdery Mildew Resistance Genes Pm60 and Pm60b from Triticum urartu to Common Wheat Using Durum as a 'Bridge'

Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici (Bgt), has limited wheat yields in many major wheat-production areas across the world. Introducing resistance genes from wild relatives into cultivated wheat can enrich the genetic resources for disease resistance breeding. The powdery mildew resistance gene Pm60 was first identified in diploid wild wheat Triticum urartu (T. urartu). In this study, we used durum as a ‘bridge’ approach to transfer Pm60 and Pm60b into hexaploid common wheat. Synthetic hexaploid wheat (SHW, AABBA^uA^u), developed by crossing T. urartu (A^uA^u) with durum (AABB), was used for crossing and backcrossing with common wheat. The Pm60 alleles were tracked by molecular markers and the resistance to powdery mildew. From BC₁F₁ backcross populations, eight recombinant types were identified based on five Pm60-flanking markers, which indicated different sizes of the introgressed chromosome segments from T. urartu. Moreover, we have selected two resistance-harboring introgression lines with high self-fertility, which could be easily used in wheat breeding system. Our results showed that the durum was an excellent ‘bridge’ for introducing the target gene from diploid T. urartu into the hexaploid cultivated wheat. Moreover, these introgression lines could be deployed in wheat resistance breeding programs, together with the assistance of the molecular markers for Pm60 alleles.

Silencing of a Wheat Ortholog of Glucan Synthase-Like Gene Reduced Resistance to Blumeria graminis f. sp. tritici

Wheat powdery mildew, caused by the obligate biotrophic ascomycete fungal pathogen Blumeria graminis f. sp. tritici (Bgt), is a major threat to wheat production worldwide. It is known that Arabidopsis thaliana glucan synthase-like 5 (AtGSL5) improves the resistance of wheat to powdery mildew by increasing its anti-penetration abilities. However, the function of glucan synthase-like (GSL) orthologs in crop species remains largely unknown. In this study, TaGSL22, a novel functional ortholog of AtGSL5, was isolated as the only Bgt-induced GSL gene in wheat. Phylogenetic analysis indicated that TaGSL22 was conserved within the group of Gramineae and showed a closer relationship to GSL orthologs from monocots than to those from dicots. The TaGSL22 transcript was highest in the wheat leaves, followed by stems then roots. TaGSL22 was localized in the cell membrane and cytoplasm of wheat protoplasts, as predicted by transmembrane structure analysis. In addition, expression of TaGSL22 was induced by the plant hormones ethylene (ETH) and salicylic acid (SA), but down-regulated by jasmonate (JA) and abscisic acid (ABA). The transcript level of TaGSL22 was up-regulated in the incompatible interaction between Bgt and wheat, whereas it remained relatively unchanged in the compatible interaction. Knocking down of TaGSL22 by virus-induced gene silencing (VIGS) induced a higher infection type in the wheat-Bgt interaction. The TaGSL22-silenced plants exhibited reduced resistance to Bgt, accompanied by decreased callose accumulation. Our study shows a conserved function of GSL genes in plant immunity associated with penetration resistance, and it indicates that TaGSL22 can be used to improve papilla composition and enhance resistance to wheat powdery mildew.

Monitoring Wheat Powdery Mildew Based on Hyperspectral, Thermal Infrared, and RGB Image Data Fusion

Powdery mildew severely affects wheat growth and yield; therefore, its effective monitoring is essential for the prevention and control of the disease and global food security. In the present study, a spectroradiometer and thermal infrared cameras were used to obtain hyperspectral signature and thermal infrared images data, and thermal infrared temperature parameters (TP) and texture features (TF) were extracted from the thermal infrared images and RGB images of wheat with powdery mildew, during the wheat flowering and filling periods. Based on the ten vegetation indices from the hyperspectral data (VI), TF and TP were integrated, and partial least square regression, random forest regression (RFR), and support vector machine regression (SVR) algorithms were used to construct a prediction model for a wheat powdery mildew disease index. According to the results, the prediction accuracy of RFR was higher than in other models, under both single data source modeling and multi-source data modeling; among the three data sources, VI was the most suitable for powdery mildew monitoring, followed by TP, and finally TF. The RFR model had stable performance in multi-source data fusion modeling (VI&TP&TF), and had the optimal estimation performance with 0.872 and 0.862 of R² for calibration and validation, respectively. The application of multi-source data collaborative modeling could improve the accuracy of remote sensing monitoring of wheat powdery mildew, and facilitate the achievement of high-precision remote sensing monitoring of crop disease status.

Diagnostic Kompetitive Allele-Specific PCR Markers of Wheat Broad-Spectrum Powdery Mildew Resistance Genes Pm21, PmV, and Pm12 Developed for High-Throughput Marker-Assisted Selection

Wheat powdery mildew is a devastating disease that seriously threatens yield worldwide. Utilization of host resistance is considered an effective strategy to minimize powdery mildew damage. Pm21, PmV, and Pm12 confer broad-spectrum resistance to wheat powdery mildew in China, of which Pm21 and PmV are allelic genes derived from the 6VS chromosome of Dasypyrum villosum, and Pm12 is derived from the 6SS chromosome of Aegilops speltoides and most likely orthologous to the former two genes. To accurately and efficiently transfer and pyramid these genes using marker-assisted selection (MAS), distinctive single-nucleotide polymorphisms (SNPs) among the exon sequences of Pm21, PmV, and Pm12 and their homologous sequences in the common wheat genome were identified and then used for developing diagnostic Kompetitive Allele-Specific PCR (KASP) markers. The markers were validated in different genotypes including transgenic vectors, transgenic lines, translocation lines, resistance stocks with documented Pm genes, and in multiple susceptible cultivars without Pm genes. As a result, we initially developed a KASP marker that can simultaneously diagnose Pm21, Pm12, and PmV. Subsequently, we obtained a highly diagnostic KASP marker for each of the three genes that could distinguish among the three genes and also accurately distinguish them from other resistant stocks with documented Pm genes and from multiple susceptible genotypes. Compared with previously reported markers, the highly diagnostic KASP markers developed in this study have the advantages of low cost, easy assay, accuracy, and potentially high throughput for MAS.

Development and Molecular Cytogenetic Identification of a New Wheat-Psathyrostachys huashanica Keng Translocation Line Resistant to Powdery Mildew

Psathyrostachys huashanica Keng, a wild relative of common wheat with many desirable traits, is an invaluable source of genetic material for wheat improvement. Few wheat-P. huashanica translocation lines resistant to powdery mildew have been reported. In this study, a wheat-P. huashanica line, E24-3-1-6-2-1, was generated via distant hybridization, ethyl methanesulfonate (EMS) mutagenesis, and backcross breeding. A chromosome karyotype of 2n = 44 was observed at the mitotic stage in E24-3-1-6-2-1. Genomic in situ hybridization (GISH) analysis revealed four translocated chromosomes in E24-3-1-6-2-1, and P. huashanica chromosome-specific marker analysis showed that the alien chromosome fragment was from the P. huashanica 4Ns chromosome. Moreover, fluorescence in situ hybridization (FISH) analysis demonstrated that reciprocal translocation had occurred between the P. huashanica 4Ns chromosome and the wheat 3D chromosome; thus, E24-3-1-6-2-1 carried two translocations: T3DS·3DL-4NsL and T3DL-4NsS. Translocation also occurred between wheat chromosomes 2A and 4A. At the adult stage, E24-3-1-6-2-1 was highly resistant to powdery mildew, caused by prevalent pathotypes in China. Further, the spike length, numbers of fertile spikelets, kernels per spike, thousand-kernel weight, and grain yield of E24-3-1-6-2-1 were significantly higher than those of its wheat parent 7182 and addition line 24-6-3-1. Thus, this translocation line that is highly resistant to powdery mildew and has excellent agronomic traits can be used as a novel promising germplasm for breeding resistant and high-yielding cultivars.

The Regulatory Network of CMPG1-V in Wheat-Blumeria graminis f. sp. tritici Interaction Revealed by Temporal Profiling Using RNA-Seq

Wheat powdery mildew (Pm), caused by Blumeria graminis f. sp. tritici (Bgt), is a prevalent fungal disease. The diploid wheat relative Haynaldia villosa (H. villosa) showed broad-spectrum resistance (BSR) to Pm. A previous study reported an E3 ligase gene, CMPG1-V from H. villosa, showing BSR to Pm. To elucidate the regulatory network mediated by CMPG1-V, in this study, gene expression profiling of CMPG1-V transgenic plant (CMPG1-V_OE) and its receptor Yangmai 158 was analyzed and compared after Bgt inoculation at four infection stages. GO and KEGG analysis revealed obvious reprogramming of SA and ABA signaling, starch/sucrose metabolism, and photosynthesis in CMPG1-V_OE, compared with those in Yangmai 158. Transcripts of SA synthesis genes SARD1 and UGT, signaling factors TGA and PRs, and SnRKs in ABA signaling were specifically upregulated in CMPG1-V_OE rather than Yangmai 158. Transcripts of LHCII in photosynthesis, GLUC and TPP in starch/sucrose metabolism were also induced distinctly in CMPG1-V_OE. WGCNA analysis showed crucial regulatory candidates of CMPG1-V, involving serine/threonine-protein kinase in phosphorylation, glucosyltransferase in flavonoid biosynthesis, defense factor WRKYs, and peroxidase in oxidative stress. Our results facilitate the deciphering of the resistant regulatory network of CMPG1-V and the identification of key candidates which might be employed in breeding programs.

Potential Role of Photosynthesis in the Regulation of Reactive Oxygen Species and Defence Responses to Blumeria graminis f. sp. tritici in Wheat

Photosynthesis is not only a primary generator of reactive oxygen species (ROS) but also a component of plant defence. To determine the relationships among photosynthesis, ROS, and defence responses to powdery mildew in wheat, we compared the responses of the Pm40-expressing wheat line L658 and its susceptible sister line L958 at 0, 6, 12, 24, 48, and 72 h post-inoculation (hpi) with powdery mildew via analyses of transcriptomes, cytology, antioxidant activities, photosynthesis, and chlorophyll fluorescence parameters. The results showed that H₂O₂ accumulation in L658 was significantly greater than that in L958 at 6 and 48 hpi, and the enzymes activity and transcripts expression of peroxidase and catalase were suppressed in L658 compared with L958. In addition, the inhibition of photosynthesis in L658 paralleled the global downregulation of photosynthesis-related genes. Furthermore, the expression of the salicylic acid-related genes non-expressor of pathogenesis related genes 1 (NPR1), pathogenesis-related 1 (PR1), and pathogenesis-related 5 (PR5) was upregulated, while the expression of jasmonic acid- and ethylene-related genes was inhibited in L658 compared with L958. In conclusion, the downregulation of photosynthesis-related genes likely led to a decline in photosynthesis, which may be combined with the inhibition of peroxidase (POD) and catalase (CAT) to generate two stages of H₂O₂ accumulation. The high level of H₂O_2, salicylic acid and PR1 and PR5 in L658 possible initiated the hypersensitive response.

Tritici) Combining Hyperspectral Imaging and an SVM Classifier

Powdery mildew (PM, Blumeria graminis f. sp. tritici) is a devastating disease for wheat growth and production. It is highly meaningful that the disease severities can be objectively and accurately identified by image visualization technology. In this study, an integral method was proposed based on a hyperspectral imaging dataset and machine learning algorithms. The disease severities of wheat leaves infected with PM were quantitatively identified based on hyperspectral images and image segmentation techniques. A technical procedure was proposed to perform the identification and evaluation of leaf-scale wheat PM, specifically including three primary steps of the acquisition and preprocessing of hyperspectral images, the selection of characteristic bands, and model construction. Firstly, three-dimensional reduction algorithms, namely principal component analysis (PCA), random forest (RF), and the successive projections algorithm (SPA), were comparatively used to select the bands that were most sensitive to PM. Then, three diagnosis models were constructed by a support vector machine (SVM), RF, and a probabilistic neural network (PNN). Finally, the best model was selected by comparing the overall accuracies. The results show that the SVM model constructed by PCA dimensionality reduction had the best result, and the classification accuracy reached 93.33% by a cross-validation method. There was an obvious improvement of the identification accuracy with the model, which achieved an 88.00% accuracy derived from the original hyperspectral images. This study can provide a reference for accurately estimating the disease severity of leaf-scale wheat PM and other plant diseases by non-contact measurement technology.

Characterization of the Powdery Mildew Resistance Gene in the Elite Wheat Cultivar Jimai 23 and Its Application in Marker-Assisted Selection

Powdery mildew infection of wheat (Triticum aestivum L.), caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease that threatens yield and quality worldwide. The most effective and preferred means for the control of the disease is to identify broad-spectrum resistance genes for breeding, especially the genes derived from elite cultivars that exhibit desirable agronomic traits. Jimai 23 is a Chinese wheat cultivar with superior agronomic performance, high-quality characteristics, and effective resistance to powdery mildew at all growth stages. Genetic analysis indicated that powdery mildew resistance in Jimai 23 was mediated by a single dominant gene, tentatively designated PmJM23. Using bulked segregant RNA-Seq (BSR-Seq), a series of markers was developed and used to map PmJM23. PmJM23 was then located at the Pm2 locus on the short arm of chromosome 5D (5DS). Resistance spectrum analysis demonstrated that PmJM23 provided a broad resistance spectrum different from that of the documented Pm2 alleles, indicating that PmJM23 is most likely a new allele of Pm2. In view of these combined agronomic, quality, and resistance findings, PmJM23 is expected to be a valuable resistance gene in wheat breeding. To efficiently use PmJM23 in breeding, the closely linked markers of PmJM23 were evaluated and confirmed to be applicable for marker-assisted selection (MAS). Using these markers, a series of resistant breeding lines with high resistance and desirable agronomic performance was selected from the crosses involving PmJM23, resulting in improved powdery mildew resistance of these lines.

Sensitivity of the U.S. Blumeria graminis f. sp. tritici Population to Demethylation Inhibitor Fungicides

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed in the United States with cultivar resistance and foliar fungicides. Despite high levels of fungicide sensitivity in other cereal mildew populations, fungicide sensitivity of U.S. B. graminis f. sp. tritici has never been evaluated. Almost 400 B. graminis f. sp. tritici isolates were collected from 15 U.S. states over 2 years and phenotyped for sensitivity to two widely used demethylation inhibitor (DMI) fungicides, tebuconazole and prothioconazole. A large range of sensitivity to both DMIs was observed, with more insensitive isolates originating from the eastern United States (Great Lakes, Mid-Atlantic, and Southeast regions) and more sensitive isolates from central states (Plains region, Arkansas, and Missouri). Cross-resistance was indicated by a positive although weak association between tebuconazole and prothioconazole sensitivities at all levels of analysis (EC₅₀ values, P < 0.0001). A possible fitness cost was also associated with prothioconazole insensitivity (P = 0.0307) when analyzed at the state population level. This is the first assessment of fungicide sensitivity in the U.S. B. graminis f. sp. tritici population, and it produced evidence of regional selection for reduced DMI efficacy. The observation of reduced sensitivity to DMI fungicides in the eastern United States underlines the importance of rotating between chemistry classes to maintain the effectiveness of DMIs in U.S. wheat production. Although cross-resistance was demonstrated, variability in the relationship of EC₅₀ values for tebuconazole and prothioconazole also suggests that multiple mechanisms influence B. graminis f. sp. tritici isolate responses to these two DMI fungicides.

Field evaluation of an unmanned aerial vehicle (UAV) sprayer: effect of spray volume on deposition and the control of pests and disease in wheat

BACKGROUND

Unmanned aerial vehicles (UAVs) are a recently developed aerial spraying technology. However, the effect of spray volume variation on deposition and pesticide control efficacy is unknown. The effect of three UAV spray volumes (9.0, 16.8 and 28.1 L ha^-1 ) using three different nozzle sizes on droplet deposition and wheat aphid and powdery mildew control efficacy was assessed. An electric air-pressure knapsack (EAP) sprayer was used as a comparison.

RESULTS

Different spray volumes significantly influenced the deposition and control efficacy of the UAV and EAP. For the UAV, a low spray volume of 9.0 L ha^-1 with a fine nozzle (nozzle LU120-01) resulted in lower deposition and control efficacy. Optimal control efficacy was achieved with coarser nozzles (nozzles LU120-02, -03) at > 16.8 L ha^-1 volume with systemic insecticide, and at 28.1 L ha^-1 with contact insecticide and fungicide. For EAP, a high spray volume led to run-off, and a spray volume of 225 L ha^-1 achieved better deposition and control efficacy.

CONCLUSION

The UAV had comparable deposition and efficacy control to the EAP at a higher spray volume (> 16.8 L ha^-1 ) with coarse nozzles, but exhibited inferior deposition and efficacy control at a lower spray volume (<9.0 L ha^-1 ) with fine nozzles. © 2019 Society of Chemical Industry.

[Effects of N application on wheat powdery mildew occurrence, nitrogen accumulation and allocation in intercropping system]

The main objective of this field experiment was to study the effects of wheat and faba bean intercropping on occurrence of wheat powdery mildew, nitrogen content, accumulation and allocation of wheat plant at 4 nitrogen levels of N₀(0 kg·hm^-2), N₁(112.5 kg·hm^-2), N₂(225 kg·hm^-2), N₃(337.5 kg·hm^-2), and to explore the relationship between N content, accumulation, allocation and the occurrence of wheat powdery mildew. The results showed that both monocropped and intercropped wheat yields increased with nitrogen application, with the highest yields of monocropped and intercropped wheat being 4146 kg·hm^-2 and 4679 kg·hm^-2 at N₂ le-vel, respectively. The occurrence and development of wheat powdery mildew become more severe with the increase of N application and area under disease progression curve (AUDPC) were averagely increased by 39.6%-55.6%(calculated with disease incidence, DI) and 92.5%-217.0% (calculated with disease severity index, DSI) with N₁, N₂ and N₃ treatments. The disease severity index was more affected by nitrogen regulation than by disease incidence. The nitrogen content and accumulation of wheat plant were significantly increased by 8.4%-51.6% and 19.7%-133.7% with nitrogen application, but there was no significant effect on N allocation ratio. Compared with monocropped wheat, yield of intercropped wheat was averagely increased by 12%, whereas, the AUDPC(DI) and AUDPC(DSI) of intercropped wheat were averagely decreased by 11.5% and 30.7%, respectively. The control effect of the disease severity index by intercropping was better than disease incidence. The nitrogen content, accumulation and nitrogen allocation ratio in intercropped wheat leaves were significantly decreased by 6.6%-12.5%, 1.4%-6.9% and 9.0%-15.5% respectively at the peak infection stage of powdery mildew. Overall findings showed that the maximum rate of nitrogen application for wheat should not exceed 225 kg·hm^-2 when taking into account both disease control and yield effect.