Showing papers on "Plant disease resistance published in 1996"
TL;DR: A novel synthetic chemical, benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), was shown to induce acquired resistance in wheat and was the most potent inducer of both resistance and gene induction.
Abstract: Systemic acquired resistance is an important component of the disease resistance repertoire of plants. In this study, a novel synthetic chemical, benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), was shown to induce acquired resistance in wheat. BTH protected wheat systemically against powdery mildew infection by affecting multiple steps in the life cycle of the pathogen. The onset of resistance was accompanied by the induction of a number of newly described wheat chemically induced (WCI) genes, including genes encoding a lipoxygenase and a sulfur-rich protein. With respect to both timing and effectiveness, a tight correlation existed between the onset of resistance and the induction of the WCI genes. Compared with other plant activators, such as 2,6-dichloroisonicotinic acid and salicylic acid, BTH was the most potent inducer of both resistance and gene induction. BTH is being developed commercially as a novel type of plant protection compound that works by inducing the plant's inherent disease resistance mechanisms.
1,120 citations
TL;DR: An overview of the conserved structural components that are predicted in the proteins encoded by R genes are provided, including structure-function analysis of R gene-encoded proteins, isolation of additional R genes, identification of functionally related components of the defense signal transduction cascade, and engineering of improved disease resistance in plants are discussed.
Abstract: The coevolution of interacting plants and microbes has given rise to a diverse array of exchanged signals and responses. Microbes that elicit a host response can be met variously with hospitable acceptance (as is the case with symbionts such as nitrogen-fixing Rhizobium bacteria), with tardy recognition and moderately effective defenses (as for most interactions that result in disease), or with a strong and rapid defense response that blocks further infection (Dixon and Lamb, 1990; Keen, 1990; Long and Staskawicz, 1993). This latter form of disease resistance forms the subject of this review and is known variously as race-specific resistance, gene-for-gene resistance, or hypersensitive resistance. Activation of gene-for-gene resistance typically depends on specific recognition of the invading pathogen by the plant (Keen, 1990). Numerous individual plant genes have been identified that control gene-for-gene resistance, and these genes are known as resistance (R) genes. Study of gene-for-gene resistance might be justified solely by the intrigue of plant-pathogen coevolution or as a model for signal transduction research in which an organism perceives and responds to its environment. However, the topic takes on greater interest dueto its pivotal impact on crop health and food production. Plant diseases cause billions of dollars in lost harvest annually, and in some instances, these losses have severe consequences for humans (Agrios, 1988; Schumann, 1991). One of the most convenient, inexpensive, and environmentally sound ways to control plant disease is to utilize disease-resistam varieties, and plant breeders make extensive use of classically defined R genes (Agrios, 1988). Recent work has revealed the structure of a number of plant R genes, and a striking degree of similarity among these genes has been observed. After briefly introducing the subject of R genes and avirulence (Avo genes, this review provides an overview of the conserved structural components that are predicted in the proteins encoded by R genes. The cloning of R genes has stimulated additional research that is also discussed, including structure-function analysis of R gene-encoded proteins, isolation of additional R genes, identification of functionally related components of the defense signal transduction cascade, and engineering of improved disease resistance in plants. RESISTANCE GENES, AVIRULENCE GENES, AND PLANT DEFENSE
634 citations
TL;DR: The C-terminus of Cf-2 carries regions of pronounced homology to the protein encoded by the unlinked Cf-9 gene, and it is suggested that this conserved region interacts with other proteins involved in activating plant defense mechanisms.
603 citations
TL;DR: The finding that mutants isolated in this way include those affected in known defense responses supports the notion that this type of screening strategy allows genetic dissection of the roles of various plant defense responses in disease resistance.
Abstract: To discover which components of plant defense responses make significant contributions to limiting pathogen attack, we screened a mutagenized population of Arabidopsis thaliana for individuals that exhibit increased susceptibility to the moderately virulent bacterial pathogen Pseudomonas syringae pv. maculicola ES4326 (Psm ES4326). The 12 enhanced disease susceptibility (eds) mutants isolated included alleles of two genes involved in phytoalexin biosynthesis (pad2, which had been identified previously, and pad4, which had not been identified previously), two alleles of the previously identified npr1 gene, which affects expression of other defense genes, and alleles of seven previously unidentified genes of unknown function. The npr1 mutations caused greatly reduced expression of the PR1 gene in response to PsmES4326 infection, but had little effect on expression of two other defense genes, BGL2 and PR5, suggesting that PR1 expression may be important for limiting growth of PsmES4326. While direct screens for mutants with quantitative pathogen-susceptibility phenotypes have not been reported previously, our finding that mutants isolated in this way include those affected in known defense responses supports the notion that this type of screening strategy allows genetic dissection of the roles of various plant defense responses in disease resistance.
594 citations
TL;DR: An RPP-nonspecific locus called EDS1 appears to be a necessary component of the resistance response specified by several RPP genes and is likely to function upstream from the convergence of disease resistance pathways in Arabidopsis.
Abstract: The interaction between Arabidopsis and the biotrophic oomycete Peronospora parasitica (downy mildew) provides an attractive model pathosystem to identify molecular components of the host that are required for genotype-specific recognition of the parasite. These components are the so-called RPP genes (for resistance to P. parasitica). Mutational analysis of the ecotype Wassilewskija (Ws-0) revealed an RPP-nonspecific locus called EDS1 (for enhanced disease susceptibility) that is required for the function of RPP genes on chromosomes 3 (RPP1/RPP14 and RPP10) and 4 (RPP12). Genetic analyses demonstrated that the eds1 mutation is recessive and is not a defective allele of any known RPP gene, mapping to the bottom arm of chromosome 3 (approximately 13 centimorgans below RPP1/RPP14). Phenotypically, the Ws-eds1 mutant seedlings supported heavy sporulation by P. parasitica isolates that are each diagnostic for one of the RPP genes in wild-type Ws-0; none of the isolates is capable of sporulating on wild-type Ws-0. Ws-eds1 seedlings exhibited enhanced susceptibility to some P. parasitica isolates when compared with a compatible wild-type ecotype, Columbia, and the eds1 parental ecotype, Ws-0. This was observed as earlier initiation of sporulation and elevated production of conidiosporangia. Surprisingly, cotyledons of Ws-eds1 also supported low sporulation by five isolates of P. parasitica from Brassica oleracea. These isolates were unable to sporulate on > 100 ecotypes of Arabidopsis, including wild-type Ws-0. An isolate of Albugo candida (white blister) from B. oleracea also sporulated on Ws-eds1, but the mutant exhibited no alteration in phenotype when inoculated with several oomycete isolates from other host species. The bacterial resistance gene RPM1, conferring specific recognition of the avirulence gene avrB from Pseudomonas syringae pv glycinea, was not compromised in Ws-eds1 plants. The mutant also retained full responsiveness to the chemical inducer of systemic acquired resistance, 2,6-dichloroisonicotinic acid; Ws-eds1 seedlings treated with 2,6-dichloroisonicotinic acid became resistant to the Ws-0-compatible and Ws-0-incompatible P. parasitica isolates Emwa1 and Noco2, respectively. In summary, the EDS1 gene appears to be a necessary component of the resistance response specified by several RPP genes and is likely to function upstream from the convergence of disease resistance pathways in Arabidopsis.
576 citations
TL;DR: The results indicate that plant resistance genes that are effective against nematodes, fungi andviruses and bacteria may be isolated based on common sequence motifs and PCR methodology.
Abstract: Plant genes for pathogen resistance can be used to engineer disease resistant crops. Oligonucleotides were designed from sequence motifs conserved between resistance genes of tobacco and Arabidopsis thaliana and used as PCR primers in potato DNA. Amplification products were obtained that were homologous to known resistance genes and linked without recombination with the nematode resistance locus Gro1 and the Phytophthora infestans resistance locus R7 of potato. Map positions of PCR–derived potato gene fragments were also correlated with resistance loci of the related tomato and tobacco genomes. Our results indicate that plant resistance genes that are effective against nematodes, fungi.viruses and bacteria may be isolated based on common sequence motifs and PCR methodology.
567 citations
TL;DR: These studies provide insights into the number of quantitative resistance loci involved in complex disease resistance, epistatic and environmental interactions, race-specificity of partial resistance locu, interactions between pathogen biology, plant development and biochemistry, and the relationship between qualitative and quantitative loci.
Abstract: Quantitative trait locus (QTL) mapping is a highly effective approach for studying genetically complex forms of plant disease resistance. With QTL mapping, the roles of specific resistance loci can be described, race-specificity of partial resistance genes can be assessed, and interactions between resistance genes, plant development, and the environment can be analyzed. Outstanding examples include: quantitative resistance to the rice blast fungus, late blight of potato, gray leaf spot of maize, bacterial wilt of tomato, and the soybean cyst nematode. These studies provide insights into the number of quantitative resistance loci involved in complex disease resistance, epistatic and environmental interactions, race-specificity of partial resistance loci, interactions between pathogen biology, plant development and biochemistry, and the relationship between qualitative and quantitative loci. QTL mapping also provides a framework for marker-assisted selection of complex disease resistance characters and the positional cloning of partial resistance genes.
552 citations
TL;DR: This work has confirmed that adult-plant resistance genes Lr13 and Lr34 singly and together have provided the most durable resistance to leaf rust in wheat throughout the world.
Abstract: Leaf rust (caused by Puccinia recondita f. sp. tritici) is the most widespread and regularly occurring rust on wheat. Genetic resistance is the most economical method of reducing yield losses due to leaf rust. To date, 46 leaf rust resistance genes have been designated and mapped in wheat. Resistance gene expression is dependent on the genetics of host-parasite interaction, temperature conditions, plant developmental stage, and interaction between resistance genes with suppressors or other resistance genes in the wheat genomes. Genes expressed in seedling plants have not provided long-lasting effective leaf rust resistance. Adult-plant resistance genes Lr13 and Lr34 singly and together have provided the most durable resistance to leaf rust in wheat throughout the world. Continued efforts to isolate, characterize, and map leaf rust resistance genes is essential given the ability of the leaf rust fungus to overcome deployed resistance genes.
382 citations
TL;DR: The ability to reconstruct the N-mediated resistance response to tobacco mosaic virus in tomato demonstrates the utility of using isolated resistance genes to protect crop plants from diseases, and it demonstrates that all the components necessary for N- mediated resistance are conserved in tomato.
Abstract: It has been proposed that cloned plant disease resistance genes could be transferred from resistant to susceptible plant species to control important crop plant diseases. The recently cloned N gene of tobacco confers resistance to the viral pathogen, tobacco mosaic virus. We generated transgenic tomato plants bearing the N gene and demonstrate that N confers a hypersensitive response and effectively localizes tobacco mosaic virus to sites of inoculation in transgenic tomato, as it does in tobacco. The ability to reconstruct the N-mediated resistance response to tobacco mosaic virus in tomato demonstrates the utility of using isolated resistance genes to protect crop plants from diseases, and it demonstrates that all the components necessary for N-mediated resistance are conserved in tomato.
321 citations
TL;DR: There is interference between the RPS2- and RPM1-mediated resistance responses, and the induction patterns of the AIG genes and ELI3 demonstrate that different resistance gene-avr gene combinations can elicit distinct defense responses.
Abstract: The Arabidopsis disease resistance gene RPS2 is involved in recognition of bacterial pathogens carrying the avirulence gene avrRpt2, and the RPM1 resistance gene is involved in recognition of pathogens carrying avrRpm1 or avrB. We identified and cloned two Arabidopsis genes, AIG1 and AIG2 (for avrRpt2-induced gene), that exhibit RPS2- and avrRpt2-dependent induction early after infection with Pseudomonas syringae pv maculicola strain ES4326 carrying avrRpt2. However, ES4326 carrying avrRpm1 or avrB did not induce early expression of AIG1 and AIG2. Conversely, ES4326 carrying avrRpm1 or avrB induced early expression of the previously isolated defense-related gene ELI3, whereas ES4326 carrying avrRpt2 did not. The induction patterns of the AIG genes and ELI3 demonstrate that different resistance gene-avr gene combinations can elicit distinct defense responses. Furthermore, by examining the expression of AIG1 and ELI3 in plants infiltrated with a mixed inoculum of ES4326 carrying avrRpt2 and ES4326 carrying avrRpm1, we found that there is interference between the RPS2- and RPM1-mediated resistance responses.
280 citations
TL;DR: The identical resistance spectrum of both lines indicates that the presence of a single member of a multigene family, Xa21, is sufficient to confer multi-isolate resistance, which has important implications for engineering disease resistance in crop plants.
Abstract: The cloned rice gene, Xa21, confers resistance to multiple pathogen isolates of Xanthomonas oryzae pv. oryzae in transgenic plants. The resistance phenotype was stably transmitted to T1 progeny and inherited as a single locus. The T1 progeny were tested for resistance to 32 X. oryzae pv. oryzae isolates from eight countries. Both the engineered line and the donor line showed resistance to 29 isolates and susceptibility to three isolates. The identical resistance spectrum of both lines indicates that the presence of a single member of a multigene family, Xa21, is sufficient to confer multi-isolate resistance. The results presented here have important implications for engineering disease resistance in crop plants.
TL;DR: A hybrid endochitinase gene under a constitutive promoter was introduced by Agrobacterium-mediated transformation into a winter-type oilseed rape inbred line and exhibited an increased tolerance to disease as compared with the nontransgenic parental plants.
Abstract: Constitutive overexpression of a protein involved in plant defense mechanisms to disease is one of the strategies proposed to increase plant tolerance to fungal pathogens. A hybrid endochitinase gene under a constitutive promoter was introduced by Agrobacterium-mediated transformation into a winter-type oilseed rape (Brassica napus var. oleifera) inbred line. Progeny from transformed plants was challenged using three different fungal pathogens (Cylindrosporium concentricum, Phoma lingam, Sclerotinia sclerotiorum) in field trials at two different geographical locations. These plants exhibited an increased tolerance to disease as compared with the nontransgenic parental plants.
TL;DR: The report on six Arabidopsis accessions that show resistance to a wild isolate of the powdery mildew pathogen, Erysiphe cichoracearum, suggests that the Arabidoscopic disease will be a suitable model system in which to investigate powdery Mildew diseases.
Abstract: This paper reports on six Arabidopsis accessions that show resistance to a wild isolate of the powdery mildew pathogen, Erysiphe cichoracearum. Resistance at 7 days post-inoculation in these accessions was characterized by limited fungal growth and sporadic development of chlorotic or necrotic lesions at inoculation sites. Three accessions, Wa-1, Kas-1 and SI-0, were highly resistant, while the other accessions permitted some fungal growth and conidiation. Papilla formation was a frequent host response; however, cell death appeared to be neither a rapid nor a common response to infection. To determine the genetic basis of resistance, segregation analyses of progeny from crosses between each of the resistant accessions and Columbia (gl1), which is susceptible to the powdery mildew pathogen, were performed. For all accessions except SI-0, resistance was conferred by a single locus. SI-0 was unique in that two unlinked loci controlled the disease reaction phenotype. In accessions Wa-1, Kas-1, Stw-0 and Su-0, powdery mildew resistance was encoded by a semi-dominant allele. However, susceptibility was dominant to resistance in accessions Te-0 and SI-0. Mapping studies revealed that powdery mildew resistances in Kas-1, Wa-1, Te-0, Su-0 and Stw-0 were controlled by five independent loci. This study suggests that the Arabidopsis powdery mildew disease will be a suitable model system in which to investigate powdery mildew diseases.
TL;DR: On the basis of the chromosomal locations of resistance alleles detected in this study, it should be feasible to combine high levels of resistance to both P. Teres f.
Abstract: Net blotch (caused by Pyrenophora teres f. teres) and spot blotch (Cochliobolus sativus) are important foliar diseases of barley in the midwestern region of the USA. To determine the number and chromosomal location of Mendelian and quantitative trait loci (QTL) controlling resistance to these diseases, a doubled haploid population (‘Steptoe’/‘Morex’) was evaluated to the pathogens at the seedling stage in the greenhouse and at the adult plant stage in the field. Alleles at two or three unlinked loci were found to confer resistance to the net blotch pathogen at the seedling stage depending on how progeny exhibiting an intermediate infection response were classified. This result was corroborated in the quantitative analysis of the raw infection response data as 2 major QTL were identified on chromosomes 4 and 6M. A third QTL was also identified on chromosome 6P. Seven QTL were identified for net blotch resistance at the adult plant stage and mapped to chromosomes 1P, 2P, 3P, 3M, 4, 6P, and 7P. The 7 QTL collectively accounted for 67.6% of the phenotypic variance under a multiple QTL model. Resistance to the spot blotch pathogen was conferred by a single gene at the seedling stage. This gene was mapped to the distal region of chromosome 1P on the basis of both qualitative and quantitative data analyses. Two QTL were identified for spot blotch resistance at the adult plant stage: the largest QTL effect mapped to chromosome 5P and the other mapped to chromosome 1P near the seedling resistance locus. Together, the 2 QTL explained 70.1% of the phenotypic variance under a multiple QTL model. On the basis of the chromosomal locations of resistance alleles detected in this study, it should be feasible to combine high levels of resistance to both P. teres f. teres and C. sativus in barley cultivars.
TL;DR: The findings suggest that the PBZ1 gene has an important function during the disease resistance response in rice, and significant homology at the amino acid level exists between the predictedPBZ1 protein and intracellular pathogenesis-related (IPR) proteins.
Abstract: Probenazole (3-allyloxy-1,2-benzisothiazole-1,1-dioxide) induces disease resistance in rice against rice blast fungus. To investigate the molecular mechanism of probenazole-induced resistance, we isolated and characterized a cDNA clone of a probenazole-inducible gene in rice, which encoded a protein designated PBZ1. Sequence analysis revealed that significant homology at the amino acid level exists between the predicted PBZ1 protein and intracellular pathogenesis-related (IPR) proteins. Accumulation of PBZ1 mRNA was not induced by wounding, but markedly induced by inoculation with rice blast fungus. In addition, it was induced sooner by inoculation with an incompatible race than that with a compatible race. On the other hand, when the accumulation of the PBZ1 mRNA was examined after treatment with probenazole-related compounds, it was not fully correlated with anti-rice blast activity. However, it was induced after treatment with N-cyano-methyl-2-chloro-isonicotinamide (NCI), which belongs to another group of compounds known to induce disease resistance. Thus, although the accumulation of the PBZ1 mRNA was not fully correlated with anti-rice blast activity, our findings suggest that the PBZ1 gene has an important function during the disease resistance response in rice.
TL;DR: The demonstration of interference between two plant disease resistance genes suggests that their products compete for a common element(s) in a signal transduction pathway leading to disease resistance.
Abstract: We demonstrate that the interaction of the avirulence gene avrRpt2 and the cognate resistance gene RPS2 interferes with the interaction of avrRpm1-RPM1 in Arabidopsis. Interference is mediated outside of the bacterial pathogen Pseudomonas syringae, presumably at the level of recognition of avr-dependent signals, yet does not require the wild-type RPS2 product. A numerical excess of P. syringae expressing avrRpm1 can overcome this interference in mixed inoculations. The interference of avrRpt2-RPS2 engagement with RPM1-dependent functions is mirrored by transcriptional activation of genes preferentially expressed during RPM1- or RPS2-mediated disease resistance reactions. This demonstration of interference between two plant disease resistance genes suggests that their products compete for a common element(s) in a signal transduction pathway leading to disease resistance.
TL;DR: It is proposed that molecular recognition of P. syringae in RPS2- and RPM1-specified resistance occurs inside of plant cells, indicating that no bacterial factors other than the avirulence gene products are required for the specific resistance response as long as they are correctly localized.
Abstract: The Arabidopsis thaliana disease resistance genes RPS2 and RPM1 belong to a class of plant disease resistance genes that encode proteins that contain an N-terminal tripartite nucleotide binding site (NBS) and a C- terminal tandem array of leucine-rich repeats. RPS2 and RPM1 confer resistance to strains of the bacterial phytopathogen Pseudomonas syringae carrying the avirulence genes avrRpt2 and avrB, respectively. In these gene-for-gene relationships, it has been proposed that pathogen avirulence genes generate specific ligands that are recognized by cognate receptors encoded by the corresponding plant resistance genes. To test this hypothesis, it is crucial to know the site of the potential molecular recognition. Mutational analysis of RPS2 protein and in vitro translation/translocation studies indicated that RPS2 protein is localized in the plant cytoplasm. To determine whether avirulence gene products themselves are the ligands for resistance proteins, we expressed the avrRpt2 and avrB genes directly in plant cells using a novel quantitative transient expression assay, and found that expression of avrRpt2 and avrB elicited a resistance response in plants carrying the corresponding resistance genes. This observation indicates that no bacterial factors other than the avirulence gene products are required for the specific resistance response as long as the avirulence gene products are correctly localized. We propose that molecular recognition of P. syringae in RPS2- and RPM1-specified resistance occurs inside of plant cells.
TL;DR: Results suggest that the tobacco myb1 gene encodes a signaling component down-stream of SA that may participate in transcriptional activation of PR genes and plant disease resistance.
Abstract: Salicylic acid (SA) plays an important role in signaling the activation of plant defense responses against pathogen attack including induction of pathogenesis-related (PR) proteins. To gain further insight into the SA-mediated signal transduction pathway, we have isolated and characterized a tobacco mosaic virus (TMV)-inducible myb oncogene homolog (myb1) from tobacco. The myb1 gene was induced upon TMV infection during both the hypersensitive response and development of systemic acquired resistance in the resistant tobacco cultivar following the rise of endogenous SA, but was not activated in the susceptible cultivar that fails to accumulate SA. The myb1 gene was also induced by incompatible bacterial pathogen Pseudomonas syringae pv. syringae during the hypersensitive response. Exogenous SA treatment rapidly (within 15 min) activated the expression of myb1 in both resistant and susceptible tobacco cultivars with the subsequent induction of PR genes occurring several hours later. Biologically active analogs of SA and 2,6-dichloroisonicotinic acid (a synthetic functional analog of SA), which induce PR genes and enhanced resistance, also activated the myb1 gene. In contrast, biologically inactive analogs were poor inducers of myb1 gene expression. Furthermore, the recombinant Myb1 protein was shown to specifically bind to a Myb-binding consensus sequence found in the promoter of the PR-1a gene. Taken together, these results suggest that the tobacco myb1 gene encodes a signaling component downstream of SA that may participate in transcriptional activation of PR genes and plant disease resistance.
TL;DR: Inheritance of resistance to rust was investigated in the self progeny of the sugarcane cultivar ‘R570’ and this gene was found linked at 10 cM with an RFLP marker revealed by probe CDSR29, the first documented report of a monogenic inheritance for disease resistance in Sugarcane.
Abstract: Inheritance of resistance to rust was investigated in the self progeny of the sugarcane cultivar ‘R570’ also used to build a RFLP genetic map. Resistance was evaluated through both field and controlled greenhouse trials. A clear-cut 3 (resistant) ∶ 1 (susceptible) segregation indicative of a probable dominant resistant gene was observed. This is the first documented report of a monogenic inheritance for disease resistance in sugarcane. This gene was found linked at 10 cM with an RFLP marker revealed by probe CDSR29. Other minor factors involved in the resistance were also detected.
TL;DR: The data show that effective long-term resistance can be obtained from a single qualitative resistance gene, despite the presence of virulence in the pathogen population, suggesting disease resistance in this endemic coevolved forest pathosystem is not exclusively polygenic.
Abstract: Genomic mapping has been used to identify a region of the host genome that determines resistance to fusiform rust disease in loblolly pine where no discrete, simply inherited resistance factors had been previously found by conventional genetic analysis over four decades. A resistance locus, behaving as a single dominant gene, was mapped by association with genetic markers, even though the disease phenotype deviated from the expected Mendelian ratio. The complexity of forest pathosystems and the limitations of genetic analysis, based solely on phenotype, had led to an assumption that effective long-term disease resistance in trees should be polygenic. However, our data show that effective long-term resistance can be obtained from a single qualitative resistance gene, despite the presence of virulence in the pathogen population. Therefore, disease resistance in this endemic coevolved forest pathosystem is not exclusively polygenic. Genomic mapping now provides a powerful tool for characterizing the genetic basis of host pathogen interactions in forest trees and other undomesticated, organisms, where conventional genetic analysis often is limited or not feasible.
TL;DR: Cytological observations on root samples from FORL-inoculated plants revealed that the beneficial effect of chitosan in reducing disease was associated with increased plant resistance to fungal colonization.
Abstract: The potential of chitosan, a non-toxic and biodegradable polymer of beta -1,4-glucosamine, for controlling fusarium crown and root rot of greenhouse-grown tomato caused by Fusarium oxysporum f.sp. radicis-lycopersici (FORL) was investigated. The amendment of plant growth substratum with chitosan at concentrations of 12.5 or 37.5 mg l-1 significantly reduced plant mortality, root rot symptoms and yield loss attributed to FORL. Maximum disease control was achieved with chitosan at 37.5 mg l-1, when plant mortality was reduced by more than 90% and fruit yield was comparable with that of non-infected plants. In the absence of FORL, chitosan did not adversely affect plant growth and fruit yield. Cytological observations on root samples from FORL-inoculated plants revealed that the beneficial effect of chitosan in reducing disease was associated with increased plant resistance to fungal colonization. In chitosan-treated plants, fungal growth was restricted to the epidermis and the cortex. Invading hyphae showed...
TL;DR: Transgenic potato plants expressing high levels of the pA13 osmotin-like protein showed an increased tolerance to the late-blight fungus Phytophthora infestans at various phases of infection, with a greater resistance at an early phase of fungal infection.
Abstract: The expression patterns of plant defense genes encoding osmotin and osmotin-like proteins imply a dual function in osmotic stress and plant pathogen defense. We have produced transgenic potato (Solanum commersonii Dun.) plants constitutively expressing sense or antisense RNAs from chimeric gene constructs consisting of the cauliflower mosaic virus 35S promoter and a cDNA (pA13) for an osmotin-like protein. Transgenic potato plants expressing high levels of the pA13 osmotin-like protein showed an increased tolerance to the late-blight fungus Phytophthora infestans at various phases of infection, with a greater resistance at an early phase of fungal infection. There was a decrease in the accumulation of osmotin-like mRNAs and proteins when antisense transformants were challenged by fungal infection, although the antisense transformants did not exhibit any alterations in disease susceptibility. Expression of pA13 sense and antisense RNAs had no effect on the development of freezing tolerance in transgenic plants when assayed under a variety of conditions including treatments with abscisic acid or low temperature. These results provide evidence of antifungal activity for a potato osmotin-like protein against the fungus P. infestans, but do not indicate that pA13 osmotin-like protein is a major determinant of freezing tolerance.
TL;DR: One hundred and ten markers were analysed for linkage in 218 F2 plants derived from two divergent cultivars of Cucumis melo, spanning 14 linkage groups covering 1390 cM of the melon genome.
Abstract: One hundred and ten markers were analysed for linkage in 218 F2 plants derived from two divergent cultivars (‘Vedrantais’ and ‘Songwhan Charmi’) of Cucumis melo (L.). Thirty-four RFLPs, 64 RAPDs, one isozyme, four disease resistance markers and one morphological marker were used to construct a genetic map spanning 14 linkage groups covering 1390 cM of the melon genome. RAPD and RFLP markers detected similar polymorphism levels. RFLPs were largely due to base substitutions rather than insertion/deletions. Twelve percent of markers showed distorted segregation. Phenotypic markers consisted of two resistance genes against Fusarium wilt (Fom-1 and Fom-2), one gene (nsv) controlling the resistance to melon necrotic spot virus, one gene (Vat) conferring resistance to Aphis gossypii, and a recessive gene for carpel numbers (3 vs 5 carpels: p).
TL;DR: One RAPD marker, specific to chromosome arm 6VS, OPH17-1900, could be used as a molecular marker for the detection of gene Pm21 in breeding materials with powdery mildew resistance introduced from H. villosa.
Abstract: A new powdery mildew resistance gene designated Pm21, from Haynaldia villosa, a relative of wheat, has been identified and incorporated into wheat through an alien translocation line. Cytogenetic a...
TL;DR: It is shown that HrpZPss induced SAR in cucumber to diverse pathogens, including the anthracnose fungus, Colletotrichum lagenarium, tobacco necrosis virus and the bacterial angular leaf spot bacterium, and that at least some PR proteins can be induced by bacterial factors that are not controlled by hrp genes.
Abstract: Systemic acquired resistance (SAR) is an inducible plant defense response and is effective against a broad spectrum of pathogens Biological induction of SAR usually follows plant cell death resulting from the plant hypersensitive response (HR) elicited by an avirulent pathogen or from disease necrosis caused by a virulent pathogen The elicitation of the HR and disease necroses by pathogenic bacteria is controlled by hrp genes Previously, it was shown that the Pseudomonas syringae 61 (Pss61) HrpZPss protein (formally harpinPss) elicited the HR in plants In this study, it is shown that HrpZPss induced SAR in cucumber to diverse pathogens, including the anthracnose fungus (Colletotrichum lagenarium), tobacco necrosis virus and the bacterial angular leaf spot bacterium (P s pv lachrymans) A hrpH mutant of Pss61, which is defective in the secretion of HrpZPss and, possibly, other protein elicitors, failed to elicit SAR Pathogenesis-related (PR) proteins, including peroxidase, β-glucanase and chitinases, were induced in cucumber plants inoculated with Pss61, C lagenarium or HrpZPss The induction patterns of PR proteins by HrpZPss and Pss61 were the same, but were different from that induced by C lagenarium Interestingly, the hrpH mutant induced two of the three identified PR proteins, despite its failure to induce SAR These results suggest that proteinaceous elicitors, such as HrpZPss, that traverse the bacterial Hrp secretion pathway are involved in the biological induction of SAR and that at least some PR proteins can be induced by bacterial factors that are not controlled by hrp genes
TL;DR: The results demonstrate the in planta efficacy of a basic chitinase protein in providing enhanced tolerance of carrot to three fungal pathogens; however, the efficacy of ch itinase gene transformation as a strategy for enhancing disease tolerance in plants can be influenced by the plant species used, the type of chit inase protein expressed, and the characteristics of the fungal pathogen.
Abstract: Three lines of cucumber cv. Endeavor, each transformed with a chitinase gene originating from petunia (acidic), tobacco (basic), or bean (basic) using Agrobacterium tumefaciens, were compared with nontransgenic plants for response to inoculation with Alternaria cucumerina, Botrytis cinerea, Colletotrichum lagenarium, and Rhizoctonia solani. In both growth chamber studies using whole plants and in vitro inoculations conducted with detached leaves, no differences in disease development (rate and final levels) were detected between transgenic and nontransgenic plants. Carrot cvs. Nanco and Golden State transformed with two chitinase genes (from petunia and tobacco) were also evaluated for response to inoculation with the pathogens Alternaria radicini, B. cinerea, R. solani, Sclerotium rolfsii, and Thielaviopsis basicola. A detached petiole inoculation method was used to compare nontransgenic and transgenic plants. The rate and final extent of lesion development after 7 days were significantly (P = 0.01) lower in the transgenic plants expressing the tobacco (basic) chitinase gene upon inoculation with B. cinerea, R. solani, and S. rolfsii, but not in plants expressing the petunia (acidic) chitinase gene. There were no detectable differences with A. radicini or T. basicola in either group of transgenic punts. These results demonstrate the in planta efficacy of a basic chitinase protein in providing enhanced tolerance of carrot to three fungal pathogens; however, the efficacy of chitinase gene transformation as a strategy for enhancing disease tolerance in plants can be influenced by the plant species used, the type of chitinase protein expressed, and the characteristics of the fungal pathogen.
TL;DR: Random amplified polymorphic DNA (RAPD) markers were used to construct a partial linkage map in a recombinant inbred population derived from the common bean for studying the genetics of disease resistance in common bean to find significant marker locus- trait associations.
Abstract: Random amplified polymorphic DNA (RAPD) markers were used to construct a partial linkage map in a recombinant inbred population derived from the common bean (Phaseolus vulgaris L.) cross BAC 6 x HT 7719 for studying the genetics of disease resistance in common bean. The linkage map spanned 545 cM and included 75 of 84 markers used in this study. The population of 128 recombinant inbred lines was evaluated for resistance to common bacterial blight, foliar resistance to web blight (WB; Thanatephorus cucumeris (Frank) Donk), and resistance to rust ( Uromyces appendiculatus var. appendiculatus (Pers.:Pers) Unger). Common bacterial blight (CBB; Xanthomonas campestris pv. phaseoli (Smith) Dye) resistance was evaluated for CBB strain Epif-IV in later-developed trifoliolate leaves and for CBB strain EK-11 in seeds, first trifoliolate leaves, later-developed trifoliolate leaves, and pods. In addition, lines were rated for plant uprightness and branch density. Two to six markers accounted for 14% to 34% of the phenotypic variation for each trait. Significant marker locus- trait associations were found for 14 mapped loci and 7 of the 9 unmapped markers. The distribution of detected QTL appeared to be nonrandom with most significant markers associated with more than one trait or closely linked to markers significantly associated with variation for a different trait. One marker, BC409 1250 , was significantly associated with WB resistance, resistance for CBB strain Epif-IV in later-developed trifoliolate leaves, and resistance for CBB strain EK-11 in first trifoliolate leaves, later-developed trifoliolate leaves, and pods. A rust resistance gene was mapped in an interval 14.6 cM from RAPD marker H19 1050 and 12.5 cM from marker AJ16 250 . Common bacterial blight (CBB; Xanthomonas campestris pv. phaseoli), web blight (WB; Thanatephorus cucumeris), and rust (Uromyces appendiculatus var. appendiculatus) are important diseases of common bean (Harter and Zaumeyer, 1944). These diseases cause economic losses due to a reduction in seed yield and seed quality in dry bean producing regions worldwide (Galvez et al., 1989; Saettler, 1989; Stavely and Pastor-Corrales, 1989). The most reliable and effective control strategy for these diseases is the
TL;DR: Analysis of primary transformants for response to several fungal pathogens of alfalfa indicated statistically significant symptom reduction only in the case of Phytophthora megasperma f.medicaginis, and only in plants overexpressing Aglul.
Abstract: cDNA sequences coding for an acidic glucanase (Aglul) that is expressed in elicited alfalfa cell suspension cultures, and a rice basic chitinase (RCH10) that is induced by elicitor and wounding, were placed into constitutive expression cassettes under control of the cauliflower mosaic virus 35S promoter or 35S enhancer sequences, and introduced in alfalfa plants of the regenerable cultivar Regen SY byAgrobacterium-mediated transformation. Southern and northern blot analysis confirmed stable incorporation and transcription, respectively, of the chimaeric genes in the transgenic plants. Active rice chitinase was expressed in alfalfa leaves, and leaves of plants transformed with theAglul sequence exhibited increased glucanase activity and the appearance of an additional glucanase band on activity gels. A glucanase of similar native electrophoretic mobility was constitutively present in root extracts of non-transformed alfalfa plants, and was induced in pathogen-infected leaves, presumably reflecting the expression pattern of the endogenousAglul gene. Thus, expression of the chimaericAglul transgene increased the amount, and broadened the tissue-type constitutive expression, of theAglul protein compared to control plants. Transgenic alfalfa plants containing a binary vector with both chimaeric genes in tandem expressed each gene to a much lesser extent than transgenic plants containing a single chimaeric gene. Expression of RCH10 in transgenic alfalfa did not appear to affect negatively theRhizobium/alfalfa interaction. Analysis of primary transformants for response to several fungal pathogens of alfalfa indicated statistically significant symptom reduction only in the case ofPhytophthora megasperma f. sp.medicaginis (Pmm), and only in plants overexpressingAglul. Resistance against Pmm segregated with glucanase expression in a cross between transgenic Regen SY and the commercial alfalfa cultivar Apollo.
TL;DR: Two dominant genes conferring complete resistance to specific isolates of the rice blast fungus, Pyricularia grisea Sacc.
Abstract: Two dominant genes conferring complete resistance to specific isolates of the rice blast fungus, Pyricularia grisea Sacc., were located on the molecular map of rice in this study. Pi-l(t) is a blast resistance gene derived from the cultivar ‘LAC23’. Its map location was determined using a pair of nearly isogenic lines (NILs) and a B6F3 segregating population from which the isoline was derived. RFLP analysis showed that Pi-l(t) is located near the end of chromosome 11, linked to RZ536 at a distance of 14.0±4.5 centiMorgans (cM). A second gene, derived from the cultivar ‘Apura’, was mapped using a rice doubled-haploid (DH) population. This gene was located on chromosome 12, flanked by RG457 and RG869, at a distance of 13.5+-4.3 cM and 17.7+-4.5 cM, respectively. The newly mapped gene on chromosome 12 may be allelic or closely linked toPi-ta. (=Pi-4(t)), a gene derived from Tetep that was previously reported to be linked to RG869 at a distance of 15.4±4.7 cM. The usefulness of markers linked to blast resistance genes will be discussed in the context of breeding for durable blast resistance.
TL;DR: Transgenic plants were produced that expressed a wide range of randomly chosen sequences of the tripartite tomato spotted wilt virus genome or its complement, but only transgenic expression of N or NS(M) gene sequences resulted in resistance to TSWV.
Abstract: Transgenic plants were produced that expressed a wide range of randomly chosen sequences of the tripartite tomato spotted wilt virus (TSWV) RNA genome or its complement. Testing the progenies of these plants revealed that only transgenic expression of N or NS(M) gene sequences resulted in resistance to TSWV.