Identification of the gene Pm47 on chromosome 7BS conferring resistance to powdery mildew in the Chinese wheat landrace Hongyanglazi

Genetic basis of an elite wheat cultivar Guinong 29 with harmonious improvement between multiple diseases resistance and other comprehensive traits

Fungal diseases, such as powdery mildew and rusts, significantly affect the quality and yield of wheat. Pyramiding diverse types of resistance genes into cultivars represents the preferred strategy to combat these diseases. Moreover, achieving collaborative improvement between diseases resistance, abiotic stress, quality, and agronomic and yield traits is difficult in genetic breeding. In this study, the wheat cultivar, Guinong 29 (GN29), showed high resistance to powdery mildew and stripe rust at both seedling and adult plant stages, and was susceptible to leaf rust at the seedling stage but slow resistance at the adult-plant stage. Meanwhile, it has elite agronomic and yield traits, indicating promising coordination ability among multiple diseases resistance and other key breeding traits. To determine the genetic basis of these elite traits, GN29 was tested with 113 molecular markers for 98 genes associated with diseases resistance, stress tolerance, quality, and adaptability. The results indicated that two powdery mildew resistance (Pm) genes, Pm2 and Pm21, confirmed the outstanding resistance to powdery mildew through genetic analysis, marker detection, genomic in situ hybridization (GISH), non-denaturing fluorescence in situ hybridization (ND-FISH), and homology-based cloning; the stripe rust resistance (Yr) gene Yr26 and leaf rust resistance (Lr) genes Lr1 and Lr46 conferred the stripe rust and slow leaf rust resistance in GN29, respectively. Meanwhile, GN29 carries dwarfing genes Rht-B1b and Rht-D1a, vernalization genes vrn-A1, vrn-B1, vrn-D1, and vrn-B3, which were consistent with the phenotypic traits in dwarf characteristic and semi-winter property; carries genes Dreb1 and Ta-CRT for stress tolerance to drought, salinity, low temperature, and abscisic acid (ABA), suggesting that GN29 may also have elite stress-tolerance ability; and carries two low-molecular-weight glutenin subunit genes Glu-B3b and Glu-B3bef which contributed to high baking quality. This study not only elucidated the genetic basis of the elite traits in GN29 but also verified the capability for harmonious improvement in both multiple diseases resistance and other comprehensive traits, offering valuable information for breeding breakthrough-resistant cultivars.

QTL Mapping of Adult Plant Resistance to Powdery Mildew in Chinese Wheat Landrace Baidatou

Wheat powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating diseases affecting wheat throughout the world. Breeding and growing resistant wheat cultivars is one of the most economic and effective methods to control the disease, and as such, identifying and mapping the new and effective resistance genes is critical. Baidatou, a Chinese wheat landrace, shows excellent field resistance to powdery mildew. To identify the resistance gene(s) in Baidatou, 170 F7:8 recombinant inbred lines (RILs) derived from the cross Mingxian 169/Baidatou were evaluated for powdery mildew response at the adult-plant stage in the experimental fields in Yangling (YL) of Shaanxi Province and Tianshui (TS) in Gansu Province in 2019, 2020, and 2021. The relative area under disease progress curve (rAUDPC) of Mingxian 169/Baidatou F7:8 RILs indicated that the resistance of Baidatou to powdery mildew was controlled by quantitative trait loci (QTLs). Based on bulk segregation analysis combined with the 660K single nucleotide polymorphism (SNP) array and genotyping by target sequencing (16K SNP) of the entire RIL population, two QTLs, QPmbdt.nwafu-2AS and QPmbdt.nwafu-3AS, were identified, and these accounted for up to 44.5% of the phenotypic variation. One of the QTLs was located on the 3.32 cM genetic interval on wheat chromosome 2AS between the kompetitive allele-specific PCR markers AX-111012288 and AX_174233809, and another was located on the 9.6 cM genetic interval on chromosome 3AS between the SNP markers 3A_684044820 and 3A_686681822. These markers could be useful for successful breeding of powdery mildew resistance in wheat.

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.

Fine mapping of powdery mildew resistance gene PmXNM in a Chinese wheat landrace Xiaonanmai

KEY MESSAGE

Powdery mildew resistance gene PmXNM, originated from the Chinese wheat landrace Xiaonanmai, was delimited to a 300.7-kb interval enriched with resistance genes. Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a globally devastating disease threatening the yield and quality of wheat worldwide. The use of broad-spectrum disease resistance genes from wheat landraces is an effective strategy to prevent this pathogen. Chinese wheat landrace Xiaonanmai (XNM) was immune to 23 tested Bgt isolates at the seedling stage. The F1, F2, and F2:4 progenies derived from the cross between XNM and Chinese Spring (CS) were used in this study. Genetic analysis revealed that powdery mildew resistance in XNM was controlled by a single dominant gene, temporarily designated PmXNM. Bulked segregant analysis and molecular mapping delimited PmXNM to the distal terminal region of chromosome 4AL flanked by markers caps213923 and kasp511718. The region carrying the PmXNM locus was approximately 300.7 kb and contained nine high-confidence genes according to the reference genome sequence of CS. Five of these genes, annotated as disease resistance RPP13-like proteins 1, were clustered in the target region. Haplotype analysis using the candidate gene-specific markers indicated that the majority of 267 common wheat accessions (75.3%) exhibited extensive gene losses at the PmXNM locus, as confirmed by aligning the targeted genome sequences of CS with those of other sequenced wheat cultivars. Seven candidate gene-specific markers have proven effective for marker-assisted introgression of PmXNM into modern elite cultivars.

Genetic Analysis and Molecular Identification of the Powdery Mildew Resistance in 116 Elite Wheat Cultivars/Lines

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease worldwide. Host resistance is the preferred method for limiting the disease epidemic, protecting the environment, and minimizing economic losses. In the present study, the reactions to powdery mildew for a collection of 600 wheat cultivars and breeding lines from different wheat-growing regions were tested using the Bgt isolate E09. Next, 116 resistant genotypes were identified and then crossed with susceptible wheat cultivars/lines to produce segregating populations for genetic analysis. Among them, 87, 19, and 10 genotypes displayed single, dual, and multiple genic inheritance, respectively. To identify the Pm gene(s) in those resistant genotypes, 16 molecular markers for 13 documented Pm genes were used to test the resistant and susceptible parents and their segregating populations. Of the 87 wheat genotypes that fitted the monogenic inheritance, 75 carried the Pm2a allele. Three, two, one, and two genotypes carried Pm21, Pm6, Pm4, and the recessive genes pm6 and pm42, respectively. Four genotypes did not carry any of the tested genes, suggesting that they might have other uncharacterized or new genes. The other 29 wheat cultivars/lines carried two or more of the tested Pm genes and/or other untested genes, including Pm2, Pm5, Pm6, and/or pm42. It was obvious that Pm2 was widely used in wheat production, whereas Pm1, Pm24, Pm33, Pm34, Pm35, Pm45, and Pm47 were not detected in any of these resistant wheat genotypes. This study clarified the genetic basis of the powdery mildew resistance of these wheat cultivars/lines to provide information for their rational utilization in different wheat-growing regions. Moreover, some wheat genotypes which may have novel Pm gene(s) were mined to enrich the diversity of resistance source.

Field response and molecular screening of European wheat germplasm against powdery mildew at the Himalayan region of Pakistan

Wheat powdery mildew possesses a significant threat to wheat crops not only on a global scale but also in the northern region of Pakistan. Recognizing the need for effective measures, the exploration and utilization of exotic germplasm take on critical importance. To address this, a series of trials were made to investigate the response of 30 European (EU) lines, in addition to the local checks (Siran, Atta-Habib (AH) and Ghanimat-e-IBGE) against wheat powdery mildew at the Himalayan region of Pakistan. The study involved field testing from 2018 to 2022 across multiple locations, resulting in 38 different environments (location × year). In addition to field evaluations, molecular genotyping was also performed. The disease was absent on the tested lines during 2018, 2019, and 2020 whereas it ranged from 0 to 100% at Chitral location during 2021, where 100% was observed only for one EU wheat line "Matrix." The disease prevailed only at Gilgit location (0-60% for EU wheat line "F236") and at Nagar location (0-10% for EU wheat lines Substance and Nelson) during the disease season of 2022. Most of the EU wheat lines showed very low ACI values, due to an overall low disease pressure. Matrix showed the maximum ACI (1.54) followed by Ritter (1.25) and Bli_autrichion (0.87), whereas the minimum (0.1) was for Substance, JB_Asano, and KWS_Loft followed by Canon (0.19), all exhibiting partial resistance. The molecular marker-based screening revealed that Pm38 was the most prevalent and detected in 100% of wheat lines followed by Pm39 (60%) and Pm8 (30%). Six wheat lines (20%) possessed all three Pm genes (Pm8, Pm38, and Pm39) concurrently. The variability observed in this study can be utilized in future breeding efforts aimed at developing resistant wheat varieties.

Genome-Wide Association Study Reveals Novel Powdery Mildew Resistance Loci in Bread Wheat

Powdery mildew (PM), caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt), significantly threatens global bread wheat production. Although the use of resistant cultivars is an effective strategy for managing PM, currently available wheat cultivars lack sufficient levels of resistance. To tackle this challenge, we conducted a comprehensive genome-wide association study (GWAS) using a diverse panel of 286 bread wheat genotypes. Over three consecutive years (2020-2021, 2021-2022, and 2022-2023), these genotypes were extensively evaluated for PM severity under field conditions following inoculation with virulent Bgt isolates. The panel was previously genotyped using the Illumina 90K Infinium iSelect assay to obtain genome-wide single-nucleotide polymorphism (SNP) marker coverage. By applying FarmCPU, a multilocus mixed model, we identified a total of 113 marker-trait associations (MTAs) located on chromosomes 1A, 1B, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6B, 7A, and 7B at a significance level of p ≤ 0.001. Notably, four novel MTAs on chromosome 6B were consistently detected in 2020-2021 and 2021-2022. Furthermore, within the confidence intervals of the identified SNPs, we identified 96 candidate genes belonging to different proteins including 12 disease resistance/host-pathogen interaction-related protein families. Among these, protein kinases, leucine-rich repeats, and zinc finger proteins were of particular interest due to their potential roles in PM resistance. These identified loci can serve as targets for breeding programs aimed at developing disease-resistant wheat cultivars.

Efficacy of zinc-based nanoparticles in alleviating the abiotic stress in plants: current knowledge and future perspectives

Due to sessile, plants are unable to avoid unfavorable environmental conditions which leads to inducing serious negative effects on plant growth, crop yield, and food safety. Instead, various approaches were employed to mitigate the phytotoxicity of these emerging contaminants from the soil-plant system. However, recent studies based on the exogenous application of ZnO NPs approve of their important positive potential for alleviating abiotic stress-induced phytotoxicity leads to ensuring global food security. In this review, we have comprehensively discussed the promising role of ZnO NPs as alone or in synergistic interactions with other plant growth regulators (PGRs) in the mitigation of various abiotic stresses, i.e., heavy metals (HMs), drought, salinity, cold and high temperatures from different crops. ZnO NPs have stress-alleviating effects by regulating various functionalities by improving plant growth and development. ZnO NPs are reported to improve plant growth by stimulating diverse alterations at morphological, physiological, biochemical, and ultrastructural levels under abiotic stress factors. We have explained the recent advances and pointed out research gaps in studies conducted in earlier years with future recommendations. Thus, in this review, we have also addressed the opportunities and challenges together with aims to uplift future studies toward effective applications of ZnO NPs in stress management.

Genome-Wide Association Study of Asian and European Common Wheat Accessions for Yield-Related Traits and Stripe Rust Resistance

Identifying novel loci of yield-related traits and resistance to stripe rust (caused by Puccinia striiformis f. sp. tritici) in wheat will help in breeding wheat that can meet projected demands in diverse environmental and agricultural practices. We performed a genome-wide association study with 24,767 single nucleotide polymorphisms (SNPs) in 180 wheat accessions that originated in 16 Asian or European countries between latitudes 30°N and 45°N. We detected seven accessions with desirable yield-related traits and 42 accessions that showed stable, high degrees of stripe rust resistance in multienvironment field assessments. A marker-trait association analysis of yield-related traits detected 18 quantitative trait loci (QTLs) in at least two test environments and two QTLs related to stripe rust resistance in at least three test environments. Five of these QTLs were identified as potentially novel QTLs by comparing their physical locations with those of known QTLs in the Chinese Spring (CS) reference genome RefSeq v1.1 published by the International Wheat Genome Sequencing Consortium; two were for spike length, one was for grain number per spike, one was for spike number, and one was for stripe rust resistance at the adult plant stage. We also identified 14 candidate genes associated with the five novel QTLs. These QTLs and candidate genes will provide breeders with new germplasm and can be used to conduct marker-assisted selection in breeding wheat with improved yield and stripe rust resistance.

Fighting wheat powdery mildew: from genes to fields

KEY MESSAGE

Host resistance conferred by Pm genes provides an effective strategy to control powdery mildew. The study of Pm genes helps modern breeding develop toward more intelligent and customized. Powdery mildew of wheat is one of the most destructive diseases seriously threatening the crop yield and quality worldwide. The genetic research on powdery mildew (Pm) resistance has entered a new era. Many Pm genes from wheat and its wild and domesticated relatives have been mined and cloned. Meanwhile, modern breeding strategies based on high-throughput sequencing and genome editing are emerging and developing toward more intelligent and customized. This review highlights mining and cloning of Pm genes, molecular mechanism studies on the resistance and avirulence genes, and prospects for genomic-assisted breeding for powdery mildew resistance in wheat.

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.

Genetic mapping of powdery mildew resistance genes in wheat landrace Guizi 1 via genotyping by sequencing

BACKGROUND

Wheat (Triticum aestivum L.) powdery mildew (Pm), which caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease worldwide that causes severe yield losses in wheat. Resistant wheat cultivars easily lose their ability to effectively resist newly emerged Bgt strains; therefore, identifying new resistance genes is necessary for breeding resistant cultivars.

METHODS AND RESULTS

Guizi 1 (GZ1) is a Chinese wheat cultivar with moderate and stable resistance to Pm. Genetic analysis indicated that the Pm resistance of GZ1 was controlled by a single dominant gene, designated PmGZ1. In total, 110 F₂ individual plants and their 2 parents were subjected to genotyping by sequencing (GBS), which yielded 23,134 high-quality single-nucleotide polymorphisms (SNPs). The SNP distributions across the 21 chromosomes ranged from 134 on chromosome 6D to 6288 on chromosome 3B. Chromosome 6A has 1866 SNPs, among which 16 are physically located between positions 307,802,221 and 309,885,836 in an approximate 2.3-cM region; this region also had the greatest SNP density. The average map distance between SNP markers was 0.1 cM. A quantitative trait locus (QTL) with a significant epistatic effect on Pm resistance was mapped to chromosome 6A. The logarithm of odds (LOD) value of PmGZ1 was 34.8, and PmGZ1 was located within the confidence interval marked by chr6a-307802221 and chr6a-309885836. Moreover, 74.7% of the phenotypic variance was explained by PmGZ1. Four candidate genes (which encoded two TaAP2-A and two actin proteins) were annotated maybe as resistance genes.

CONCLUSIONS

The present results provide valuable information for wheat genetic improvement, QTL fine mapping, and candidate gene validation.

Identification of the Powdery Mildew Resistance in Chinese Wheat Cultivar Heng 4568 and its Evaluation in Marker-Assisted Selection

Powdery mildew induced by Blumeria graminis f. sp. Tritici (Bgt) has a devastating impact on global wheat yield and quality. Host resistance is the most effective and economical means to control this disease. In this study, Heng 4568, an elite wheat cultivar, shows high resistance to 12 Bgt isolates from different regions in China at the seedling stage. Genetic analysis demonstrates that the powdery mildew resistance in Heng 4568 is conferred by a single dominant locus, temporarily designated PmH4568. Furthermore, PmH4568 is mapped to the reported Pm2 interval on chromosome 5DS with five Pm2 linked markers and flanked by the markers Bwm20 and Bwm21 with a genetic distance of 0.3 and 0.6 cM, respectively. To further investigate the relationship between PmH4568 and Pm2, the diagnostic marker Pm2b-map-3 of Pm2 is used to genotype the F_2:3 population derived from the cross Heng 4568 × Daimai 2173. Notably, there is no recombination found, indicating that PmH4568 is also probably a Pm2 allele. In addition, five closely linked markers as well as one diagnostic marker are successfully developed and tested in 16 wheat cultivars from different agro-ecological areas in China, which have potential applications in molecular breeding by marker-assisted selection.

Explicating the cross-talks between nanoparticles, signaling pathways and nutrient homeostasis during environmental stresses and xenobiotic toxicity for sustainable cultivation of cereals

Precision farming using nanoparticles is a cutting-edge technology for safe cultivation of crop plants in marginal areas afflicted with environmental/climatic stresses like salinity, drought, extremes of temperature, ultraviolet B stress or polluted with xenobiotics like toxic heavy metals and fluoride. Major cereal crops like rice, wheat, maize, barley, sorghum and millets which provide the staple food for the entire global population are mainly glycophytes and are extremely susceptible to abiotic stress-induced oxidative injuries. Nanofertilization/exogenous spraying of beneficial nanoparticles alleviates the oxidative damages in cereals by altering the homeostasis of phytohormones like abscisic acid, gibberellins, cytokinins, auxins, salicylic acid, jasmonic acid and melatonin and by triggering the synthesis of gasotransmitter nitric oxide. Signaling cross-talks of nanoparticles with plant growth regulators enable activation of the defence machinery, comprising of antioxidants, thiol-rich compounds and glyoxalases and restrict xenobiotic mobilization by suppressing the expression of associated transporters. Accelerated nutrient uptake and grain biofortification under the influence of nanoparticles result in optimum crop productivity under sub-optimal conditions. However, over-dosing of even beneficial nanoparticles promotes severe phytotoxicity. Hence, the concentration of nanoparticles and mode of administering need to be thoroughly standardized before large-scale field applications, to ensure sustainable cereal cultivation with minimum ecological imbalance.

Mining for New Sources of Resistance to Powdery Mildew in Genetic Resources of Winter Wheat

Genetic pathogen control is an economical and sustainable alternative to the use of chemicals. In order to breed resistant varieties, information about potentially unused genetic resistance mechanisms is of high value. We phenotyped 8,316 genotypes of the winter wheat collection of the German Federal ex situ gene bank for Agricultural and Horticultural Crops, Germany, for resistance to powdery mildew (PM), Blumeria graminis f. sp. tritici, one of the most important biotrophic pathogens in wheat. To achieve this, we used a semi-automatic phenotyping facility to perform high-throughput detached leaf assays. This data set, combined with genotyping-by-sequencing (GBS) marker data, was used to perform a genome-wide association study (GWAS). Alleles of significantly associated markers were compared with SNP profiles of 171 widely grown wheat varieties in Germany to identify currently unexploited resistance conferring genes. We also used the Chinese Spring reference genome annotation and various domain prediction algorithms to perform a domain enrichment analysis and produced a list of candidate genes for further investigation. We identified 51 significantly associated regions. In most of these, the susceptible allele was fixed in the tested commonly grown wheat varieties. Eleven of these were located on chromosomes for which no resistance conferring genes have been previously reported. In addition to enrichment of leucine-rich repeats (LRR), we saw enrichment of several domain types so far not reported as relevant to PM resistance, thus, indicating potentially novel candidate genes for the disease resistance research and prebreeding in wheat.

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.

Development of Novel Wheat-Aegilops longissima 3S1 Translocations Conferring Powdery Mildew Resistance and Specific Molecular Markers for Chromosome 3S1

Powdery mildew of wheat, caused by Blumeria graminis f. sp. tritici, is a destructive disease of common wheat. Cultivation of resistant varieties is the most cost-effective disease management strategy. Previous studies reported that chromosome 3S^l#2 present in Chinese Spring (CS)-Aegilops longissima 3S^l#2(3B) disomic substitution line TA3575 conferred resistance to powdery mildew. In this study, we further located the powdery mildew resistance gene(s) to the short arm of chromosome 3S^l#2 (3S^l#2S) by evaluating for B. graminis f. sp. tritici resistance of newly developed CS-Ae. longissima 3S^l#2 translocation lines. Meanwhile, TA7545, a previously designated CS-Ae. longissima 3S^l#3 disomic addition line, was reidentified as an isochromosome 3S^l#3S addition line and evaluated to confer resistance to powdery mildew, thus locating the resistance gene(s) to the short arm of chromosome 3S^l#3 (3S^l#3S). Based on transcriptome sequences of TA3575, 10 novel chromosome 3S^lS-specific markers were developed, of which 5 could be used to distinguish between 3S^l#2S and 3S^l#3S derived from Ae. longissima accessions TL20 and TA1910 (TAM4) and the remaining 5 could identify both 3S^l#2S and 3S^l#3S. Also, CL897, one of five markers specific to both 3S^l#2S and 3S^l#3S, could be used to detect Pm13 located at chromosome 3S^l#1S from Ae. longissima accession TL01 in diverse wheat genetic backgrounds. The powdery mildew resistance genes on chromosomes 3S^l#2S and 3S^l#3S, the CS-Ae. longissima 3S^l#2 translocation lines, and the 3S^lS-specific markers developed in this study will facilitate the transfer of B. graminis f. sp. tritici resistance genes into common wheat and provide new germplasm resources for powdery mildew resistance breeding.

Characterization of PmDGM Conferring Powdery Mildew Resistance in Chinese Wheat Landrace Duanganmang

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is a devastating disease that threatens yield and quality. Host resistance is considered the most effective and preferred means to control this disease. Wheat landrace Duanganmang (DGM) showed high resistance or near immunity to Blumeria graminis f. sp. tritici mixture from Henan Province, China. DGM was crossed with highly susceptible Chinese wheat landrace Huixianhong (HXH) and cultivar 'Shimai 15' (SM15) to produce genetic populations. The resistance of DGM to Blumeria graminis f. sp. tritici isolate E09 was shown to be controlled by a single dominant Mendelian factor, tentatively designated PmDGM. Marker analysis and 55K single nucleotide polymorphism (SNP) array scanning showed that this gene was positioned in the Pm5 interval (2.4 cM or 1.61 Mb) flanked by Xhenu099 and Xmp1158 in the Chinese Spring reference genome. Homology-based cloning and sequence analysis demonstrated that DGM has the identical NLR gene (Pm5e) and RXL gene reported in Fuzhuang 30 (FZ30), conferring and modifying powdery mildew resistance, respectively. However, based on the different reaction patterns to the Blumeria graminis f. sp. tritici isolate B15 between DGM and FZ30, the authors speculate that DGM may have two tightly linked genes that could not be separated in the current mapping population, one of which is PmDGM and the other being Pm5e. Hence, this study provides a valuable resistance resource for improvement of powdery mildew resistance.

Characterization of PmHHXM, a New Broad-Spectrum Powdery Mildew Resistance Gene in Chinese Wheat Landrace Honghuaxiaomai

Powdery mildew, caused by fungal pathogen Blumeria graminis f. sp. tritici, is an agronomically important and widespread wheat disease causing severe yield losses. Deployment of broad-spectrum disease resistance genes is the preferred strategy to prevent this pathogen. Chinese wheat landrace Honghuaxiaomai (HHXM) was resistant to all 23 tested B. graminis f. sp. tritici isolates at the seedling stage. The F₁, F₂, and F_2:3 progenies derived from the cross HHXM × Yangmai 158 were used in this study, and genetic analysis revealed that a single dominant gene, designated PmHHXM, conferred resistance to B. graminis f. sp. tritici isolate E09. Bulked segregant analysis and molecular mapping initially located PmHHXM to the distal region of chromosome 4AL. To fine map PmHHXM, we identified two critical recombinants from 592 F₂ plants and delimited PmHHXM to a 0.18-cM Xkasp475200 to Xhnu552 interval covering 1.77 Mb, in which a number of disease resistance-related gene clusters were annotated. Comparative mapping of this interval revealed a perturbed synteny among Triticeae species. This study reports the new powdery mildew resistance gene PmHHXM, which seems different from three known quantitative trait loci/genes identified on chromosome 4AL and has significant values for further genetic improvement. Analysis of the polymorphisms of 13 cosegregating markers between HHXM and 170 modern wheat cultivars indicates that Xhnu227 and Xsts478700 developed here are ideal for marker-assisted introgression of this locus in wheat breeding.

Identification and validation of a novel locus, Qpm-3BL, for adult plant resistance to powdery mildew in wheat using multilocus GWAS

BACKGROUND

Powdery mildew (PM), one of the major diseases in wheat, severely damages yield and quality, and the most economical and effective way to address this issue is to breed disease-resistant cultivars. Accordingly, 371 landraces and 266 released cultivars in Henan Province were genotyped by a 660 K microarray and phenotyped for adult plant resistance (APR) to PM from 2017 to 2020, and these datasets were used to conduct multilocus genome-wide association studies (GWASs).

RESULTS

Thirty-six varieties showed stable APR in all the environments, and eleven quantitative trait nucleotides (QTNs) were found by multiple methods across multiple environments and best linear unbiased prediction (BLUP) values to be significantly associated with APR. Among these stable QTNs, four were previously reported, three were newly discovered in this study, and the others need to be further investigated. The major and newly discovered QTN, Qpm-3BL, was located at chr03BL_AX-109,052,670, while another newly discovered QTN, Qpm-1BL, was located between chr01BL_AX-108,771,002 and chr01BL_AX-110,117,322. Five and eight landraces were identified to be resistant based on Qpm-1BL (haplotype TC) and Qpm-3BL (allele T), respectively. To validate Qpm-3BL, a new kompetitive allele-specific PCR (KASP) marker was developed to scan 155 F₂ individuals, and the average resistance score supported the value of Qpm-3BL in marker-assisted breeding. Near Qpm-3BL, PmBMYD was identified by KEGG, gene expression and comparative genomics analyses to be a candidate. Its resistance mechanism may involve gene tandem repeats.

CONCLUSIONS

This study reveals a previously unknown gene for PM resistance that is available for marker-assisted breeding.

Multi-Locus Genome-Wide Association Study of Four Yield-Related Traits in Chinese Wheat Landraces

Wheat (Triticum aestivum L.) is one of the most important crops in the world. Here, four yield-related traits, namely, spike length, spikelets number, tillers number, and thousand-kernel weight, were evaluated in 272 Chinese wheat landraces in multiple environments. Five multi-locus genome-wide association studies (FASTmrEMMA, ISIS EN-BLASSO, mrMLM, pKWmEB, and pLARmEB) were performed using 172,711 single-nucleotide polymorphisms (SNPs) to identify yield-related quantitative trait loci (QTL). A total of 27 robust QTL were identified by more than three models. Nine of these QTL were consistent with those in previous studies. The remaining 18 QTL may be novel. We identified a major QTL, QTkw.sicau-4B, with up to 18.78% of phenotypic variation explained. The developed kompetitive allele-specific polymerase chain reaction marker for QTkw.sicau-4B was validated in two recombinant inbred line populations with an average phenotypic difference of 16.07%. After combined homologous function annotation and expression analysis, TraesCS4B01G272300 was the most likely candidate gene for QTkw.sicau-4B. Our findings provide new insights into the genetic basis of yield-related traits and offer valuable QTL to breed wheat cultivars via marker-assisted selection.

Bulked Segregant RNA-Seq Provides Distinctive Expression Profile Against Powdery Mildew in the Wheat Genotype YD588

Wheat powdery mildew, caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt), is a destructive disease leading to huge yield losses in production. Host resistance can greatly contribute to the control of the disease. To explore potential genes related to the powdery mildew (Pm) resistance, in this study, we used a resistant genotype YD588 to investigate the potential resistance components and profiled its expression in response to powdery mildew infection. Genetic analysis showed that a single dominant gene, tentatively designated PmYD588, conferred resistance to powdery mildew in YD588. Using bulked segregant RNA-Seq (BSR-Seq) and single nucleotide polymorphism (SNP) association analysis, two high-confidence candidate regions were detected in the chromosome arm 2B, spanning 453,752,054-506,356,791 and 584,117,809-664,221,850 bp, respectively. To confirm the candidate region, molecular markers were developed using the BSR-Seq data and mapped PmYD588 to an interval of 4.2 cM by using the markers YTU588-004 and YTU588-008. The physical position was subsequently locked into the interval of 647.1-656.0 Mb, which was different from those of Pm6, Pm33, Pm51, Pm52, Pm63, Pm64, PmQ, PmKN0816, MlZec1, and MlAB10 on the same chromosome arm in its position, suggesting that it is most likely a new Pm gene. To explore the potential regulatory genes of the R gene, 2,973 differentially expressed genes (DEGs) between the parents and bulks were analyzed using gene ontology (GO), clusters of orthologous group (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Based on the data, we selected 23 potential regulated genes in the enriched pathway of plant-pathogen interaction and detected their temporal expression patterns using an additional set of wheat samples and time-course analysis postinoculation with Bgt. As a result, six disease-related genes showed distinctive expression profiles after Bgt invasion and can serve as key candidates for the dissection of resistance mechanisms and improvement of durable resistance to wheat powdery mildew.

Screening and functional characterization of candidate resistance genes to powdery mildew from Dasypyrum villosum#4 in a wheat line Pm97033

KEY MESSAGE

Three genes designated DvLox, Pm21#4, and Pm21#4-H identified in a wheat-Dasypyrum villosum#4 T6V#4S·6DL translocation line Pm97033 conferred wheat for powdery mildew resistance. Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most devastating diseases in wheat. To date, only a few genes conferring resistance to wheat PM are cloned. Dasypyrum villosum is a wild relative of wheat, which provides Pm21 conferring wheat immunity to PM. In this study, we obtained many differentially expressed genes (DEGs) from a wheat-D. villosum#4 T6V#4S·6DL translocation line Pm97033 using RNA-sequencing. Among them, 7 DEGs associated with pathogen resistance were up-regulated in front of Bgt infection. Virus-induced gene silencing and transformation assays demonstrated that two of them, DvLox and Pm21#4 encoding a lipoxygenase and a encoding coiled-coil/nucleotide-binding site/leucine-rich repeat resistance protein, conferred wheat PM resistance. The transgenic wheat plants expressing DvLox enhanced PM resistance, and the transgenic wheat plants expressing Pm21#4 showed PM immunity. The Pm21#4-silenced Pm97033 plants by the cluster regularly interspaced short palindromic repeats-associated endonuclease (CRISPR/Cas9) system were susceptible to PM. Thus, Pm21#4 is a key gene contributing PM immune resistance in Pm97033. Constitutively expression of Pm21#4-H, which is silenced in Pm97033 and D. villosum#4, endowed a PM-susceptible wheat variety Fielder with PM immune resistance.

Mapping Powdery Mildew (Blumeria graminis f. sp. tritici) Resistance in Wild and Cultivated Tetraploid Wheats

Wheat is the most widely grown crop and represents the staple food for one third of the world’s population. Wheat is attacked by a large variety of pathogens and the use of resistant cultivars is an effective and environmentally safe strategy for controlling diseases and eliminating the use of fungicides. In this study, a collection of wild and cultivated tetraploid wheats (Triticum turgidum) were evaluated for seedling resistance (SR) and adult plant resistance (APR) to powdery mildew (Blumeria graminis) and genotyped with a 90K single nucleotide polymorphism (SNP) array to identify new sources of resistance genes. The genome-wide association mapping detected 18 quantitative trait loci (QTL) for APR and 8 QTL for SR, four of which were identical or at least closely linked to four QTL for APR. Thirteen candidate genes, containing nucleotide binding sites and leucine-rich repeats, were localized in the confidence intervals of the QTL-tagging SNPs. The marker IWB6155, associated to QPm.mgb-1AS, was located within the gene TRITD1Av1G004560 coding for a disease resistance protein. While most of the identified QTL were described previously, five QTL for APR (QPm.mgb-1AS, QPm.mgb-2BS, QPm.mgb-3BL.1, QPm.mgb-4BL, QPm.mgb-7BS.1) and three QTL for SR (QPm.mgb-3BL.3, QPm.mgb-5AL.2, QPm.mgb-7BS.2) were mapped on chromosome regions where no resistance gene was reported before. The novel QTL/genes can contribute to enriching the resistance sources available to breeders.

Mapping Powdery Mildew Resistance Gene pmYBL on Chromosome 7B of Chinese Wheat (Triticum aestivum L.) Landrace Youbailan

Chinese wheat landrace Youbailan has excellent resistance to powdery mildew caused by Blumeria graminis f. sp. tritici. In the present study, genetic analysis indicated that a recessive gene, tentatively designated pmYBL, was responsible for the powdery mildew resistance of Youbailan. pmYBL was located in the 695-to-715-Mb genomic region of chromosome 7BL, with 19 gene-linked single-nucleotide polymorphism (SNP) markers. It was flanked by SNP1-12 and SNP1-2 with genetic distances of 0.6 and 1.8 centimorgans, respectively. The disease reaction patterns of Youbailan and four cultivars (lines) carrying the powdery mildew (Pm) genes located on chromosome arm 7BL indicated that pmYBL may be allelic or closely linked to these genes. All of the SNP markers linked to pmYBL were diagnostic, indicating that these markers will be useful for pyramiding pmYBL using marker-assisted selection.

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.

Fine-Mapping of the Powdery Mildew Resistance Gene mlxbd in the Common Wheat Landrace Xiaobaidong

Powdery mildew, which is caused by Blumeria graminis f. sp. tritici (Bgt), is a disease of wheat worldwide. Xiaobaidong is a Chinese wheat landrace, which still maintains good resistance against powdery mildew. To obtain more genetic markers closely linked to the powdery mildew resistance gene mlxbd and narrow the candidate region for its isolation, new simple sequence repeats and cross intron-spanning markers were designed based on the genome sequence of Triticum aestivum cultivar Chinese Spring chromosome 7BL. The flanking markers 7BLSSR49 and WGGC5746 were found to be tightly linked to mlxbd at genetic distances of 0.4 cM and 0.3 cM, respectively. The resistance locus was mapped to a 63.40 kb and 0.29 Mb region of the Chinese Spring genome and Zavitan genome, respectively. The linked markers of mlxbd could be used as diagnostic markers for mlxbd. The linked molecular markers and delineated genomic region in the sequenced Chinese Spring genome will assist the future map-based cloning of mlxbd.

Identification of a Recessive Gene PmQ Conferring Resistance to Powdery Mildew in Wheat Landrace Qingxinmai Using BSR-Seq Analysis

Wheat powdery mildew is caused by Blumeria graminis f. sp. tritici (Bgt), a biotrophic fungal species. It is very important to mine new powdery mildew (Pm) resistance genes for developing resistant wheat cultivars to reduce the deleterious effects of the disease. This study was carried out to characterize the Pm gene in Qingxinmai, a winter wheat landrace from Xinjiang, China. Qingxinmai is resistant to many Bgt isolates collected from different wheat fields in China. F₁, F₂, and F_2:3 generations of the cross between Qingxinmai and powdery mildew susceptible line 041133 were developed. It was confirmed that a single recessive gene, PmQ, conferred the seedling resistance to a Bgt isolate in Qingxinmai. Bulked segregant analysis-RNA-Seq (BSR-Seq) was performed on the bulked homozygous resistant and susceptible F_2:3 families, which detected 57 single nucleotide polymorphism (SNP) variants that were enriched in a 40 Mb genomic interval on chromosome arm 2BL. Based on the flanking sequences of the candidate SNPs extracted from the Chinese Spring reference genome, 485 simple sequence repeat (SSR) markers were designed. Six polymorphic SSR markers, together with nine markers that were anchored on chromosome arm 2BL, were used to construct a genetic linkage map for PmQ. This gene was placed in a 1.4 cM genetic interval between markers Xicsq405 and WGGBH913 corresponding to 4.9 Mb physical region in the Chinese Spring reference genome. PmQ differed from most of the other Pm genes identified on chromosome arm 2BL based on its position and/or origin. However, this gene and Pm63 from an Iranian common wheat landrace were located in a similar genomic region, so they may be allelic.

A rare gain of function mutation in a wheat tandem kinase confers resistance to powdery mildew

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive diseases that pose a great threat to wheat production. Wheat landraces represent a rich source of powdery mildew resistance. Here, we report the map-based cloning of powdery mildew resistance gene Pm24 from Chinese wheat landrace Hulutou. It encodes a tandem kinase protein (TKP) with putative kinase-pseudokinase domains, designated WHEAT TANDEM KINASE 3 (WTK3). The resistance function of Pm24 was validated by transgenic assay, independent mutants, and allelic association analyses. Haplotype analysis revealed that a rare 6-bp natural deletion of lysine-glycine codons, endemic to wheat landraces of Shaanxi Province, China, in the kinase I domain (Kin I) of WTK3 is critical for the resistance function. Transgenic assay of WTK3 chimeric variants revealed that only the specific two amino acid deletion, rather than any of the single or more amino acid deletions, in the Kin I of WTK3 is responsible for gaining the resistance function of WTK3 against the Bgt fungus.

Discovery of powdery mildew resistance gene candidates from Aegilops biuncialis chromosome 2Mb based on transcriptome sequencing

Powdery mildew is one of the most widespread diseases of wheat. The development and deployment of resistant varieties are one of the most economical and effective methods to manage this disease. Our previous study showed that the gene(s) at 2Mb in Chinese Spring (CS)-Aegilops biuncialis 2Mb disomic addition line TA7733 conferred a high level of resistance to powdery mildew of wheat. In this study, resistance spectrum of TA7733 was assayed by using 15 Blumeria graminis f. sp. tritici (Bgt) isolates prevalent in different regions of China. The result indicated that TA7733 was highly resistant to all tested Bgt isolates and the gene(s) on chromosome 2Mb conferred broad-spectrum resistance to powdery mildew. In order to characterize mechanism of powdery mildew resistance by identifying candidates R-genes derived from Ae. biuncialis chromosome 2Mb and develop 2Mb-specific molecular markers, we performed RNA-seq analysis on TA7733 and CS. In total we identified 7,278 unigenes that showed specific expression in TA7733 pre and post Bgt-infection when compared to CS. Of these 7,278 unigenes, 295 were annotated as putative resistance (R) genes. Comparatively analysis of R-gene sequences from TA7733 and CS and integration CS Ref Seq v1.0 were used to develop R-gene specific primers. Of 295 R-genes we identified 53 R-genes were specific to 2Mb and could be involved in powdery mildew resistance. Functional annotation of majority of the 53 R-genes encoded nucleotide binding leucine rich repeat (NLR) protein. The broad-spectrum resistance to powdery mildew in TA7733 and availability of 2Mb-derived putative candidate R-gene specific molecular markers identified in this study will lay foundations for transferring powdery mildew resistance from 2Mb to common wheat by inducing CS-Ae. biuncialis homoeologous recombination. Our study also provides useful candidates for further isolation and cloning of powdery mildew resistance gene(s) from Ae. biuncialis chromosome 2Mb.

Identification of a New Powdery Mildew Resistance Gene pmDHT at or Closely Linked to the Pm5 Locus in the Chinese Wheat Landrace Dahongtou

Chinese wheat landrace Dahongtou was resistant to 35 of 38 tested Chinese isolates of Blumeria graminis f. sp. tritici at the seedling stage. Genetic analysis of the F₂ populations and their derived F_2:3 families of crosses of Dahongtou with the susceptible varieties Mingxian 169 and Huixianhong indicated that the resistance of Dahongtou to B. graminis f. sp. tritici isolate E09 was conferred by a single recessive gene, tentatively designated as pmDHT. The gene was mapped to chromosome arm 7BL and flanked by markers Xwmc526/XBE443877 and Xgwm611/Xwmc511 at genetic distances of 0.8 and 0.3 cM, respectively. The chromosomal position of pmDHT was similar to the multi-allelic Pm5 locus on 7BL. Allelism tests with crosses of Dahongtou with Fuzhuang 30 (Pm5e) and Xiaobaidong (mlxbd) indicated that pmDHT was allelic to both Pm5e and mlxbd. However, pmDHT showed a different pattern of resistance to the 38 B. graminis f. sp. tritici isolates compared with wheat lines with Pm5a, Pm5b, Pm5e, mlxbd, and PmHYM and also differed from PmSGA. Thus, pmDHT was identified most likely as a new allele or at least a closely linked gene of the Pm5 locus. This gene can be transferred into susceptible wheat cultivars/lines and pyramided with other resistance genes through marker-assisted selection to improve powdery mildew resistance.

Genome-wide association study reveals new loci for yield-related traits in Sichuan wheat germplasm under stripe rust stress

BACKGROUND

As one of the most important food crops in the world, increasing wheat (Triticum aestivum L.) yield is an urgent task for global food security under the continuous threat of stripe rust (caused by Puccinia striiformis f. sp. tritici) in many regions of the world. Molecular marker-assisted breeding is one of the most efficient ways to increase yield. Here, we identified loci associated to multi-environmental yield-related traits under stripe rust stress in 244 wheat accessions from Sichuan Province through genome-wide association study (GWAS) using 44,059 polymorphic markers from the 55 K single nucleotide polymorphism (SNP) chip.

RESULTS

A total of 13 stable quantitative trait loci (QTLs) were found to be highly associating to yield-related traits, including 6 for spike length (SL), 3 for thousand-kernel weight (TKW), 2 for kernel weight per spike (KWPS), and 2 for both TKW and KWPS, in at least two test environments under stripe rust stress conditions. Of them, ten QTLs were overlapped or very close to the reported QTLs, three QTLs, QSL.sicau-1AL, QTKW.sicau-4AL, and QKWPS.sicau-4AL.1, were potentially novel through the physical location comparison with previous QTLs. Further, 21 candidate genes within three potentially novel QTLs were identified, they were mainly involved in the regulation of phytohormone, cell division and proliferation, meristem development, plant or organ development, and carbohydrate transport.

CONCLUSIONS

QTLs and candidate genes detected in our study for yield-related traits under stripe rust stress will facilitate elucidating genetic basis of yield-related trait and could be used in marker-assisted selection in wheat yield breeding.

Applications of Nanotechnology in Plant Growth and Crop Protection: A Review

In the era of climate change, global agricultural systems are facing numerous, unprecedented challenges. In order to achieve food security, advanced nano-engineering is a handy tool for boosting crop production and assuring sustainability. Nanotechnology helps to improve agricultural production by increasing the efficiency of inputs and minimizing relevant losses. Nanomaterials offer a wider specific surface area to fertilizers and pesticides. In addition, nanomaterials as unique carriers of agrochemicals facilitate the site-targeted controlled delivery of nutrients with increased crop protection. Due to their direct and intended applications in the precise management and control of inputs (fertilizers, pesticides, herbicides), nanotools, such as nanobiosensors, support the development of high-tech agricultural farms. The integration of biology and nanotechnology into nonosensors has greatly increased their potential to sense and identify the environmental conditions or impairments. In this review, we summarize recent attempts at innovative uses of nanotechnologies in agriculture that may help to meet the rising demand for food and environmental sustainability.

Applications of Nanotechnology in Plant Growth and Crop Protection: A Review

In the era of climate change, global agricultural systems are facing numerous, unprecedented challenges. In order to achieve food security, advanced nano-engineering is a handy tool for boosting crop production and assuring sustainability. Nanotechnology helps to improve agricultural production by increasing the efficiency of inputs and minimizing relevant losses. Nanomaterials offer a wider specific surface area to fertilizers and pesticides. In addition, nanomaterials as unique carriers of agrochemicals facilitate the site-targeted controlled delivery of nutrients with increased crop protection. Due to their direct and intended applications in the precise management and control of inputs (fertilizers, pesticides, herbicides), nanotools, such as nanobiosensors, support the development of high-tech agricultural farms. The integration of biology and nanotechnology into nonosensors has greatly increased their potential to sense and identify the environmental conditions or impairments. In this review, we summarize recent attempts at innovative uses of nanotechnologies in agriculture that may help to meet the rising demand for food and environmental sustainability.

Molecular Mapping of a Recessive Powdery Mildew Resistance Gene in Wheat Cultivar Tian Xuan 45 Using Bulked Segregant Analysis with Polymorphic Single Nucleotide Polymorphism Relative Ratio Distribution

Powdery mildew is a destructive foliar disease of wheat worldwide. Wheat cultivar Tian Xuan 45 exhibits resistance to the highly virulent isolate HY5. Genetic analysis of the F₂ and F_2:3 populations of a cultivar Ming Xian 169/Tian Xuan 45 cross revealed that the resistance to HY5 was controlled by a single recessive gene, temporarily designated as PmTx45. A Manhattan plot with the relative frequency distribution of single nucleotide polymorphisms (SNPs) was used to rapidly narrow down the possible chromosomal regions of the associated genes. This microarray-based bulked segregant analysis (BSA) largely improved traditional analytical methods. PmTx45 was located in chromosomal bin 4BL5-0.86-1.00 and was flanked by SNP marker AX-110673642 and intron length polymorphism (ILP) marker ILP-4B01G269900 with genetic distances of 3.0 and 2.6 cM, respectively. Molecular detection in a panel of wheat cultivars using the markers linked to PmTx45 showed that the presence of PmTx45 in commercial wheat cultivars was rare. Resistance spectrum and chromosomal position analyses indicated that PmTx45 may be a novel recessive gene with moderate powdery mildew resistance. This new microarray-based BSA method is feasible and effective and has the potential application for mapping genes in wheat in marker-assisted breeding.

Characterization of Pm63, a powdery mildew resistance gene in Iranian landrace PI 628024

A new powdery mildew resistance gene conferring a wide spectrum of resistance to Bgt isolates in the USA, Pm63 , was identified in Iranian wheat landrace PI 628024 and mapped to the terminal region of the long arm of chromosome 2B. Powdery mildew is a globally important wheat disease causing severe yield losses, and host resistance is the preferred strategy for managing this disease. The objective of this study was to characterize a powdery mildew resistance gene in Iranian landrace PI 628024, which exhibited a wide spectrum of resistance to representative Blumeria graminis f. sp. tritici (Bgt) isolates collected from different regions of the USA. An F₂ population and F_2:3 lines derived from the cross PI 628024 × CItr 11349 were used in this study, and genetic analysis indicated that a single dominant gene, designated Pm63, conferred resistance to Bgt isolate OKS(14)-B-3-1. Linkage analysis located Pm63 to an interval of about 13.1 Mb on the long arm of chromosome 2B, spanning 710.3-723.4 Mb in the Chinese Spring reference sequence. Bin mapping assigned Pm63 to the terminal bin 2BL6-0.89-1.0, 1.1 cM proximal to STS marker Xbcd135-2 and 0.6 cM distal to SSR marker Xstars419. Allelism tests indicated that Pm63 is a new powdery mildew resistance gene, which differs from other genes in the terminal bin by origin, genomic location, and responses to a set of 16 representative US Bgt isolates. Pm63 can be widely used to enhance powdery mildew resistance in the Great Plains, western, and southeastern regions of the USA.

Development of SNP, KASP, and SSR Markers by BSR-Seq Technology for Saturation of Genetic Linkage Map and Efficient Detection of Wheat Powdery Mildew Resistance Gene Pm61

The gene Pm61 that confers powdery mildew resistance has been previously identified on chromosome arm 4AL in Chinese wheat landrace Xuxusanyuehuang (XXSYH). To facilitate the use of Pm61 in breeding practices, the bulked segregant analysis-RNA-Seq (BSR-Seq) analysis, in combination with the information on the Chinese Spring reference genome sequence, was performed in the F_2:3 mapping population of XXSYH × Zhongzuo 9504. Two single nucleotide polymorphism (SNP), two Kompetitive Allele Specific PCR (KASP), and six simple sequence repeat (SSR) markers, together with previously identified polymorphic markers, saturated the genetic linkage map for Pm61, especially in the proximal side of the target gene that was short of gene-linked markers. In the newly established genetic linkage map, Pm61 was located in a 0.71 cM genetic interval and can be detected in a high throughput scale by the KASP markers Xicsk8 and Xicsk13 or by the standard PCR-based markers Xicscx497 and Xicsx538. The newly saturated genetic linkage map will be useful in molecular marker assisted-selection of Pm61 in breeding for disease resistant cultivar and in its map-based cloning.

Pm223899, a new recessive powdery mildew resistance gene identified in Afghanistan landrace PI 223899

A new recessive powdery mildew resistance gene, Pm223899, was identified in Afghanistan wheat landrace PI 223899 and mapped to an interval of about 831 Kb in the terminal region of the short arm of chromosome 1A. Wheat powdery mildew, a globally important disease caused by the biotrophic fungus Blumeria graminis f.sp. tritici (Bgt), has occurred with increased frequency and severity in recent years, and some widely deployed resistance genes have lost effectiveness. PI 223899 is an Afghanistan landrace exhibiting high resistance to Bgt isolates collected from the Great Plains. An F₂ population and F_2:3 lines derived from a cross between PI 223899 and OK1059060-126135-3 were evaluated for response to Bgt isolate OKS(14)-B-3-1, and the bulked segregant analysis (BSA) approach was used to map the powdery mildew resistance gene. Genetic analysis indicated that a recessive gene, designated Pm223899, conferred powdery mildew resistance in PI 223899. Linkage analysis placed Pm223899 to an interval of about 831 Kb in the terminal region of chromosome 1AS, spanning 4,504,697-5,336,062 bp of the Chinese Spring reference sequence. Eight genes were predicted in this genomic region, including TraesCS1AG008300 encoding a putative disease resistance protein RGA4. Pm223899 was flanked proximally by a SSR marker STARS333 (1.4 cM) and distally by the Pm3 locus (0.3 cM). One F₂ recombinant was identified between Pm3 and Pm223899 using a Pm3b-specific marker, indicating that Pm223899 is most likely a new gene, rather than an allele of the Pm3 locus. Pm223389 confers a high level of resistance to Bgt isolates collected from Pennsylvania, Oklahoma, Nebraska, and Montana. Therefore, Pm223389 can be used to enhance powdery mildew resistance in these states. Pm3b-1 and STARS333 have the potential to tag Pm223389 in wheat breeding.

Pm61: a recessive gene for resistance to powdery mildew in wheat landrace Xuxusanyuehuang identified by comparative genomics analysis

A single recessive powdery mildew resistance gene Pm61 from wheat landrace Xuxusanyuehuang was mapped within a 0.46-cM genetic interval spanning a 1.3-Mb interval of the genomic region of chromosome arm 4AL. Epidemics of powdery mildew incited by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt) have caused significant yield reductions in many wheat (Triticum aestivum)-producing regions. Identification of powdery mildew resistance genes is required for sustainable improvement of wheat for disease resistance. Chinese wheat landrace Xuxusanyuehuang was resistant to several Bgt isolates at the seedling stage. Genetic analysis based on the inoculation of Bgt isolate E09 on the F₁, F₂, and F_2:3 populations produced by crossing Xuxusanyuehuang to susceptible cultivar Mingxian 169 revealed that the resistance of Xuxusanyuehuang was controlled by a single recessive gene. Bulked segregant analysis and simple sequence repeat (SSR) mapping placed the gene on chromosome bin 4AL-4-0.80-1.00. Comparative genomics analysis was performed to detect the collinear genomic regions of Brachypodium distachyon, rice, sorghum, Aegilops tauschii, T. urartu, and T. turgidum ssp. dicoccoides. Based on the use of 454 contig sequences and the International Wheat Genome Sequence Consortium survey sequence of Chinese Spring wheat, four EST-SSR and seven SSR markers were linked to the gene. An F₅ recombinant inbred line population derived from Xuxusanyuehuang × Mingxian 169 cross was used to develop the genetic linkage map. The gene was localized in a 0.46-cM genetic interval between Xgwm160 and Xicsx79 corresponding to 1.3-Mb interval of the genomic region in wheat genome. This is a new locus for powdery mildew resistance on chromosome arm 4AL and is designated Pm61.

Characterization of Pm59, a novel powdery mildew resistance gene in Afghanistan wheat landrace PI 181356

A new powdery mildew resistance gene, designated Pm59, was identified in Afghanistan wheat landrace PI 181356, and mapped in the terminal region of the long arm of chromosome 7A. Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is an important foliar disease of wheat worldwide. In the Great Plains of the USA, Bgt isolates virulent to widely used powdery mildew resistance genes, such as Pm3a, were previously identified. The objectives of this study were to characterize the powdery mildew resistance gene in Afghanistan landrace PI 181356, which exhibited high resistance to Bgt isolates collected in southern Great Plains, and identify molecular markers for marker-assisted selection. An F₂ population and F_2:3 lines derived from a cross between PI 181356 and OK1059060-126135-3 were used in this study. Genetic analysis indicated that PI 181356 carries a single dominant gene, designated Pm59, in the terminal region of the long arm of chromosome 7A. Pm59 was mapped to an interval between sequence tag site (STS) markers Xmag1759 and Xmag1714 with genetic distances of 0.4 cM distal to Xmag1759 and 5.7 cM proximal to Xmag1714. Physical mapping suggested that Pm59 is in the distal bin 7AL 0.99-1.00. Pm59 is a novel powdery mildew resistance gene, and confers resistance to Bgt isolates collected from the Great Plains and the state of Montana. Therefore, Pm59 can be used to breed powdery mildew-resistant cultivars in these regions. Xmag1759 is ideal for marker-assisted selection of Pm59 in wheat breeding.

Dissection of the multigenic wheat stem rust resistance present in the Montenegrin spring wheat accession PI 362698

BACKGROUND

Research to identify and characterize stem rust resistance genes in common wheat, Triticum aestivum, has been stimulated by the emergence of Ug99-lineage races of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici (Pgt), in Eastern Africa. The Montenegrin spring wheat landrace PI 362698 was identified as a source of Pgt resistance. This accession exhibits resistance to multiple Ug99-lineage and North American Pgt races at seedling and adult-plant stages. A recombinant inbred population was developed by crossing the susceptible line LMPG-6 with a single plant selection of PI 362698. A genetic map was constructed using the Illumina iSelect 90 K wheat assay and the markers csLv34, NB-LRR3, and wMAS000003 and quantitative trait locus (QTL) analysis was performed.

RESULTS

QTL analysis identified five significant QTLs (α = 0.05) on chromosomes 2B, 3B, 6A, 6D, and 7A associated with wheat stem rust resistance. The QTL on chromosome 3B was identified using both field data from Kenya (Pgt Ug99-lineage races) and seedling data from Pgt race MCCF. This QTL potentially corresponds to Sr12 or a new allele of Sr12. The multi-pathogen resistance gene Sr57 located on chromosome 7D is present in PI 362698 according to the diagnostic markers csLv34 and wMAS000003, however a significant QTL was not detected at this locus. The QTLs on chromosomes 2B, 6A, and 6D were identified during seedling trials and are thought to correspond to Sr16, Sr8a, and Sr5, respectively. The QTL identified on chromosome 7A was detected using MCCF seedling data and may be Sr15 or a potentially novel allele of recently detected Ug99 resistance QTLs.

CONCLUSIONS

The combination of resistance QTLs found in PI 362698 is like the resistance gene combination present in the broadly resistant cultivar Thatcher. As such, PI 362698 may not be a landrace as previously thought. PI 362698 has been crossed with North Dakota wheat germplasm for future breeding efforts. Additional work is needed to fully understand why the combination of genes present in PI 362698 and 'Thatcher' provide such durable resistance.

Characterization of a new Pm2 allele associated with broad-spectrum powdery mildew resistance in wheat line Subtil

Wheat powdery mildew is a severe disease affecting yield and quality. Host resistance was proved to be effective and environment-friendly. Wheat line Subtil is an elite germplasm resource resistant to 28 of 30 tested Bgt isolates. Genetic analysis showed that the powdery mildew resistance in Subtil was conferred by a single dominant gene, temporarily designated PmSub. Using bulked segregant analysis, PmSub was mapped to chromosome arm 5DS, and flanked by the markers Bwm16 and Cfd81/Bwm21 at 5.0 and 0.9 cM, respectively. Allelism tests further confirmed PmSub was allelic with documented Pm2 alleles. Then, homologous sequences of Pm2a related sequence was cloned from Subtil and Chinese Spring. It was completely identical to the reported Pm2a sequence, but significantly different from that of Chinese Spring. A marker SWGI067 was developed based on the sequence divergence of homologous sequence in Subtil and Chinese Spring. SWGI067 was closely linked to PmSub, indicating that the gene PmSub itself was different from the cloned Pm2a related sequence. Meanwhile, Subtil produced significantly different reaction pattern compared with other genotypes with Pm genes at or near Pm2 locus. Therefore, PmSub was most likely a new allele of Pm2. PmSub has opportunities for marker-assisted selecting for high-efficiency wheat improvement.

Use of Lentinan To Control Sharp Eyespot of Wheat, and the Mechanism Involved

Lentinan (LNT), a complex polysaccharide with a β-(1→3)-linked backbone of d-glucose residues, has been reported to inhibit plant diseases. Our objective was to explore the efficacy and action mechanism of LNT used as a seed dressing to control sharp eyespot of wheat. Seed dressing promoted wheat growth. At control germination rates of 50%, 8 g of LNT/100 kg of seeds of the Jimai 22, Shannong 23, and Luyuan 502 cultivars significantly increased seed germination to 54%, 52%, and 51%, respectively. Seven days after emergence, the heights and root activity of wheat treated with LNT were significantly greater than those of controls. These effects were dose-dependent. At this time, the plant heights of Jimai 22, Shannong 23, and Luyuan 502 cultivars were 9.52, 8.52, and 10.52 cm, respectively, significantly higher than that of the controls. LNT prevented the development of wheat sharp eyespot. In the highly susceptible Jimai 22 cultivar, sharp eyespot development was reduced by 33.7%, 31.9%, and 30.4% at 7, 14, and 21 days after germination. LNT somewhat increased phenylalanine ammonia-lyase, peroxidase, and superoxide dismutase activity; reduced the malondialdehyde content; increased chlorophyll a and b levels; and enhanced the root vigor of wheat. These effects peaked 7 days after germination. LNT increased transcription of the genes encoding alternative oxidase (AOX) and β-1,3-glucanase (GLU), the salicylic acid signaling pathway-related gene NbPR1a, and the sharp eyespot resistance-related gene RS33. A significant dose-effect relationship was evident in terms of AOX transcription; we thus speculate that AOX may be the target gene.

Transposon insertion resulted in the silencing of Wx-B1n in Chinese wheat landraces

A novel Wx-B1 allele was characterized; a transposon insertion resulted in the loss of its function, which is different from the previously reported gene silencing mechanisms at the Wx-B1 locus. The waxy protein composition of 53 Chinese wheat landraces was analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional gel electrophoresis; of these, 10 did not show the expression of Wx-A1 (four accession) or Wx-B1 (six accessions) protein. The results of molecular marker detection revealed that the Wx-B1 allele (Wx-B1n) showed normal expression, inconsistent with the findings of SDS-PAGE for the Xiaobaipi accession. Further cloning of the 9160-bp region covering the Wx-B1 coding region and 3'-downstream region revealed that a 2178-bp transposon fragment had been inserted at 2462 bp within the tenth exon of Wx-B1n ORF, leading to the absence of Wx-B1 protein. Sequence analysis indicated that the insertion possessed the structural features of invert repeat and target repeat elements, we deduced that it was a transposon. Further PCR analysis revealed that this fragment had moved, but not copied itself, from 3B chromosome to the current location in Wx-B1n. Therefore, the reason for the inactivation of Wx-B1n was considerably different from those for the inactivation of Wx-B1b, Wx-B1k, and Wx-B1m; to our knowledge, this kind of structural mutation has never been reported in Wx-B1 alleles. This novel allele is interesting, because it was not associated with the deletion of other quality-related genes included in the 67 kb region lost with the common null allele Wx-B1b. The null Wx-B1n might be useful for investigating gene inactivation and expression as well as for enriching the genetic resource pool for the modification of the amylose/amylopectin ratio, thereby improving wheat quality.

Homoeologous recombination-based transfer and molecular cytogenetic mapping of powdery mildew-resistant gene Pm57 from Aegilops searsii into wheat

Pm57, a novel resistant gene against powdery mildew, was transferred into common wheat from Ae. searsi and further mapped to 2S ^s #1L at an interval of FL0.75 to FL0.87. Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases of wheat causing reduction in grain yield and quality. Host plant resistance is the most effective and environmentally safe approach to control this disease. Tests of a set of Chinese Spring-Ae. searsii (S^sS^s, 2n = 2x = 14) Feldman & Kislev ex K. Hammer disomic addition lines with a mixed isolate of the powdery mildew fungus identified a novel resistance gene(s), designed as Pm57, which was located on chromosome 2S^s#1. Here, we report the development of ten wheat-Ae. searsii recombinants. The wheat chromosomes involved in five of these recombinants were identified by FISH and SSR marker analysis and three of them were resistant to powdery mildew. Pm57 was further mapped to the long arm of chromosome 2S^s#1 at a fraction length interval of FL 0.75 to FL 0.87. The recombinant stocks T2BS.2BL-2S^s#1L 89-346 (TA5108) with distal 2S^s#1L segments of 28% and 89(5)69 (TA5109) with 33% may be useful in wheat improvement. The PCR marker X2L4g9p4/HaeIII was validated to specifically identify the Ae. searsii 2S^s#1L segment harboring Pm57 in T2BS.2BL-2S^s#1L against 16 wheat varieties and advanced breeding lines, and the development of more user-friendly KASP markers is underway.

Collinearity Analysis and High-Density Genetic Mapping of the Wheat Powdery Mildew Resistance Gene Pm40 in PI 672538

The wheat powdery mildew resistance gene Pm40, which is located on chromosomal arm 7BS, is effective against nearly all prevalent races of Blumeria graminis f. sp tritici (Bgt) in China and is carried by the common wheat germplasm PI 672538. A set of the F1, F2 and F2:3 populations from the cross of the resistant PI 672538 with the susceptible line L1034 were used to conduct genetic analysis of powdery mildew resistance and construct a high-density linkage map of the Pm40 gene. We constructed a high-density linkage genetic map with a total length of 6.18 cM and average spacing between markers of 0.48 cM.Pm40 is flanked by Xwmc335 and BF291338 at genetic distances of 0.58 cM and 0.26 cM, respectively, in deletion bin C-7BS-1-0.27. Comparative genomic analysis based on EST-STS markers established a high level of collinearity of the Pm40 genomic region with a 1.09-Mbp genomic region on Brachypodium chromosome 3, a 1.16-Mbp genomic region on rice chromosome 8, and a 1.62-Mbp genomic region on sorghum chromosome 7. We further anchored the Pm40 target intervals to the wheat genome sequence. A putative linear index of 85 wheat contigs containing 97 genes on 7BS was constructed. In total, 9 genes could be considered as candidates for the resistances to powdery mildew in the target genomic regions, which encoded proteins that were involved in the plant defense and response to pathogen attack. These results will facilitate the development of new markers for map-based cloning and marker-assisted selection of Pm40 in wheat breeding programs.

Characterization of a Segregation Distortion Locus with Powdery Mildew Resistance in a Wheat-Thinopyrum intermedium Introgression Line WE99

Exploitation of host resistance is important for controlling powdery mildew of wheat (Triticum aestivum L.). In this study, a wheat-Thinopyrum intermedium introgression line, designated WE99, conferred seedling resistance to 47 of 49 Blumeria graminis f. sp. tritici isolates. Genetic analysis demonstrated that the resistance segregation deviated significantly from a single gene Mendelian ratio. However, marker analysis indicated that only a single recessive resistance gene, temporarily designated PmWE99, conferred powdery mildew resistance (Pm). PmWE99 was mapped to chromosome arm 2BS and linked to the three simple-sequence repeat markers Gwm148, Gwm271, and Barc55. Using race spectrum analysis, PmWE99 was shown to be significantly different from the documented genes Pm42 and MlIW170 located on chromosome arm 2BS and, thus, appeared to be a new Pm gene. Examination of the genotype frequencies in the F_2:3 families showed that a genetic variation in the PmWE99 interval that favored the transmission of the WE99 allele could be the cause of the deviated segregation. Further investigation revealed that the abnormal segregation only occurred at the PmWE99 interval and was not common at other loci in this population. Identification of PmWE99 will increase the diversity of the Pm genes for wheat improvement.

Characterization of a New Pm2 Allele Conferring Powdery Mildew Resistance in the Wheat Germplasm Line FG-1

Powdery mildew has a negative impact on wheat production. Novel host resistance increases the diversity of resistance genes and helps to control the disease. In this study, wheat line FG-1 imported from France showed a high level of powdery mildew resistance at both the seedling and adult stages. An F2 population and F2:3 families from the cross FG-1 × Mingxian 169 both fit Mendelian ratios for a single dominant resistance gene when tested against multiple avirulent Blumeria tritici f. sp. tritici (Bgt) races. This gene was temporarily designated PmFG. PmFG was mapped on the multi-allelic Pm2 locus of chromosome 5DS using seven SSR, 10 single nucleotide polymorphism (SNP)-derived and two SCAR markers with the flanking markers Xbwm21/Xcfd81/Xscar112 (distal) and Xbwm25 (proximal) at 0.3 and 0.5 cM being the closest. Marker SCAR203 co-segregated with PmFG. Allelism tests between PmFG and documented Pm2 alleles confirmed that PmFG was allelic with Pm2. Line FG-1 produced a significantly different reaction pattern compared to other lines with genes at or near Pm2 when tested against 49 Bgt isolates. The PmFG-linked marker alleles detected by the SNP-derived markers revealed significant variation between FG-1 and other lines with genes at or near Pm2. It was concluded that PmFG is a new allele at the Pm2 locus. Data from seven closely linked markers tested on 31 wheat cultivars indicated opportunities for marker-assisted pyramiding of this gene with other genes for powdery mildew resistance and additional traits.