Core and variable antimicrobial resistance genes in the gut microbiomes of Chinese and European pigs

Monitoring the prevalence of antimicrobial resistance genes(ARGs)is vital for addressing the global crisis of antibiotic-resistant bacterial infections.Despite its importance,the characterization of ARGs and microbiome structures,as well as the identification of indicators for routine ARG monitoring in pig farms,are still lacking,particularly concerning variations in antimicrobial exposure in different countries or regions.Here,metagenomics and random forest machine learning were used to elucidate the ARG profiles,microbiome structures,and ARG contamination indicators in pig manure under different antimicrobial pressures between China and Europe.Results showed that Chinese pigs exposed to high-level antimicrobials exhibited higher total and plasmid-mediated ARG abundances compared to those in European pigs(P<0.05).ANT(6)-Ib,APH(3')-IIIa,and tet(40)were identified as shared core ARGs between the two pig populations.Furthermore,the core ARGs identified in pig populations were correlated with those found in human populations within the same geographical regions.Lactobacillus and Prevotella were identified as the dominant genera in the core microbiomes of Chinese and European pigs,respectively.Forty ARG markers and 43 biomarkers were able to differentiate between the Chinese and European pig manure samples with accuracies of 100%and 98.7%,respectively.Indicators for assessing ARG contamination in Chinese and European pigs also achieved high accuracy(r=0.72-0.88).Escherichia flexneri in both Chinese and European pig populations carried between 21 and 37 ARGs.The results of this study emphasize the importance of global collaboration in reducing antimicrobial resistance risk and provide validated indicators for evaluating the risk of ARG contamination in pig farms.

Fine-mapping of a candidate gene for web blotch resistance in Arachis hypogaea L.

Peanut(Arachis hypogaea L.)is a globally important oil crop.Web blotch is one of the most important foliar diseases affecting peanut,which results in serious yield losses worldwide.Breeding web blotch-resistant peanut varieties is the most effective and economically viable method for minimizing yield losses due to web blotch.In the current study,a bulked segregant analysis with next-generation sequencing was used to analyze an F2:3 segregating population and identify candidate loci related to web blotch resistance.Based on the fine-mapping of the candidate genomic interval using kompetitive allele-specific PCR(KASP)markers,we identified a novel web blotch resistance-related locus spanning approximately 169 kb on chromosome 16.This region included four annotated genes,of which only Arahy.35VVQ3 had a non-synonymous single nucleotide polymorphism in the coding region between the two parents.Two markers(Chr.16.12872635 and Chr.16.12966357)linked to this gene were shown to be co-segregated with the resistance of peanut web blotch by 72 randomly selected recombinant inbred lines(RIL),which could be used in marker-assisted breeding of resistant peanut varieties.

Turnip mosaic virus pathogenesis and host resistance mechanisms in Brassica

Turnip mosaic virus(TuMV)is a devastating potyvirus pathogen that infects a wide variety of both cultivated and wild Brassicaceae plants.We urgently need more information and understanding of TuMV pathogenesis and the host responses involved in disease development in cruciferous crops.TuMV displays great versatility in viral pathogenesis,especially in its replication and intercellular movement.Moreover,in the coevolutionary arms races between TuMV and its hosts,the virus has evolved to co-opt host factors to facilitate its infection and counter host defense responses.This review mainly focuses on recent advances in understanding the viral factors that contribute to the TuMV infection cycle and the host resistance mechanism in Brassica.Finally,we propose some future research directions on TuMV pathogenesis and control strategies to design durable TuMV-resistant Brassica crops.

Mobile genetic elements facilitate the transmission of antibiotic resistance genes in multidrug-resistant Enterobacteriaceae from duck farms

Multidrug-resistant(MDR)Enterobacteriaceae critically threaten duck farming and public health.The phenotypes,genotypes,and associated mobile genetic elements(MGEs)of MDR Enterobacteriaceae isolated from 6 duck farms in Zhejiang Province,China,were investigated.A total of 215 isolates were identified as Escherichia coli(64.65%),Klebsiella pneumoniae(12.09%),Proteus mirabilis(10.23%),Salmonella(8.84%),and Enterobacter cloacae(4.19%).Meanwhile,all isolates were resistant to at least two antibiotics.Most isolates carried tet(A)(85.12%),blaTEM(78.60%)and sul1(67.44%)resistance genes.Gene co-occurrence analysis showed that the resistance genes were associated with IS26 and integrons.A conjugative IncFII plasmid pSDM004 containing all the above MGEs was detected in Proteus mirabilis isolate SDM004.This isolate was resistant to 18 antibiotics and carried the blaNDM-5 gene.MGEs,especially plasmids,are the primary antibiotic resistance gene transmission route in duck farms.These findings provide a theoretical basis for the rational use of antibiotics in farms which are substantial for evaluating public health and food safety.

Fate and Behavior of Tetracycline Resistance Genes in Activated Carbon Adsorption

The accessibility of tetracycline resistance gene (tetG) into the pores of activated carbon (AC), as well as the impact of the pore size distribution (PSD) of AC on the uptake capacity of tetG, were investigated using eight types of AC (four coal-based and four wood-based). AC showed the capability to admit tetG and the average reduction of tetG for coal-based and wood-based ACs at the AC dose of 1 g·L-1 was 3.12 log and 3.65 log, respectively. The uptake kinetic analysis showed that the uptake of the gene followed the pseudo-second-order kinetics reaction, and the uptake rate constant for the coal-based and wood-based ACs was in the range of 5.97 × 10-12 - 4.64 × 10-9 and 7.02 × 10-11 - 1.59 × 10-8 copies·mg-1·min-1, respectively. The uptake capacity analysis by fitting the obtained experiment data with the Freundlich isotherm model indicated that the uptake constant (KF) values were 1.71 × 103 - 8.00 × 109 (copies·g-1)1-1/n for coal-based ACs and 7.00 × 108 - 3.00 × 1010 (copies·g-1)1-1/n for wood-based ones. In addition, the correlation analysis between KF values and pore volume as well as pore surface at different pore size regions of ACs showed that relatively higher positive correlation was found for pores of 50 - 100 Å, suggesting ACs with more pores in this size region can uptake more tetG. The findings of this study are valuable as reference for optimizing the adsorption process regarding antibiotic resistance-related concerns in drinking water treatment.

Dissemination of Resistance Integrons and Genes Coding for Blse and Cabapenemases in the Urban Drainage Network in Cote d’Ivoire

Antibiotic resistance has become a major threat to human health worldwide. Environment, particularly the water environment, has long been overlooked as a player in the antibiotic resistance cycle, although its role remains unclear. These can provide an ideal setting for the acquisition and dissemination of antibiotic resistance, as they are frequently affected by anthropogenic activities. The objective of this study was to establish a diffusion map of resistance integrons used as genetic markers of resistance associated with antibiotic resistance conferring genes (ARGs). Total DNA extracts from non-cultivable bacterial communities were used for the analyses. These communities were obtained from wastewater samples from 14 sites upstream and downstream of drainage channels or effluents in the cities of Abidjan, Bouaké, and Yamoussoukro. The results obtained correspond to the number of positives among the treated samples (n = 39). Among the genetic markers of dissemination, class 1 integrons were the most evident in 94.8% of samples in Abidjan (93.3%), Bouaké (100%) and Yamoussoukro (91.6%). Class 2 integrons and class 3 integrons were found respectively in 41% and 51% of all samples. Genes coding for β-lactamases and blaTEM was identified in almost all samples at a rate of 97.4%. A co-presence of the three genes blaTEM, blaSHV and blaCTX-M is also remarkable in the sites of the city of Yamoussoukro. Among the genes coding for carbapenemases, only blaKPC 17.94%, blaNDM 30.76% and blaOXA48 38.46% were detected in the samples.

Characterization of wheat monogenic lines with known Sr genes and wheat cultivars for resistance to three new races of Puccinia graminis f. sp. tritici in China

Wheat stem rust, caused by Puccinia graminis f. sp. tritici(Pgt), is a potentially devastating fungal disease of wheat worldwide. The present study was to evaluate the resistance of 42 wheat monogenic lines with known stem rust resistance(Sr) genes and 69 wheat cultivars to three new Pgt races(34C0MRGQM, 34C3MKGQM, and 34C6MTGSM)identified from aeciospores at the seedling and adult-plant stages. The phenotyping results revealed that monogenic lines harboring resistance genes Sr9e, Sr17, Sr21, Sr22, Sr26, Sr30, Sr31, Sr33, Sr35, Sr36, Sr37, Sr38, Sr47, SrTmp,and SrTt3 were effectively resistant to all three Pgt races at the seedling and adult-plant stages. In contrast, monogenic lines containing Sr5, Sr6, Sr7b, Sr9a, Sr9d, Sr9f, Sr9g, Sr9b, Sr16, Sr24, Sr28, and Sr39 were highly susceptible to these races at both seedling and adult-plant stages. The other lines with Sr8a, Sr10, Sr11, Sr13, Sr14, Sr15, Sr18, Sr20,Sr19, Sr23, Sr25, Sr27, Sr29, Sr32, and Sr34, displayed variable levels of resistance to one or two of the tested races.Seedling infection types(ITs) and adult-plant infection responses(IRs) indicated that 41(59.4%) of the wheat cultivars showed high resistance to all the three races. Molecular marker analysis showed that four wheat culitvars likely carried Sr2, 20 wheat culitvars likely carried Sr31, 9 wheat culitvars likely carried Sr38, and none of the cultivars carried Sr24,Sr25, and Sr26. Our results provide a scientific basis for rational utilization of the tested Sr genes and wheat cultivars against these novel Pgt races.

Genomic location of Gb1, a unique gene conferring wheat resistance to greenbug biotype F

Greenbug(Schizaphis graminum, Rondani) is a serious insect pest in many wheat growing regions and has been infesting cereal crops in the USA for over a century. Continuous occurrence of new greenbug biotypes makes it essential to explore all greenbug resistant sources available to manage this pest. Gb1, a recessive greenbug resistance gene in DS28A, confers resistance to several economically important greenbug biotypes and is the only gene found to be resistant to greenbug biotype F. A set of 174 F_(2:3)lines from the cross DS28A × Custer was evaluated for resistance to greenbug biotype F in 2020 and 2022. Selective genotyping of the corresponding F_(2) population using single nucleotide polymorphism(SNP) markers generated by genotyping-by-sequencing(GBS) led to the identification of a candidate genomic region for Gb1. Thus, SSR markers previously mapped in this region were used to genotype the entire F2population,and kompetitive allele specific PCR(KASP) markers were also developed from SNPs in the target region.Gb1 was placed in the terminal region of the short arm of chromosome 1A, and its location was confirmed in a second population derived from the cross DS28A × PI 697274. The combined data analysis from the two mapping populations delimited Gb1 to a < 1 Mb interval between 13,328,200 and 14,241,426 bp on1AS.

High-resolution genetic mapping and identification of candidate genes for the wheat stem rust resistance gene Sr8155B1

Stem rust,caused by Puccinia graminis f.sp.tritici(Pgt),threatens global wheat production.Development of cultivars with increased resistance to stem rust by identification,mapping,and deployment of resistance genes is the best strategy for controlling the disease.In this study,we performed fine mapping and characterization of the all-stage stem rust resistance(Sr)gene Sr8155B1 from the durum wheat line 8155-B1.In seedling tests of biparental populations,Sr8155B1 was effective against six Chinese Pgt races tested.In a segregating population of 5060 gametes,Sr8155B1 was mapped to a 0.06-cM region flanked by markers Pku2772 and Pku43365,corresponding to 1.5-and 2.7-Mb regions in the Svevo and Chinese Spring reference genomes.Both regions include several typical nucleotide-binding leucine-rich repeat(NLR)and protein kinase genes that represent candidate genes.Among them,three NLR genes and three receptor-like protein kinases were highly polymorphic between the parental lines and their transcripts were upregulated in the homozygous resistant line TdR2 relative to its susceptible sister line TdS4.Four markers(Pku2772,Pku43365,Pku2950,and Pku3721)developed in this study,together with seedling resistance responses,correctly predicted Sr8155B1 absence or presence in 78 tetraploid wheat genotypes tested.The presence of Sr8155B1 in tetraploid wheat accessions CItr 14916,PI 197492,and PI 197493 was confirmed by mapping in three F_(2)populations.The genetic map and linked markers developed in this study may accelerate the deployment of Sr8155B1-mediated resistance in wheat breeding programs.

Trifunctional Cu-Mesh/Cu_(2)O@FeO Nanoarrays for Highly Efficient Degradation of Antibiotic, Inactivation of Antibiotic-Resistant Bacteria, and Damage of Antibiotics Resistance Genes

Trifunctional Cu-mesh/Cu_(2)O@FeO nanoarrays heterostructure is designed and fabricated by integrating CuCu_(2)O@FeO nanoarrays onto Cu-mesh(CM)via an in situ growth and phase transformation process.It is successfully applied to efficiently mitigate the antibiotic pollution,including degradation of antibiotics,inactivation of antibiotic-resistant bacteria(ARB),and damage of antibiotics resistance genes(ARGs).Under visible-light irradiation,CM/CuCu_(2)O@FeO nanoarrays exhibit a superior degradation efficiency on antibiotics(e.g.,up to 99%in 25 min for tetracycline hydrochloride,TC),due to the generated reactive oxygen species(ROS),especially the dominant·O^(2−).It can fully inactivate E.coli(HB101)with initial number of~108 CFU mL^(−1) in 10 min,which is mainly attributed to the synergistic effects of 1D nanostructure,dissolved metal ions,and generated ROS.Meanwhile,it is able to damage ARGs after 180 min of photodegradation,including tetA(vs TC)of 3.3 log 10,aphA(vs kanamycin sulfate,KAN)of 3.4 log 10,and tnpA(vs ampicillin,AMP)of 4.4 log 10,respectively.This work explores a green way for treating antibiotic pollution under visible light.

Preliminary Study on the Treatment Efficiency of Pasteurized Lime Thermal Alkaline Hydrolysis for Excess Activated Sludge and Reduction of Tetracycline Resistance Genes

Thermal alkaline hydrolysis is a common pretreatment method for the utilization of excess activated sludge(EAS).Owing to strict environment laws and need for better energy utilization,new methods were developed in this study to improve the efficiency of pretreatment method.Direct thermal hydrolysis(TH),pasteurized thermal hydrolysis(PTH),and alkaline pasteurized thermal hydrolysis(PTH+CaO and PTH+NaOH)methods were used to treat EAS.Each method was compared and analyzed in terms of dissolution in ammonium nitrogen(NH_(4)^(+)-N)and soluble COD(SCOD)in EAS.Furthermore,the removal of tetracycline resistance genes(TRGs)and class 1 transposon gene intI1 from EAS was investigated.The NH_(4)^(+)-N and SCOD concentrations in EAS treated by PTH were 1.24 and 2.58 times higher than those of TH.However,the removal efficiency of total TRGs and intI1 between the groups was comparable.The SCOD concentration of the PTH+NaOH group was 4.37 times higher than that of the PTH group,and the removal efficiency of total TRGs was increased by 9.52%compared with that by PTH.The NH_(4)^(+)-N and SCOD concentrations of the PTH+CaO group could reach 85.04%and 92.14%of the PTH+NaOH group,but the removal efficiency of total TRGs by PTH+CaO was 19.78%lower than that by PTH+NaOH.Thus,to reduce the financial cost in actual operation,lime(CaO)can be used instead of a strong alkali(NaOH),and pasteurized steam at 70℃ instead of conventional high-temperature heating to treat EAS.This study provides a reference for the development of alkaline hydrolysis under moderate temperatures along with the removal of TRGs in EAS.

Effects of Microplastics on Expression of Resistance Genes and Virulence Genes of Vibrio alginolyticus

[Objectives]To study the effects of microplastics on antibiotic resistance genes and virulence genes of Vibrio alginolyticus,so as to provide a certain reference for controlling marine pollution,curbing the spread of environmental antibiotic resistance genes and virulence genes,formulating environmental policies,and maintaining food safety.[Methods]After adding V.alginolyticus into the artificial seawater,they were divided into three groups,namely blank control group(BLK),polyvinyl chloride microplastic group(PVC group)and polyvinyl alcohol microplastic group(PVA group).Aerated culture experiments were carried out,and the effects of microplastics on the expression of resistance genes and virulence genes of V.alginolyticus were studied by PCR and qPCR methods.[Results]The presence of microplastics significantly changed the resistance gene structure of V.alginolyticus.Compared with the control group,the cfxA and cfr resistance genes were detected in the microplastic group.However,only PVC group detected blaZ resistance gene,and only PVA group did not detect aaC resistance gene.In addition,compared with the control group,the expressions of virulence genes in the microplastic group were all down-regulated(P<0.01).[Conclusions]This study provides some reference for curbing the spread of environmental antibiotic resistance genes and virulence genes,formulating environmental policies,and maintaining food safety,but the specific mechanisms of drug resistance and virulence need further research.

Molecular Screening of Rice Cultivated in Benin for the Identification of Xanthomonas oryzae Pv. oryzae and Bacterial Leaf Blight Resistance Genes

One of the most devastating diseases of rice worldwide is bacterial blight (BLB) caused by Xanthomonas oryzae pv. Oryzae (Xoo). In Benin, Xoo was first described in 2013 on wild rice Oryzae longistaminata. So far, no study has been done on Beninese Xoo strains. We do not know whether the pathogen has already passed into the rice varieties grown, or if they are exposed to other bacteria. Whereas the use of resistant varieties, carrying resistance genes, is the only highly effective and environmentally friendly way to control this disease, no information is available on these Xoo resistance genes in rice varieties grown in Benin apart from the one we recently. This study aims to identify Beninese Xoo strains, causing BLB and screen rice varieties grown in Benin for the main resistance genes. Diseased rice leaves showing typical symptoms of fire blight collected from different rice fields in the three phytogeographic areas of Benin were analyzed by PCR for Xoo-specific sequence identification. Furthermore, seventy-five collected rice accessions were screened to identify xa5, Xa7, xa13, and Xa21 resistance genes to Xoo. The results reveal that Xanthomonas oryzae was identified in two fields in Banikouara and one in Malanville. On the other hand, Sphingomonas sp. has been identified in several other rice fields in Benin. Forty-seven of seventy-five rice accessions examined (62.66%) carried Xoo resistance genes with 3 (4%) and 40 (53.33%) of xa5 and Xa21 respectively. None of the accessions had either Xa7 or xa13 resistance genes. Three accessions possess both xa5 and Xa21 genes. Isogenic lines IRBB60 and IRBB21, supposed to be a positive control, presented a Xoo sensitivity allele. These results indicate that Xoo has moved from the wild rice variety to the cultivated variety in northern Benin and varietal improvement programs must be implemented with varieties having several resistance genes for the efficient response against a possible BLB pandemic in Benin.

UV-Based Advanced Oxidation Processes for Antibiotic Resistance Control: Efficiency, Influencing Factors, and Energy Consumption

Antibiotic resistant bacteria(ARB)with antibiotic resistance genes(ARGs)can reduce or eliminate the effectiveness of antibiotics and thus threaten human health.The United Nations Environment Programme considers antibiotic resistance the first of six emerging issues of concern.Advanced oxidation processes(AOPs)that combine ultraviolet(UV)irradiation and chemical oxidation(primarily chlorine,hydrogen peroxide,and persulfate)have attracted increasing interest as advanced water and wastewater treatment technologies.These integrated technologies have been reported to significantly elevate the efficiencies of ARB inactivation and ARG degradation compared with direct UV irradiation or chemical oxidation alone due to the generation of multiple reactive species.In this study,the performance and underlying mechanisms of UV/chlorine,UV/hydrogen peroxide,and UV/persulfate processes for controlling ARB and ARGs were reviewed based on recent studies.Factors affecting the process-specific efficiency in controlling ARB and ARGs were discussed,including biotic factors,oxidant dose,UV fluence,pH,and water matrix properties.In addition,the cost-effectiveness of the UV-based AOPs was evaluated using the concept of electrical energy per order.The UV/chlorine process exhibited a higher efficiency with lower energy consumption than other UV-based AOPs in the wastewater matrix,indicating its potential for ARB inactivation and ARG degradation in wastewater treatment.Further studies are required to address the trade-off between toxic byproduct formation and the energy efficiency of the UV/chlorine process in real wastewater to facilitate its optimization and application in the control of ARB and ARGs.

Performance Parameters:Demobilization Antibiotic Resistant Bacteria(ARB)and Carrying Genes(ARG)in Wastewater Disinfection

The UV irradiation is used for removing Antibiotic Resistant Bacteria(ARB)and Antibiotic Resistance Genes(ARG)from wastewater treatment.Bacteriophages are viruses that infect within bacteria,are recognized for bacterial control.The influence of some parameters in quantification and performance influencing of pathogen demobilization could be considered in disinfection of wastewater.The comparison of Polyvalent phage(NE1)versus Coliphage(NE4)in suppressing a bacterium Escherichia coli(NDM-1:b-lactam-resistant)with UV irradiation was observed the efficacy in reduction of cells in the disinfection and parameter process.The results with the effect of UV-C irradiation on NDM-1 infected with 1%of NE4 showed a decrease of cells from 8×10^(6)to 2×10^(5)in 60 min with UV-C dose.The NDM1(E.coli)was infected with 1%of NE4(Polyvalent Phage)under magnetic stirring for 1 h,the cells count was 8×10^(6).After 1 h in UV-C e×posure,the cells number reached 3×10^(5).The NDM1 that was e×posed in 1 h of UV-C irradiation and then was infected with 1%of NE4.Cells counting were done 24 h after this procedure.These cells were e×posed in UV-C and showed a reduction in the number of cells from 1×10^(8)to 4×10^(5)after 60 min.The results indicate that bacteriophages can mitigate bacteria species,and combined the conventional water disinfection technologies that can support the microbial safety control strategies.

Recent Progress in Elucidating the Structure, Function and Evolution of Disease Resistance Genes in Plants

Plants employ multifaceted mechanisms to fight with numerous pathogens in nature. Resistance （R） genes are the most effective weapons against pathogen invasion since they can specifically recognize the corresponding pathogen effectors or associated protein（s） to activate plant immune responses at the site of infection. Up to date, over 70 R genes have been isolated from various plant species. Most R proteins contain conserved motifs such as nucleotide-binding site （NBS）, leucine-rich repeat （LRR）, Toll-interleukin-1 receptor domain （TIR, homologous to cytoplasmic domains of the Drosophila Toll protein and the manamalian intefleukin-1 receptor）, coiled-coil （CC） or leucine zipper （LZ） structure and protein kinase domain （PK）. Recent results indicate that these domains play significant roles in R protein interactions with effector proteins from pathogens and in activating signal transduction pathways involved in innate immunity. This review highlights an overview of the recent progress in elucidating the structure, function and evolution of the isolated R genes in different plant-pathogen interaction systems.

Molecular Tagging of a New Resistance Gene to Maize Dwarf Mosaic Virus Using Microsatellite Markers

With joint analysis based on the parents, F 1, F 2 and backcrosses, the authors found that the resistance of the maize inbred line Huangzaosi to the maize dwarf mosaic virus strain B was conditioned by a major gene and polygene, and identified a new major gene. Bulked segregate and microsatellite analysis of a F 2 progeny from the combination of Huangzaosi×Mo17 were used to identify the resistance gene, mdm1(t), on the long arm of chromosome 6. This new resistance gene is tightly linked to and located between the microsatellite markers loci, phi077 and bnlg391. The linkage distances between phi077-mdm1(t) and mdm1(t)-bnlg391 are 4.74 centiMorgan (cM) and 6.72 cM respectively.

Cloning and Analysis of a Disease Resistance Gene Homolog from Soybean

Conserved domains e.g. nucleotide binding site (NBS) were found in several cloned plant disease resistance genes. Based on the NBS domain, resistance gene analogs (RGAs) have been isolated previously and were used as probes to screen a soybean (Glycine max L. Merr.) cDNA library. A full-length cDNA, KR3, was obtained by screening the library and rapid amplification of cDNA ends (RACE) method. Sequence analysis revealed that the cDNA is 2 353 bp in length and the open reading frame (ORF) codes for a polypeptide of 636 amino acids with a Toll-Interleukin-1 receptor (TIR) and a NBS domain. Sequence alignment showed that it was similar to N gene of tobacco. The phylogenetic tree analysis of R proteins with NBS from higher plants was performed. The KR3 gene has low copies in soybean genome and its expression was induced by exogenous salicylic acid (SA).

Genotypic Analysis of Rice Blast Resistance Genes Pi-ta and Pi-b in Japonica Rice Varieties and Lines in Jiangsu Province

Pi-ta and Pi-b, the first cloned rice blast resistant genes, have been wide- ly used in rice blast resistance breeding for their lasting and stable resistance. To define the distribution of Pi-ta and Pi-b in japonica rice in Jiangsu, the genotypes of resistance genes Pi-ta and Pi-b in 40 varieties and 665 new lines were detected using functional markers of Pi-ta/pi-ta and Pi-b^pi-b alleles. The results showed that the resistance alleles of Pi-ta and Pi-b were widely spread in japonica rice varieties, and the distribution frequency of Pi-b was higher than that of Pi-ta. Most of the Lianjing serial varieties didn＇t carry the two resistance genes, but the two resistance genes were widely distributed in Wujing serial varieties. There was no significant dif- ference in distribution frequency of Pi-ta between new lines and commercial vari- eties. However, the distribution frequency of Pi-b in new lines was higher than that in commercial varieties. It was indicated that artificial selection was conducive to the improvement of distribution frequency of Pi-b in rice varieties. Among the 4 genotypes, the distribution frequency of pi-taJPi-b was highest （60.0%）, followed by Pi-ta/ Pi-b （33.5%） and pi-ta/pi-b （3.9%）. The frequency of Pi-taJpi-b was lowest, account- ing for only 2.6%. In terms of source of resistance genes in the four combinations, the resistant allele Pi-ta might be from parents of Wuxiangjing14, Wujing15 or Nanjing44, and Pi-b might come from parents of Wujing13, Wuxiangjing14, Wujing15 or Nanjing44. The analysis on the genotypic frequencies in offspring of the rice vari- eties showed that the resistance genotype of Pi-ta/Pi-b had the highest frequency in the cross combination of Nanjing44//Wujing13/Kantou194.

Molecular Detection of Resistance Genes to Stripe Rust and Powdery Mildew in Common Wheat Cultivar Yunmai52

Yunmai52, developed by crossing with common wheat-Haynaldia villosa6AL/6VS translocation line 92R149 as a resistant parent in 1992, was a common wheat cultivar approved and released in 2007 in Yunnan Province, China, which is characterized by high resistance to powdery mildew and stripe rust. In this study,an F_2 population derived from a cross K78S/Yunmai52 was constructed to investigate the resistance genes, where K78 S is a wheat male sterile line susceptible to powdery mildew and stripe rust. Phenotypic identification of the parents, F_1 and F_2 populations and chi-square analyses showed that F_1 population was immune to stripe rust and powdery mildew; the segregation ratio of resistance and susceptibility to powdery mildew（χ~2=1.10χ~2_（1,0.05）=3.84） and stripe rust（χ~2=0.15χ~2_（1,0.05）=3.84） fit to a 3：1 ratio in F_2 population, indicating that Yunmai52 harbors a dominant stripe rust resistance gene and a dominant powdery mildew resistance gene. The individuals were further detected with a marker co-segregated with Pm21（SCAR_（1400）） and two markers closely linked with Yr26（XWe173 and Xbarc181）. The results showed that polymorphic bands could be amplified between the parents and between resistance and susceptibility gene pools at the same locus. Randomly 96 individuals of F_2 population were selected for verification. The results showed that the phenotype was significantly correlated with the genotype. The detection accuracy of markers SCAR_（1400）, XWe173 and Xbarc181 was 100%, 97.91% and 92.70%, respectively.Yunmai52 harbored powdery mildew resistance gene Pm21 and stripe rust resistance gene Yr26, which were both derived from 6AL/6VS translocation line 92R149.In addition, the results also demonstrate that Pm21 and Yr26 are two genes conferring durable resistance to powdery mildew and stripe rust in wheat.