Publications by authors named "Tika Adhikari"

28 Publications

  • Page 1 of 1

Recurrent ear bleed with profound bilateral sensorineural hearing loss: A case of Munchausen syndrome.

SAGE Open Med Case Rep 2021 12;9:2050313X211000869. Epub 2021 Mar 12.

Department of Internal Medicine, Jigme Dorji Wangchuck National Referral Hospital, Thimphu, Bhutan.

Factitious disorders and Munchausen syndromes present with history and physical symptoms to all specialties, and they are often extensively evaluated. Diagnosis of Munchausen syndrome is a challenge and patients often do not receive the correct diagnosis and appropriate care especially in settings where access to mental health professionals is difficult. We present a case of recurrent bleed from the right ear, bilateral profound hearing loss and jerky movement of limbs that was extensively evaluated and followed up for 4 years until a diagnosis of Munchausen syndrome was reached. This case reports the risk of harm to the patient and wastage of healthcare resources unless physicians begin to actively evaluate for factitious disorders.
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http://dx.doi.org/10.1177/2050313X211000869DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7958153PMC
March 2021

Comparative Genome Analyses of 18 Tomato Isolates Reveals Phylogenetic and Race Specific Signatures.

Front Microbiol 2020 30;11:573755. Epub 2020 Nov 30.

Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC, United States.

Host resistance is one of the few strategies available to combat the soil borne pathogenic fungus Understanding pathogen diversity in populations is key to successfully deploying host resistance. In this study the genomes of 18 isolates of races 1 ( = 2), 2 ( = 4), and 3 ( = 12) from Japan, California, and North Carolina were sequenced and mapped to the reference genome of JR2 (from tomato). The genomes were analyzed for phylogenetic and pathogen specific signatures to classify specific strains or genes for future research. Four highly clonal lineages/groups were discovered, including a lineage unique to North Carolina isolates, which had the rare MAT1-1 mating type. No evidence for recombination between isolates of different mating types was observed, even in isolates of different mating types discovered in the same field. By mapping these 18 isolates genomes to the JR2 reference genome, 193 unique candidate effectors were found using SignalP and EffectorP. Within these effectors, 144 highly conserved effectors, 42 mutable effectors (truncated or present in some isolates but absent in others), and 7 effectors present in highly variable regions of the chromosomes were discovered. Of the 144 core effectors, 21 were highly conserved in and , 7 of which have no known function. Within the non-core effectors 30 contained large numbers of non-synonymous mutations, while 15 of them contained indels, frameshift mutations, or were present on highly variable regions of the chromosome. Two of these highly variable region effectors (HVREs) were only present in race 2 isolates, but not in race 3 isolates. The race 1 effector was also present in a highly variable region. These data may suggest that these highly variable regions are enriched in race determinant genes, consistent with the two-speed genome hypothesis.
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http://dx.doi.org/10.3389/fmicb.2020.573755DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7734093PMC
November 2020

, a Major Threat to Tomato Production: Current Status and Future Prospects for Its Management.

Front Plant Sci 2020 16;11:606395. Epub 2020 Nov 16.

Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC, United States.

The guava root-knot nematode, (Syn. ), is an emerging pathogen to many crops in the world. This nematode can cause chlorosis, stunting, and reduce yields associated with the induction of many root galls on host plants. Recently, this pathogen has been considered as a global threat for tomato ( L.) production due to the lack of known resistance in commercially accepted varieties and the aggressiveness of . Both conventional morphological and molecular approaches have been used to identify , an important first step in an integrated management. To combat root-knot nematodes, integrated disease management strategies such as crop rotation, field sanitation, biocontrol agents, fumigants, and resistant cultivars have been developed and successfully used in the past. However, the resistance in tomato varieties mediated by known genes does not control . Here, we review the current knowledge on geographic distribution, host range, population biology, control measures, and proposed future strategies to improve control in tomato.
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http://dx.doi.org/10.3389/fpls.2020.606395DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7701057PMC
November 2020

Opportunities and Challenges in Studies of Host-Pathogen Interactions and Management of in Tomatoes.

Plants (Basel) 2020 Nov 22;9(11). Epub 2020 Nov 22.

Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC 27695, USA.

Tomatoes ( L.) are a valuable horticultural crop that are grown and consumed worldwide. Optimal production is hindered by several factors, among which , the cause of Verticillium wilt, is considered a major biological constraint in temperate production regions. is difficult to mitigate because it is a vascular pathogen, has a broad host range and worldwide distribution, and can persist in soil for years. Understanding pathogen virulence and genetic diversity, host resistance, and plant-pathogen interactions could ultimately inform the development of integrated strategies to manage the disease. In recent years, considerable research has focused on providing new insights into these processes, as well as the development and integration of environment-friendly management approaches. Here, we discuss the current knowledge on the race and population structure of including pathogenicity factors, host genes, proteins, enzymes involved in defense, and the emergent management strategies and future research directions for managing Verticillium wilt in tomatoes.
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http://dx.doi.org/10.3390/plants9111622DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7700276PMC
November 2020

Pathogenomics Characterization of an Emerging Fungal Pathogen, f. sp. in Greenhouse Tomato Production Systems.

Front Microbiol 2020 27;11:1995. Epub 2020 Aug 27.

Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC, United States.

In recent years, greenhouse-grown tomato () plants showing vascular wilt and yellowing symptoms have been observed between 2015 and 2018 in North Carolina (NC) and considered as an emerging threat to profitability. In total, 38 putative isolates were collected from symptomatic tomatoes in 12 grower greenhouses and characterized to infer pathogenic and genomic diversity, and mating-type () idiomorphs distribution. Morphology and polymerase chain reaction (PCR) markers confirmed that all isolates were f. sp. (FOL) and most of them were race 3. Virulence analysis on four different tomato cultivars revealed that virulence among isolates, resistance in tomato cultivars, and the interaction between the isolates and cultivars differed significantly ( < 0.001). Cultivar 'Happy Root' (, and genes for resistance) was highly resistant to FOL isolates tested. We sequenced and examined for the presence of 15 pathogenicity genes from different classes (, , , , , , , , , , , , , and ), and 14 () genes to use as genetic markers to identify and differentiate pathogenic isolates of FOL. Sequence data analysis showed that five pathogenicity genes, , , , and were present in all isolates while , , , , , , , and genes were dispersed among isolates. Two genes, and , were absent in all isolates. Of the 14 genes assessed, , and were identified in most isolates while the remaining genes varied among isolates. All isolates harbored one of the two mating-type ( or ) idiomorphs, but not both. The gene was present only in race 1 isolates. Diversity assessments based on sequences of the effector SIX3 and the translation elongation factor 1-α encoding genes and α, respectively were the most informative to differentiate pathogenic races of FOL and resulted in race 1, forming a monophyletic clade while race 3 comprised multiple clades. Furthermore, phylogeny-based on and α gene sequences showed that the predominant race 3 from greenhouse production systems significantly overlapped with previously designated race 3 isolates from various regions of the globe.
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http://dx.doi.org/10.3389/fmicb.2020.01995DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7482420PMC
August 2020

Gene Genealogies Reveal High Nucleotide Diversity and Admixture Haplotypes Within Three Species Associated with Tomato and Potato.

Phytopathology 2020 Aug 18;110(8):1449-1464. Epub 2020 Jun 18.

Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC 27695.

Early blight (EB) and leaf blight are two destructive diseases of tomato in North Carolina (NC), caused by and , respectively. During the last decade, EB caused by has increased in potato-producing areas in Wisconsin (WI). We collected 152 isolates of three spp. associated with tomato and potato in NC and WI and used the gene genealogical approach to compare the genetic relationships among them. Two nuclear genes: the glyceraldehyde-3-phosphate dehydrogenase (), RNA polymerase second largest subunit (), and the rDNA internal transcribed spacer () region of these isolates were sequenced. Besides, sequences of the locus from international isolates described in previous studies were included for comparison purposes. A set of single nucleotide polymorphisms was assembled to identify locus-specific and species-specific haplotypes. Nucleotide diversity varied among gene sequences and species analyzed. For example, the estimates of nucleotide diversity and Watterson's theta were higher in than in . and . There was little or no polymorphisms in the sequences and thus restricted haplotype placement. The sequences were less informative to detect haplotype diversity in . and , yet six haplotypes were detected in . The sequences enabled strongly supported phylogenetic inferences with the highest haplotype diversity and belonged to five haplotypes (AaH1 to AaH5), which consisted of only from NC. However, 13 haplotypes were identified within and among and sequences. Among them, six (AsAlH1 to AsAlH6) were identical to previously reported haplotypes in global samples and the remaining were new haplotypes. The most divergent haplotypes were AaH1, AsAlH2/AsAlH3, and AsAlH4 and consisted exclusively of , , and , respectively. Neutrality tests suggested an excess of mutations and population expansion, and selection may play an important role in nucleotide diversity of spp.
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http://dx.doi.org/10.1094/PHYTO-12-19-0487-RDOI Listing
August 2020

Advances and Challenges in Bacterial Spot Resistance Breeding in Tomato ( L.).

Int J Mol Sci 2020 Mar 3;21(5). Epub 2020 Mar 3.

Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695, USA.

Bacterial spot is a serious disease of tomato caused by at least four species of . These include (race T1), (race T2), (races T3 and T4), and with the distinct geographical distribution of each group. Currently, and are two major bacterial pathogens of tomato in North America, with (race T4) dominating in east-coast while dominating in the Midwest. The disease causes up to 66% yield loss. Management of this disease is challenging due to the lack of useful chemical control measures and commercial resistant cultivars. Although major genes for resistance () and quantitative resistance have been identified, breeding tomato for resistance to bacterial spot has been impeded by multiple factors including the emergence of new races of the pathogen that overcome the resistance, multigenic control of the resistance, linkage drag, non-additive components of the resistance and a low correlation between seedling assays and field resistance. Transgenic tomato with and genes was effective against multiple races of . However, it has not been commercialized because of public concerns and complex regulatory processes. The genomics-assisted breeding, effectors-based genomics breeding, and genome editing technology could be novel approaches to achieve durable resistance to bacterial spot in tomato. The main goal of this paper is to understand the current status of bacterial spot of tomato including its distribution and pathogen diversity, challenges in disease management, disease resistance sources, resistance genetics and breeding, and future prospectives with novel breeding approaches.
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http://dx.doi.org/10.3390/ijms21051734DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7084486PMC
March 2020

Assessing Rate-Reducing Foliar Resistance to Anthracnose Crown Rot and Fruit Rot in Strawberry.

Plant Dis 2020 Feb 16;104(2):398-407. Epub 2019 Dec 16.

Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695.

Anthracnose fruit rot and anthracnose crown rot (ACR) caused by two species complexes of the fungus referred to as and , respectively, are major pathogens of strawberry in North Carolina. Anthracnose epidemics are common when susceptible cultivars and asymptomatic planting stocks carrying quiescent infection or hemibiotrophic infection (HBI) are planted. The main objective of this study was to assess resistance to HBI and ACR in strawberry. Strawberry cultivars and breeding lines were spray inoculated with isolates of or . Four epidemiological parameters providing estimates of rate-reducing resistance to HBI and ACR in strawberry cultivars and lines were evaluated in repeated experiments in controlled environments in a greenhouse. HBI severity, measured as the percentage of total leaf area covered by acervuli, was estimated visually and by image analysis. ACR severity was rated weekly for wilt symptoms, and relative area under disease progress curve scores were calculated for comparing strawberry cultivars and lines. Significant differences ( ≤ 0.005) in HBI severity were found among strawberry genotypes; however, the correlations were not remarkable between species ( 0.4251). Although significant variation in resistance was observed for ACR, this was also weakly correlated ( = 0.2430) with resistance to HBI. Overall, rate-reducing resistance to HBI and ACR in strawberry identified in this study could be utilized in breeding programs to develop durable resistance to anthracnose in North Carolina.
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http://dx.doi.org/10.1094/PDIS-04-19-0687-REDOI Listing
February 2020

Phenotypic and Genetic Diversity of Populations from Tomato in North Carolina.

Phytopathology 2019 Sep 5;109(9):1533-1543. Epub 2019 Aug 5.

Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695.

Bacterial spot caused by spp. is one of the most devastating diseases of tomato in North Carolina (NC). In total, 290 strains of spp. from tomato in NC collected over 2 years (2015 and 2016) were analyzed for phenotypic and genetic diversity. In vitro copper and streptomycin sensitivity assays revealed that >95% ( = 290) of the strains were copper tolerant in both years, whereas 25% ( = 127) and 46% ( = 163) were streptomycin tolerant in 2016 and 2015, respectively. Using BOX repetitive element PCR assay, fingerprint patterns showed four haplotypes (H1, H2, H3, and H4) among the strains analyzed. The multiplex real-time quantitative PCR on a subset of representative strains ( = 45) targeting the highly conserved gene identified strains from tomato in NC that belonged to . Race profiling of the representative strains ( = 45) on tomato and pepper differentials confirmed that ∼9 and 91% of strains are tomato races T3 and T4, respectively. Additionally, PCR assays and sequence alignments confirmed that the , , ( copper tolerance gene cluster), and genes are present in the strains analyzed. Phylogenetic and comparative sequence analyses of six genomic regions (elongation factor G [], glyceraldehyde-3-phosphate dehydrogenase A [], citrate synthase [], gyrase subunit B [], ABC transporter sugar permease [], and GTP binding protein []) suggested that 13 and 74% of strains from NC were genetically similar to races T3 and T4 from Florida, respectively. Our results provide insights that bacterial spot management practices in tomato should focus on deploying resistance genes to combat emerging pathogenic races of and overcome the challenges currently posed by intense use of copper-based bactericides.
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http://dx.doi.org/10.1094/PHYTO-01-19-0019-RDOI Listing
September 2019

Inheritance of Resistance to Colletotrichum gloeosporioides and C. acutatum in Strawberry.

Phytopathology 2019 Mar 7;109(3):428-435. Epub 2019 Feb 7.

1 Department of Horticultural Science; and.

Information on the inheritance of resistance to Colletotrichum gloeosporioides and C. acutatum hemibiotrophic infections (HBI) in strawberry leaf tissue and the genetic control of anthracnose crown rot (ACR) in crown tissue are relatively unknown. Six parental genotypes were crossed in a half-diallel mating design to generate 15 full-sib families. HBI and ACR experiments were conducted concurrently. Both seedlings and parental clones were inoculated with 1 × 10 conidia/ml of C. gloeosporioides or C. acutatum. Percent sporulating leaf area, wilt symptoms, and relative area under the disease progress curve were calculated to characterize resistance among genotypes and full-sib families. Low dominance/additive variance ratios for C. acutatum HBI (0.13) and C. gloeosporioides ACR (0.20) were observed, indicating additive genetic control of resistance to these traits. Heritability estimates were low for C. acutatum HBI (0.25) and C. gloeosporioides HBI (0.16) but moderate for C. gloeosporioides ACR (0.61). A high genetic correlation (r = 0.98) between resistance to C. acutatum HBI and C. gloeosporioides HBI was observed, suggesting that resistance to these two Colletotrichum spp. may be controlled by common genes in strawberry leaf tissue. In contrast, negative genetic correlations between ACR and both HBI traits (r = -0.85 and -0.61) suggest that resistance in crown tissue is inherited independently of resistance in leaf tissue in the populations tested. Overall, these findings provide valuable insight into the genetic basis of resistance, and the evaluation and deployment of resistance to HBIs and ACR in strawberry breeding programs.
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http://dx.doi.org/10.1094/PHYTO-08-18-0283-RDOI Listing
March 2019

A New Map Location of Gene for Resistance to Septoria Tritici Blotch in Wheat.

Crop Sci 2015 Jan-Feb;55(1):35-43. Epub 2014 Oct 31.

Department of Plant Sciences, University of California, Davis, CA 95616-8515, USA, and Howard Hughes Medical Institute, Chevy Chase, MD 20815-6789, USA.

Septoria tritici blotch (STB), caused by (synonym: ; asexual stage: ), is an important disease of wheat worldwide. Management of the disease usually is by host resistance or fungicides. However, has developed insensitivity to most commonly applied fungicides so there is a continuing need for well-characterized sources of host resistance to accelerate the development of improved wheat cultivars. Gene has been a useful source of major resistance, but its mapping location has not been well characterized. Based on linkage to a single marker, a previous study assigned to a location on the short arm of chromosome 6D. However, the results from the present study show that this reported location is incorrect. Instead, linkage analysis revealed that is located on the short arm of wheat chromosome 7A, completely linked to microsatellite (SSR) locus and flanked by loci (12.4 cM distal) and (2.1 cM proximal). Linkage between and was validated in BCF progeny of other crosses, and analyses of the flanking markers with deletion stocks showed that the gene is located on 7AS between fraction lengths 0.73 and 0.83. This revised location of is different from those for other STB resistance genes previously mapped in hexaploid wheat but is approximately 20 cM proximal to an STB resistance gene mapped on the short arm of chromosome 7A in . The markers described in this study are useful for accelerating the deployment of in wheat breeding programs.
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http://dx.doi.org/10.2135/cropsci2013.11.0766DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5089079PMC
October 2014

Genome-wide association study reveals novel quantitative trait Loci associated with resistance to multiple leaf spot diseases of spring wheat.

PLoS One 2014 30;9(9):e108179. Epub 2014 Sep 30.

Center for Integrated Pest Management and Department of Plant Pathology, North Carolina State University, Raleigh, North Carolina, United States of America.

Accelerated wheat development and deployment of high-yielding, climate resilient, and disease resistant cultivars can contribute to enhanced food security and sustainable intensification. To facilitate gene discovery, we assembled an association mapping panel of 528 spring wheat landraces of diverse geographic origin for a genome-wide association study (GWAS). All accessions were genotyped using an Illumina Infinium 9K wheat single nucleotide polymorphism (SNP) chip and 4781 polymorphic SNPs were used for analysis. To identify loci underlying resistance to the major leaf spot diseases and to better understand the genomic patterns, we quantified population structure, allelic diversity, and linkage disequilibrium. Our results showed 32 loci were significantly associated with resistance to the major leaf spot diseases. Further analysis identified QTL effective against major leaf spot diseases of wheat which appeared to be novel and others that were previously identified by association analysis using Diversity Arrays Technology (DArT) and bi-parental mapping. In addition, several identified SNPs co-localized with genes that have been implicated in plant disease resistance. Future work could aim to select the putative novel loci and pyramid them in locally adapted wheat cultivars to develop broad-spectrum resistance to multiple leaf spot diseases of wheat via marker-assisted selection (MAS).
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0108179PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4182470PMC
June 2015

Phenotypic and Molecular Diversity of Cochliobolus sativus Populations from Wheat.

Plant Dis 2013 Jan;97(1):62-73

Center for Integrated Pest Management and Department of Plant Pathology, North Carolina State University, 840 Main Campus Drive, Partners II Suite 1400, Centennial Campus, Raleigh 27606.

Spot blotch, caused by Cochliobolus sativus, is a devastating foliar disease of wheat in Nepal and in the Northern Great Plains of the United States. However, limited information on variation in virulence and genetic structure of C. sativus from wheat is available. In this study, pathogenic variation of 96 isolates of C. sativus from the Hill and Plain areas in Nepal (n = 48) and in the Central and Northern areas in North Dakota (n = 48) were evaluated on 12 differential wheat lines. DNA polymorphisms in all isolates were analyzed using eight selected amplified fragment length polymorphism primer combinations. Phenotypic data analysis showed the isolates varied greatly and were classified into 47 pathotypes. Cluster analysis indicated the isolates fell into three distinct groups with low, intermediate, and high virulence. Population genetic analysis revealed significant linkage disequilibrium ( = 0.066 to 0.292), indicating that sexual reproduction plays little or no role in evolution and disease epidemiology in wheat fields. Furthermore, the corrected standardized fixation index (G″ = 0.05 and 0.02) showed no evidence of genetic differentiation in C. sativus populations. Collectively, these results confirmed high pathogenic and molecular diversity in the C. sativus populations collected from wheat foliar infections and will be useful to assist in developing resistant cultivars to manage this disease.
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http://dx.doi.org/10.1094/PDIS-01-12-0092-REDOI Listing
January 2013

Mixed model association mapping for fusarium head blight resistance in tunisian-derived durum wheat populations.

G3 (Bethesda) 2011 Aug 1;1(3):209-18. Epub 2011 Aug 1.

Sources of resistance to Fusarium head blight (FHB) in wheat are mostly restricted to Chinese hexaploid genotypes. The effort to incorporate the resistance from hexaploid wheat or wild relatives to cultivated durum wheat (Triticum turgidum L. var. durum Desf.) have not been successful in providing resistance to the level of the donor parents. In this study, we used 171 BC(1)F(6) and 169 BC(1)F(7) lines derived from crossing of four Tunisian tetraploid sources of resistance (Tun7, Tun18, Tun34, Tun36) with durum cultivars 'Ben,' 'Maier,' 'Lebsock,' and 'Mountrail' for association studies. The Tun18 and Tun7 FHB resistances were found to be comparable to the best hexaploid wheat sources. A new significant QTL for FHB resistance was identified on the long arm of chromosome 5B (Qfhs.ndsu-5BL) with both association and classical QTL mapping analysis. Linkage disequilibrium (LD) blocks extending up to 40 cM were evident in these populations. The linear mixed model considering the structure (Q or P) and the kinship matrix (K(T)) estimated by restricted maximum likelihood (REML) was identified as the best for association studies in a mixture of wheat populations from a breeding program. The results of association mapping analysis also demonstrated a region on the short arm of chromosome 3B as potentially linked to FHB resistance. This region is in proximity of major FHB resistance gene fhb1 reported in hexaploid wheat. A possibility of having susceptibility or suppressor of resistance gene(s) on durum wheat chromosome 2A was further confirmed in this material, explaining the problem in developing resistant genotypes without counter selection against this region.
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http://dx.doi.org/10.1534/g3.111.000489DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276138PMC
August 2011

Pathogenic and genetic diversity of Xanthomonas translucens pv. undulosa in North Dakota.

Phytopathology 2012 Apr;102(4):390-402

Department of Plant Pathology, North Dakota State University, Department 7660, P.O. Box 6050, Fargo 58108, ND, USA.

Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa, has become more prevalent recently in North Dakota and neighboring states. From five locations in North Dakota, 226 strains of X. translucens pv. undulosa were collected and evaluated for pathogenicity and then selected strains were inoculated on a set of 12 wheat cultivars and other cereal hosts. The genetic diversity of all strains was determined using repetitive sequence-based polymerase chain reaction (rep-PCR) and insertion sequence-based (IS)-PCR. Bacterial strains were pathogenic on wheat and barley but symptom severity was greatest on wheat. Strains varied greatly in aggressiveness, and wheat cultivars also showed differential responses to several strains. The 16S ribosomal DNA sequences of the strains were identical, and distinct from those of the other Xanthomonas pathovars. Combined rep-PCR and IS-PCR data produced 213 haplotypes. Similar haplotypes were detected in more than one location. Although diversity was greatest (≈92%) among individuals within a location, statistically significant (P ≤ 0.001 or 0.05) genetic differentiation among locations was estimated, indicating geographic differentiation between pathogen populations. The results of this study provide information on the pathogen diversity in North Dakota, which will be useful to better identify and characterize resistant germplasm.
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http://dx.doi.org/10.1094/PHYTO-07-11-0201DOI Listing
April 2012

A Two-Step Molecular Detection Method for Pyrenophora tritici-repentis Isolates Insensitive to QoI Fungicides.

Plant Dis 2011 Dec;95(12):1558-1564

Department of Plant Pathology, North Dakota State University, NDSU Department 7660, P.O. Box 6050, Fargo, ND 58108.

Tan spot, caused by Pyrenophora tritici-repentis, is an important disease of wheat worldwide. To manage tan spot, quinone outside inhibitor (QoI) fungicides such as azoxystrobin and pyraclostrobin have been applied in many countries. QoI fungicides target the cytochrome b (cyt b) site in complex III of mitochondria and, thus, pose a serious risk for resistance development. The resistance mechanism to QoI fungicides is mainly due to point mutations in the cyt b gene. The objective of this study was to develop a molecular detection method for the four currently known mutations responsible for shifts in sensitivity toward QoI fungicides in P. tritici-repentis. Twelve specific primers were designed based on sequences from the National Center for Biotechnology Information accessions AAXI01000704 and DQ919068 and used to generate a fragment of the cyt b gene which possesses four known single-nucleotide polymorphisms (SNPs). These mutant clones served as positive controls because QoI-insensitive and -reduced-sensitive isolates of P. tritici-repentis have not yet been reported in the United States. The partial cyt b gene clones were sequenced to identify the SNPs at sites G143A and F129L. Genomic DNA of the mutated partial cyt b gene clones and the European QoI-insensitive and -reduced-sensitive isolates of P. tritici-repentis possessing G143A (GCT) and F129L (TTA, TTG, and CTC) mutations were amplified by polymerase chain reaction (PCR) using two specific primer pairs and were further digested with three specific restriction enzymes (BsaJI, Fnu4HI, and MnlI). The results of the digested PCR product from genomic DNA of known QoI-insensitive and -reduced-sensitive isolates of P. tritici-repentis had DNA bands consistent with the mutation GCT at G143A and the mutations TTA, TTG, and CTC at F129L. The amplified region at the F129 site also had 99% sequence similarity with P. teres, the net blotch pathogen of barley. To validate mutations, we further tested two isolates of P. teres known to have reduced sensitivity to QoI fungicides possessing the mutations TTA and CTC at F129L. After PCR amplification and restriction digestion, DNA bands identical to those observed for the partial cyt b mutant clones were detected. These results suggest that this newly developed two-step molecular detection method is rapid, robust, and specific to monitor QoI-insensitive and -reduce-dsensitive isolates of P. tritici-repentis.
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http://dx.doi.org/10.1094/PDIS-05-11-0413DOI Listing
December 2011

Association mapping of quantitative resistance to Phaeosphaeria nodorum in spring wheat landraces from the USDA National Small Grains Collection.

Phytopathology 2011 Nov;101(11):1301-10

Department of Plant Pathology, North Dakota State University, Frago, ND, USA.

Stagonospora nodorum blotch (SNB), caused by Phaeosphaeria nodorum, is a destructive disease of wheat (Triticum aestivum) found throughout the United States. Host resistance is the only economically feasible option for managing the disease; however, few SNB-resistant wheat cultivars are known to exist. In this study, we report findings from an association mapping (AM) of resistance to P. nodorum in 567 spring wheat landraces of diverse geographic origin. The accessions were evaluated for seedling resistance to P. nodorum in a greenhouse. Phenotypic data and 625 polymorphic diversity array technology (DArT) markers have been used for linkage disequilibrium (LD) and association analyses. The results showed that seven DArT markers on five chromosomes (2D, 3B, 5B, 6A, and 7A) were significantly associated with resistance to P. nodorum. Genetic regions on 2D, 3B, and 5B correspond to previously mapped quantitative trait loci (QTL) conferring resistance to P. nodorum whereas the remaining QTL appeared to be novel. These results demonstrate that the use of AM is an effective method for identifying new genomic regions associated with resistance to P. nodorum in spring wheat landraces. Additionally, the novel resistance found in this study could be useful in wheat breeding aimed at controlling SNB.
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http://dx.doi.org/10.1094/PHYTO-03-11-0076DOI Listing
November 2011

Genetic differentiation at microsatellite loci among populations of Mycosphaerella graminicola from California, Indiana, Kansas, and North Dakota.

Phytopathology 2011 Oct;101(10):1251-9

Department of Plant Pathology, North Dakota State University, Fargo, ND, USA.

Mycosphaerella graminicola causes Septoria tritici blotch (STB) in wheat (Triticum aestivum) and is considered one of the most devastating pathogens of that crop in the United States. Although the genetic structures of M. graminicola populations from different countries have been analyzed using various molecular markers, relatively little is known about M. graminicola populations from geographically distinct areas of the United States and, in particular, of those from spring versus winter wheat. These are exposed to great differences in environmental conditions, length and season of host-free periods, and resistance sources used in geographically separated wheat breeding programs. Thus, there is more likely to be genetic differentiation between populations from spring versus winter wheat than there is among those within each region. To test this hypothesis, 330 single-spore isolates of M. graminicola representing 11 populations (1 from facultative winter wheat in California, 2 from spring wheat in North Dakota, and 8 from winter wheat in Indiana and Kansas) were analyzed for mating type frequency and for genetic variation at 17 microsatellite or simple-sequence repeat (SSR) loci. Analysis of clone-corrected data revealed an equal distribution of both mating types in the populations from Kansas, Indiana, and North Dakota, but a deviation from a 1:1 ratio in the California population. In total, 306 haplotypes were detected, almost all of which were unique in all 11 populations. High levels of gene diversity (H = 0.31 to 0.56) were observed within the 11 populations. Significant (P ≤ 0.05) gametic disequilibrium, as measured by the index of association (rBarD), was observed in California, one Indiana population (IN1), and three populations (KS1, KS2, and KS3) in Kansas that could not be explained by linkage. Corrected standardized fixation index (G″(ST)) values were 0.000 to 0.621 between the 11 populations and the majority of pairwise comparisons were statistically significant (P ≤ 0.001), suggesting some differentiation between populations. Analysis of molecular variance showed that there was a small but statistically significant level of genetic differentiation between populations from spring versus winter wheat. However, most of the total genetic variation (>98%) occurred within spring and winter wheat regions while <2% was due to genetic differentiation between these regions. Taken together, these results provide evidence that sexual recombination occurs frequently in the M. graminicola populations sampled and that most populations are genetically differentiated over the major spring- and winter-wheat-growing regions of the United States.
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http://dx.doi.org/10.1094/PHYTO-08-10-0212DOI Listing
October 2011

Trichothecene profiling and population genetic analysis of Gibberella zeae from barley in North Dakota and Minnesota.

Phytopathology 2011 Jun;101(6):687-95

CRA-PAV Centro di Ricerca per la Patologia Vegetale, Via C. G. Bertero 22, 00156 Roma, Italy.

Gibberella zeae, the principal cause of Fusarium head blight (FHB) of barley, contaminates grains with several mycotoxins, which creates a serious problem for the malting barley industry in the United States, China, and Europe. However, limited studies have been conducted on the trichothecene profiles and population genetic structure of G. zeae isolates collected from barley in the United States. Trichothecene biosynthesis gene (TRI)-based polymerase chain reaction (PCR) assays and 10 variable number tandem repeat (VNTR) markers were used to determine the genetic diversity and compare the trichothecene profiles of an older population (n = 115 isolates) of G. zeae collected in 1997 to 2000 with a newer population (n = 147 isolates) collected in 2008. Samples were from across the major barley-growing regions in North Dakota and Minnesota. The results of TRI-based PCR assays were further validated using a subset of 32 and 28 isolates of G. zeae by sequence analysis and gas chromatography, respectively. TRI-based PCR assays revealed that all the G. zeae isolates in both populations had markers for deoxynivalenol (DON), and the frequencies of isolates with a 3-acetyldeoxynivalenol (3-ADON) marker in the newer population were ≈11-fold higher than those among isolates in the older population. G. zeae populations from barley in the Midwest of the United States showed no spatial structure, and all the isolates were solidly in clade 7 of G. zeae, which is quite different from other barley-growing areas of world, where multiple species of G. zeae are commonly found in close proximity and display spatial structure. VNTR analysis showed high gene diversity (H = 0.82 to 0.83) and genotypic diversity but low linkage disequilibrium (LD = 0.02 to 0.07) in both populations. Low genetic differentiation (F(ST) = 0.013) and high gene flow (Nm = 36.84) was observed between the two populations and among subpopulations within the same population (Nm = 12.77 to 29.97), suggesting that temporal and spatial variations had little influence on population differentiation in the Upper Midwest. Similarly, low F(ST) (0.02) was observed between 3-ADON and 15-acetyldeoxynivalenol populations, indicating minor influence of the chemotype of G. zeae isolates on population subdivision, although there was a rapid increase in the frequencies of isolates with the 3-ADON marker in the Upper Midwest between the older collection made in 1997 to 2000 and the newer collection made in 2008. This study provides information to barley-breeding programs for their selection of isolates of G. zeae for evaluating barley genotypes for resistance to FHB and DON accumulation.
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http://dx.doi.org/10.1094/PHYTO-04-10-0101DOI Listing
June 2011

Identification and Characterization of Novel Isolates of Pyrenophora tritici-repentis from Arkansas.

Plant Dis 2010 Feb;94(2):229-235

Department of Plant Pathology, North Dakota State University, NDSU Dept. 7660, P.O. Box 6050, Fargo, ND 58108.

Tan spot, caused by Pyrenophora tritici-repentis, is an important foliar disease of wheat (Triticum aestivum) worldwide. In a preliminary study, P. tritici-repentis isolates from Arkansas were shown to vary in virulence relative to isolates from other regions of the United States. Therefore, the aim of the current study was to characterize both pathogenic and molecular variations in P. tritici-repentis isolates from Arkansas. The virulence of 93 isolates of P. tritici-repentis was evaluated by inoculating five differential wheat cultivars/lines. Based on virulence phenotypes, 63 isolates were classified as race 1, and 30 isolates were assigned to race 3. A subset of 42 isolates was selected for molecular characterization with the presence or absence of the ToxA and ToxB genes. The results showed that 36 isolates out of 42 tested by polymerase chain reaction (PCR) and Southern analysis lacked the ToxA and ToxB genes. Six isolates harboring the ToxA and ToxB genes induced necrosis and chlorosis on Glenlea and 6B365, respectively. Thirteen ToxA gene-deficient isolates also caused necrosis and chlorosis on Glenlea and 6B365, respectively; however, they did not fit current race classification. In contrast, the remaining 23 ToxA gene-deficient isolates did not cause necrosis, but induced chlorosis on 6B365, showing a disease profile for race 3. When the virulence of AR LonB2 (an isolate with unclassified race) was compared with known races 1, 3, and 5 of P. tritici-repentis on 20 winter wheat cultivars from Arkansas, the virulence phenotypes differed substantially. Taken together, the ToxA and ToxB gene-deficient isolates of P. tritici-repentis that induce necrosis and/or chlorosis may produce a novel toxin(s) on wheat.
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http://dx.doi.org/10.1094/PDIS-94-2-0229DOI Listing
February 2010

Tsn1-mediated host responses to ToxA from Pyrenophora tritici-repentis.

Mol Plant Microbe Interact 2009 Sep;22(9):1056-68

Department of Plant Pathology, North Dakota State University, Fargo, ND, USA.

The toxin sensitivity gene Tsn1 interacts with Ptr ToxA (ToxA), a host-selective toxin produced by the necrotrophic fungus Pyrenophora tritici-repentis. The molecular mechanisms associated with cell death in sensitive wheat cultivars following ToxA application are not well understood. To address this question, we used the Affymetrix GeneChip Wheat Genome Array to compare gene expression in a sensitive wheat cultivar possessing the Tsn1 gene with the insensitive wheat cv. Nec103, which lacks the Tsn1 gene. This analysis was performed at early timepoints after infiltration with ToxA (e.g., 0.5 to 12 h postinfiltration [hpi]); at this time, ToxA is known to internalize into mesophyll cells without visible cell death symptoms. Gene expression also was monitored at later timepoints (24 to 48 hpi), when ToxA causes extensive damage in cellular compartments and visible cell death. At both early and late timepoints, numerous defense-related genes were induced (2- to 197-fold increases) and included genes involved in the phenylpropanoid pathway, lignification, and the production of reactive oxygen species (ROS). Furthermore, a subset of host genes functioning in signal transduction, metabolism, and as transcription factors was induced as a consequence of the Tsn1-ToxA interaction. Nine genes known to be involved in the host defense response and signaling pathways were selected for analysis by quantitative real-time polymerase chain reaction, and the expression profiles of these genes confirmed the results obtained in microarray experiments. Histochemical analyses of a sensitive wheat cultivar showed that H(2)O(2) was present in leaves undergoing cell death, indicating that ROS signaling is a major event involved in ToxA-mediated cell death. The results suggest that recognition of ToxA via Tsn1 triggers transcriptional reprogramming events similar to those reported for avirulence-resistance gene interactions, and that host-derived genes play an important role in the modulation of susceptibility to P. tritici-repentis.
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http://dx.doi.org/10.1094/MPMI-22-9-1056DOI Listing
September 2009

Molecular Mapping of the Stb4 Gene for Resistance to Septoria tritici Blotch in Wheat.

Phytopathology 2004 Nov;94(11):1198-206

ABSTRACT Breeding wheat for resistance is the most effective means to control Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici). At least eight genes that confer resistance to STB in wheat have been identified. Among them, the Stb4 locus from the wheat cv. Tadinia showed resistance to M. graminicola at both seedling and adult-plant stages. However, no attempt has been made to map the Stb4 locus in the wheat genome. A mapping population of 77 F10 recombinant-inbred lines (RILs) derived from a three-way cross between the resistant cv. Tadinia and the susceptible parent (Yecora Rojo x UC554) was evaluated for disease resistance and molecular mapping. The RILs were tested with Argentina isolate I 89 of M. graminicola for one greenhouse season in Brazil during 1999, with an isolate from Brazil (IPBr1) for one field season in Piracicaba (Brazil) during 2000, and with Indiana tester isolate IN95-Lafayette-1196-WW-1-4 in the greenhouse during 2000 and 2001. The ratio of resistant:susceptible RILs was 1:1 in all three tests, confirming the single-gene model for control of resistance to STB in Tadinia. However, the patterns of resistance and susceptibility were different between the Indiana isolate and those from South America. For example, the ratio of RILs resistant to both the Indiana and Argentina isolates, resistant to one but susceptible to the other, and susceptible to both isolates was approximately 1:1:1:1, indicating that Tadinia may contain at least two genes for resistance to STB. A similar pattern was observed between the Indiana and Brazil isolates. The gene identified with the Indiana tester isolate was assumed to be the same as Stb4, whereas that revealed by the South American isolates may be new. Bulked-segregant analysis was used to identify amplified fragment length polymorphism (AFLP) and microsatellite markers linked to the presumed Stb4 gene. The AFLP marker EcoRI-ACTG/MseI-CAAA5 and microsatellite Xgwm111 were closely linked to the Stb4 locus in coupling at distances of 2.1 and 0.7 centimorgans (cM), respectively. A flanking marker, AFLP EAGG/ M-CAT10, was 4 cM from Stb4. The Stb4 gene was in a potential supercluster of resistance genes near the centromere on the short arm of wheat chromosome 7D that also contained Stb5 plus five previously identified genes for resistance to Russian wheat aphid. The microsatellite marker Xgwm111 identified in this study may be useful for facilitating the transfer of Stb4 into improved cultivars of wheat.
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http://dx.doi.org/10.1094/PHYTO.2004.94.11.1198DOI Listing
November 2004

Identification and Molecular Mapping of a Gene in Wheat Conferring Resistance to Mycosphaerella graminicola.

Phytopathology 2003 Sep;93(9):1158-64

ABSTRACT Septoria tritici leaf blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici), is an economically important disease of wheat. Breeding for resistance to STB is the most effective means to control this disease and can be facilitated through the use of molecular markers. However, molecular markers linked to most genes for resistance to STB are not yet available. This study was conducted to test for resistance in the parents of a standard wheat mapping population and to map any resistance genes identified. The population consisted of 130 F(10) recombinant-inbred lines (RILs) from a cross between the synthetic hexaploid wheat W7984 and cv. Opata 85. Genetic analysis indicated that a single major gene controls resistance to M. graminicola in this population. This putative resistance gene is now designated Stb8 and was mapped with respect to amplified fragment length polymorphism (AFLP) and microsatellite markers. An AFLP marker, EcoRI-ACG/MseI-CAG5, was linked in repulsion with the resistance gene at a distance of approximately 5.3 centimorgans (cM). Two flanking microsatellite markers, Xgwm146 and Xgwm577, were linked to the Stb8 gene on the long arm of wheat chromosome 7B at distances of 3.5 and 5.3 cM, respectively. The microsatellite markers identified in this study have potential for use in marker-assisted selection in breeding programs and for pyramiding of Stb8 with other genes for resistance to M. graminicola in wheat.
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http://dx.doi.org/10.1094/PHYTO.2003.93.9.1158DOI Listing
September 2003

Real-time PCR Quantification and Mycotoxin Production of Fusarium graminearum in Wheat Inoculated with Isolates Collected from Potato, Sugar Beet, and Wheat.

Phytopathology 2007 Jul;97(7):835-41

ABSTRACT Fusarium graminearum causes Fusarium head blight (FHB) in small grains worldwide. Although primarily a pathogen of cereals, it also can infect noncereal crops such as potato and sugar beet in the United States. We used a real-time polymerase chain reaction (PCR) method based on intergenic sequences specific to the trichodiene synthase gene (Tri5) from F. graminearum. TaqMan probe and primers were designed and used to estimate DNA content of the pathogen (FgDNA) in the susceptible wheat cv. Grandin after inoculation with the 21 isolates of F. graminearum collected from potato, sugar beet, and wheat. The presence of nine mycotoxins was analyzed in the inoculated wheat heads by gas chromatography and mass spectrometry. All isolates contained the Tri5 gene and were virulent to cv. Grandin. Isolates of F. graminearum differed significantly in virulence (expressed as disease severity), FgDNA content, and mycotoxin accumulation. Potato isolates showed greater variability in producing different mycotoxins than sugar beet and wheat isolates. Correlation analysis showed a significant (P < 0.001) positive relationship between FgDNA content and FHB severity or deoxynivalenol (DON) production. Moreover, a significant (P < 0.001) positive correlation between FHB severity and DON content was observed. Our findings revealed that F. graminearum causing potato dry rot and sugar beet decay could be potential sources of inoculum for FHB epidemics in wheat. Real-time PCR assay provides sensitive and accurate quantification of F. graminearum in wheat and can be useful for monitoring the colonization of wheat grains by F. graminearum in controlled environments, and evaluating wheat germplasms for resistance to FHB.
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http://dx.doi.org/10.1094/PHYTO-97-7-0835DOI Listing
July 2007

Genetic and molecular analyses in crosses of race 2 and race 7 of albugo Candida.

Phytopathology 2003 Aug;93(8):959-65

ABSTRACT The inheritance of avirulence and polymorphic molecular markers in Albugo candida, the cause of white rust of crucifers, was studied in crosses of race 2 (Ac2), using isolates MiAc2-B1 or MiAc2-B5 (metalaxyl-insensitive and virulent to Brassica juncea cv. Burgonde) with race 7 (Ac7), using isolate MsAc7-A1 (metalaxyl-sensitive and virulent to B. rapa cv. Torch). Hybrids were obtained via co-inoculation onto a common susceptible host. Putative F(1) progeny were selfed to produce F(2) progeny. The parents and F(1) progeny were examined for virulence on the differential cultivars B. juncea cv. Burgonde and B. rapa cv. Torch. Segregation of avirulence or virulence of F(2) populations was analyzed on cv. Torch. Putative F(1) hybrids were confirmed by random amplified polymorphic DNA markers specific for each parent. Avirulence or virulence of F (2) progeny to B. rapa cv. Torch suggested 3:1 in each of three populations, supporting the hypothesis of a single dominant avirulence gene. Amplified fragment length polymorphism markers also segregated in regular Mendelian fashion among F(2) progeny derived from two F(1) hybrids (Cr2-5 and Cr2-7) of Cross-2. This first putative avirulence gene in A. candida was designated AvrAc1. These results suggest that a single dominant gene controls avirulence in race Ac2 to B. rapa cv. Torch and provides further evidence for the gene-for-gene relationship in the Albugo-Brassica pathosystem.
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http://dx.doi.org/10.1094/PHYTO.2003.93.8.959DOI Listing
August 2003

Comparative mycotoxin profiles of Gibberella zeae populations from barley, wheat, potatoes, and sugar beets.

Appl Environ Microbiol 2008 Nov 12;74(21):6513-20. Epub 2008 Sep 12.

Department of Plant Pathology, North Dakota State University, Fargo, ND 58105, USA.

Gibberella zeae is one of the most devastating pathogens of barley and wheat in the United States. The fungus also infects noncereal crops, such as potatoes and sugar beets, and the genetic relationships among barley, wheat, potato, and sugar beet isolates indicate high levels of similarity. However, little is known about the toxigenic potential of G. zeae isolates from potatoes and sugar beets. A total of 336 isolates of G. zeae from barley, wheat, potatoes, and sugar beets were collected and analyzed by TRI (trichothecene biosynthesis gene)-based PCR assays. To verify the TRI-based PCR detection of genetic markers by chemical analysis, 45 representative isolates were grown in rice cultures for 28 days and 15 trichothecenes and 2 zearalenone (ZEA) analogs were quantified using gas chromatography-mass spectrometry. TRI-based PCR assays revealed that all isolates had the deoxynivalenol (DON) marker. The frequencies of isolates with the 15-acetyl-deoxynivalenol (15-ADON) marker were higher than those of isolates with the 3-acetyl-deoxynivalenol (3-ADON) marker among isolates from all four crops. Fusarium head blight (FHB)-resistant wheat cultivars had little or no influence on the diversity of isolates associated with the 3-ADON and 15-ADON markers. However, the frequency of isolates with the 3-ADON marker among isolates from the Langdon, ND, sampling site was higher than those among isolates from the Carrington and Minot, ND, sites. In chemical analyses, DON, 3-ADON, 15-ADON, b-ZEA, and ZEA were detected. All isolates produced DON (1 to 782 microg/g) and ZEA (1 to 623 microg/g). These findings may be useful for monitoring mycotoxin contamination and for formulating FHB management strategies for these crops.
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http://dx.doi.org/10.1128/AEM.01580-08DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2576685PMC
November 2008

Use of Partial Host Resistance in the Management of Bacterial Blight of Rice.

Plant Dis 1999 Oct;83(10):896-901

Division of Entomology and Plant Pathology, International Rice Research Institute (IRRI), MCPO Box 3127, 1271 Makati City, Philippines.

The progress of bacterial blight epidemics, caused by Xanthomonas oryzae pv. oryzae, varies with environment. The irrigated lowland rice production environment in central Terai (plain) is less conducive to the disease than the irrigated lowland rice production environment in eastern Terai in Nepal. The effect of partial resistance on bacterial blight was studied in central Terai during the wet seasons of 1994, 1995, and 1996. Three partially resistant rice cultivars, Sabitri, Laxmi, and IR54 (possessing the Xa4 gene), and susceptible check IR24 were included in this study. Analysis of pooled data from the 3 years of experiments indicated that rice cultivars differed in resistance based on three epidemiological parameters: disease severity (DS), area under the disease progress curve (AUDPC), and rate of disease increase (r). Estimates of DS, AUDPC, and r were reduced and yield loss was negligible in the partially resistant cultivar Laxmi compared with the susceptible check IR24. IR54, which has partial resistance to X. oryzae pv. oryzae, also showed low DS, AUDPC, and r, which prevented yield loss due to bacterial blight. The locally adapted cultivar Sabitri showed intermediate estimates of DS, AUDPC, r, and yield loss. Earlier and more severe disease developed in the susceptible check IR24, resulting in a yield loss of 22%. Yield losses were mainly due to reductions in number of tillers, number of grains per panicle, and 1,000-grain weight. These data indicate that the use of rice cultivars with high levels of partial resistance will be an effective tool for the management of bacterial blight in central Terai and similar environments in Nepal.
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http://dx.doi.org/10.1094/PDIS.1999.83.10.896DOI Listing
October 1999

Virulence of Xanthomonas oryzae pv. oryzae on Rice Lines Containing Single Resistance Genes and Gene Combinations.

Plant Dis 1999 Jan;83(1):46-50

Division of Entomology and Plant Pathology, International Rice Research Institute (IRRI), P.O. Box 933, Manila, The Philippines.

Fifty isolates of Xanthomonas oryzae pv. oryzae were collected from different rice-producing districts of Nepal and evaluated for their virulence on these 11 rice lines having from one to four resistance genes: IRBB4 (Xa4), IRBB5 (xa5), IRBB7 (Xa7), IRBB8 (xa8), IRBB10 (Xa10), IRBB14 (Xa14), and IRBB21 (Xa21), two-gene combination AY4+5 (Xa4 and xa5), three-gene combinations NH21-37-1-1 (Xa4, xa5, and xa13) and NH24-10-1-3 (Xa4, xa5, and Xa21), and four-gene combination NH56-1-44-4 (Xa4, xa5, xa13, and Xa21). The ability of an isolate to cause lesions with different lengths across the lines was interpreted as virulence. Isolates that were consistently associated with high or low virulence were statistically differentiated. Most isolates produced large lesions on near-isogenic lines with single genes and small lesions on lines with different gene combinations. Based on infection responses on the two-, three-, and four-gene combinations, five virulence groups were identified. Isolates in virulence group I were widely distributed. The line × isolate interactions were generally not significant with gene combinations, indicating a low possibility of specificity. A line with a four-gene combination, NH56, showed wider spectrum and higher level of resistance to X. oryzae pv. oryzae than the other lines. The results of this study will facilitate the deployment of effective resistance to X. oryzae pv. oryzae in Nepal.
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http://dx.doi.org/10.1094/PDIS.1999.83.1.46DOI Listing
January 1999