Combinations Of Resistance Genes Research Articles

Specificity of Induction of Glycopeptide Antibiotic Resistance in the Producing Actinomycetes.

Glycopeptide antibiotics are drugs of last resort for treating severe infections caused by Gram-positive pathogens. It is widely believed that glycopeptide-resistance determinants (van genes) are ultimately derived from the producing actinomycetes. We hereby investigated the relationship between the antimicrobial activity of vancomycin and teicoplanins and their differential ability to induce van gene expression in Actinoplanes teichomyceticus—the producer of teicoplanin—and Nonomuraea gerenzanensis—the producer of the teicoplanin-like A40926. As a control, we used the well-characterized resistance model Streptomyces coelicolor. The enzyme activities of a cytoplasmic-soluble d,d-dipeptidase and of a membrane-associated d,d-carboxypeptidase (corresponding to VanX and VanY respectively) involved in resistant cell wall remodeling were measured in the actinomycetes grown in the presence or absence of subinhibitory concentrations of vancomycin, teicoplanin, and A40926. Results indicated that actinomycetes possess diverse self-resistance mechanisms, and that each of them responds differently to glycopeptide induction. Gene swapping among teicoplanins-producing actinomycetes indicated that cross-talking is possible and provides useful information for predicting the evolution of future resistance gene combinations emerging in pathogens.

Spatio-temporal connectivity and host resistance influence evolutionary and epidemiological dynamics of the canola pathogen Leptosphaeria maculans.

Genetic, physiological and physical homogenization of agricultural landscapes creates ideal environments for plant pathogens to proliferate and rapidly evolve. Thus, a critical challenge in plant pathology and epidemiology is to design durable and effective strategies to protect cropping systems from damage caused by pathogens. Theoretical studies suggest that spatio‐temporal variation in the diversity and distribution of resistant hosts across agricultural landscapes may have strong effects on the epidemiology and evolutionary potential of crop pathogens. However, we lack empirical tests of spatio‐temporal deployment of host resistance to pathogens can be best used to manage disease epidemics and disrupt pathogen evolutionary dynamics in real‐world systems. In a field experiment, we simulated how differences in Brassica napus resistance deployment strategies and landscape connectivity influence epidemic severity and Leptosphaeria maculans pathogen population composition. Host plant resistance, spatio‐temporal connectivity [stubble loads], and genetic connectivity of the inoculum source [composition of canola stubble mixtures] jointly impacted epidemiology (disease severity) and pathogen evolution (population composition). Changes in population composition were consistent with directional selection for the ability to infect the host (infectivity), leading to changes in pathotype (multilocus phenotypes) and infectivity frequencies. We repeatedly observed decreases in the frequency of unnecessary infectivity, suggesting that carrying multiple infectivity genes is costly for the pathogen. From an applied perspective, our results indicate that varying resistance genes in space and time can be used to help control disease, even when resistance has already been overcome. Furthermore, our approach extends our ability to test not only for the efficacy of host varieties in a given year, but also for durability over multiple cropping seasons, given variation in the combination of resistance genes deployed.

Characterization of antimicrobial resistance genes in Haemophilus parasuis isolated from pigs in China.

BackgroundHaemophilus parasuis is a common porcine respiratory pathogen that causes high rates of morbidity and mortality in farmed swine. We performed a molecular characterization of antimicrobial resistance genes harbored by H. parasuis from pig farms in China.MethodsWe screened 143 H. parasuis isolates for antimicrobial susceptibility against six fluoroquinolone antibiotics testing by the broth microdilution method, and the presence of 64 antimicrobial resistance genes by PCR amplification and DNA sequence analysis. We determined quinolone resistance determining region mutations of DNA gyrase (gyrA and gyrB) and topoisomerase IV (parC and parE). The genetic relatedness among the strains was analyzed by pulsed-field gel electrophoresis.ResultsSusceptibility test showed that all isolates were low resistance to lomefloxacin (28.67%), levofloxacin (20.28%), norfloxacin (22.38%), ciprofloxacin (23.78%), however, high resistance levels were found to nalidixic acid (82.52%) and enrofloxacin (55.94%). In addition, we found 14 antimicrobial resistance genes were present in these isolates, including blaTEM-1, blaROB-1, ermB, ermA, flor, catl, tetB, tetC, rmtB, rmtD, aadA1, aac(3′)-llc, sul1, and sul2 genes. Interestingly, one isolate carried five antibiotic resistance genes (tetB, tetC, flor, rmtB, sul1). The genes tetB, rmtB, and flor were the most prevalent resistance genes in H. parasuis in China. Alterations in the gyrA gene (S83F/Y, D87Y/N/H/G) were detected in 81% of the strains and parC mutations were often accompanied by a gyrA mutation. Pulsed-field gel electrophoresis typing revealed 51 unique patterns in the isolates carrying high-level antibiotic resistance genes, indicating considerable genetic diversity and suggesting that the genes were spread horizontally.DiscussionThe current study demonstrated that the high antibiotic resistance of H. parasuis in piglets is a combination of transferable antibiotic resistance genes and multiple target gene mutations. These data provide novel insights for the better understanding of the prevalence and epidemiology of antimicrobial resistance in H. parasuis.

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

BackgroundResearch 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.ResultsQTL 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.ConclusionsThe 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.

Virulence genes in isolates of Klebsiella pneumoniae from the UK during 2016, including among carbapenemase gene-positive hypervirulent K1-ST23 and 'non-hypervirulent' types ST147, ST15 and ST383.

Klebsiella pneumoniae is a concern because of its multidrug resistance and the ability of hypervirulent types, especially capsular type K1-clonal complex 23 (K1-CC23), to cause community-acquired, life-threatening infections. Hypervirulent types carry an array of virulence genes including rmpA/rmpA2, coding for capsule up-regulation. We sought to identify isolates carrying these elements among submissions to the UK national reference laboratory during 2016. Virulence elements and carbapenemase genes were sought by PCR or from whole genome sequences. Isolates were typed by variable number tandem repeat analysis or by multi locus sequence typing from whole genome sequences. Long read nanopore sequencing was carried out on two isolates.Results/Key findings. Twelve of 1090 isolates (1.1 %) belonged to hypervirulent K1-CC23, with one carrying blaOXA-48 (KpvST23L_OXA-48). A further 24 rmpA/rmpA2-positive isolates were detected: eight belonged to hypervirulent types of capsular types K2 and K54; and 14 belonged to 'non-hypervirulent' ST147, ST15 and ST383 and also carried carbapenemase gene(s). Virulence, heavy metal and antibiotic resistance gene contents were compared from whole genome sequences of KpvST23L_OXA-48 and one of the ST147 isolates carrying blaNDM-1. They carried 94/96 and 26/96 of the virulence genes sought, and 23/23 and 9/23 of the heavy metal resistance genes, respectively. In the ST147 isolate, rmpA/rmpA2 and the aerobactin siderophore cluster were on a large virulence plasmid together with resistance genes. The yersiniabactin cluster was widely present among carbapenemase gene-positive isolates, including among those that were rmpA/rmpA2-negative. Our results highlight a combination of virulence and resistance genes, which could lead to untreatable invasive infections.

Harimaru: a new potato variety for a local specialty.

‘Harimaru’ is a new potato variety bred from a cross between ‘Saikai 35’ as a female parent and ‘Pike’ as a male parent. Marker selection was performed for 1,647 seedlings to combine resistance genes to late blight (R1), Potato virus Y (Rychc), Potato virus X (Rx1), and golden cyst nematode (H1). In total, 194 selected clones were evaluated in the field, among which the best clone was officially released as ‘Harimaru’. Its yield was slightly lower than the local standard variety, ‘May Queen’. However, it produces tasty potatoes, that do not become mushy with long boiling times despite its high starch content. ‘Harimaru’ may become a local specialty potato and its multiple resistance to potato viruses may allow cultivation using homemade seed tubers from the previous season’s crop.

Genetic Analysis of Adult Plant Resistance Genes to Stem Rust in Some Egyptian Bread Wheat Cultivars

Adult plant resistance (APR) to stem rust in seven Egyptian wheat cultivars i.e., Giza 168, Misr 1, Misr 2, Sakha 94, Gemmeiza 12, Sids 13 and Sids 14 and five stem rust resistance genes i.e., Sr9e, Sr11, Sr13, Sr28 and SrPl, were characterized during 2014/2015, 2015/2016 and 2016/2017 growing seasons at Sids Research Station. Stem rust resistance in seven Egyptian wheat cultivars was experimentally measured using two epidemiological parameters; final rust severity (FRS %) and area under disease progress curve (AUDPC). All of these parameters were found to be lower in the partially resistant (PR) cultivars; Giza-168, Sids-14, Sakha-94 and Gemmeiza-12, rather than those in the highly susceptible or fast-rusting cultivars; Misr-1, Misr-2 and Sids-13 as well as the check variety; Morocco. The partially resistant (PR) cultivars were slightly affected by stem rust infection resulting in little or few grain yield loss (%), less than the highly susceptible or fast-rusting cultivars which were severely rusted and showed high loss in grain yield under field conditions. F1 plants resulted from the crosses between these cultivars and the five stem rust resistance genes were planted, during 2014/2015 growing season, to produce F2 seeds. The resulted F2 plants were tested under field conditions in 2016/2017 at adult stage against a mixture of Puccinia graminis f.sp. tritici races. Segregations of F2 plants indicated that the stem rust resistance gene; Sr13 was identified in all the tested wheat cultivars, except Misr 2. While SrPl was detected in the three wheat cultivars i.e., Sids 14, Sakha 94 and Gemmeiza 12, Also the three wheat cultivars; Giza 168, Sids 13 and Gemmeiza 12 proved to have the resistance gene Sr9e. The stem rust resistance gene Sr28; was found only in the two cultivars, Giza 168 and Sids 14, but Sr11 was identified in three wheat cultivars i.e., Giza 168, Sids 13 and Gemmeiza 12. A combination or pyramiding of multiple genes for stem rust resistance in one particular wheat cultivar prolonged their life expectancy and gives it the potentiality to be more durable.

Inheritance of Virulence, Construction of a Linkage Map, and Mapping Dominant Virulence Genes in Puccinia striiformis f. sp. tritici Through Characterization of a Sexual Population with Genotyping-by-Sequencing.

Puccinia striiformis f. sp. tritici, the wheat stripe rust pathogen, is a dikaryotic, biotrophic, and macrocyclic fungus. Genetic study of P. striiformis f. sp. tritici virulence was not possible until the recent discovery of Berberis spp. and Mahonia spp. as alternate hosts. To determine inheritance of virulence and map virulence genes, a segregating population of 119 isolates was developed by self-fertilizing P. striiformis f. sp. tritici isolate 08-220 (race PSTv-11) on barberry leaves under controlled greenhouse conditions. The progeny isolates were phenotyped on a set of 29 wheat lines with single genes for race-specific resistance and genotyped with simple sequence repeat (SSR) markers, single nucleotide polymorphism (SNP) markers derived from secreted protein genes, and SNP markers from genotyping-by-sequencing (GBS). Using the GBS technique, 10,163 polymorphic GBS-SNP markers were identified. Clustering and principal component analysis grouped these markers into six genetic groups, and a genetic map, consisting of six linkage groups, was constructed with 805 markers. The six clusters or linkage groups resulting from these analyses indicated a haploid chromosome number of six in P. striiformis f. sp. tritici. Through virulence testing of the progeny isolates, the parental isolate was found to be homozygous for the avirulence loci corresponding to resistance genes Yr5, Yr10, Yr15, Yr24, Yr32, YrSP, YrTr1, Yr45, and Yr53 and homozygous for the virulence locus corresponding to resistance gene Yr41. Segregation was observed for virulence phenotypes in response to the remaining 19 single-gene lines. A single dominant gene or two dominant genes with different nonallelic gene interactions were identified for each of the segregating virulence phenotypes. Of 27 dominant virulence genes identified, 17 were mapped to two chromosomes. Markers tightly linked to some of the virulence loci may facilitate further studies to clone these genes. The virulence genes and their inheritance information are useful for understanding the host-pathogen interactions and for selecting effective resistance genes or gene combinations for developing stripe rust resistant wheat cultivars.

Antimicrobial resistance and underlying mechanisms in Staphylococcus aureus isolates.

To investigate the antimicrobial susceptibility of 97 clinical Staphylococcus aureus (S. aureus) strains against 14 antimicrobials and corresponding resistance mechanisms. The antimicrobial susceptibility of the isolates was determined using a disk diffusion method and antimicrobial resistance genes were screened by polymerase chain reaction. Mutations responsible for ciprofloxacin and rifampicin resistance were investigated by polymerase chain reaction and DNA sequencing. All isolates were found to be susceptible to vancomycin. Various rates of resistance to penicillin (83.5%), ampicillin (77.3%), erythromycin (63.9%), tetracycline (16.5%), amoxicillin/clavulanic acid (16.5%), ciprofloxacin (15.5%), trimethoprim/sulfamethoxazole (15.5%), oxacillin (13.4%), fusidic acid (12.4%), rifampin (6.2%), clindamycin (6.2%), gentamicin (6.2%) and mupirocin (5.2%) were determined. In addition, different combinations of resistance genes were identified among resistant isolates. Ciprofloxacin resistant isolates had mutations in codon 84 (Ser84Leu) and 106 (Gly106Asp) in the gyrA gene. Mutations in grlA were mostly related to Ser80Phe substitution. Leu466Ser mutation in the rpoB gene was detected in all rifampin resistant isolates. All methicillin resistant S. aureus isolates were SCCmec type V. In conclusion, it was determined that the isolates were resistant to different classes of antimicrobials at varying rates and resistance was mediated by different genetic mechanisms. Therefore, continuous monitoring of resistance in S. aureus strains is necessary to control their resistance for clinically important antimicrobials.

Evaluation of Stem Rust (Puccinia graminis f.sp tritici) Seedling Resistance in Kenyan Bread Wheat (Triticum aestivum L.) Mutant Lines

Race TTKSK (Ug99) of stem rust is a serious threat to wheat production worldwide because of its wide virulence on many cultivars and its rapid spread over countries. The objective of this study was to determine resistance to Puccinia graminis f.sp. tritici races of TTKTK and TTKSK at seedling stage among the wheat mutant lines. Duma, Kwale and NJBWII mutant lines were used since the parents are susceptible. Sixty three mutant lines along with six checks of NJBWII, Kwale, Duma, Cacuke, Robin and Kingbird were evaluated in the greenhouse at Kenya Agriculture and Livestock Organization, Njoro. A high frequency of mutant lines, 53.6% and 88.4% were resistant to TTKTK and TTKSK respectively, with low infection types ranging from “;” to “2+”. In addition, frequency of susceptibility was 46.38% for TTKTK and 11.59% for TTKSK on the evaluated genotypes. Resistance in these genotypes may be due to uncharacterized resistance genes or gene combinations that could not be resolved with the collection of races used. The information presented, when combined with the previous characterization of stem rust resistance genes will be useful for plant breeders in rationalizing germplasm enhancement programs.

Combination of rice blast resistance genes in the genotypes of russian rice varieties with the use of marker assisted selection

Grain productivity of rice is significantly reduced by dangerous disease blast. Therefore, the development of resistant high yielding rice varieties with the Pi group of genes is important. Use of molecular markers linked with the loci of resistance significantly optimizes the breeding process.
 The purpose of the research is to develop rice lines combining 2-6 loci of resistance to blast: Pi-1, Pi-2, Pi-33, Pi-ta, Pi-b, Pi-40 by molecular marking.
 Materials and Methods. As donors of resistance genes foreign samples were used, recipient Russian varieties. In the studies we used micro-satellites markers and PCR analysis.
 Results. In the first stage of the research as a result of hybridization domestic lines with genes Pi-l, Pi-2, Pi-33 were obtained. At the second stage hybrids with all 3 genes were developed. In the third stage genes Pi-b and Pi-ta and on the fourth Pi-40 were introduced.
 Conclusion. As a result, rice genotypes, combining 6 loci of blast resistance were developed with use of marker assisted selection.

Distribution of macrolide resistance mechanisms in Bulgarian clinical isolates of Streptococcus pyogenes during the years of 2013-2016.

Objectives of the present study was to determine and evaluate the distribution of genetic mechanisms associated with certain phenotypes of macrolide resistance in Bulgarian GAS isolated during the years of 2013-2016. All GAS strains were screened for the macrolide resistance genes erm(A), erm(B) and mef(A), using multiplex polymerase chain reaction (PCR). The minimal inhibitory concentrations (MICs) of erythromycin, azithromycin, clarithromycin, clindamycin were determined by E-tests. Almost 23% of GAS isolates obtained in 2013-2014 and near 40% of them in 2015-2016 contained various elements of resistance. The predominant gene was mef(A), which encodes an efflux pump (M-phenotype), identified in 57.84% of the macrolide-resistant strains. The next frequently prevalent mechanism was a combination of mef(A) and erm(B) in 22.55%, which determined high-level inducible or constitutive resistance to macrolides, lincosamides and streptogramins (iMLSB or cMLSB). The highest MIC value (>256mg/L) was detected in association with erm(B) (p<0.05). The MIC range was observed to be much higher in the isolates with combinations of resistance genes vs. those with mef genes alone (p<0.05). The data about the distribution and prevalence of macrolide resistance mechanisms obtained in this study can help in the treatment of persistent and recurrent GAS infections and in the correct choice of empiric therapy.

Surveillance of the activity of solithromycin (CEM-101) against bacteria from respiratory tract infections

The activity of solithromycin, a fourth-generation macrolide and novel fluoroketolide, was evaluated by determining its minimum inhibitory concentration (MIC) (via Clinical and Laboratory Standards Institute broth microdilution) against 2797 contemporary clinical respiratory tract isolates collected from North America, Europe, Asia-Pacific and other regions of the world in 2012–13. Solithromycin was very active against Streptococcus pneumoniae and Streptococcus pyogenes, with MIC90 of 0.25 and 0.12 µg/mL, respectively. Isolates with combined macrolide resistance genes ermB and mefE had a higher solithromycin MIC distribution, but the highest MIC recorded was 1 µg/mL for one S. pneumoniae isolate from Japan and one S. pyogenes isolate from China.Solithromycin was active against methicillin-susceptible Staphylococcus aureus (MIC90 0.12 µg/mL) but not against methicillin-resistant S. aureus (MRSA) (MIC90 >32 µg/mL). However, MRSA strains most commonly observed with community-associated infections (i.e. SCCmec IV) were more susceptible than other MRSA SCCmec types. Gram-negative pathogens that cause community-acquired respiratory tract infections (Haemophilus influenzae and Moraxella catarrhalis) were inhibited by solithromycin isolated from worldwide locations (MIC90 2 and 0.25 µg/mL, respectively).These data support the continued development of solithromycin for the treatment of community-acquired pneumonia globally.

Determination of resistance and virulence genes in Enterococcus faecalis and E. faecium strains isolated from poultry and their genotypic characterization by ADSRRS-fingerprinting

The aim of this study was to determine the antimicrobial resistance of E. faecalis and E. faecium strains isolated from poultry and to carry out genotypic characterization thereof with the ADSRRS-fingerprinting method (amplification of DNA fragments surrounding rare restriction sites) and analysis of the genetic relatedness between the isolates with different resistance and virulence determinants. Samples were collected from 70 4-week-old chickens and tested for Enterococcus. Minimum inhibitory concentrations of 11 antimicrobials were determined using the broth microdilution method. Detection of antibiotic resistance and virulence genes was performed using PCR, and molecular analysis was carried out using the ADSRRS-fingerprinting method. The highest percentage of strains was resistant to tetracycline (60.5%) and erythromycin (54.4%), and a large number exhibited high-level resistance to both kanamycin (42.1%) and streptomycin (34.2%). Among 8 genes encoding AME, the tested strains showed mainly the presence of [aph(3′)-IIIa], [ant(6)-Ia], [aac(6′)-Ie-aph(2′′)-Ia], and [ant(9)-Ia] genes. Phenotypic resistance to erythromycin was encoded in 98.4% strains by the erm B gene. Genotypic resistance to tetracycline in E. faecium was associated with the presence of tet M and tet L (respectively, in 95.5 and 57.7% of the isolates); in contrast, E. faecalis strains were characterized mainly by the presence of tet O (83.3%). The virulence profile was homogenous for all E. faecium strains and included only efa Afm and ccf genes. All E. faecalis strains exhibited efa Afs, gel E, and genes encoding sex pheromones. The strains tested exhibited 34 genotypic profiles. Comparative analysis of phenotypic and genotypic resistance and virulence profiles and confrontation thereof with the genotypes of the strains tested showed that strains assigned to a particular genotype have an identical phenotypic resistance profile and a panel of resistance and virulence genes. The results of this study confirm that poultry can be a reservoir of resistant E. faecium and E. faecalis strains with multiple combinations of resistance and virulence genes, whose specific panel determines not only phenotypic characteristics but also has a strong correlation with the genotypic profiles of the strains.

Evaluating the contribution of Yr genes to stripe rust resistance breeding through marker-assisted detection in wheat

Numerous stripe rust resistance genes have been identified from wheat, and new virulent races of Puccinia striiformis f. sp. tritici have also emerged in recent years. Deployment of diverse combinations of resistance genes is an efficient way to combat virulent evolution of strip rust pathogen. In this study, publically available molecular markers were used to identify the distribution of 36 Yr genes in 672 wheat accessions. The effectiveness of Yr genes individually and in combinations was also evaluated in field conditions. The result showed effective resistance of some recently applied genes, such as Yr15 and Yr65. It also showed the lost efficacy of some once widely used genes, such as Yr9 and Yr10. Moreover, significant additive effects were observed in some gene combinations, such as Yr9 + Yr18 and Yr30 + Yr46. Proper deploying of Yr genes and utilizing the positive interactions will be helpful for durable resistance breeding in wheat.

Early selection of potato clones with resistance genes: the relationship between combined resistance and agronomical characteristics

Cultivating resistant varieties of potato is the most effective and environmentally safe method of protecting against pests and diseases that affect potato crops. Therefore, potato breeding is focused on developing more resistant varieties so that the use of plant health products can be reduced during the cultivation cycle. Resistance to late blight, viruses and nematodes is the most important agricultural requirement. The use of molecular markers allows for the effective selection of resistant genotypes at early stages of breeding. However, the impact of early selection for resistance on the agronomic value of the final selected clones is a cause of concern for breeders. This study investigates the relationship between the presence of the combined resistance genes H1, Ry-fsto and Rpi-phu1, which confer resistance to nematodes, potato virus Y and late blight, respectively, and certain agricultural traits. The agronomic performance of most clones with and without the identified resistance genes was similar in terms of tuber yield, tuber size, tuber shape regularity, eye depth and tuber defect intensity. Some combinations with Ry-fsto may produce higher yields but may also be associated with more tuber defects. No negative relationships were observed between the combined resistance genes H1 + Ry-fsto + Rpi-phu1 and potato quality.

Marker assisted introgression of blast (Pi-2 and Pi-54) genes in to the genetic background of elite, bacterial blight resistant indica rice variety, Improved Samba Mahsuri

Improved Samba Mahsuri (ISM), a bacterial blight (BB) resistant (possessing Xa21, xa13 and xa5), high-yielding rice variety possessing fine-grain type has been recently released for cultivation and is becoming increasingly popular across many parts of India. However, the new variety is highly susceptible to blast disease, which limits its spread. In the present study, we attempted to improve blast resistance of ISM by introgressing two major blast resistance genes (Pi-2 and Pi-54) by marker-assisted backcross breeding through two separate sets of backcrosses, one involving transfer of Pi-2 and another involving Pi-54. At each backcross generation, closely linked PCR-based markers were used to select plants possessing either Pi-2 (first cross) or Pi-54 (second cross) along with Xa21, xa13 and microsatellite markers polymorphic between donor and recurrent parents were used to select plants that have maximum contribution from the recurrent parent genome (background selection). Selected BC2F1 plant possessing Pi-2 was intercrossed with a selected BC2F1 plant possessing Pi-54 and the resultant intercross F1 was selfed to generate intercross F1 possessing the two blast and two BB resistance genes. The intercross F1s were then selfed to generate intercross F2s possessing different combination of resistance genes in homozygous condition including the four-gene pyramid lines. The homozygous lines were advanced further through pedigree method of selection. When selected gene-pyramid lines possessing both blast and BB resistance genes were screened against the two diseases, they exhibited high level of disease resistance. Further, all the gene-pyramid lines possessed grain type identical to ISM and yielded equivalent to or better than the original variety. This is the first report documenting the stacking of two major genes for blast (Pi-2 + Pi-54) and two major genes for BB (Xa21 + xa13) in rice through marker-assisted backcross breeding in a elite cultivar Improved Samba Mahsuri.

Characterization of Lr75: a partial, broad-spectrum leaf rust resistance gene in wheat.

Here, we describe a strategy to improve broad-spectrum leaf rust resistance by marker-assisted combination of two partial resistance genes. One of them represents a novel partial adult plant resistance gene, named Lr75. Leaf rust caused by the fungal pathogen Puccinia triticina is a damaging disease of wheat (Triticum aestivum L.). The combination of several, additively-acting partial disease resistance genes has been proposed as a suitable strategy to breed wheat cultivars with high levels of durable field resistance. The Swiss winter wheat cultivar 'Forno' continues to show near-immunity to leaf rust since its release in the 1980s. This resistance is conferred by the presence of at least six quantitative trait loci (QTL), one of which is associated with the morphological trait leaf tip necrosis. Here, we used a marker-informed strategy to introgress two 'Forno' QTLs into the leaf rust-susceptible Swiss winter wheat cultivar 'Arina'. The resulting backcross line 'ArinaLrFor' showed markedly increased leaf rust resistance in multiple locations over several years. One of the introgressed QTLs, QLr.sfr-1BS, is located on chromosome 1BS. We developed chromosome 1B-specific microsatellite markers by exploiting the Illumina survey sequences of wheat cv. 'Chinese Spring' and mapped QLr.sfr-1BS to a 4.3cM interval flanked by the SSR markers gwm604 and swm271. QLr.sfr-1BS does not share a genetic location with any of the described leaf rust resistance genes present on chromosome 1B. Therefore, QLr.sfr-1BS is novel and was designated as Lr75. We conclude that marker-assisted combination of partial resistance genes is a feasible strategy to increase broad-spectrum leaf rust resistance. The identification of Lr75 adds a novel and highly useful gene to the small set of known partial, adult plant leaf rust resistance genes.

Development of common wheat lines with the recombinant arm 1RS as a source of new combinations of disease and pest resistance genes

A combination of recombinant-inbred lines of the F6 generation from the cross B-16 ќ AR 7086 between lines with two wheat-rye translocations, 1BL/1RS from the Petkus and 1AL/1RS from the rye Insave, was developed. Using gliadin and secalin loci as genetic markers we identified recombinant arm 1RS in positions 1A and 1B in about 10% of lines. The rest of lines with the rye material may also carry recombinant 1RS, which can be identified with DNA markers. Lines with recombinant arm 1RS may serve as a source of new combination of rye genes for disease and pest resistance.

Evaluation of tomato entries with different combinations of resistance genes to tomato yellow leaf curl disease in Tunisia

AbstractTomato yellow leaf curl virus (TYLCV) is one of the most widespread begomoviruses transmitted by the whitefly Bemisia tabaci that cause tomato yellow leaf curl virus diseases (TYLCDs). TYLCD losses can be especially severe in open‐field tomato (Solanum lycopersicum L.) crops. TYLCV is particularly well known and widespread in the Mediterranean (Med) countries where TYLCD control is mostly based on insecticidal control of B. tabaci populations. Unfortunately, Tunisian B. tabaci populations include Middle East‐Asia Minor I and the Med species that have developed resistance to many classes of insecticides. Therefore, TYLCD‐resistant cultivars are essential for sustainable disease management. Six TYLCD resistance genes (Ty) have been introgressed from wild species into cultivated tomato and are available for breeding. Information on the Ty genes or gene combinations is useful for breeding resistant cultivars. To this end, 14 tomato lines carrying different Ty gene combinations and two susceptible tomato entries were evaluated for TYLCD incidence and severity in two field trials during late season in Tunisia. Entries with Ty‐1/Ty‐3 + Ty‐2 offered the highest levels of resistance in Tunisia.