Tuberculosis associated with infliximab, a tumor necrosis factor alpha-neutralizing agent.

BACKGROUND: Infliximab is a humanized antibody against tumor necrosis factor alpha (TNF-alpha) that is used in the treatment of Crohn's disease and rheumatoid arthritis. Approximately 147,000 patients throughout the world have received infliximab. Excess TNF-alpha in association with tuberculosis may cause weight loss and night sweats, yet in animal models it has a protective role in the host response to tuberculosis. There is no direct evidence of a protective role of TNF-alpha in patients with tuberculosis. METHODS: We analyzed all reports of tuberculosis after infliximab therapy that had been received as of May 29, 2001, through the MedWatch spontaneous reporting system of the Food and Drug Administration. RESULTS: There were 70 reported cases of tuberculosis after treatment with infliximab, for a median of 12 weeks. In 48 patients, tuberculosis developed after three or fewer infusions. Forty of the patients had extrapulmonary disease (17 had disseminated disease, 11 lymph node disease, 4 peritoneal disease, 2 pleural disease, and 1 each meningeal, enteric, paravertebral, bone, genital, and bladder disease). The diagnosis was confirmed by a biopsy in 33 patients. Of the 70 reports, 64 were from countries with a low incidence of tuberculosis. The reported frequency of tuberculosis in association with infliximab therapy was much higher than the reported frequency of other opportunistic infections associated with this drug. In addition, the rate of reported cases of tuberculosis among patients treated with infliximab was higher than the available background rates. CONCLUSIONS: Active tuberculosis may develop soon after the initiation of treatment with infliximab. Before prescribing the drug, physicians should screen patients for latent tuberculosis infection or disease.

Proactive safety surveillance.

Growth in health information systems presents opportunities to enhance postmarketing safety surveillance of medical products. Spontaneous suspected side effect reports provide the foundation, but we need to 'proactively' improve their quality and our strategies to seek signals. In our more familiar 'reactive' mode, we examine hypotheses from inquiries or publicity. Such responsive evaluations remain essential but may miss latent information on unsuspected risks. Efficient techniques to disclose hidden clusters and associations may emerge through adaptation of approaches from industrial quality control and other disciplines. Data-driven techniques like exploratory analysis, control charts, and time series modeling may help in sifting through accumulated data and in screening consecutive submissions to discern hints of new product hazards or of more specific understanding about previously identified potential side effects. We also need to cultivate non-spontaneous data for hypothesis generation as well as testing, the systematic epidemiologic evaluation of questions and concerns. This hypothesis testing function will assume greater importance if proactive safety surveillance methods yield larger numbers of putatively positive findings. Whether from spontaneous reports or other sources, signals that could have arisen by chance alone usually represent only clues to potential hazards until or unless they can be verified through independent studies.

Stevens-Johnson syndrome and toxic epidermal necrolysis after vaccination: reports to the vaccine adverse event reporting system.

We conducted a telephone survey of reports of Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) to the Vaccine Adverse Event Reporting System. We identified six cases of SJS or TEN after vaccination without other obvious triggers, suggesting that SJS and TEN might very rarely be caused by vaccination. Confirmation of this hypothesis will likely require controlled studies.

The MLA6 coiled-coil, NBS-LRR protein confers AvrMla6-dependent resistance specificity to Blumeria graminis f. sp. hordei in barley and wheat.

The barley Mla locus confers multiple resistance specificities to the obligate fungal biotroph, Blumeria (= Erysiphe) graminis f. sp. hordei. Interspersed within the 240 kb Mla complex are three families of resistance gene homologs (RGHs). Probes from the Mla-RGH1 family were used to identify three classes of cDNAs. The first class is predicted to encode a full-length CC-NBS-LRR protein and the other two classes contain alternatively spliced, truncated variants. Utilizing a cosmid that contains a gene corresponding to the full-length candidate cDNA, two single-cell expression assays were used to demonstrate complementation of AvrMla6-dependent, resistance specificity to B. graminis in barley and wheat. The first of these assays was also used to substantiate previous genetic data that the Mla6 allele requires the signaling pathway component, Rar1, for function. Computational analysis of MLA6 and the Rar1-independent, MLA1 protein reveals 91.2% identity and shows that the LRR domain is subject to diversifying selection. Our findings demonstrate that highly related CC-NBS-LRR proteins encoded by alleles of the Mla locus can dictate similar powdery mildew resistance phenotypes yet still require distinct downstream signaling components.

The epidemiology of fatalities reported to the vaccine adverse event reporting system 1990-1997.

PURPOSE: To examine the fatalities reported to the federally administered Vaccine Adverse Event Reporting System (VAERS), a passive surveillance system, in its first 7 years. METHODS: The working data set included variables such as demographic information, dates of vaccination, adverse event onset and death, vaccines administered, and vaccination facility data. Frequencies for these data and state reporting rates were calculated. RESULTS: A total of 1266 fatalities were reported to VAERS during July 1990 through June 1997. The number of death reports peaked in 1992-1993 and then declined. The overall median age of cases was 0.4 years, with a range of 1 day to 104 years. Nearly half of the deaths were attributed to sudden infant death syndrome (SIDS). CONCLUSIONS: The trend of decreasing numbers of deaths reported to VAERS since 1992-1993 follows that observed for SIDS overall for the US general population following implementation of the 'Back to Sleep' program. These data may support findings of past controlled studies showing that the association between infant vaccination and SIDS is coincidental and not causal. VAERS reports of death after vaccination may be stimulated by the temporal association, rather than by any causal relationship.

Rds and Rih mediate hypersensitive cell death independent of gene-for-gene resistance to the oat crown rust pathogen Puccinia coronata f. sp. avenae.

The Pca crown rust resistance cluster in the diploid Avena genus confers gene-for-gene specificity to numerous isolates of Puccinia coronata f. sp. avenae. Recombination breakpoint analysis indicates that specificities conferred by the Pca cluster are controlled by at least five distinct genes, designated Pc81, Pc82, Pc83, Pc84, and Pc85. Avena plants with the appropriate genotype frequently respond to P. coronata by undergoing hypersensitive cell death at the sites of fungal infection. Autofluorescence of host cells in response to P. coronata occurs in plants that develop visible necrotic lesions but not in plants that lack this phenotype. Two newly described, non-Pc loci were shown to control hypersensitive cell death. Rds (resistance-dependent suppressor of cell death) suppresses the hypersensitive response (HR), but not the resistance, mediated by the Pc82 resistance gene. In contrast, Rih (resistance-independent hypersensitive cell death) confers HR in both resistant and susceptible plants. Linkage analysis indicates that Rds is unlinked to the Pca cluster, whereas Rih is tightly linked to it. These results indicate that multiple synchronous pathways affect the development of hypersensitive cell death and that HR is not essential for resistance to crown rust. Further characterization of these genes will clarify the relationship between plant disease resistance and localized hypersensitive cell death.

An anchored AFLP- and retrotransposon-based map of diploid Avena.

A saturated genetic map of diploid oat was constructed based on a recombinant inbred (RI) population developed from a cross between Avena strigosa (Cereal Introduction, C.I. 3815) and A. wiestii (C.I. 1994). This 513-locus map includes 372 AFLP (amplified fragment length polymorphism) and 78 S-SAP (sequence-specific-amplification polymorphism) markers, 6 crown-rust resistance loci, 8 resistance-gene analogs (RGAs), one morphological marker, one RAPD (random amplified polymorphic DNA) marker, and is anchored by 45 grass-genome RFLP (restriction fragment length polymorphism) markers. This new A. strigosa x A. wiestii RI map is colinear with a diploid Avena map from an A. atlantica x A. hirtula F2 population. However, some linkage blocks were rearranged as compared to the RFLP map derived from the progenitor A. strigosa x A. wiestii F2 population. Mapping of Bare-1-like sequences via sequence-specific AFLP indicated that related retrotransposons had considerable heterogeneity and widespread distribution in the diploid Avena genome. Novel amplified fragments detected in the RI population suggested that some of these retrotransposon-like sequences are active in diploid Avena. Three markers closely linked to the Pca crown-rust resistance cluster were identified via AFLP-based bulk-segregant analysis. The derived STS (sequence-tagged-site) marker, Agx4, cosegregates with Pc85, the gene that provides resistance specificity to crown-rust isolate 202 at the end of the cluster. This framework map will be useful in gene cloning, genetic mapping of qualitative genes, and positioning QTL (quantitative trait loci) of agricultural importance.

Postlicensure safety surveillance for varicella vaccine.

CONTEXT: Since its licensure in 1995, the extensive use of varicella vaccine and close surveillance of the associated anecdotal reports of suspected adverse effects provide the opportunity to detect potential risks not observed before licensure because of the relatively small sample size and other limitations of clinical trials. OBJECTIVES: To detect potential hazards, including rare events, associated with varicella vaccine, and to assess case reports for clinical and epidemiological implications. DESIGN AND SETTING: Postlicensure case-series study of suspected vaccine adverse events reported to the US Vaccine Adverse Event Reporting System (VAERS) from March 17, 1995, through July 25, 1998. MAIN OUTCOME MEASURES: Numbers of reported adverse events, proportions, and reporting rates (reports per 100,000 doses distributed). RESULTS: VAERS received 6574 case reports of adverse events in recipients of varicella vaccine, a rate of 67.5 reports per 100,000 doses sold. Approximately 4% of reports described serious adverse events, including 14 deaths. The most frequently reported adverse events were rashes, possible vaccine failures, and injection site reactions. Misinterpretation of varicella serology after vaccination appeared to account for 17% of reports of possible vaccine failures. Among 251 patients with herpes zoster, 14 had the vaccine strain of varicella zoster virus (VZV), while 12 had the wild-type virus. None of 30 anaphylaxis cases was fatal. An immunodeficient patient with pneumonia had the vaccine strain of VZV in a lung biopsy. Pregnant women occasionally received varicella vaccine through confusion with varicella zoster immunoglobulin. Although the role of varicella vaccine remained unproven in most serious adverse event reports, there were a few positive rechallenge reports and consistency of many cases with syndromes recognized as complications of natural varicella. CONCLUSION: Most of the reported adverse events associated with varicella vaccine are minor, and serious risks appear to be rare. We could not confirm a vaccine etiology for most of the reported serious events; several will require further study to clarify whether varicella vaccine plays a role. Education is needed to ensure appropriate use of varicella serologic assays and to eliminate confusion between varicella vaccine and varicella zoster immunoglobulin. JAMA. 2000;284:1271-1279

The Mla (powdery mildew) resistance cluster is associated with three NBS-LRR gene families and suppressed recombination within a 240-kb DNA interval on chromosome 5S (1HS) of barley.

Powdery mildew of barley, caused by Erysiphe graminis f. sp. hordei, is a model system for investigating the mechanism of gene-for-gene interaction between large-genome cereals and obligate-fungal pathogens. A large number of loci that confer resistance to this disease are located on the short arm of chromosome 5(1H). The Mla resistance-gene cluster is positioned near the telomeric end of this chromosome arm. AFLP-, RAPD-, and RFLP-derived markers were used to saturate the Mla region in a high-resolution recombinant population segregating for the (Mla6 + Mla14) and (Mla13 + Ml-Ru3) resistance specificities. These tightly linked genetic markers were used to identify and develop a physical contig of YAC and BAC clones spanning the Mla cluster. Three distinct NBS-LRR resistance-gene homologue (RGH) families were revealed via computational analysis of low-pass and BAC-end sequence data derived from Mla-spanning clones. Genetic and physical mapping delimited the Mla-associated, NBS-LRR gene families to a 240-kb interval. Recombination within the RGH families was at least 10-fold less frequent than between markers directly adjacent to the Mla cluster.

Mitochondrial transcript processing and restoration of male fertility in T-cytoplasm maize.

Cytoplasmic male sterility (CMS) systems have been useful in the production of hybrid seed in a number of crops. The Texas or T-cytoplasmic male-sterile (cms-T) system was used extensively in the 1960s to eliminate the need for hand detasseling in hybrid maize production. As a consequence of the 1970 epidemic of southern corn leaf blight, cms-T is no longer widely used commercially. However, it has been developed as a model system to study the genetic and molecular mechanisms underlying male sterility and fertility restoration. Male sterility in T-cytoplasm maize results from the action of a T-cytoplasm-specific mitochondrial gene, T-urf13. Full (or partial) fertility restoration of T-cytoplasm maize is mediated by the Rf2 nuclear restorer in combination with one of three other restorers: Rf1, Rf8, or Rf*. Rf2 encodes a protein highly similar to mitochondrial aldehyde dehydrogenases; Rf1, Rf8, and Rf* each mediate discrete T-urf13 mitochondrial transcript processing events. To test the functionality of Rf1, Rf8, or Rf*, a T-cytoplasm transformation system is under development. AFLP bulk-segregant analysis has been used to identify DNA markers closely linked to the Rf8 locus. These tools will provide a foundation for determining mechanisms of nuclear-directed mitochondrial RNA processing and fertility restoration.

Hair loss after routine immunizations.

CONTEXT: Alopecia is a recognized adverse effect of numerous medications, but vaccines are not normally considered a cause for unexpected loss of hair. OBJECTIVE: To describe case reports of hair loss after routine vaccines and to assess the hypothesis that vaccinations might induce hair loss. DESIGN: Case series with telephone follow-up. METHODS: Review of spontaneous reports to the Food and Drug Administration, the Centers for Disease Control and Prevention, and the Vaccine Adverse Event Reporting System. MAIN OUTCOME MEASURE: Loss of hair following immunization. RESULTS: A total of 60 evaluable reports submitted since 1984 and coded for "alopecia" after immunizations included 16 with positive rechallenge (hair loss after vaccination on more than 1 occasion), 4 of which were definite and 12 possible or probable. Of the 60 cases, 46 had received hepatitis B vaccines. Both of the currently available recombinant products, as well as the former plasma-derived product, were represented. Females predominated in all age groups. The majority of patients recovered, but clinical features, such as intervals from vaccination until onset and the extent and reversibility of hair loss, varied widely. Nine patients reported previous medication allergy. CONCLUSION: There may be an association, probably very rare, between vaccinations and hair loss. More than 1 pathophysiologic mechanism may be responsible. Since apparently nonrandom distributions by vaccine, age, and sex could reflect biased case ascertainment, further research will be needed in defined populations with consistent case detection.

A large community outbreak of salmonellosis caused by intentional contamination of restaurant salad bars.

CONTEXT: This large outbreak of foodborne disease highlights the challenge of investigating outbreaks caused by intentional contamination and demonstrates the vulnerability of self-service foods to intentional contamination. OBJECTIVE: To investigate a large community outbreak of Salmonella Typhimurium infections. DESIGN: Epidemiologic investigation of patients with Salmonella gastroenteritis and possible exposures in The Dalles, Oregon. Cohort and case-control investigations were conducted among groups of restaurant patrons and employees to identify exposures associated with illness. SETTING: A community in Oregon. Outbreak period was September and October 1984. PATIENTS: A total of 751 persons with Salmonella gastroenteritis associated with eating or working at area restaurants. Most patients were identified through passive surveillance; active surveillance was conducted for selected groups. A case was defined either by clinical criteria or by a stool culture yielding S Typhimurium. RESULTS: The outbreak occurred in 2 waves, September 9 through 18 and September 19 through October 10. Most cases were associated with 10 restaurants, and epidemiologic studies of customers at 4 restaurants and of employees at all 10 restaurants implicated eating from salad bars as the major risk factor for infection. Eight (80%) of 10 affected restaurants compared with only 3 (11%) of the 28 other restaurants in The Dalles operated salad bars (relative risk, 7.5; 95% confidence interval, 2.4-22.7; P<.001). The implicated food items on the salad bars differed from one restaurant to another. The investigation did not identify any water supply, food item, supplier, or distributor common to all affected restaurants, nor were employees exposed to any single common source. In some instances, infected employees may have contributed to the spread of illness by inadvertently contaminating foods. However, no evidence was found linking ill employees to initiation of the outbreak. Errors in food rotation and inadequate refrigeration on ice-chilled salad bars may have facilitated growth of the S Typhimurium but could not have caused the outbreak. A subsequent criminal investigation revealed that members of a religious commune had deliberately contaminated the salad bars. An S Typhimurium strain found in a laboratory at the commune was indistinguishable from the outbreak strain. CONCLUSIONS: This outbreak of salmonellosis was caused by intentional contamination of restaurant salad bars by members of a religious commune.

Vaccine Safety Datalink project: a new tool for improving vaccine safety monitoring in the United States. The Vaccine Safety Datalink Team.

OBJECTIVE: To fill the large "gaps and limitations" in current scientific knowledge of rare vaccine adverse events identified in recent reviews of the Institute of Medicine. METHODS: Computerized information on immunization, medical outcomes, and potential confounders on more than 500 000 children 0 to 6 years of age is linked annually at several health maintenance organizations to create a large cohort for multiple epidemiologic studies of vaccine safety. RESULTS: Analysis of 3 years of follow-up data shows that 549 488 doses of diphtheria-tetanus-pertussis (DTP) and 310 618 doses of measles-mumps-rubella (MMR) vaccines have been administered to children in the study cohort. Analyses for associations between vaccines and 34 medical outcomes are underway. Screening of automated data shows that seizures are associated with receipt of DTP on the same day (relative risk [RR], 2.1; 95% confidence interval [CI], 1.1 to 4.0) and 8 to 14 days after receipt of MMR (RR, 3.0; 95% CI, 2.1 to 4.2). The diversity of vaccination exposures in this large cohort permits us to show that an apparent association of seizures 8 to 14 days after Haemophilus influenzae type b vaccine (RR, 1.6; 95% CI, 1.2 to 2.1) was attributable to confounding by simultaneous MMR vaccination; the association disappears with appropriate adjustment (RR, 1.0; 95% CI, 0.7 to 1.4). CONCLUSION: Preliminary design, data collection, and analytic capability of the Vaccine Safety Datalink project has been validated by replication of previous known associations between seizures and DTP and MMR vaccines. The diversity in vaccine administration schedules permits potential disentangling of effects of simultaneous and combined vaccinations. The project provides a model of public health-managed care collaborations in addition to an excellent infrastructure for safety and other studies of vaccines.

Rf8 and Rf* mediate unique T-urf13-transcript accumulation, revealing a conserved motif associated with RNA processing and restoration of pollen fertility in T-cytoplasm maize.

Rf8 is a newly described nuclear gene that can substitute for Rf1 to partially restore pollen fertility to male-sterile, T-cytoplasm maize. Families segregating for Rf8 were used to investigate the mechanism of this fertility restoration and to compare it to the restoration conditioned by Rf1. Although Rf8 is unlinked to the rf1 locus, it also alters T-urf13 mitochondrial transcript accumulation and reduces the accumulation of the URF13 protein. Like the 1.6- and 0.6-kilobase (kb) T-urf13 transcripts that accumulate in T-cytoplasm plants carrying Rf1, 1.42- and 0.42-kb transcripts accumulate in plants that are partially restored by Rf8. A survey of T-cytoplasm maize lines, inbreds, and F1 hybrids by mitochondrial RNA gel blot analyses revealed that Rf8 is rare in maize germplasm. These surveys revealed the presence of another rare, weak restorer factor, Rf*, which is uniquely associated with the accumulation of 1.4- and 0.4-kb T-urf13 transcripts. Primer extension analyses position the 5' termini of the 1.42/0.42-kb and 1.4/0.4-kb transcripts at +137 and +159 nucleotides, respectively, 3' of the AUG initiation codon of the T-urf13 reading frame. The conserved motif, 5'-CNACNNU-3', overlaps the 5' termini of the Rf1-, Rf8-, and Rf*-associated transcripts and the 380 nucleotide, Rf3-associated orf107 transcript from cytoplasmic male sterility sorghum. These results demonstrate that multiple unlinked, nuclear genes can have similar but distinct effects on the expression of the unique T-urf13 mitochondrial coding sequence to restore pollen fertility to T-cytoplasm maize.

Mutator-induced mutations of the rf1 nuclear fertility restorer of T-cytoplasm maize alter the accumulation of T-urf13 mitochondrial transcripts.

Dominant alleles of the rf1 and rf2 nuclear-encoded fertility restorer genes are necessary for restoration of pollen fertility in T-cytoplasm maize. To further characterize fertility restoration mediated by the Rf1 allele, 123,500 gametes derived from plants carrying the Mutator transposable element family were screened for rf1-mutant alleles (rf1-m) Four heritable rf1-m alleles were recovered from these populations. Three rf1-m alleles were derived from the progenitor allele Rf1-IA153 and one was derived from Rf1-Ky21. Cosegregation analysis revealed 5.5- and 2.4-kb Mu1-hybridizing EcoRI restriction fragments in all of the male-sterile and none of the male-fertile plants in families segregating for rf1-m3207 and rf1-m3310, respectively. Mitochondrial RNA gel blot analyses indicated that all four rf1-m alleles in male-sterile plants cosegregated with the altered steady-state accumulation of 1.6- and 0.6-kb T-urf13 transcripts, demonstrating that these transcripts are Rf1 dependent. Plants carrying a leaky mutant, rf1-m7323, revealed variable levels of Rf1-associated, T-urf13 transcripts and the degree of pollen fertility. The ability to obtain rf1-m derivatives from Rf1 indicates that Rf1 alleles produce a functional gene product necessary for the accumulation of specific T-urf13 transcripts in T-cytoplasm maize.

Variation in the ratio of physical to genetic distance in intervals adjacent to the Mla locus on barley chromosome 1H.

Variants of the pulsed-field gel electrophoresis technique were used in conjunction with two-dimensional DNA gel electrophoresis (2-DDGE) to determine the ratio of physical to genetic distance in two genetically defined intervals on barley chromosome 1H.2-DDGE analysis demonstrated that two loci that define a 0.3 cM interval, as determined by hybridization with BCD249, reside on a single 450-kb MluI fragment. This result indicates a maximum ratio of physical to genetic distance in this interval of 1500 kb/cM as compared to 3.7-4.2 Mb/cM for the barley genome as a whole. High molecular weight (HMW) DNA restricted with NotI and probed sequentially with MWG068 and BCD249 yield diffuse bands at approximately 2.8 Mb and 3.0 Mb in the C.I. 16151 and C.I. 16155 parental lines, respectively. These results suggest the maximum ratio of physical to genetic distance in the interval defined by these probes is 7.8 Mb/cM. Unique HMW DNA restriction fragment length polymorphisms (RFLP) were attributed to the presence of recombination breakpoints. Data from the recombination breakpoint analysis were used to estimate a ratio of physical to genetic distance of 2.5 Mb/cM in the Xbcd249.2-Xmwg068 interval and 0.465 Mb/cM in the Xbcd249.1-Xbcd249.2 interval. Both physical linkage and recombination breakpoint analysis indicate the Xbcd249.1-Xbcd249.2 interval is approximately five-fold smaller, physically, than the Xbcd249.2-Xmwg068 interval.

The rf2 nuclear restorer gene of male-sterile T-cytoplasm maize.

The T cytoplasm of maize serves as a model for the nuclear restoration of cytoplasmic male sterility. The rf2 gene, one of two nuclear genes required for fertility restoration in male-sterile T-cytoplasm (cmsT) maize, was cloned. The protein predicted by the rf2 sequence is a putative aldehyde dehydrogenase, which suggests several mechanisms that might explain Rf2-mediated fertility restoration in cmsT maize. Aldehyde dehydrogenase may be involved in the detoxification of acetaldehyde produced by ethanolic fermentation during pollen development, may play a role in energy metabolism, or may interact with URF13, the mitochondrial protein associated with male sterility in cmsT maize.

Comparative mapping of homoeologous group 1 regions and genes for resistance to obligate biotrophs in Avena, Hordeum, and Zea mays.

The colinearity of markers linked with resistance loci on linkage group A of diploid oat, on the homoeologous groups in hexaploid oat, on barley chromosome 1H, and on homoeologous maize chromosomes was determined. Thirty-two DNA probes from homoeologous group 1 chromosomes of the Gramineae were tested. Most of the heterologous probes detected polymorphisms that mapped to linkage group A of diploid oat, two linkage groups of hexaploid oat, barley chromosome 1H, and maize chromosomes 3, 6, and 8. Many of these DNA markers appeared to have conserved linkage relationships with resistance and prolamin loci in Avena, Hordeum, and Zea mays. These resistance loci included the Pca crown rust resistance cluster in diploid oat, the R203 crown rust resistance locus in hexaploid oat, the Mla powdery mildew resistance cluster in barley, and the rp3, wsm1, wsm2, mdm1, ht2, and htn1 resistance loci in maize. Prolamin encoding loci included Avn in diploid oat and Hor1 and Hor2 in barley. A high degree of colinearity was revealed among the common RFLP markers on the small chromosome fragments among these homoeologous groups. Key words : disease resistance, colinearity, Gramineae, cereals.

Restriction fragment length polymorphisms linked to genes for resistance to crown rust (Puccinia coronata) in near-isogenic lines of hexaploid oat (Avena sativa).

Crown rust, perhaps the most important fungal disease of oat, is caused by Puccinia coronata. An examination of near-isogenic lines (NILs) of hexaploid oat (Avena sativa) was conducted to identify markers linked to genes for resistance to crown rust. These lines were created such that a unique resistance gene is present in each of the two recurrent parent backgrounds. The six NILs of the current study, X434-II, X466-I, and Y345 (recurrent parent C237-89) and D486, D494, and D526 (recurrent parent Lang), thus provide a pair of lines to study each of three resistance genes. Restriction fragment length polymorphisms and resistance loci were mapped using BC1F2 populations. Three markers were found linked to a locus for resistance to crown rust race 203, the closest at 1.9 cM in line D494 and 3.8 cM in line X466-I. In lines D526 and Y345 a marker was placed 1.0 and 1.9 cM, respectively, from the locus conferring resistance to crown rust race 345, and in D486 and X434-II a marker mapped at 8.0 and 10.2 cM from the locus for resistance to rust race 264B.

Recombination of alleles conferring specific resistance to powdery mildew at the Mla locus in barley.

In barley (Hordeum vulgare L.), the Mla locus conditions reaction to the powdery mildew fungus Erysiphe graminis f.sp. hordei. Enrichment for genetic recombinants in the Mla region is possible by screening for recombination events between the flanking endosperm storage proteins hordeins C and B. Reciprocal crosses were made between the Franger (C.I. 16151) and Rupee (C.I. 16155) lines carrying the (Mla6 + Mla14) and Mla13 alleles, respectively. Recombinants were identified from F2 segregants by analyzing the extracted hordein polypeptides by sodium dodecyl sulphate - polyacrylamide gel electrophoresis. Two hundred and seventy-six recombinant gametes were identified from the 1800 seeds that were screened. Recombination of Mla alleles was analyzed by inoculating F4 recombinant lines with three isolates of E. graminis (A27, 5874, and CR3), which recognize specific Mla alleles. The linkage order established is Hor1-Mla6-Mla13-Mla14-Hor2. The genetic distances between Hor1-Mla6, Mla6-Mla13, and Mla13-Hor2, obtained using Mapmaker 3.0b F3 intercross analysis, are 3.9, 0.2, and 5.2 cM, respectively.