Dominant Resistance Gene Research Articles

Improved versions of rice maintainer line, APMS 6B, possessing two resistance genes, Xa21 and Xa38, exhibit high level of resistance to bacterial blight disease

APMS 6B is the stable maintainer of the CMS line APMS 6A, which is the female parent of the popular Indian rice hybrid DRRH 3. APMS 6B has good combining ability and plant stature but is highly susceptible to bacterial blight (BB) disease. In order to improve the BB resistance of APMS 6B, we pyramided two major, dominant BB resistance genes, Xa21 and Xa38, through marker-assisted backcross breeding (MABB). Improved Samba Mahsuri (ISM) was used as the donor for Xa21 while PR 114 (Xa38) served as the donor for Xa38. Individual crosses [APMS 6B/ISM and APMS 6B/PR 114 (Xa38)] were performed, and true F1 plants were then backcrossed with APMS 6B and the MABB process was continued till BC3. A single positive BC3F1 plant identified from both the crosses with maximum genotypic and phenotypic similarity with APMS 6B was selfed to generate BC3F2s. At BC3F2 generation, plants homozygous for either Xa21 or Xa38 were identified and further confirmed for the absence of two major fertility restorer genes, Rf3 and Rf4. A single such homozygous BC3F2 plant, each from both the crosses, was then inter-mated to generate ICF1s (inter-cross F1s). Selected ICF1 plants possessing both the BB resistance genes were selfed to generate ICF2s. A total of 42 ICF2 plants homozygous for both Xa21 and Xa38 were identified and screened with parental polymorphic SSR markers to identify the best F2 plants having the maximum recurrent parent genome recovery. Twelve best ICF2 plants were advanced up to ICF5. The ICF5 lines displayed very high level of BB resistance and were similar to APMS 6B in terms of agro-morphological characters. Further, most of these lines also showed complete maintenance ability and such lines are being advanced for conversion to WA-CMS lines.

The Sw-5 Gene Cluster: Tomato Breeding and Research Toward Orthotospovirus Disease Control.

The Sw-5 gene cluster encodes protein receptors that are potentially able to recognize microbial products and activate signaling pathways that lead to plant cell immunity. Although there are several Sw-5 homologs in the tomato genome, only one of them, named Sw-5b, has been extensively studied due to its functionality against a wide range of (thrips-transmitted) orthotospoviruses. The Sw-5b gene is a dominant resistance gene originally from a wild Peruvian tomato that has been used in tomato breeding programs aiming to develop cultivars with resistance to these viruses. Here, we provide an overview starting from the first reports of Sw-5 resistance, positional cloning and the sequencing of the Sw-5 gene cluster from resistant tomatoes and the validation of Sw-5b as the functional protein that triggers resistance against orthotospoviruses. Moreover, molecular details of this plant–virus interaction are also described, especially concerning the roles of Sw-5b domains in the sensing of orthotospoviruses and in the signaling cascade leading to resistance and hypersensitive response.

Differential Shape of Geminivirus Mutant Spectra Across Cultivated and Wild Hosts With Invariant Viral Consensus Sequences.

Geminiviruses (family Geminiviridae) possess single-stranded circular DNA genomes that are replicated by cellular polymerases in plant host cell nuclei. In their hosts, geminivirus populations behave as ensembles of mutant and recombinant genomes, known as viral quasispecies. This favors the emergence of new geminiviruses with altered host range, facilitating new or more severe diseases or overcoming resistance traits. In warm and temperate areas several whitefly-transmitted geminiviruses of the genus Begomovirus cause the tomato yellow leaf curl disease (TYLCD) with significant economic consequences. TYLCD is frequently controlled in commercial tomatoes by using the dominant Ty-1 resistance gene. Over a 45 day period we have studied the diversification of three begomoviruses causing TYLCD: tomato yellow leaf curl virus (TYLCV), tomato yellow leaf curl Sardinia virus (TYLCSV) and tomato yellow leaf curl Malaga virus (TYLCMaV, a natural recombinant between TYLCV and TYLCSV). Viral quasispecies resulting from inoculation of geminivirus infectious clones were examined in plants of susceptible tomato (ty-1/ty-1), heterozygous resistant tomato (Ty-1/ty-1), common bean, and the wild reservoir Solanum nigrum. Differences in virus fitness across hosts were observed while viral consensus sequences remained invariant. However, the complexity and heterogeneity of the quasispecies were high, especially in common bean and the wild host. Interestingly, the presence or absence of the Ty-1 allele in tomato did not lead to differences in begomovirus mutant spectra. However, the fitness decrease of TYLCSV and TYLCV in tomato at 45 dpi might be related to an increase in CP (Coat protein) mutation frequency. In Solanum nigrum the recombinant TYLCMaV, which showed lower fitness than TYLCSV, at 45 dpi actively explored Rep (Replication associated protein) ORF but not the overlapping C4. Our results underline the importance of begomovirus mutant spectra during infections. This is especially relevant in the wild reservoir of the viruses, which has the potential to maintain highly diverse mutant spectra without modifying their consensus sequences.

A bean common mosaic virus (BCMV)-resistance gene is fine-mapped to the same region as Rsv1-h in the soybean cultivar Suweon 97.

In the soybean cultivar Suweon 97, BCMV-resistance gene was fine-mapped to a 58.1-kb region co-localizing with the Soybean mosaic virus (SMV)-resistance gene, Rsv1-h raising a possibility that the same gene is utilized against both viral pathogens. Certain soybean cultivars exhibit resistance against soybean mosaic virus (SMV) or bean common mosaic virus (BCMV). Although several SMV-resistance loci have been reported, the understanding of the mechanism underlying BCMV resistance in soybean is limited. Here, by crossing a resistant cultivar Suweon 97 with a susceptible cultivar Williams 82 and inoculating 220 F2 individuals with a BCMV strain (HZZB011), we observed a 3:1 (resistant/susceptible) segregation ratio, suggesting that Suweon 97 possesses a single dominant resistance gene against BCMV. By performing bulked segregant analysis with 186 polymorphic simple sequence repeat (SSR) markers across the genome, the resistance gene was determined to be linked with marker BARSOYSSR_13_1109. Examining the genotypes of nearby SSR markers on all 220 F2 individuals then narrowed down the gene between markers BARSOYSSR_13_1109 and BARSOYSSR_13_1122. Furthermore, 14 previously established F2:3 lines showing crossovers between the two markers were assayed for their phenotypes upon BCMV inoculation. By developing six more SNP (single nucleotide polymorphism) markers, the resistance gene was finally delimited to a 58.1-kb interval flanked by BARSOYSSR_13_1114 and SNP-49. Five genes were annotated in this interval of the Williams 82 genome, including a characteristic coiled-coil nucleotide-binding site-leucine-rich repeat (CC-NBS-LRR, CNL)-type of resistance gene, Glyma13g184800. Coincidentally, the SMV-resistance allele Rsv1-h was previously mapped to almost the same region, thereby suggesting that soybean Suweon 97 likely relies on the same CNL-type R gene to resist both viral pathogens.

Mapping of a dominant rust resistance gene revealed two R genes around the major Rust_QTL in cultivated peanut (Arachis hypogaea L.)

A consensus rust QTL was identified within a 1.25 cM map interval of A03 chromosome in cultivated peanut. This map interval contains a TIR-NB-LRR R gene and four pathogenesis-related genes. Disease resistance in plants is manifested due to the specific interaction between the R gene product and its cognate avirulence gene product (AVR) in the pathogen. Puccinia arachidis Speg. causes rust disease and inflicts economic damages to peanut. Till now, no experimental evidence is known for the action of R gene in peanut for rust resistance. A fine mapping approach towards the development of closely linked markers for rust resistance gene was undertaken in this study. Phenotyping of an RIL population at five environments for field rust score and subsequent QTL analysis has identified a 1.25cM map interval that harbored a consensus major Rust_QTL in A03 chromosome. This Rust_QTL is flanked by two SSR markers: FRS72 and SSR_GO340445. Both the markers clearly identified strong association of the mapped region with rust reaction in both resistant and susceptible genotypes from a collection of 95 cultivated peanut germplasm. This 1.25cM map interval contained 331.7kb in the physical map of A. duranensis and had a TIR-NB-LRR category R gene (Aradu.Z87JB) and four glucan endo-1,3 β glucosidase genes (Aradu.RKA6M, Aradu.T44NR, Aradu.IWV86 and Aradu.VG51Q). Another resistance gene analog was also found in the vicinity of mapped Rust_QTL. The sequence between SSR markers, FRS72 and FRS49, contains an LRR-PK (Aradu.JG217) which is equivalent to RHG4 in soybean. Probably, the protein kinase domain in AhRHG4 acts as an integrated decoy for the cognate AVR from Puccinia arachidis and helps the TIR-NB-LRR R-protein to initiate a controlled program cell death in resistant peanut plants.

The pepper Bs4C proteins are localized to the endoplasmic reticulum (ER) membrane and confer disease resistance to bacterial blight in transgenic rice.

SummaryTranscription activator‐like effector (TALE)‐dependent dominant disease resistance (R) genes in plants, also referred to as executor R genes, are induced on infection by phytopathogenic bacteria of the genus Xanthomonas harbouring the corresponding TALE genes. Unlike the traditional R proteins, the executor R proteins do not determine the resistance specificity and may function broadly in different plant species. The executor R gene Bs4C‐R in the resistant genotype PI 235047 of the pepper species Capsicum pubescens (CpBs4C‐R) confers disease resistance to Xanthomonas campestris pv. vesicatoria (Xcv) harbouring the TALE genes avrBsP/avrBs4. In this study, the synthetic genes of CpBs4C‐R and two other Bs4C‐like genes, the susceptible allele in the genotype PI585270 of C. pubescens (CpBs4C‐S) and the CaBs4C‐R homologue gene in the cultivar ‘CM334’ of Capsicum annum (CaBs4C), were characterized in tobacco (Nicotiana benthamiana) and rice (Oryza sativa). The Bs4C genes induced cell death in N. benthamiana. The functional Bs4C‐eCFP fusion proteins were localized to the endoplasmic reticulum (ER) membrane in the leaf epidermal cells of N. benthamiana. The Xa10 promoter‐Bs4C fusion genes in transgenic rice conferred strain‐specific disease resistance to Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial blight in rice, and were specifically induced by the Xa10‐incompatible Xoo strain PXO99A(pHM1avrXa10). The results indicate that the Bs4C proteins from pepper species function broadly in rice and the Bs4C protein‐mediated cell death from the ER is conserved between dicotyledonous and monocotyledonous plants, which can be utilized to engineer novel and enhanced disease resistance in heterologous plants.

Dn10, a New Gene Conferring Resistance to Russian Wheat Aphid Biotype 2 in Iranian Wheat Landrace PI 682675

Russian wheat aphid [RWA, Diuraphis noxia (Mordvilko)] is a serious pest of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) that causes heavy yield losses in many countries, and RWA biotype 2 (RWA2) is virulent to most RWA resistance genes. The objective of this study was to characterize a gene for resistance to RWA2 in Iranian landrace PI 682675, a single‐plant selection from PI 624151. F2:3 and F3:4 families derived from cross PI 682675 × Zhengyou 6 were used to map the resistance gene. PI 682675 carries a dominant resistance gene, Dn10, flanked by simple sequence repeat markers Xgwm437 and Xwmc488 on chromosome 7DL. Physical mapping indicated that Dn10 resides in bin 7DL 0.1 to 0.77, whereas Dn2401 and Dn626580 that also confer resistance to RWA2 were physically mapped to 7DS. Allelism tests showed that Dn10 was located ∼17.4 cM from Dn2401 and 22.2 cM from Dn626580. Dn10 is a new resistance gene that should be used widely in wheat breeding.

Mapping of a novel, major late blight resistance locus in the diploid (1EBN) Mexican Solanum pinnatisectum Dunal on chromosome VII

AbstractLate blight caused by the oomycete Phytophthora infestans (Mont.) de Bary (Pi) is the most important foliar disease of potato worldwide. An intraspecific hybrid between individuals of a resistant and a susceptible S. pinnatisectum accession was backcrossed to the susceptible parent to generate a segregating population for late blight resistance consisting of 84 plants. In detached‐leaflet assays, reaction to late blight segregated in a 1r:1s manner in BC1 progeny indicating the presence of a single dominant resistance gene. A genetic map was constructed based on 1,583 DArT/SSR markers which were allocated to 12 linkage groups, covering 1,793.5 cM with an average marker distance of 1.1 cM. The late blight resistance locus derived from S. pinnatisectum was mapped on chromosome VII. In comparison with the previously reported resistance genes Rpi1 and Rpi2, the new target resistance locus most likely is located on the opposite arm of chromosome VII. Results of this study will serve as a basis for future fine mapping of the late blight resistance locus and the development of locus‐specific markers for marker‐assisted selection.

Rbc2, a new dominant gene for resistance of soybean to Cowpea mild mottle virus: Inheritance and mapping

Abstract The objective of this work was to study the inheritance of soybean resistance to Soybean Steam Necrosis (SSN) and to map the resistance gene(s), using an F2 population from the cross between the soybean cultivars BRS 133 (resistant) and CD 206 (susceptible). A phenotypic evaluation was performed under controlled conditions, in a greenhouse. In a population of 114 F2 plants, 92 were resistant, and 22 were susceptible. The result is compatible with the inheritance of one dominant gene (χ2=1.98, P = 15.97%). Analysis of F1 and backcross populations confirmed the inheritance of one dominant gene. Bulk segregant analysis (BSA) was used as the mapping strategy. The resistance gene was mapped on chromosome 18 of the soybean genome, between markers Sat_308 and Satt303. This dominant gene is located on the same chromosome where the recessive SSN resistance gene rbc1 was mapped, at 8cM distance, and was named Rbc2.

Genome-wide association mapping of the architecture of susceptibility to the root-knot nematode Meloidogyne incognita in Arabidopsis thaliana.

Summary Susceptibility to the root‐knot nematode Meloidogyne incognita in plants is thought to be a complex trait based on multiple genes involved in cell differentiation, growth and defence. Previous genetic analyses of susceptibility to M. incognita have mainly focused on segregating dominant resistance genes in crops. It is not known if plants harbour significant genetic variation in susceptibility to M. incognita independent of dominant resistance.To study the genetic architecture of susceptibility to M. incognita, we analysed nematode reproduction on a highly diverse set of 340 natural inbred lines of Arabidopsis thaliana with genome‐wide association mapping. We observed a surprisingly large variation in nematode reproduction among these lines.Genome‐wide association mapping revealed four quantitative trait loci (QTLs) located on chromosomes 1 and 5 of A. thaliana significantly associated with reproductive success of M. incognita, none of which harbours typical resistance gene homologues. Mutant analysis of three genes located in two QTLs showed that the transcription factor BRASSINAZOLE RESISTANT1 and an F‐box family protein may function as (co‐)regulators of susceptibility to M. incognita in Arabidopsis.Our data suggest that breeding for loss‐of‐susceptibility, based on allelic variants critically involved in nematode feeding, could be used to make crops more resilient to root‐knot nematodes.

Soybean mosaic virus: a successful potyvirus with a wide distribution but restricted natural host range.

Soybean mosaic virus (SMV) is a species within the genus Potyvirus, family Potyviridae, which includes almost one-quarter of all known plant RNA viruses affecting agriculturally important plants. The Potyvirus genus is the largest of all genera of plant RNA viruses with 160 species. The filamentous particles of SMV, typical of potyviruses, are about 7500Å long and 120Å in diameter with a central hole of about 15Å in diameter. Coat protein residues are arranged in helices of about 34Å pitch having slightly less than nine subunits per turn. The SMV genome consists of a single-stranded, positive-sense, polyadenylated RNA of approximately 9.6kb with a virus-encoded protein (VPg) linked at the 5' terminus. The genomic RNA contains a single large open reading frame (ORF). The polypeptide produced from the large ORF is processed proteolytically by three viral-encoded proteinases to yield about 10 functional proteins. A small ORF, partially overlapping the P3 cistron, pipo, is encoded as a fusion protein in the N-terminus of P3 (P3N+PIPO). SMV's host range is restricted mostly to two plant species of a single genus: Glycine max (cultivated soybean) and G.soja (wild soybean). SMV is transmitted by aphids non-persistently and by seeds. The variability of SMV is recognized by reactions on cultivars with dominant resistance (R) genes. Recessive resistance genes are not known. As a consequence of its seed transmissibility, SMV is present in all soybean-growing areas of the world. SMV infections can reduce significantly seed quantity and quality (e.g. mottled seed coats, reduced seed size and viability, and altered chemical composition). The most effective means of managing losses from SMV are the planting of virus-free seeds and cultivars containing single or multiple R genes. The interactions of SMV with soybean genotypes containing different dominant R genes and an understanding of the functional role(s) of SMV-encoded proteins in virulence, transmission and pathogenicity have been investigated intensively. The SMV-soybean pathosystem has become an excellent model for the examination of the genetics and genomics of a uniquely complex gene-for-gene resistance model in a crop of worldwide importance.

Inheritance and Allelic Relationship Among Downy Mildew Resistance Genes in Pearl Millet.

Pearl millet downy mildew (DM), caused by Sclerospora graminicola, is of serious economic concern to pearl millet farmers in the major crop-growing areas of the world. To study the inheritance and allelic relationship among genes governing resistance to this disease, three DM-resistant pearl millet lines (834B, IP 18294-P1, and IP 18298-P1) and one susceptible line (81B) were selected on the basis of disease reaction under greenhouse conditions against two isolates of S. graminicola (Sg 526-1 and Sg 542-1). Three resistant parents were crossed with the susceptible parent to generate F1, F2, and backcross BC1P1 (susceptible parent × F1) and BC1P2 (resistant parent × F1) generations for inheritance study. To carry out a test for allelism, the three resistant parents were crossed with each other to generate F1 and F2 generations. The different generations of these crosses were screened for disease reaction against two isolates (Sg 526-1 and Sg 542-1) by artificial inoculation under greenhouse conditions. The segregation pattern of resistance in the F2 and corresponding backcross generations revealed that resistance to DM is controlled by a single dominant gene in 834B and IP 18294-P1 and by two dominant genes in IP 18298-P1. A test for allelism inferred that a single dominant gene for resistance in 834B is nonallelic to that which governs resistance in IP 18294-1, whereas one of the two dominant genes for DM resistance in IP 18298-P1 against the test isolates is allelic to the gene for DM resistance in 834B and a second gene is allelic to the resistance gene present in IP 18294-P1.

Transfer of Downy Mildew Resistance from Wild Basil (Ocimum americanum) to Sweet Basil (O. basilicum).

Sweet basil (Ocimum basilicum) is susceptible to downy mildew caused by the oomycete foliar pathogen Peronospora belbahrii. No resistant varieties of sweet basil are commercially available. Here, we report on the transfer of resistance gene Pb1 from the highly resistant tetraploid wild basil O. americanum var. americanum (PI 500945, 2n = 4x = 48) to the tetraploid susceptible O. basilicum 'Sweet basil' (2n = 4x = 48). F1 progeny plants derived from the interspecific hybridization PI 500945 × Sweet basil were resistant, indicating that the gene controlling resistance (Pb1) is dominant, but sterile due to the genetic distance between the parents. Despite their sterility, F1 plants were pollinated with the susceptible parent and 115 first backcross generation to the susceptible parent (BCs1) embryos were rescued in vitro. The emerging BCs1 plants segregated, upon inoculation, 5:1 resistant/susceptible, suggesting that resistance in F1 was controlled by a pair of dominant genes (Pb1A and Pb1A'). Thirty-one partially fertile BCs1 plants were self-pollinated to obtain BCs1-F2 or were backcrossed to Sweet basil to obtain the second backcross generation to the susceptible parent (BCs2). In total, 1 BCs1-F2 and 22 BCs2 progenies were obtained. The BCs1-F2 progeny segregated 35:1 resistant/susceptible, as expected from a tetraploid parent with two dominant resistant genes. The 22 BCs2 progenies segregated 1:1 resistant/susceptible (for a BCs1 parent that carried one dominant gene for resistance) or 5:1 (for a BCs1 parent that carried two dominant genes for resistance) at a ratio of 4:1. The data suggest that a pair of dominant genes (Pb1A and Pb1A') residing on a two homeologous chromosomes is responsible for resistance of PI 500945 against P. belbahrii.

Linkage between the I-3 gene for resistance to Fusarium wilt race 3 and increased sensitivity to bacterial spot in tomato.

The negative association between the I - 3 gene and increased sensitivity to bacterial spot is due to linkage drag (not pleiotropy) and may be remedied by reducing the introgression size. Fusarium wilt is one of the most serious diseases of tomato (Solanum lycopersicum L.) throughout the world. There are three races of the pathogen (races 1, 2 and 3), and the deployment of three single, dominant resistance genes corresponding to each of these has been the primary means of controlling the disease. The I-3 gene was introgressed from S. pennellii and confers resistance to race 3. Although I-3 provides effective control, it is negatively associated with several horticultural traits, including increased sensitivity to bacterial spot disease (Xanthomonas spp.). To test the hypothesis that this association is due to linkage with unfavorable alleles rather than to pleiotropy, we used a map-based approach to develop a collection of recombinant inbred lines varying for portions of I-3 introgression. Progeny of recombinants were evaluated for bacterial spot severity in the field for three seasons, and disease severities were compared between I-3 introgression haplotypes for each recombinant. Results indicated that increased sensitivity to bacterial spot is not associated with the I-3 gene, but rather with an upstream region of the introgression. A survey of public and private inbred lines and hybrids indicates that the majority of modern I-3 germplasm contains a similarly sized introgression for which the negative association with bacterial spot likely persists. In light of this, it is expected that the development and utilization of a reduced I-3 introgression will significantly improve breeding efforts for resistance to Fusarium wilt race 3.

A New Resistance Gene against Potato Late Blight Originating from Solanum pinnatisectum Located on Potato Chromosome 7.

Late blight, caused by the pathogen Phytophthora infestans, is one of the most devastating diseases of potato. Here, we describe a new single dominant resistance gene, Rpi2, from the Mexican diploid wild species Solanum pinnatisectum that confers high level and broad spectrum resistance to late blight. The Rpi2 locus confers full resistance to complex isolates of P. infestans, for which race specificity has not yet been demonstrated. This new gene, flanked by the RFLP-derived marker SpT1756 and AFLP-derived marker SpAFLP2 with a minimal genetic distance of 0.8 cM, was mapped to potato chromosome 7. Using the genomic sequence data of potato, we estimated that the physical distance of the nearest marker to the resistance gene was about 27 kb. The map location and other evidence indicated that this resistance locus was different from the previously reported resistance locus Rpi1 on the same chromosome from S. pinnatisectum. The presence of other reported resistance genes in the target region, such as Gro1-4, I-3, and three NBS-LLR like genes, on a homologous tomato genome segment indicates the Rpi2-related region is a hotspot for resistance genes. Comparative sequence analysis showed that the order of nine markers mapped to the Rpi2 genetic map was highly conserved on tomato chromosome 7; however, some rearrangements were observed in the potato genome sequence. Additional markers and potential resistance genes will promote accurate location of the site of Rpi2 and help breeders to introduce this resistance gene into different cultivars by marker-aided selection.

Identification and molecular genetic mapping of Chili veinal mottle virus (ChiVMV) resistance genes in pepper (Capsicum annuum)

Chili veinal mottle virus (ChiVMV) threatens the agricultural production of peppers (Capsicum annuum) in Asia and Africa. In this study, we evaluated ChiVMV resistance in the four pepper varieties CV3, CV4, CV8, and CV9. Segregation analyses revealed that CV3 and CV8 contain the single dominant resistance gene Cvr1, and CV9 contains the single recessive resistance gene cvr4. SNP markers were developed and used to map the Cvr1 gene in CV3 to the short arm of chromosome 6 where NLR genes are clustered. In CV4 oligogenic resistance loci were detected. A genotyping-by-sequencing (GBS) combined with modified sliding window approach mapped two resistance loci, to chromosomes 6 and 10. The development of SNP markers and the resulting knowledge of genomic positioning will assist in breeding ChiVMV-resistant pepper varieties and in the fine mapping of ChiVMV resistance genes.

High prevalence of OXA-type carbapenemases among Acinetobacter baumannii strains in a teaching hospital of Tehran.

Nosocomial infection caused by carbapenem-resistant Acinetobacter baumannii (CRAB) has created a public health concern all around the world. In this study, 100 isolates of CRAB from hospitalized patients during 2015-2016 at Imam Khomeini Hospital were investigated to determine the rates of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains using Kirby-Bauer disk diffusion method. The minimum inhibitory concentrations (MICs) of six antibiotics were determined by broth microdilution method. Multiplex polymerase chain reaction (PCR) was performed to detect blaOXA-51 like and blaOXA-58 like, blaOXA-23 like, and blaOXA-24 like that are encoding resistance to carbapenems. All CRAB isolates were MDR and XDR and 2% of them were pandrug-resistant (PDR), whereas colistin, polymyxin B, and tigecycline were the most effective agents. All isolates were positive for blaOXA-51 like by PCR. The frequency of blaOXA-23 like and blaOXA-24 like was 81% and 22%, respectively. Findings of this study showed that very few therapeutic options remained for the treatment of CRAB infections and blaOXA-23 like is a dominant resistance gene in CRAB at this hospital.

Cytogenetic analysis and mapping of leaf rust resistance in Aegilops speltoides Tausch derived bread wheat line Selection2427 carrying putative gametocidal gene(s).

Leaf rust (Puccinia triticina) is a major biotic stress affecting wheat yields worldwide. Host-plant resistance is the best method for controlling leaf rust. Aegilops speltoides is a good source of resistance against wheat rusts. To date, five Lr genes, Lr28, Lr35, Lr36, Lr47, and Lr51, have been transferred from Ae. speltoides to bread wheat. In Selection2427, a bread wheat introgresed line with Ae. speltoides as the donor parent, a dominant gene for leaf rust resistance was mapped to the long arm of chromosome 3B (LrS2427). None of the Lr genes introgressed from Ae. speltoides have been mapped to chromosome 3B. Since none of the designated seedling leaf rust resistance genes have been located on chromosome 3B, LrS2427 seems to be a novel gene. Selection2427 showed a unique property typical of gametocidal genes, that when crossed to other bread wheat cultivars, the F1 showed partial pollen sterility and poor seed setting, whilst Selection2427 showed reasonable male and female fertility. Accidental co-transfer of gametocidal genes with LrS2427 may have occurred in Selection2427. Though LrS2427 did not show any segregation distortion and assorted independently of putative gametocidal gene(s), its utilization will be difficult due to the selfish behavior of gametocidal genes.

Fine-mapping and identification of a novel locus Rsc15 underlying soybean resistance to Soybean mosaic virus.

Rsc15, a novel locus underlying soybean resistance to SMV, was fine mapped to a 95-kb region on chromosome 6. The Rsc15- mediated resistance is likely attributed to the gene GmPEX14 , the relative expression of which was highly correlated with the accumulation of H 2 O 2 along with the activities of POD and CAT during the early stages of SMV infection in RN-9. Soybean mosaic virus (SMV) causes severe yield losses and seed quality deterioration in soybean [Glycine max (L.) Merr.] worldwide. A series of single dominant SMV resistance genes have been identified on respective soybean chromosomes 2, 13 and 14, while one novel locus, Rsc15, underlying resistance to the virulent SMV strain SC15 from soybean cultivar RN-9 has been recently mapped to a 14.6-cM region on chromosome 6. However, candidate gene has not yet been identified within this region. In the present study, we aimed to fine map the Rsc15 region and identify candidate gene(s) for this invaluable locus. High-resolution fine-mapping revealed that the Rsc15 gene was located in a 95-kb genomic region which was flanked by the two simple sequence repeat (SSR) markers SSR_06_17 and BARCSOYSSR_06_0835. Allelic sequence comparison and expression profile analysis of candidate genes inferred that the gene Glyma.06g182600 (designated as GmPEX14) was the best candidate gene attributing for the resistance of Rsc15, and that genes encoding receptor-like kinase (RLK) (i.e., Glyma.06g175100 and Glyma.06g184400) and serine/threonine kinase (STK) (i.e., Glyma.06g182900 and Glyma.06g183500) were also potential candidates. High correlations were established between the relative expression level of GmPEX14 and the hydrogen peroxide (H2O2) concentration and activities of catalase (CAT) and peroxidase (POD) during the early stages of SMV-SC15 infection in RN-9. The results of the present study will be useful in marker-assisted breeding for SMV resistance and will lead to further understanding of the molecular mechanisms of host resistance against SMV.

Marker-Assisted Development and Evaluation of Near-Isogenic Lines for Broad-Spectrum Powdery Mildew Resistance Gene Pm2b Introgressed into Different Genetic Backgrounds of Wheat.

At present, most of released wheat cultivars or breeding lines in China are susceptible to powdery mildew (Pm) (caused by Blumeria graminis f. sp. tritici, Bgt), so there is an urgent need to rapidly transfer effective and broad-spectrum Pm resistance genes into elite cultivars/lines. Near-isogenic lines (NILs) with short target gene region are very important in molecular breeding and map-based cloning and can be developed by combining marker-assisted selection and conventional phenotypic identification. However, no Pm gene NILs were reported by using this method in the previous studies. A new broad-spectrum dominant resistance gene Pm2b, derived from the Chinese wheat breeding line KM2939, conferred high resistance to Pm at both the seedling and adult stages. In this study, with the aid of forward and background selection (FS and BS) using molecular markers, the Pm2b gene was introgressed into three elite susceptible commercial cultivars Shimai 15, Shixin 828, and Kenong 199 through the back-crossing procedure. With the appropriate backcrossing generations, selected population sizes and marker number for BS, the homozygous resistant BC3F2:3 NILs of Pm2b gene in the three genetic backgrounds with the highest recipient genome composition of about 99%, confirmed by simple sequence repeat markers and 660K single nucleotide polymorphic array, were developed and evaluated for the powdery mildew resistance and agronomic traits. The different resistance and similar or improved agronomic performance between Pm2b NILs and their corresponding recurrent parents indicated their potential value in the marker-assisted breeding of the Pm2b gene. Moreover, the development of four flanked diagnostic markers (CFD81, BWM25, BWM20, and BWM21) of the Pm2 gene can effectively assist the forward selection and accelerate the transfer and use of this resistance gene.