Showing papers on "Plant disease resistance published in 1993"
TL;DR: It is reported here that regenerated tobacco plants containing stilbene synthase genes are more resistant to infection by Botrytis cinerea, the first report of increased disease resistance in transgenic plants based on an additional foreign phytoalexin.
Abstract: Although phytoalexins have long been inferred to be important in the defence of plants against fungal infection, there are few reports showing that they provide resistance to infection. Several plants, including grapevine, synthesize the stilbene-type phytoalexin resveratrol when attacked by pathogens. Stilbenes with fungicidal potential are formed in several unrelated plant species, such as peanut (Arachis hypogaea), grapevine (Vitis vinifera) and pine (Pinus sylvestris). Stilbene biosynthesis only specifically requires the presence of stilbene synthase. Furthermore, the precursor molecules for the formation of hydroxy-stilbenes are malonyl-CoA and p-coumaroyl-CoA, both present in plants. To investigate the potential of stilbene biosynthetic genes in a strategy of engineering pathogen resistance, we isolated stilbene synthase genes from grapevine, where they are expressed at a high level, and transferred them into tobacco. We report here that regenerated tobacco plants containing these genes are more resistant to infection by Botrytis cinerea. This is, to our knowledge, the first report of increased disease resistance in transgenic plants based on an additional foreign phytoalexin.
670 citations
TL;DR: It is demonstrated that constitutive high-level expression of PR-1a in transgenic tobacco results in tolerance to infection by two oomycete pathogens, Peronospora tabacina and Phytophthora parasitica var.
Abstract: Expression of pathogenesis-related protein 1a (PR-1a), a protein of unknown biochemical function, is induced to high levels in tobacco in response to pathogen infection. The induction of PR-1a expression is tightly correlated with the onset of systemic acquired resistance (SAR), a defense response effective against a variety of fungal, viral, and bacterial pathogens. While PR-1a has been postulated to be involved in SAR, and is the most highly expressed of the PR proteins, evidence for its role is lacking. In this report, we demonstrate that constitutive high-level expression of PR-1a in transgenic tobacco results in tolerance to infection by two oomycete pathogens, Peronospora tabacina and Phytophthora parasitica var. nicotianae.
531 citations
TL;DR: Genetic analysis indicated that in each of the four rps mutants, susceptibility was due to a single mutation mapping to the same locus on chromosome 4, suggesting that there is natural variation at the RPS2 locus among wild populations of Arabidopsis.
Abstract: A molecular genetic approach was used to identify and characterize plant genes that control bacterial disease resistance in Arabidopsis. A screen for mutants with altered resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) expressing the avirulence gene avrRpt2 resulted in the isolation of four susceptible rps (resistance to P. syringae) mutants. The rps mutants lost resistance specifically to bacterial strains expressing avrRpt2 as they retained resistance to Pst strains expressing the avirulence genes avrB or avrRpm1. Genetic analysis indicated that in each of the four rps mutants, susceptibility was due to a single mutation mapping to the same locus on chromosome 4. Identification of a resistance locus with specificity for a single bacterial avirulence gene suggests that this locus, designated RPS2, controls specific recognition of bacteria expressing the avirulence gene avrRpt2. Ecotype Wu-0, a naturally occurring line that is susceptible to Pst strains expressing avrRpt2, appears to lack a functional allele at RPS2, demonstrating that there is natural variation at the RPS2 locus among wild populations of Arabidopsis.
312 citations
TL;DR: Inheritance studies showed that the VPM1-derived seedling resistances to stem rust, stripe rust, leaf rust, and powdery mildew were controlled by single genes; the genes for rust resistance were designated Sr38, Yr17, and Lr37, respectively, whereas the gene for resistance to powdery Mildew was postulated to be Pm4b.
Abstract: Inheritance studies showed that the VPM1-derived seedling resistances to stem rust, stripe rust, leaf rust, and powdery mildew were controlled by single genes; the genes for rust resistance were de...
304 citations
01 Jan 1993
TL;DR: The use of polymorphic single genes to facilitate the process of plant breeding was proposed early in this Century and selection for characters with easily detectable phenotypes can simplify the recovery of genes of interest linked to them and more difficult to score.
Abstract: The use of polymorphic single genes to facilitate the process of plant breeding was proposed early in this Century (Sax, 1923). The basic principle is that selection for characters with easily detectable phenotypes can simplify the recovery of genes of interest linked to them and more difficult to score. The first marker loci available were those that have an obvious impact on the morphology of the plant. Genes that affect form, coloration, male sterility or disease resistance among others have been genetically analysed in many plant species. In some well characterized crops like maize, tomato, pea, barley or wheat, tens or even hundreds of such genes have been assigned to different chromosomes (O’Brien, 1990).
244 citations
TL;DR: The objective of this study was to identify quantitative trait loci (QTL) and type-of-gene action for GLS resistance in segregating families of three single-cross populations of maize using restriction fragment length polymorphisms (RFLPs).
Abstract: Gray leaf spot (GLS) (caused by Cercospora zeae-maydis Theon & Daniels) is a fungal disease of the maize (Zea mays L.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type-of-gene action for GLS resistance in segregating families of three single-cross populations of maize using restriction fragment length polymorphisms (RFLPs) (.)
202 citations
Book•
01 Jan 1993
TL;DR: Problems and Prospects of Stress Resistance Breeding problems and prospects of stress resistance Breeding in Lentil Screening for Resistance to Biotic Stresses and Strategies for Breeding Disease-Resistant Crop Varieties.
Abstract: Problems and Prospects of Stress Resistance Breeding Problems and Prospects of Stress Resistance Breeding in Lentil Screening for Resistance to Biotic Stresses Screening for Disease Resistance in Faba Bean Mechanisms of Resistance to Fungal Pathogens in Cool-Season Food Legumes Screening for Resistance to Abiotic Stresses Mechanisms of Resistance to Cold, Heat and Drought in Cool-Season Food Legumes, With Special Reference to Chickpea and Pea Tools for Stress Resistance Breeding Mutagenesis and Chromosome Manipulation for Stress Resistance in Cool-Season Food Legumes Strategies for Stress Resistance Breeding Strategies for Breeding Disease-Resistant Crop Varieties.
166 citations
TL;DR: Transgenic tobacco plants that express the genome-linked protein/proteinase-coding region of the potyvirus tobacco vein mottling virus (TVMV) were produced and tested for their reaction to inoculation with TVMV and two other potyviruses, indicating that some, but not all, televisionMV genes can be used to confer protection against poty viruses in plants.
Abstract: Transgenic tobacco plants that express the genome-linked protein/proteinase-coding region of the potyvirus tobacco vein mottling virus (TVMV) were produced and tested for their reaction to inoculation with TVMV and two other potyviruses. These plants did not develop disease symptoms after being inoculated with large doses of TVMV but were as susceptible to infection by the other potyviruses as were control plants. Lines of tobacco that express the coat protein- or the nonstructural cylindrical inclusion protein-coding regions were also produced. The coat protein transgenic plants were protected against all three potyviruses, and the cylindrical inclusion transgenic plants were susceptible to all three potyviruses. These results indicate that some, but not all, TVMV genes can be used to confer protection against potyviruses in plants. The results also suggest that combinations of viral genes in transgenic plants might improve protection against potyviruses.
155 citations
Book•
01 Jan 1993
TL;DR: Partial table of contents: IMPACT Influence of Biotechnology on Biocontrol of Take-All Disease of Wheat (B. Hemming & J. Houghton) MOLECULAR GENETIC RESEARCH in DISEASE CONTROL Protein Secretion by Plant Pathogenic Bacteria (S. Thomson).
Abstract: Partial table of contents: IMPACT Influence of Biotechnology on Biocontrol of Take-All Disease of Wheat (B. Hemming & J. Houghton) MOLECULAR GENETIC RESEARCH IN DISEASE CONTROL Protein Secretion by Plant Pathogenic Bacteria (S. He, et al.) INTRODUCTION OF DISEASE RESISTANCE INTO PLANTS Virus Resistance Through Expression of Coat Protein Genes (R. Beachy) Proteinase Inhibitors in the Potato Response to Wounding (J. Sanchez-Serrano, et al.) Role of Phenolics in Plant Disease Resistance (J. Mitraux & I. Raskin) APPLICATION OF BIOTECHNOLOGY FOR IMPROVING BIOLOGICAL CONTROL Genetic Engineering of Microorganisms for Improved Biocontrol Activity (I. Chet, et al.) Biological Control of Plant Pests and Pathogens Alternative Approaches (J. Thomson) Diagnostic Techniques for Plant Pathogens (S. Miller & T. Joaquim) Index.
111 citations
TL;DR: Analysis of a series of hybrid and mutant isolates of PVXHB and PVXCP4 which were inoculated to plants and protoplasts of Rx and rx cultivars of potato concludes that elicitation of the resistance is affected by amino acids 121 and 127 of the viral coat protein, with codon 121 being the major determinant.
102 citations
01 Jan 1993
TL;DR: Depletion of in planta salicylic acid in transgenic salicylate hydroxylase (NahG)containing plants, has shown that this phenolic compound is essential for expression of several modes of plant disease resistance.
Abstract: Depletion of in planta salicylic acid in transgenic salicylate hydroxylase (NahG)containing plants, has shown that this phenolic compound is essential for expression of several modes of plant disease resistance. These include i) the rapid defense response found in some cases of genetically determined resistance, ii) the manifestation of disease symptoms in cases where genetic resistance is not acting, and iii) the induced, broad spectrum resistance known as systemic acquired resistance. These results indicate a common salicylic acid-dependent mechanism involved in disease resistance. We are also conducting experiments aimed at genetically dissecting the pathways regulating disease resistance using Arabidopsis thaliana and several pathogen systems. Some of the results of these analyses have been mutants with constitutive expression of PR genes and disease resistance (cim mutants). Another mutant class forms HR-like lesions and are activated for pathways involved in SAR as if these plants perceive pathogens in their absence (Isd. mutants).
TL;DR: The data provide a basis for the isolation of the RPP5 locus by positional cloning as a first step towards understanding recognitional specificity in plant-pathogen interactions at a molecular level.
Abstract: Peronospora parasitica causes downy mildew on crucifers. An isolate of P. parasitica (denoted NoCO2) was identified that infected Arabidopsis plants of the land race Columbia (Col-0) but not plants of land race Landsberg erecta (La-er). Segregation analysis of F2 plants derived from a La-er x Col-0 cross established that the resistance was inherited as a single locus, denoted RPP5. Macroscopic and microscopic examinations of inoculated La-er and Col-0 cotyledons showed that restriction of fungal growth in La-er was accompanied by massive callose accumulation and death of plant cells in direct contact with points of attempted fungal penetration. La-er x Col-0 F1 plants exhibited an intermediate resistance response in all aspects of fungal development, indicating that RPP5 is semi-dominant in its action. F8 recombinant inbred lines generated between La-er and Col-0 were used to map RPP5 to a narrow interval (<1.1 cM) on chromosome 4, utilizing existing restriction fragment length polymorphic (RFLP) markers and newly generated random amplified polymorphic DNA (RAPD) markers. The data provide a basis for the isolation of the RPP5 locus by positional cloning as a first step towards understanding recognitional specificity in plant-pathogen interactions at a molecular level.
TL;DR: The powdery mildew disease resistance gene Ml(La) was found to belong to a locus on barely chromosome 2 and it is suggested that this locus be designated MlLa.
Abstract: The powdery mildew disease resistance gene Ml(La) was found to belong to a locus on barely chromosome 2. We suggest that this locus be designated MlLa. Linkage analysis was carried out on 72 chromosome-doubled, spring-type progeny lines from a cross between the winter var 'Vogelsanger Gold' and the spring var 'Alf'. A map of chromosome 2 spanning 119cM and flanked by two peroxidase gene loci was constructed. In addition to the Laevigatum resistance locus the map includes nine RFLP markers, the two peroxidase gene loci and the six-row locus in barley.
TL;DR: A new disease resistance locus in Arabidopsis, RPS3, was identified using a previously cloned avirulence gene from a non-Arabidopsis pathogen, which confer avrB-specific disease resistance, suggesting that these genes may be homologs.
Abstract: A new disease resistance locus in Arabidopsis, RPS3, was identified using a previously cloned avirulence gene from a non-Arabidopsis pathogen. The avrB avirulence gene from the soybean pathogen Pseudomonas syringae pv. glycinea was transferred into a P. syringae pv. tomato strain that is virulent on Arabidopsis, and conversion to avirulence was assayed on Arabidopsis plants. The avrB gene had avirulence activity on most, but not all, Arabidopsis ecotypes. Of 53 ecotypes examined, 45 were resistant to a P. syringae pv. tomato strain carrying avrB, and eight were susceptible. The inheritance of this resistance was examined using crosses between the resistant ecotype Col-0 and the susceptible ecotype Bla-2. In F2 plants from this cross, the ratio of resistant:susceptible plants was approximately 3:1, indicating that resistance to P. syringae expressing avrB is determined by a single dominant locus in ecotype Col-0, which we have designated RPS3. Using RFLP analysis, RPS3 was mapped to chromosome 3, adjacent to markers M583 and G4523, and < or = 1 cM from another disease resistance locus, RPM1. In soybean, resistance to P. syringae strains that carry avrB is controlled by the locus RPG1. Thus, RPG1 and RPS3 both confer avrB-specific disease resistance, suggesting that these genes may be homologs.
TL;DR: The experimental approach to understanding the genetic basis of resistance to Gibberella is to estimate the genetic linkage between available molecular markers and the character, measured as the amount of diseased tissue 40 days after inoculation of a suspension of Fusarium graminearum, the conidial form of G. zeae.
Abstract: The basic prerequisite for an efficient breeding program to improve levels of resistance to pathogens in plants is the identification of genes controlling the resistance character. If the response to pathogens is under the control of a multilocus system, the utilization of molecular markers becomes essential. Stalk and ear rot caused by Gibberella zeae is a widespread disease of corn: resistance to G. zeae is quantitatively inherited. Our experimental approach to understanding the genetic basis of resistance to Gibberella is to estimate the genetic linkage between available molecular markers and the character, measured as the amount of diseased tissue 40 days after inoculation of a suspension of Fusarium graminearum, the conidial form of G. zeae, into the first stalk internode. Sensitive and resistant parental inbreds were crossed to obtain F1 and F2 populations: the analysis of the segregation of 95 RFLP (restriction fragment length polymorphism) clones and 10 RAPD (random amplified polymorphic DNA) markers was performed on a population of 150 F2 individuals. Analysis of resistance was performed on the F3 families obtained by selfing the F2 plants. Quantitative trait loci (QTL) detection was based either on analysis of regression coefficients between family mean value and allele values in the F2 population, or by means of interval mapping, using MAPMAKER-QTL. A linkage map of maize was obtained, in which four to five genomic regions are shown to carry factors involved in the resistance to G. zeae.
TL;DR: Bacterial wilt resistance was not associated with resistance to bacterial root invasion but with the capability of the plant to limit P. solanacearum colonization in the stem, complementary to absence of external wilt symptoms used in breeding programmes for resistance.
Abstract: High populations of Pseudomonas solanacearum were detected in some, but not all stems of bacterial wilt resistant (‘CRA 66’, ‘Hawaii 7996’ and ‘Caraibo’) and susceptible (‘Floradel’) tomatoes. Latent infection, i.e. spread of P. solanacearum into xylem vessels, was confirmed in Caraibo, Hawaii 7996 and ‘CRA 66’ (the resistant parent of Caraibo). None of the plants within the resistant cultivars wilted and those cultivars were characterized by tolerance of the vascular tissues to high bacterial densities. In contrast, plants of cultivar Floradel showed consistent symptoms and wilted rapidly, with higher mean bacterial density than resistant cultivars. Bacterial wilt resistance was not associated with resistance to bacterial root invasion but with the capability of the plant to limit P. solanacearum colonization in the stem. The extent of bacterial colonization is proposed as a criterion to quantify tolerance, complementary to absence of external wilt symptoms used in breeding programmes for resistance.
TL;DR: Multiple regression analyses revealed that the percentage of diseased plants following inoculation was an important predictor of disease levels of the same genotypes in a field experiment with natural disease transmission, validates the use of inoculation methods for large-scale resistance testing in this system.
Abstract: Cloned genotypes of Silene alba differed in the percentage of plants that became diseased following floral and bud inoculation with six isolates of the fungus Ustilago violacea. The three flower and bud inoculation methods used in the study had little effect on the resistance ranking of the genotypes. No differences in virulence were found among the six fungal isolates. Multiple regression analyses revealed that the percentage of diseased plants following inoculation was an important predictor of disease levels of the same genotypes in a field experiment with natural disease transmission. This result validates the use of inoculation methods for large-scale resistance testing in this system (..)
TL;DR: The feasibility of identifying molecular markers linked to disease resistance genes in oats was investigated utilizing random primers in conjunction with polymerase chain reaction technology, offering an effective means of identifying useful molecular markers and of applying them to plant breeding selection strategies.
Abstract: The feasibility of identifying molecular markers linked to disease resistance genes in oats was investigated utilizing random primers in conjunction with polymerase chain reaction technology. A pair of near-isogenic oat lines were screened for polymorphic DNA fragments linked to the stem rust resistance gene Pg3. Two primers were identified which amplified DNA fragments that were polymorphic between the lines analyzed. One primer (ACOpR-2) was shown to be completely linked to the Pg3 locus; the other primer was not linked to either the ACOpR-2 or the Pg3 loci. This type of analysis, combined with rapid leaf disc DNA extraction techniques, offers an effective means of identifying useful molecular markers and of applying them to plant breeding selection strategies.
TL;DR: It is concluded that nonsenescence alone cannot account for, and should not be used as the sole breeding criterion for, resistance to charcoal rot in sorghum.
Abstract: Nonsenescence is a delayed leaf and plant death resistance mechanism in sorghum that circumvents the detrimental effects of reduced soil moisture combined with high temperatures during post-anthesis growth. This drought-tolerance mechanism is often equated with charcoal rot resistance, a widespread root and stalk disease of great destructive potential. Therefore, the inheritance of charcoal rot resistance was investigated directly, by exposure of sorghum to Macrophomina phaseolina, the causal organism, and indirectly, by determination of the inheritance of nonsenescence. Sorghum families derived from diallel crosses between two nonsenescent, resistant inbreds (B35, SC599-11E) and two senescent, susceptible inbreds (BTx378, BTx623) were evaluated in 1989 at College Station and at Lubbock, Texas, under controlled and field conditions. We determined that nonsenescence was regulated by dominant and recessive epistatic interactions between two nonsenescence-inducing loci and a third locus with modifying effects. The same conclusion was reached for charcoal rot resistance. The presence of different genetic mechanisms within SC599-11E for nonsenescence and charcoal rot resistance verifies that these two forms of resistance are not different manifestations of a single trait, i.e., they are not to be equated with each other. We conclude that nonsenescence alone cannot account for, and should not be used as the sole breeding criterion for, resistance to charcoal rot in sorghum.
TL;DR: Resistance to powdery mildew is characterized by a very low disease incidence and a strongly restricted mycelium growth and lack of sporulation.
Abstract: Since the late 1980s powdery mildew, designated Oidium lycopersicum, frequently invaded the tomato crop in Western Europe All commercial cultivars are susceptible To screen for resistance in wild species a reliable and efficient disease test was developed Young plants with two to three true leaves are inoculated at high relative humidity by spraying with a freshly prepared suspension of 2×104 conidia, ml−1 Symptoms are periodically evaluated according to a scale based on the percentage of leaf area with mycelium One hundred and twenty seven accessions, representing eight wild Lycopersicon species, were screened for resistance to O lycopersicum A large variation in resistance was found between species L hirsutum was the most resistant species; L pennellii was moderately resistant; species of the subgeneric group of L esculentum and of the ‘peruvianum-complex’ were all susceptible L parviflorum was classified separately due to a large variation between accessions Except for this species, a low variation was found between accessions within species High levels of resistance were observed in four accessions of L hirsutum, in one of L parviflorum and in one of L peruvianum This resistance is characterized by a very low disease incidence and a strongly restricted mycelium growth and lack of sporulation
TL;DR: Phenylalanine ammonia lyase activity was studied in different genotypes of pearl millet with varying degrees of susceptibility to downy mildew disease, after inoculating with Pathotype 1 of Sclerospora graminicola to find the activity was well-correlated with the degree of host resistance to the pathogen.
Abstract: Phenylalanine ammonia lyase (PAL) activity was studied in different genotypes of pearl millet with varying degrees of susceptibility to downy mildew disease, after inoculating with Pathotype 1 of Sclerospora graminicola. In resistant genotypes, the enzyme activity significantly increased 24 h after fungal inoculation while in the susceptible genotypes, the activity decreased. The increase or decrease in enzyme activity was well-correlated with the degree of host resistance to the pathogen. A time-course of change in activity of PAL after inoculation showed a considerable difference between resistant and susceptible genotypes. Studies on the activity of PAL in different parts of pearl millet seedlings revealed that in the resistant genotype, enzyme activity significantly increased at 24 h post-inoculation only in the shoot portion, whereas in mesocotyl and root the activity decreased. In susceptible seedlings, enzyme activity decreased at 24 h post-inoculation in shoot, mesocotyl and root. The activity of PAL was also found to be pathotype-specific. Histochemical tests for lignin were positive in infected cells in the resistant genotypes. The role of PAL in imparting resistance to pearl millet against downy mildew disease is discussed.
TL;DR: Results are presented demonstrating the antifungal effect of some of these proteins in vitro, as well as the synergy between specific chitinases and $\beta $ -1,3-glucanases in transgenic tomato plants expressing a specific combination of genes encoding these enzymes.
Abstract: Virus and fungal resistance traits are important targets in the genetic engineering of agricultural and horticultural crops. We have engineered resistance against potato virus X in important commercial potato cultivars. Four years of field trials with resistant potatoes have demonstrated the commercial feasibility of improving potato cultivars by selectively adding new traits while preserving intrinsic properties. In our pursuit for a broad resistance against fungi we have focused on the exploitation of genes encoding antifungal proteins. We present results demonstrating the antifungal effect of some of these proteins in vitro, as well as the synergy between specific chitinases and $\beta $ -1,3-glucanases. We also report high level resistance against Fusarium oxysporum in transgenic tomato plants expressing a specific combination of genes encoding these enzymes.
TL;DR: The results indicate that rhm is tightly linked to two restriction fragment length polymorphism (RFLP) marker loci (UMC85 and p144) that map to the short arm of chromosome 6.
Abstract: The recessive gene rhm confers chlorotic-lesion resistance to Bipolaris maydis race O, the southern corn leaf blight pathogen, in otherwise susceptible maize plants. Because of inconsistencies enco...
Journal Article•
TL;DR: Transgenic plants containing DNA constructs that fuse the hmg2 promoter to a reporter gene have been used to analyze both tissue specificity and patterns of defense-related expression, and this gene may serve as a valuable tool in engineering new disease-resistance mechanisms.
Abstract: Plants have evolved a broad array of defense mechanisms involved in disease resistance. These include synthesis of phytoalexin antibiotics and proteinase inhibitors, deposition of cell wall materials, and accumulation of hydrolytic enzymes such as chitinases. Resistance appears to depend on the ability of the host to recognize the pathogen rapidly and induce these defense responses in order to limit pathogen spread. Application of molecular technologies has yielded significant new information on mechanisms involved in pathogen recognition, signal transduction, and defense-related gene activation, and is leading to novel strategies for engineering enhanced disease resistance. We are using these approaches to analyze regulation of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR), a key enzyme mediating the production of terpenoid defense compounds. This enzyme is encoded by four genes in tomato; hmg2 gene expression is specifically associated with responses to pathogen or defense elicitors. Transgenic plants containing DNA constructs that fuse the hmg2 promoter to a reporter gene have been used to analyze both tissue specificity and patterns of defense-related expression. Because this gene is rapidly induced in tissues directly surrounding the site of ingress by a variety of pathogens, it may serve as a valuable tool in engineering new disease-resistance mechanisms.
Journal Article•
TL;DR: The feasibility of using bulk segregant analysis to identify molecular markers for disease resistance genes in oats was investigated, utilizing random primers in conjunction with polymerase chain reaction technology.
Abstract: The feasibility of using bulk segregant analysis to identify molecular markers for disease resistance genes in oats was investigated, utilizing random primers in conjunction with polymerase chain reaction technology. Random primers were screened for the amplification of polymorphic DNA fragments on two pools of genomic DNA isolated from plants that were homozygous for the presence and absence of the crown rust resistance gene Pc68. Ten primers were identified that amplified polymorphic DNA fragments. Of these, one was tightly linked, in repulsion, to the target gene, while the other nine were not linked to this trait. The relatively low cost of polymerase chain reaction technology, coupled with rapid leaf disc genomic DNA extraction techniques should result in the effective use of this linked marker in oat breeding selection programs.
TL;DR: SR1 tobacco was transformed with a cDNA fragment of the potato virus Y strain N (PVYN) 605 genome which contained the 3' end of the NIb polymerase gene, the coat protein (CP) coding sequence, and most of the viral 3' untranslated region, and partial resistance to PVYN 605 was observed.
Abstract: We transformed SR1 tobacco with a cDNA fragment of the potato virus Y strain N (PVYN) 605 genome which contained the 3' end of the NIb polymerase gene, the coat protein (CP) coding sequence, and most of the viral 3' untranslated region. Complete resistance to several PVY strains was obtained in plants of the R2 generation. The resistance to PVYN and PVYO strains was maintained when the plants were inoculated dually with the potato potyviruses V or A (PVV or PVA). Only partial resistance to PVYN 605 was observed in plants containing the CP coding sequence in an antisense orientation. Both the "sense" and "antisense" plants accumulated CP transcripts and possessed multiple copies of the transgene. Systemic spread of the virus was studied by grafting experiments. The transgenic PVYN 605 CP was undetectable in healthy plants. This protein accumulated in plants of PVY-susceptible CP-transgenic line 4B5-31 when infected by PVYO, PVA, or PVV, but not in plants of line 4B5-S4, that were resistant to PVY and tolerant to PVA or PVV. To assess the role of the transgenic PVYN 605 CP in protection, we transformed plants with a construct bearing a frame-shift mutation at the beginning of the CP coding sequence, and observed partial protection from PVYN 605. Several hypotheses to explain these resistance mechanisms are discussed.
TL;DR: Results of linkage studies indicate that resistance to watermelon mosaic virus type 2 (WMV2) is conferred by the same gene, probably Zym, or perhaps by two closely linked genes.
Abstract: Cucurbita moschata ‘Menina’ originating from Portugal is known to carry a single dominant gene, Zym, for zucchini yellow mosaic virus (ZYMV) resistance. Resistance to watermelon mosaic virus type 2 (WMV2) was found in the same cultivar. In resistant plants, WMV2 migration from inoculated leaves or cotyledons seems to be limited and blocked. Resistance to WMV2 is conferred by one dominant gene and is effective against eight strains from different geographic origins. Results of linkage studies, based on co-inoculation of plants with WMV2 and ZYMV, indicate that resistance to these two viruses is conferred by the same gene, probably Zym, or perhaps by two closely linked genes.
TL;DR: The results suggest that, by using mature-plant resistance, an almost continuous variation in stable levels of mature- plant resistance can be developed.
Abstract: Resistance to downy mildew [Peronospora parasitica (pers.) ex. Fr.] in broccoli (Brassica oleracea L. Italica Group) depends on plant age. Seedling resistance seems to be independent of mature-plant resistance, where a mature plant is defined as having eight or more leaves. Our results suggest that, by using mature-plant resistance, an almost continuous variation in stable levels of mature-plant resistance can be developed. Similarities in the response of mature plants of various lines to isolates from California, Washington, New York, and South Carolina indicated that the predominant race was the same at all locations [...]