Home About us Contact
|
Home About us Contact | ||
|
|
||
Genetic Resistance (genetic + resistance)
Selected AbstractsCharacterization of Wheat Random Amplified Polymorphic DNA Markers Associated with the H11 Hessian Fly Resistance GeneJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 8 2006Dhia Bouktila Abstract In Tunisia, the Hessian fly Mayetiola destructor Say is a major pest of durum wheat (Triticum durum Desf.) and bread wheat (T. aestivum L.). Genetic resistance is the most efficient and economical method of control of this pest. To date, 31 resistance genes, designated H1,H31, have been identified in wheat. These genes condition resistance to the insect genes responsible for virulence. Using wheat cultivars differing for the presence of an individual Hessian fly resistance gene and random amplified polymorphic DNA (RAPD) analysis, we have identified a polymorphic 386-bp DNA marker (Xgmib1-1A.1) associated with the H11 Hessian fly resistance gene. Blast analysis showed a high identity with a short region in the wild wheat (T. monococcum) genome, adjacent to the leaf rust resistance Lr10 gene. A genetic linkage was reported between this gene (Lr10) and Hessian fly response in wheat. These data were used for screening Hessian fly resistance in Tunisian wheat germplasm. Xgmib1-1A.1-like fragments were detected in four Tunisian durum and bread wheat varieties. Using these varieties in Hessian fly breeding programs in Tunisia would be of benefit in reducing the damage caused by this fly. (Managing editor: Li-Hui Zhao) [source] Genetic resistance to Teladorsagia circumcincta: IgA and parameters at slaughter in Churra sheepPARASITE IMMUNOLOGY, Issue 6 2005M. MARTÍNEZ-VALLADARES SUMMARY Previous experiments have shown that genetic resistance to infection by Teladorsagia circumcincta in sheep can be measured by the level of IgA in gastric mucus, jointly with other parameters. The aim of this study has been to observe the influence of IgA on adult worms. The experiment was carried out with Churra sheep experimentally infected with T. circumcincta. At slaughter, gastric content, gastric mucus, blood samples and faeces were recovered to determine the number of eggs in utero, length of adult females, worm burden, number of L4, titre of serum pepsinogen, peripheral eosinophilia and eggs per gram (epg). IgA activity in gastric mucus, serum, nasal secretions and saliva were tested against somatic antigen from fourth-stage larvae (L4), somatic antigen from the adult stage and excretory,secretory (E/S) antigen from the adult stage. The results showed a significant correlation between serum IgA and gastric mucus (P < 0·01) as well as in nasal secretions (P < 0·01). We found negative correlations between IgA activity in gastric mucus with the eggs in utero and with adult female length. Furthermore there were also strong relationships between the peripheral eosinophilia with serum (P < 0·01) and gastric mucus IgA activity (P < 0·01). Moreover serum pepsinogen and the number of L4 at slaughter were related (P < 0·01). [source] Monitoring of Venturia inaequalis harbouring the QoI resistance G143A mutation in French orchards as revealed by PCR assaysPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 1 2009Séverine Fontaine Abstract BACKGROUND: Genetic resistance to QoI fungicides may account for recent failures to control Venturia inaequalis (Cooke) Winter in French orchards. Two PCR-based assays were developed to detect the G143A point mutation in the fungal mitochondrial cytochrome b gene. The mutation is known to confer a high level of resistance to QoI fungicides. Occurrence of the G143A mutation in French field isolates collected from 2004 to 2007 was monitored. RESULTS: The QoI-resistant cytochrome b allele was specifically detected either following the cleavage of the amplified marker by a restriction endonuclease (CAPS assay) or its amplification using an allele-specific PCR primer. Using either method, the G143A mutation was found in 42% of the 291 field samples originating from French orchards in which apple scab proved difficult to be controlled. Monitoring of the G143A mutation in orchards located in 15 French administrative regions indicated that the mutation was detected at least once in nine of the regions, and its presence ranged from 33% to 64% of the orchards analysed in 2004 and in 2007 respectively. CONCLUSION: The PCR-based methods developed in this study efficiently reveal the presence of the G143A mutation in French V. inaequalis field populations. Copyright © 2008 Society of Chemical Industry [source] Inheritance of resistance to broomrape (Orobanche cumana Wallr.) race F in a sunflower line derived from wild sunflower speciesPLANT BREEDING, Issue 1 2007L. Velasco Abstract Genetic resistance to broomrape (Orobanche cumana Wallr.) race F in sunflower line J1, derived from the wild perennial species Helianthusgrosseserratus Martens and Helianthus divaricatus L., has been reported to be controlled by dominant alleles at a single locus, Or6. However, deviations from this monogenic inheritance have been observed. The objective of the present study was to gain insight into the inheritance of resistance to broomrape race F in the sunflower line J1. F1, F2, F3 and BC generations from crosses between J1 and three susceptible lines, P21, NR5 and HA821 were evaluated. F1 hybrids showed both resistant (R) and moderately resistant (MR) plants, the latter having a maximum of five broomrape stalks per plant compared with >10 in the susceptible parents. This indicated incomplete dominance of the Or6 alleles. F2 plants were classified as R, MR or susceptible (more than five broomrape stalks per plant). Three different segregation ratios were observed: 3 : 1, 13 : 3 and 15 : 1 (R + MR : S), suggesting the presence of a second gene, Or7, whose expression was influenced by the environment. A digenic model was confirmed, based on the evaluation of F2:3 families. [source] Backcross breeding for improved resistance to common bacterial blight in pinto bean (Phaseolus vulgaris L.)PLANT BREEDING, Issue 3 2005N. Mutlu Abstract Common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli reduces common bean (Phaseolus vulgaris L.) yield and quality worldwide. Genetic resistance provides effective disease control; however. a high level of resistance is difficult to attain and does not exist in pinto bean, the most important dry bean market class in North America. Our objective was to determine if a backcross breeding approach with the aid of molecular markers linked to quantitative trait loci (QTL) for resistance to CBB in a donor parent could be used to attain higher levels of resistance to CBB in pinto bean. QTL conditioning CBB resistance from the donor parent XAN 159 were introgressed into the recurrent parent,Chase'using classical backcross breeding and intermittent marker-assisted selection.,Chase'pinto bean is moderately resistant and the breeding line XAN 159 is highly resistant to Xanthomonas campestris. Marker assays confirmed the presence of independent QTL from GN no. 1 Sel 27 and XAN 159 in advanced backcross-derived pinto bean lines with improved CBB resistance. Agronomic characteristics of,Chase'were fully recovered in the backcross-derived lines. An important QTL for CBB resistance from XAN 159 on linkage group B6 was not introgressed because tight linkage between this QTL and the dominant V allele that causes an unacceptable black-mottled seed coat colour pattern in pinto bean could not be broken. [source] EFFECTS OF MIGRATION ON THE GENETIC COVARIANCE MATRIXEVOLUTION, Issue 10 2007Frédéric Guillaume In 1996, Schluter showed that the direction of morphological divergence of closely related species is biased toward the line of least genetic resistance, represented by gmax, the leading eigenvector of the matrix of genetic variance,covariance (the G -matrix). G is used to predict the direction of evolutionary change in natural populations. However, this usage requires that G is sufficiently constant over time to have enough predictive significance. Here, we explore the alternative explanation that G can evolve due to gene flow to conform to the direction of divergence between incipient species. We use computer simulations in a mainland,island migration model with stabilizing selection on two quantitative traits. We show that a high level of gene flow from a mainland population is required to significantly affect the orientation of the G -matrix in an island population. The changes caused by the introgression of the mainland alleles into the island population affect all aspects of the shape of G (size, eccentricity, and orientation) and lead to the alignment of gmax with the line of divergence between the two populations' phenotypic optima. Those changes decrease with increased correlation in mutational effects and with a correlated selection. Our results suggest that high migration rates, such as those often seen at the intraspecific level, will substantially affect the shape and orientation of G, whereas low migration (e.g., at the interspecific level) is unlikely to substantially affect the evolution of G. [source] First hybrid plane trees to show resistance against canker stain (Ceratocystis fimbriata f. sp. platani)FOREST PATHOLOGY, Issue 5 2004A. Vigouroux Summary Canker stain, caused by the ascomycete Ceratocystis fimbriata f. sp. platani, is a major threat to plane trees in Europe. The American plane tree (Platanus occidentalis) carries some genetic resistance, but this species is not adapted to the climatic conditions in Europe. Therefore, hybrids between susceptible oriental plane trees (Platanus orientalis) and resistant P. occidendalis were screened for disease resistance in France. Among 960 hybrids, we found 18 individuals which survived two successive inoculations. These putatively resistant trees were cut back and, after 18 months, on each tree 12 of the newly produced shoots as well as two roots, were inoculated again. From these trees, only one showed complete and another one partial resistance. This selection process resulting in the resistant clone ,Vallis clausa' is described in detail. Résumé La maladie du chancre coloré provoquée par l'ascomycète Ceratocystis fimbriata f. sp. platani, constitue une menace majeure pour le platane en Europe. Le platane américain (Platanus occidentalis) recèle une résistance génétique mais est très mal acclimaté aux conditions de milieu de l'Europe. Des hybrides entre le platane d'orient (Platanus orientalis) et des clones résistants de P. occidentalis ont donc été sélectionnés pour la résistance au chancre. Parmi les 960 hybrides, 18 individus ont survécu à deux inoculations successives sur le tronc. Rabattus, ces arbres, après 18 mois, ont été inoculés sur 12 des rejets produits par arbre, ainsi que sur deux de leurs racines. De ces arbres, seul un sujet a montré une résistance totale aux deux niveaux, un autre arbre montrant une résistance un peu moins complète. Zusammenfassung Der Platanenkrebs, verursacht durch den Ascomyceten Ceratocystis fimbriata f.sp. platani ist eine grosse Bedrohung für die Platanen in Europa. Die Amerikanische Platane (Platanus occidentalis) verfügt über eine gewisse Resistenz, aber diese Baumart ist nicht an die klimatischen Bedingungen in Europa angepasst. Deshalb wurden Hybriden zwischen anfälligen Platanen (Platanus orientalis) und resistenten P. occidentalis in Frankreich auf ihre Resistenz geprüft. Von 960 Hybriden überlebten 18 Individuen zwei aufeinander folgende Inokulationen. Diese möglicherweise resistenten Bäume wurden auf den Stock gesetzt und nach 18 Monaten wurden jeweils 12 der Neutriebe und zwei Wurzeln pro Pflanze erneut inokuliert. Hierbei zeigte ein Baum völlige, ein zweiter teilweise Resistenz. Dieser Selektionsprozess, welcher den resistenten Klon ,Vallis clausa' ergab, wird im Detail beschrieben. [source] Novel variants within the coding regions of the Slc11A1 gene identified in Bos taurus and Bos indicus breedsJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 1 2008R. Martínez Summary Although in the cow the genetic resistance to brucellosis has been previously attributed to the Slc11A1 gene encoding Nramp1 protein, none of the mutations described to date seems to be the cause. To be able to associate another polymorphism of the gene to brucellosis resistance, we characterized the gene and identified in different breeds of Bos taurus and Bos indicus, six new variants among a total of 11 single nucleotide mutations, of which five occurred in the coding sequence (three are missense mutations), one in the promoter region and five in introns. The allelic and genotypic frequencies calculated revealed differences (p < 0.05) among the breeds studied. [source] Evidence of pesticide resistance in medium-sized mammalian pests: a case study with 1080 poison and Australian rabbitsJOURNAL OF APPLIED ECOLOGY, Issue 4 2002Laurie E. Twigg Summary 1Toxicant-resistance is a potential, or very real, problem with many pest-control programmes world-wide. However, apart from rodents, pesticide-resistance has not been well documented in vertebrates. We assessed the potential impact of developing resistance to 1080 in rabbit populations with differing levels of historical exposure to 1080-baiting programmes in south-western Australia. 2The sensitivity to 1080 of three out of the four populations of rabbits Oryctolagus cuniculus examined had decreased significantly since Australian rabbits were last tested over 25 years ago. The lethal dose50 (LD50) values for these populations, as determined from formal toxicity trials, ranged from 0·744 to 1·019 mg pure 1080 kg,1, and were significantly greater (P < 0·05) than the previously reported values for Australian rabbits (LD50 range 0·34,0·46 mg pure 1080 kg,1). The LD50 value for the fourth population (0·584 mg pure 1080 kg,1), which has had the least exposure to 1080, did not differ from that reported previously (P > 0·05). 3The lethal dose99 (LD99) values for the four rabbit populations tested ranged from 1·181 to 1·666 mg pure 1080 kg,1, and suggested that, theoretically, all rabbits should be killed during routine baiting campaigns provided that there is no loss of active ingredient from the bait. In reality, the efficacy of 1080 poison bait laid in trails for controlling free-ranging rabbits was reduced in those populations where rabbits had decreased sensitivity to 1080. Mean reductions in rabbit numbers 7,9 days after trail baiting of resistant and sensitive populations ranged from 51·2% to 65·2%, and from 76·4% to 76·5%, respectively. 4These findings suggest that genetic resistance to 1080 is developing in at least some populations of Australian rabbits. This has world-wide implications for agricultural protection and wildlife conservation programmes that rely on a 1080-baiting strategy for reducing the impact of vertebrate pests. [source] Lateral plate asymmetry, diet and parasitism in threespine sticklebackJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2001T. E. Reimchen Individuals with random left,right departures from bilateral symmetry are predicted to exhibit fitness reduction including increased parasitism. In an insular lake population of stickleback (Gasterosteus aculeatus) from the Queen Charlotte Islands, Western Canada, phenotypes with high or low number of lateral bony plates exhibited increased plate asymmetry relative to modal phenotypes. Asymmetric lateral plate phenotypes had increased prevalence and to a lesser extent intensity of parasitism relative to symmetric individuals, suggesting that differences in genetic resistance to pathogens contributed to unequal parasitism. The effect occurred mainly in the larger adults and during the warmest season, which may be due to the high metabolic costs incurred during the summer breeding season. Dietary differences between symmetric and asymmetric phenotypes were also detected and could contribute to unequal infection rates by mediating exposure to infected prey items. Our study, which is one of the first long-term field assessments of asymmetry and parasitism, yields results that are consistent with studies linking asymmetry to reduced fitness and indicate that lateral plate asymmetry can be an indicator of poor individual quality, despite its apparent directionality. [source] Biology of the European large raspberry aphid (Amphorophora idaei): its role in virus transmission and resistance breakdown in red raspberryAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2009Lindsay S. McMenemy Abstract 1,The European large raspberry aphid Amphorophora idaei Börner is the most important vector of viral diseases afflicting commercially grown red raspberry (Rubus idaeus L.) in Northern Europe, with European raspberry production amounting to 416 000 tonnes per annum. This review synthesizes existing knowledge on its biology and interactions with other organisms, including its host plant and the viral pathogens it vectors. 2,Information about trophic interactions with other insect herbivores and natural enemies is reviewed. Vine weevils Otiorhynchus sulcatus compromise aphid resistance in some raspberry cultivars, increasing A. idaei abundance by 80%. Parasitoids show mixed success in parasitizing A. idaei, although Aphidius ervi attack rates more than doubled when A. idaei fed on a partially susceptible raspberry cultivar, compared with a resistant variety. These findings are discussed in the context of potential biological control as part of an integrated pest and disease management framework. 3,Amphorophora idaei transmits four known viruses: Black raspberry necrosis virus, Raspberry leaf mottle virus, Raspberry leaf spot virus and Rubus yellow net virus, with A. idaei taking as little as 2 min to transmit some viruses. 4,Existing control strategies, including resistant cultivars, insecticides and eradication of disease from parent plants, are described. In particular, strong selection pressures have resulted in A. idaei overcoming genetic resistance in many raspberry cultivars and most insecticides are now ineffective. 5,Future directions for the sustained control of A. idaei are suggested, taking into consideration the possible effects of climate change and also changes in agronomic practices in U.K. agriculture. [source] An ex ante economic and policy analysis of research on genetic resistance to livestock disease: trypanosomosis in AfricaAGRICULTURAL ECONOMICS, Issue 2-3 2001Cesar A. Falconi Abstract This paper undertakes an ex ante economic analysis of research on how resistance to trypanosomosis-a dominant livestock disease in Africa-can be maintained and enhanced while retaining and reinforcing characteristics of economic importance to farmers, and on how,trypanotolerance' can be imparted to susceptible animals while retaining their other important traits. The results indicate that potential benefits to research-historically field-based but increasingly biotechnology-driven-range from two to nine times potential costs and that the internal rate of return on investments can be six times the real interest rate. Field-based research, while exhibiting lower potential benefits on aggregate than does biotechnology research, is also less costly and, because of its more immediate payback, has higher internal rates of return. Returns to biotechnology research hinge on close links with field-based research and on strategic but relatively small incremental human and capital investments. The results also suggest that further research is needed to consistently identify and track the impacts of alternative intellectual property rights (IPRs) options on the levels and distributions of biotechnology research benefits. [source] Drought Stress and Preharvest Aflatoxin Contamination in Agricultural Commodity: Genetics, Genomics and ProteomicsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 10 2008Baozhu Guo Abstract Throughout the world, aflatoxin contamination is considered one of the most serious food safety issues concerning health. Chronic problems with preharvest aflatoxin contamination occur in the southern US, and are particularly troublesome in corn, peanut, cottonseed, and tree nuts. Drought stress is a major factor to contribute to preharvest aflatoxin contamination. Recent studies have demonstrated higher concentration of defense or stress-related proteins in corn kernels of resistant genotypes compared with susceptible genotypes, suggesting that preharvest field condition (drought or not drought) influences gene expression differently in different genotypes resulting in different levels of "end products": PR(pathogenesis-related) proteins in the mature kernels. Because of the complexity of Aspergillus -plant interactions, better understanding of the mechanisms of genetic resistance will be needed using genomics and proteomics for crop improvement. Genetic improvement of crop resistance to drought stress is one component and will provide a good perspective on the efficacy of control strategy. Proteomic comparisons of corn kernel proteins between resistant or susceptible genotypes to Aspergillus flavus infection have identified stress-related proteins along with antifungal proteins as associated with kernel resistance. Gene expression studies in developing corn kernels are in agreement with the proteomic studies that defense-related genes could be upregulated or downregulated by abiotic stresses. [source] Phymatotrichum (cotton) root rot caused by Phymatotrichopsis omnivora: retrospects and prospectsMOLECULAR PLANT PATHOLOGY, Issue 3 2010SRINIVASA RAO UPPALAPATI SUMMARY Phymatotrichum (cotton or Texas) root rot is caused by the soil-borne fungus Phymatotrichopsis omnivora (Duggar) Hennebert. The broad host range of the fungus includes numerous crop plants, such as alfalfa and cotton. Together with an overview of existing knowledge, this review is aimed at discussing the recent molecular and genomic approaches that have been undertaken to better understand the disease development at the molecular level with the ultimate goal of developing resistant germplasm. Taxonomy:Phymatotrichopsis omnivora (Duggar) Hennebert [synonym Phymatotrichum omnivorum (Shear) Duggar] is an asexual fungus with no known sexual stage. Mitosporic botryoblastospores occasionally form on epigeous spore mats in nature, but perform no known function and do not contribute to the disease cycle. The fungus has been affiliated erroneously with the polypore basidiomycete Sistotrema brinkmannii (Bres.) J. Erikss. Recent phylogenetic studies have placed this fungus in the ascomycete order Pezizales. Host range and disease symptoms: The fungus infects most dicotyledonous field crops, causing significant losses to cotton, alfalfa, grape, fruit and nut trees and ornamental shrubs in the south-western USA, northern Mexico and possibly parts of central Asia. However, this fungus does not cause disease in monocotyledonous plants. Symptoms include an expanding tissue collapse (rot) of infected taproots. In above-ground tissues, the root rot results in vascular discoloration of the stem and rapid wilting of the leaves without abscission, and eventually the death of the plant. Characteristic mycelial strands of the pathogen are typically present on the root's surface, aiding diagnosis. Pathogenicity: Confocal imaging of P. omnivora interactions with Medicago truncatula roots revealed that infecting hyphae do not form any specialized structures for penetration and mainly colonize cortical cells and eventually form a mycelial mantle covering the root's surfaces. Cell wall-degrading enzymes have been implicated in penetration and symptom development. Global gene expression profiling of infected M. truncatula revealed roles for jasmonic acid, ethylene and the flavonoid pathway during disease development. Phymatotrichopsis omnivora apparently evades induced host defences and may suppress the host's phytochemical defences at later stages of infection to favour pathogenesis. Disease control: No consistently effective control measures are known. The long-lived sclerotia and facultative saprotrophism of P. omnivora make crop rotation ineffective. Chemical fumigation methods are not cost-effective for most crops. Interestingly, no genetic resistance has been reported in any of the susceptible crop species. [source] Magnaporthe oryzae isolates causing gray leaf spot of perennial ryegrass possess a functional copy of the AVR1-CO39 avirulence geneMOLECULAR PLANT PATHOLOGY, Issue 3 2006REBECCA PEYYALA SUMMARY Gray leaf spot of perennial ryegrass (Lolium perenne) is a severe foliar disease caused by the ascomycete fungus Magnaporthe oryzae (formerly known as Magnaporthe grisea). Control of gray leaf spot is completely dependent on the use of fungicides because currently available perennial ryegrass cultivars lack genetic resistance to this disease. M. oryzae isolates from perennial ryegrass (prg) were unable to cause disease on rice cultivars CO39 and 51583, and instead triggered a hypersensitive response. Southern hybridization analysis of DNA from over 50 gray leaf spot isolates revealed that all of them contain sequences corresponding to AVR1-CO39, a host specificity gene that confers avirulence to rice cultivar CO39, which carries the corresponding resistance gene Pi-CO39(t). There was also an almost complete lack of restriction site polymorphism at the avirulence locus. Cloning and sequencing of the AVR1-CO39 gene (AVR1-CO39Lp) from 16 different gray leaf spot isolates revealed just two point mutations, both of which were located upstream of the predicted open reading frame. When an AVR1-CO39Lp gene copy was transferred into ML33, a rice pathogenic isolate that is highly virulent to rice cultivar CO39, the transformants were unable to cause disease on CO39 but retained their virulence to 51583, a rice cultivar that lacks Pi-CO39(t). These data demonstrate that the AVR1-CO39 gene in the gray leaf spot pathogens is functional, and suggest that interaction of AVR1-CO39Lp and Pi-CO39(t) is responsible, at least in part, for the host specificity expressed on CO39. This indicates that it may be possible to use the Pi-CO39(t) resistance gene as part of a transgenic strategy to complement the current deficiency of gray leaf spot resistance in prg. Furthermore, our data indicate that, if Pi-CO39(t) can function in prg, the resistance provided should be broadly effective against a large proportion of the gray leaf spot pathogen population. [source] Physiology and molecular aspects of Verticillium wilt diseases caused by V. dahliae and V. albo-atrumMOLECULAR PLANT PATHOLOGY, Issue 2 2006EMILIE F. FRADIN SUMMARY Introduction:,Verticillium spp. are soil-borne plant pathogens responsible for Verticillium wilt diseases in temperate and subtropical regions; collectively they affect over 200 hosts, including many economically important crops. There are currently no fungicides available to cure plants once they are infected. Taxonomy:, Kingdom: Fungi, phylum: Ascomycota, subphylum, Pezizomycotina, class: Sordariomycetes, order: Phyllachorales, genus: Verticillium. Host range and disease symptoms:, Over 200 mainly dicotyledonous species including herbaceous annuals, perennials and woody species are host to Verticillium diseases. As Verticillium symptoms can vary between hosts, there are no unique symptoms that belong to all plants infected by this fungus. Disease symptoms may comprise wilting, chlorosis, stunting, necrosis and vein clearing. Brown vascular discoloration may be observed in stem tissue cross-sections. Pathogenicity:,Verticillium spp. have been reported to produce cell-wall-degrading enzymes and phytotoxins that all have been implicated in symptom development. Nevertheless, evidence for a crucial role of toxins in pathogenicity is inconsistent and therefore not generally accepted. Microsclerotia and melanized mycelium play an important role in the disease cycle as they are a major inoculum source and are the primary long-term survival structures. Resistance:, Different defence responses in the prevascular and the vascular stage of Verticillium wilt diseases determine resistance. Although resistance physiology is well established, the molecular processes underlying this physiology remain largely unknown. Resistance against Verticillium largely depends on the isolation of the fungus in contained parts of the xylem tissues followed by subsequent elimination of the fungus. Although genetic resistance has been described in several plant species, only one resistance locus against Verticillium has been cloned to date. Useful website:,http://cbr-rbc.nrc-cnrc.gc.ca/services/cogeme/ [source] Sugar-beet powdery mildew (Erysiphe betae)MOLECULAR PLANT PATHOLOGY, Issue 3 2002Sally Francis Summary Erysiphe betae causes sugar-beet powdery mildew, a serious fungal foliar disease resulting in sugar yield losses of up to 30%. The fungus occurs world-wide in all regions where sugar beet is grown and it also infects other edible beet crops, e.g. beetroots (garden beets). Unlike other powdery mildews, E. betae has so far received relatively little attention from pathologists and the precise mechanisms by which it infects its host remain unclear. Sources of genetic resistance have been identified in cultivated and wild Beta germplasm and molecular markers developed linked to Pm, the only single major R gene described so far, and also to QTL. Taxonomy:,Erysiphe betae (Vañha) Weltz.,Kingdom Fungi, Subdivision Ascomycotina, Class Pyrenomycetes, Order Erysiphales, Family Erysiphaceae, Genus Erysiphe. Identification:, Superficial persistent mycelium; unbranched erect conidiophores; conidia ripen singly, are hyaline, ovoid, 30,50 µm × 15,20 µm; cleistothecia globose, dark brown/black, 80,120 µm in diameter; mostly 4,8 asci per cleistothecium, mostly 2 or 3 spores per ascus. Host range:, A monophagous parasite specific to Beta species. Disease symptoms:, Infected foliage and inflorescences bear numerous powdery, white colonies. Under favourable environmental conditions the colonies coalesce, host tissue develops chlorosis and usually senesces early. Cleistothecia develop on heavily infected leaves in late summer and are small black/dark brown globose bodies resting on the mycelial surface. Control:, Chemical control and partial genetic resistance. [source] Genetic resistance to Teladorsagia circumcincta: IgA and parameters at slaughter in Churra sheepPARASITE IMMUNOLOGY, Issue 6 2005M. MARTÍNEZ-VALLADARES SUMMARY Previous experiments have shown that genetic resistance to infection by Teladorsagia circumcincta in sheep can be measured by the level of IgA in gastric mucus, jointly with other parameters. The aim of this study has been to observe the influence of IgA on adult worms. The experiment was carried out with Churra sheep experimentally infected with T. circumcincta. At slaughter, gastric content, gastric mucus, blood samples and faeces were recovered to determine the number of eggs in utero, length of adult females, worm burden, number of L4, titre of serum pepsinogen, peripheral eosinophilia and eggs per gram (epg). IgA activity in gastric mucus, serum, nasal secretions and saliva were tested against somatic antigen from fourth-stage larvae (L4), somatic antigen from the adult stage and excretory,secretory (E/S) antigen from the adult stage. The results showed a significant correlation between serum IgA and gastric mucus (P < 0·01) as well as in nasal secretions (P < 0·01). We found negative correlations between IgA activity in gastric mucus with the eggs in utero and with adult female length. Furthermore there were also strong relationships between the peripheral eosinophilia with serum (P < 0·01) and gastric mucus IgA activity (P < 0·01). Moreover serum pepsinogen and the number of L4 at slaughter were related (P < 0·01). [source] Role of 2,4-Diacetylphloroglucinol-Producing Fluorescent Pseudomonas spp. in the Defense of Plant RootsPLANT BIOLOGY, Issue 1 2007D. M. Weller Abstract: Plants have evolved strategies of stimulating and supporting specific groups of antagonistic microorganisms in the rhizosphere as a defense against diseases caused by soilborne plant pathogens owing to a lack of genetic resistance to some of the most common and widespread soilborne pathogens. Some of the best examples of natural microbial defense of plant roots occur in disease suppressive soils. Soil suppressiveness against many different diseases has been described. Take-all is an important root disease of wheat, and soils become suppressive to take-all when wheat or barley is grown continuously in a field following a disease outbreak; this phenomenon is known as take-all decline (TAD). In Washington State, USA and The Netherlands, TAD results from the enrichment during monoculture of populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas fluorescens to a density of 105 CFU/g of root, the threshold required to suppress the take-all pathogen, Gaeumannomyces graminis var. tritici. 2,4-DAPG-producing P. fluorescens also are enriched by monoculture of other crops such as pea and flax, and evidence is accumulating that 2,4-DAPG producers contribute to the defense of plant roots in many different agroecosystems. At this time, 22 distinct genotypes of 2,4-DAPG producers (designated A - T, PfY and PfZ) have been defined by whole-cell repetitive sequence-based (rep)-PCR analysis, restriction fragment length polymorphism (RFLP) analysis of phlD, and phylogenetic analysis of phlD, but the number of genotypes is expected to increase. The genotype of an isolate is predictive of its rhizosphere competence on wheat and pea. Multiple genotypes often occur in a single soil and the crop species grown modulates the outcome of the competition among these genotypes in the rhizosphere. 2,4-DAPG producers are highly effective biocontrol agents against a variety of plant diseases and ideally suited for serving as vectors for expressing other biocontrol traits in the rhizosphere. [source] Disease complex in coffee involving Meloidogyne arabicida and Fusarium oxysporumPLANT PATHOLOGY, Issue 3 2000B. Bertrand Coffee corky-root disease, also called corchosis, was first detected in 1974 in a small area of Costa Rica where the root-knot nematode Meloidogyne arabicida is the dominant species. An epidemiological study revealed a constant association between Meloidogyne spp. and Fusarium sp. in cases of corky root. No corky root appears to have been reported in association with Meloidogyne exigua, which is the prevalent root-knot nematode on coffee in Costa Rica. Fusarium spp. are often cited as components of disease complexes in association with nematodes. Combined inoculations using M. arabicida or M. exigua with Fusarium oxysporum under controlled conditions showed that only the combination with M. arabicida produced corky-root symptoms on Coffea arabica cvs Caturra or Catuai. Fusarium oxysporum alone was nonpathogenic. Meloidogyne exigua or M. arabicida alone caused galls and reduction in shoot height, but no corky-root symptoms. When cultivars susceptible and resistant to M. arabicida were studied under field conditions for 5 years, all the susceptible cultivars exhibited corky-root symptoms on 40,80% of their root systems. Cultivars that were resistant to M. arabicida but not to M. exigua showed no corky root. These observations lead to the conclusion that corky-root disease has a complex etiology, and emphasize the dominant role of M. arabicida as a predisposing agent to subsequent invasion by F. oxysporum. Consequently, genetic resistance to M. arabicida appears to provide an effective strategy against the disease. [source] Drug-resistant tuberculosis: Past, present, futureRESPIROLOGY, Issue 3 2010Chen-Yuan CHIANG ABSTRACT In a population of Mycobacterium tuberculosis, random chromosomal mutation that results in genetic resistance to anti-tuberculosis (TB) drugs occurs at a relatively low frequency. Anti-TB drugs impose selection pressure so that mycobacterial mutants gradually outnumber susceptible bacilli and emerge as the dominant strains. Resistance to two or more anti-TB drugs represents cumulative results of sequential mutation. The fourth report on global anti-TB drug resistance provides the latest data on the extent of such problem in the world. The median prevalence of multi-drug-resistant TB (MDR-TB) in new TB cases was 1.6%, and in previously treated TB cases 11.7%. Of the half a million MDR-TB cases estimated to have emerged in 2006, 50% were in China and India. The optimal duration of any given combination of anti-TB drugs for treatment of MDR- and extensively drug-resistant TB (XDR-TB) has not been defined in controlled clinical trials. Standardized treatment may be feasible for MDR-TB patients not previously treated with second-line drugs, but a different strategy needs to be applied in the treatment of MDR-TB patients who have received second-line drugs before. Unfortunately, the reliability of drug susceptibility testing of most second-line anti-TB drugs is still questionable. Drug-resistant TB is not necessarily less virulent. Findings from modelling exercise warned that if MDR-TB case detection and treatment rates increase to the World Health Organization target of 70%, without simultaneously increasing MDR-TB cure rates, XDR-TB prevalence could increase exponentially. Prevention of development of drug resistance must be accorded the top priority in the era of MDR-/XDR-TB. [source] Molecular strategies to enhance the genetic resistance of grapevines to powdery mildewAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2010I.B. DRY Abstract The Eurasian winegrape Vitis vinifera has little or no genetic resistance to the major fungal pathogens, powdery mildew (Erysiphe necator) and downy mildew (Plasmopora viticola). These pathogens were first introduced into French vineyards from North America in the 1800s before spreading to all major grape producing regions of the world. As a result, grape production is highly dependent on the use of fungicides. With the increasing financial and environmental costs of chemical application and the emergence of fungicide-resistant strains, the introduction of natural genetic resistance against these fungal pathogens is a high priority for viticultural industries worldwide. We are utilising a number of different molecular approaches to increase our understanding of the basis of resistance to these important major fungal pathogens and to identify potential new sources of genetic resistance. This review will outline the progress and the potential of each of these different molecular strategies to the generation of fungal-resistant grapevine germplasm. [source] | |||||||||||||||||||