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Plant Resistance (plant + resistance)
Kinds of Plant Resistance Selected AbstractsSignificance of Flavonoids in Plant Resistance and Enhancement of Their BiosynthesisPLANT BIOLOGY, Issue 6 2005D. Treutter Abstract: The roles of flavonoids in plant defence against pathogens, herbivores, and environmental stress are reviewed and their significant contribution to plant resistance is discussed. The induction of flavonoids is of particular interest for gathering evidence of their roles. Tools are mentioned which may enhance flavonoid biosynthesis and accumulation. These include metabolic engineering and UV light. The induction of defence-related flavonoids is modified by other determining factors and competition between growth and secondary metabolism may exist. In an evolutionary context, stress-related oxidative pressure may have been a major trigger for the distribution and abundance of flavonoids. UV protection is one of their most significant, or even the most significant, functional role for flavonoids. The multi-functionality of these compounds, however, often complicates the interpretation of experimental results but, overall, it supports the importance of flavonoids. [source] Variation in resistance to the root-knot nematode Meloidogyne incognita in tomato genotypes bearing the Mi genePLANT PATHOLOGY, Issue 2 2005M. Jacquet Root-knot nematodes (Meloidogyne spp.) are among the main pathogens of tomato (Lycopersicon esculentum) worldwide. Plant resistance is currently the method of choice for controlling these pests and all the commercially available resistant cultivars carry the dominant Mi gene, which confers resistance to the three main species Meloidogyne arenaria, M. incognita and M. javanica. However the emergence of virulent biotypes able to overcome the tomato resistance gene may constitute a severe limitation to such a control strategy. To date, little was known of the possible influence of the homozygous vs heterozygous allelic state of the Mi locus, or the tomato genetic background, on the expression of the resistance. In order to test both these factors, the resistance was evaluated of a large panel of L. esculentum genotypes (selected from the Vilmorin germplasm stock collection) to seven M. incognita lines avirulent or virulent against the Mi gene. Plant resistance was estimated by counting the egg masses on the root systems after inoculation with second-stage juveniles (J2). Reproduction of the nematodes was similar or, more often, significantly higher on heterozygous tomato genotypes than on homozygous ones, suggesting a possible dosage effect of the Mi gene. Data also indicated that the tomato genetic background had a major effect on the variations observed in nematode reproduction, especially when tomato genotypes were heterozygous for the Mi gene. These results have important consequences in terms of breeding strategies and durability of the resistance conferred by the Mi gene. [source] Tolerance to herbivory, and not resistance, may explain differential success of invasive, naturalized, and native North American temperate vinesDIVERSITY AND DISTRIBUTIONS, Issue 2 2008Isabel W. Ashton ABSTRACT Numerous hypotheses suggest that natural enemies can influence the dynamics of biological invasions. Here, we use a group of 12 related native, invasive, and naturalized vines to test the relative importance of resistance and tolerance to herbivory in promoting biological invasions. In a field experiment in Long Island, New York, we excluded mammal and insect herbivores and examined plant growth and foliar damage over two growing seasons. This novel approach allowed us to compare the relative damage from mammal and insect herbivores and whether damage rates were related to invasion. In a greenhouse experiment, we simulated herbivory through clipping and measured growth response. After two seasons of excluding herbivores, there was no difference in relative growth rates among invasive, naturalized, and native woody vines, and all vines were susceptible to damage from mammal and insect herbivores. Thus, differential attack by herbivores and plant resistance to herbivory did not explain invasion success of these species. In the field, where damage rates were high, none of the vines were able to fully compensate for damage from mammals. However, in the greenhouse, we found that invasive vines were more tolerant of simulated herbivory than native and naturalized relatives. Our results indicate that invasive vines are not escaping herbivory in the novel range, rather they are persisting despite high rates of herbivore damage in the field. While most studies of invasive plants and natural enemies have focused on resistance, this work suggests that tolerance may also play a large role in facilitating invasions. [source] Ontogenetic switches from plant resistance to tolerance: minimizing costs with age?ECOLOGY LETTERS, Issue 3 2007Karina Boege Abstract Changes in herbivory and resource availability during a plant's development should promote ontogenetic shifts in resistance and tolerance, if the costs and benefits of these basic strategies also change as plants develop. We proposed and tested a general model to detect the expression of ontogenetic tradeoffs for these two alternative anti-herbivory strategies in Raphanus sativus. We found that ontogenetic trajectories occur in both resistance and tolerance but in opposite directions. The juvenile stage was more resistant but less tolerant than the reproductive stage. The ontogenetic switch from resistance to tolerance was consistent with the greater vulnerability of young plants to leaf damage and with the costs of resistance and tolerance found at each stage. We posit that the ontogenetic perspective presented here will be helpful in resolving the current debate on the existence and detection of a general resistance,tolerance tradeoff. [source] Impact of chemical elicitor applications on greenhouse tomato plants and population growth of the green peach aphid, Myzus persicaeENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2006Anthony J. Boughton Abstract Recent advances in the understanding of plant signaling pathways have opened the way for using elicitor-induced plant resistance as a tactic for protecting plants against arthropod pests. Four common elicitors of induced responses in tomato, Lycopersicon esculentum Mill. (Solanaceae), were evaluated with regard to phytotoxicity, induction of plant defensive proteins, and effects on population growth and fecundity of a common pest, the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae). Ethephon and methyl jasmonate (MJ) treatments caused varying degrees of phytotoxicity. Ethephon caused pronounced changes in plant growth form and severe, dose-dependent negative impacts on plant growth and flowering. Effects with MJ were milder, but still caused temporary inhibition of development, leading to smaller plants and delayed flowering. The commercial elicitors benzothiadiazole (BTH) and harpin did not cause detectable phytotoxicity. The highest doses of ethephon and MJ significantly increased leaf peroxidase (POD) levels but only MJ treatments significantly increased polyphenol oxidase (PPO) levels. BTH and harpin had no detectable effects on POD and PPO. Populations of green peach aphids grew significantly more slowly on plants treated with BTH or MJ than on control plants or plants treated with harpin or ethephon. Slowed aphid population growth on BTH-treated plants was due to significant reductions in aphid fecundity, although this was independent of changes in time to onset of reproduction or time to death. Aphid fecundity was also reduced on MJ-treated plants relative to controls, but this difference was not statistically significant, suggesting that other mechanisms are involved in slowing aphid population growth on MJ-treated plants. Growth of aphid populations on plants treated with a MJ,BTH mixture was reduced almost as much as with treatments of MJ alone, suggesting that antagonism between JA-dependant and SA-dependent plant signaling pathways is only mild with regard to induced defenses against aphids. [source] Trade-offs between the shade-avoidance response and plant resistance to herbivores?FUNCTIONAL ECOLOGY, Issue 6 2005Tests with mutant Cucumis sativus Summary 1Plants exhibit adaptations to many stresses, including light competition and herbivory. The expression of these traits may interact negatively, potentially instigating a trade-off. 2We employed a combination of genetically altered Cucumis sativus varieties and phenotypic manipulations to test for trade-offs in field experiments. The different genetic lines of C. sativus were altered in their phytochrome-mediated shade responses and the production of terpenoid defence compounds. 3Cucumber plants constitutively expressing the shade-avoidance response had 93% more herbivory by specialist beetles compared with wild types. The long-hypocotyl mutants also produced leaves with fewer trichomes, greater toughness and a higher carbon to nitrogen ratio (C : N) than wild types. Plants lacking defensive cucurbitacins had 23% longer internodes than the cucurbitacin-producing line. 4We then manipulated the plant phenotype by artificially imposing neighbours' shade on plants with and without cucurbitacins. As expected, plants responded to shade by growing longer hypocotyls and first internodes, but few trade-offs were found between plant line and shade treatment and, although herbivory levels were very low, there was a trend towards reduced damage on shaded plants. 5The use of genetically altered plant lines provided strong evidence for the trade-off hypothesis, while phenotypic manipulations did not support the hypothesis. [source] Evaluating Tripsacum -introgressed maize germplasm after infestation with western corn rootworms (Coleoptera: Chrysomelidae)JOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2009D. A. Prischmann Abstract Maize (Zea mays L.) is a valuable commodity throughout the world, but corn rootworms (Chrysomelidae: Diabrotica spp.) often cause economic damage and increase production costs. Current rootworm management strategies have limitations, and in order to create viable management alternatives, researchers have been developing novel maize lines using Eastern gamagrass (Tripsacum dactyloides L.) germplasm, a wild relative of maize that is resistant to rootworms. Ten maize Tripsacum -introgressed inbred lines derived from recurrent selection of crosses with gamagrass and teosinte (Zea diploperennis Iltis) recombinants and two public inbred lines were assessed for susceptibility to western corn rootworm (Diabrotica virgifera virgifera LeConte) and yield in a two-year field study. Two experimental maize inbred lines, SDG11 and SDG20, had mean root damage ratings that were significantly lower than the susceptible public line B73. Two other experimental maize inbred lines, SDG12 and SDG6, appeared tolerant to rootworm damage because they exhibited yield increases after rootworm infestation in both years. In the majority of cases, mean yield per plant of experimental maize lines used in yield analyses was equal to or exceeded that of the public inbred lines B73 and W64A. Our study indicates that there is potential to use Tripsacum -introgressed maize germplasm in breeding programs to enhance plant resistance and/or tolerance to corn rootworms, although further research on insect resistance and agronomic potential of this germplasm needs to be conducted in F1 hybrids. [source] Effect of generalist insect herbivores on introduced Lepidium draba (Brassicaceae): implications for the enemy release hypothesisJOURNAL OF APPLIED ENTOMOLOGY, Issue 7 2008K. P. Puliafico Abstract The enemy release hypothesis (ERH) states that decreased regulation by natural enemies allows plants to increase in distribution, abundance and vigour following their introduction into an exotic range. Invasive plants rarely escape herbivory entirely, and for hoary cress [Lepidium draba L. (Brassicaceae)] it has been demonstrated that generalist insect abundance is greater in its introduced North American range than in the native European range. We assessed the role of increased generalist herbivory on hoary cress using representatives of four important herbivore niches commonly found in the introduced range. We experimentally examined the density dependent impact of these herbivores individually and in combination on hoary cress in a series of greenhouse experiments. We found that defoliation of the oligophagous diamondback moth Plutella xylostella (L.) (Lep., Plutellidae) had the strongest and most consistent impact, while damage by the stem-mining weevil Ceutorhynchus americanus Buchanan (Col., Curculionidae) tended to have the highest per capita effect. Plant response to feeding by the oligophagous crucifer flea beetle Phyllotreta cruciferae (Goeze) (Col., Chrysomelidae) was minor despite obvious feeding damage, and the impact of the polyphagous tarnished plant bug Lygus hesperus Knight (Het., Miridae) was negligible. In multiple-species experiments, herbivore impacts were usually additive. In general, we found that hoary cress can tolerate high densities of oligophagous insect herbivory and effectively resisted attack by the polyphagous L. hesperus, but also the oligophagous C. americanus. Our results indicate that a combination of plant resistance and tolerance allows hoary cress to withstand increased generalist herbivore load in its introduced range, consistent with the predictions of the ERH. [source] Effect of eggplant transformed with oryzacystatin gene on Myzus persicae and Macrosiphum euphorbiaeJOURNAL OF APPLIED ENTOMOLOGY, Issue 2 2006A. P. O. Ribeiro Abstract:, The effect of a genetically modified eggplant line expressing oryzacystatin on Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas) was examined. The transgenic eggplant reduced the net reproductive rate (R0), the instantaneous rate of population increase (r), and the finite rate of population increase (,) of both aphids species compared with a control eggplant line. The mean generation time (T) of the aphids was unaffected by the transgenic plants. Age-specific mortality rates of M. persicae and M. euphorbiae were higher on transgenic plants. These results indicate that expression of oryzacystatin in eggplant has a negative impact on population growth and mortality rates of M. persicae and M. euphorbiae and could be a source of plant resistance for pest management of these aphids. [source] Antixenosis mechanism of resistance in pigeonpea to the pod borer, Helicoverpa armigeraJOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2006D. A. Kumari Abstract:, The noctuid pod borer, Helicoverpa armigera, is one of the most important pests of pigeonpea, and plant resistance is an important component for minimizing the extent of losses caused by this pest. To develop insect-resistant cultivars, it is important to understand the contributions of different components of resistance, and therefore, we studied the antixenosis mechanism of resistance to H. armigera in a diverse array of pigeonpea genotypes under no-choice, dual-choice, and multi-choice conditions. Antixenosis for oviposition was observed in case of ICPL 187-1, ICP 7203-1, ICPL 88039, T 21, ICPL 84060, and ICPL 332 under no-choice, dual-choice and multi-choice conditions. However, the number of eggs laid on ICPL 88039, T 21 and ICP 7203-1 did not differ significantly from those on ICPL 87 under dual-choice conditions. The susceptible check, ICPL 87 was highly preferred for oviposition. The genotypes ICP 7203-1, ICPL 187-1, T 21, ICPL 332, and ICPL 84060 can be used as sources of non-preference mechanism of resistance in pigeonpea improvement programs to breed for resistance to H. armigera. [source] Susceptibility of source plants to Sugarcane Fiji disease virus influences the acquisition and transmission of the virus by the planthopper vector Perkinsiella saccharicidaJOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2006K. Dhileepan Abstract:, Fiji leaf gall (FLG) caused by Sugarcane Fiji disease virus (SCFDV) is transmitted by the planthopper Perkinsiella saccharicida. FLG is managed through the identification and exploitation of plant resistance. The glasshouse-based resistance screening produced inconsistent transmission results and the factors responsible for that are not known. A series of glasshouse trials conducted over a 2-year period was compared to identify the factors responsible for the erratic transmission results. SCFDV transmission was greater when the virus was acquired by the vector from a cultivar that was susceptible to the virus than when the virus was acquired from a resistant cultivar. Virus acquisition by the vector was also greater when the vector was exposed to the susceptible cultivars than when exposed to the resistant cultivar. Results suggest that the variation in transmission levels is due to variation in susceptibility of sugarcane cultivars to SCFDV used for virus acquisition by the vector. [source] Regulation of Eukaryotic Initiation Factor 4E and Its Isoform: Implications for Antiviral Strategy in PlantsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 10 2006Yu-Yang Zhang Abstract In recent years, biotechnology has permitted regulation of the expression of endogenous plant genes to improve agronomically important traits. Genetic modification of crops has benefited from emerging knowledge of new genes, especially genes that exhibit novel functions, one of which is eukaryotic initiation factor 4E (eIF4E). eIF4E is one of the most important translation initiation factors involved in eukaryotic initiation. Recent research has demonstrated that virus resistance mediated by eIF4E and its isoform eIF (iso)4E occurs in several plant-virus interactions, thus indicating a potential new role for eIF4E/eIF(iso)4E in resistance strategies against plant viruses. In this review, we briefly describe eIF4E activity in plant translation, its potential role, and functions of the eIF4E subfamily in plant-virus interactions. Other initiation factors such as eIF4G could also play a role in plant resistance against viruses. Finally, the potential for developing eIF4E-mediated resistance to plant viruses in the future is discussed. Future research should focus on elucidation of the resistance mechanism and spectrum mediated by eIF4E. Knowledge of a particular plant-virus interaction will help to deepen our understanding of eIF4E and other eukaryotic initiation factors, and their involvement in virus disease control. (Managing editor: Li-Hui Zhao) [source] Characterization of Reactions to Powdery Mildew (Podosphaera pannosa) in Resistant and Susceptible Rose GenotypesJOURNAL OF PHYTOPATHOLOGY, Issue 5 2007A. Dewitte Abstract Fungal development of powdery mildew Podosphaera pannosa (Wallr.: Fr.) de Bary on rose leaves depends on constitutive or induced resistance mechanisms present in attacked rose genotypes. The relationship between fungal development and plant resistance was investigated microscopically on young greenhouse leaves of four rose genotypes with different levels of resistance: Rosa wichuraiana, R. laevigata anemoides and R. hybrida cultivars ,Excelsa' and ,Gomery'. Induced plant reactions, hydrogen peroxide production and cross sections through infected leaves were examined. The variation in development of the fungus on these rose genotypes depended on the relative presence of normal haustoria, abnormal haustoria, induced cell reactions, papilla formation or physical barriers. Formation of papillae could arrest up to one third of the successful penetrations. Papillae formation was often succeeded by total cell reaction. Abnormal haustoria were detected as rudimentary haustoria, haustoria with abnormal shape or haustoria without extra haustorial matrix. Post-haustorial cell reactions, with and without cell collapse, were detected. In non-collapsed cells, appositions were directed to both cell wall and haustorium. This was followed by accumulation of non-identified, probably antifungal compounds. Both single and multicell reactions occurred. Hydrogen peroxide was detected during papilla formation and induced cell reactions. [source] Virulence Frequences of Puccinia triticina in Germany and the European Regions of the Russian FederationJOURNAL OF PHYTOPATHOLOGY, Issue 1 2007V. Lind Abstract From 2001 to 2003, leaf rust was collected in different regions of Germany and the Russian Federation to generate single spore isolates and to study the structure of the pathogen populations by analyses of virulence. The virulence of isolates was tested with 38 near-isogenic lines each carrying a different resistance gene. The analyses of variance revealed significant effects for the frequency of virulent isolates, the regions and most interactions with years and regions, but no significance was found for the effects of years. In Germany, an increase of virulence frequencies was detected for Lr1 and Lr2a while a decrease was found for Lr3a, Lr3bg and Lr3ka. Such clear trends did not occur in Russia which may be due to the great agroclimatic differences between regions. The variance of the frequency of virulent isolates was used to estimate adequate sample sizes for the analysis of regional populations of leaf rust. This procedure resulted in more reliable information about the dynamic processes within the pathogen populations. In 2002 and 2003, all pathotypes in Germany had a combined virulence to Lr1, Lr2a, Lr2b, Lr15, Lr17 and Lr20 supplemented by a few other genes. The complexity of virulence was lower in the most frequent pathotypes. In Russia virulence to the alleles at locus Lr3 was very common. Using detached leaf segments in Germany and Russia it turned out that the most virulent pathotypes carry 34 and 32 virulence genes, respectively. Virulence to Lr9, Lr19, Lr24 and Lr38 was rare or even absent. The use of major genes, not overcome by corresponding virulent pathotypes, may contribute to more durable types of resistance in case they are combined with genes having different effects, e.g. adult plant resistance. [source] Drought and salinity: A comparison of their effects on mineral nutrition of plantsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2005Yuncai Hu Abstract The increasing frequency of dry periods in many regions of the world and the problems associated with salinity in irrigated areas frequently result in the consecutive occurrence of drought and salinity on cultivated land. Currently, 50% of all irrigation schemes are affected by salinity. Nutrient disturbances under both drought and salinity reduce plant growth by affecting the availability, transport, and partitioning of nutrients. However, drought and salinity can differentially affect the mineral nutrition of plants. Salinity may cause nutrient deficiencies or imbalances, due to the competition of Na+ and Cl, with nutrients such as K+, Ca2+, and NO. Drought, on the other hand, can affect nutrient uptake and impair acropetal translocation of some nutrients. Despite contradictory reports on the effects of nutrient supply on plant growth under saline or drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and when the drought or salt stress is severe. A better understanding of the role of mineral nutrients in plant resistance to drought and salinity will contribute to an improved fertilizer management in arid and semi-arid areas and in regions suffering from temporary drought. This paper reviews the current state of knowledge on plant nutrition under drought and salinity conditions. Specific topics include: (1) the effects of drought and salt stress on nutrient availability, uptake, transport, and accumulation in plants, (2) the interactions between nutrient supply and drought- or salt-stress response, and (3) means to increase nutrient availability under drought and salinity by breeding and molecular approaches. Trockenstress und Salzstress , Vergleich der Auswirkungen auf die mineralische Ernährung von Pflanzen Eine Zunahme von Trockenperioden in vielen Ländern der Welt und assoziierte Probleme der Versalzung in bewässerten Gebieten führen häufig zu gleichzeitigem Auftreten von Trockenheit und Salinität. Gegenwärtig sind weltweit ungefähr 50 % aller Bewässerungsflächen durch Salinität beeinträchtigt. Nährstoffstörungen bei Trocken- und Salzstress beeinträchtigen die Verfügbarkeit, den Transport und die Verteilung von Nährelementen in der Pflanze und reduzieren somit das Pflanzenwachstum. Trocken- und Salzstress können sich jedoch unterschiedlich auf die Nährstoffversorgung der Pflanzen auswirken. Salinität kann aufgrund der Konkurrenz zwischen Na+ bzw. Cl, und Nährelementen wie K+, Ca2+ und NO Nährstoffmängel oder -ungleichgewichte in den Pflanzen verursachen. Trockenstress kann sowohl die Nährstoffaufnahme als auch den akropetalen Transport einiger Elemente beeinträchtigen. Trotz kontroverser Schlussfolgerungen in der Literatur hinsichtlich der Wechselbeziehungen von Nährstoffangebot und Trocken- bzw. Salzstress auf das Pflanzenwachstum ist allgemein akzeptiert, dass Nährstoffzufuhr das Pflanzenwachstum nicht verbessert, wenn ausreichend Nährstoffe im Boden verfügbar sind oder bei stark ausgeprägter Trockenheit oder Salinität. Ein besseres Verständnis der Rolle von Mineralstoffen in der Toleranz von Pflanzen gegenüber Trocken- oder Salzstress dürfte gerade in ariden und semi-ariden Gebieten sowie in Regionen, die unter periodischer Trockenheit leiden, zu verbesserten Düngestrategien beitragen. In der vorliegenden Arbeit wird der gegenwärtige Kenntnisstand der mineralischen Ernährung bei Trockenheit und Salinität diskutiert. Schwerpunkte der Betrachtungen sind (1) die Auswirkungen von Trockenheit und Salzstress auf die Verfügbarkeit, die Aufnahme, den Transport und die Anreicherung von Nährelementen in der Pflanze, (2) Wechselbeziehungen zwischen dem Nährstoffangebot und Trockenheit oder Salinität sowie (3) Maßnahmen zur Verbesserung der Nährstoffverfügbarkeit bei Trockenheit und Salzstress mittels züchterischer und molekularbiologischer Ansätze. [source] From bacterial avirulence genes to effector functions via the hrp delivery system: an overview of 25 years of progress in our understanding of plant innate immunityMOLECULAR PLANT PATHOLOGY, Issue 6 2009JOHN W. MANSFIELD SUMMARY Cloning the first avirulence (avr) gene has led not only to a deeper understanding of gene-for-gene interactions in plant disease, but also to fundamental insights into the suppression of basal defences against microbial attack. This article (focusing on Pseudomonas syringae) charts the development of ideas and research progress over the 25 years following the breakthrough achieved by Staskawicz and coworkers. Advances in gene cloning technology underpinned the identification of both avr and hrp genes, the latter being required for the activation of the defensive hypersensitive reaction (HR) and pathogenicity. The delivery of Avr proteins through the type III secretion machinery encoded by hrp gene clusters was demonstrated, and the activity of the proteins inside plant cells as elicitors of the HR was confirmed. Key roles for avr genes in pathogenic fitness have now been established. The rebranding of Avr proteins as effectors, proteins that suppress the HR and cell wall-based defences, has led to the ongoing search for their targets, and is generating new insights into the co-ordination of plant resistance against diverse microbes. Bioinformatics-led analysis of effector gene distribution in genomes has provided a remarkable view of the interchange of effectors and also their functional domains, as the arms race of attack and defence drives the evolution of microbial pathogenicity. The application of our accrued knowledge for the development of disease control strategies is considered. [source] Histopathology and PR-protein markers provide insight into adult plant resistance to stripe rust of wheatMOLECULAR PLANT PATHOLOGY, Issue 2 2008JENNIFER MOLDENHAUER SUMMARY Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a serious disease of wheat. The spring wheat cultivar Kariega expresses complete adult plant resistance to stripe rust, whereas Avocet S is susceptible. In former studies, quantitative trait loci (QTL) analysis of doubled haploid lines derived from a Kariega × Avocet S cross revealed two major QTL (QYr.sgi-7D and QYr.sgi-2B.1) and two minor QTL (QYr.sgi-1A and QYr.sgi-4A.1) responsible for the adult resistance of Kariega in the field. Avocet S contains none of these QTL. In the present study, stripe rust development was compared, by means of fluorescence and confocal laser scanning microscopy, in flag leaves of Kariega, Avocet S and six doubled haploid (DH) lines, containing all four, none or one QTL. Depending on the QTL present, the infection types of the DH lines ranged from resistant to fully susceptible. No differences in fungal growth were observed during the first 5 days post inoculation (dpi), whereas the mean length of the fungal colonies started to differ at 6 dpi. Interestingly, MP 51 carrying QYr.sgi-7D responded with lignification to the fungal growth without restricting it, whereas MP 35 containing QYr.sgi-2B.1 did not show lignified host tissue, but fungal growth was restricted. RT PCR experiments with sequences of pathogenesis-related (PR) proteins resulted in a slightly stronger induction of PR 1, 2 and 5, known markers for the hypersensitive reaction, and peroxidases in MP 51, whereas a second band for chitinases was detected in MP 35 only. [source] Optimization of pathogenicity assays to study the Arabidopsis thaliana,Xanthomonas campestris pv. campestris pathosystemMOLECULAR PLANT PATHOLOGY, Issue 3 2005DAMIEN MEYER SUMMARY The cruciferous weed Arabidopsis thaliana and the causal agent of black rot disease of Crucifers Xanthomonas campestris pv. campestris (Xcc) are both model organisms in plant pathology. Their interaction has been studied successfully in the past, but these investigations suffered from high variability. In the present study, we describe an improved Arabidopsis,Xcc pathosystem that is based on a wound inoculation procedure. We show that after wound inoculation, Xcc colonizes the vascular system of Arabidopsis leaves and causes typical black rot symptoms in a compatible interaction, while in an incompatible interaction bacterial multiplication is inhibited. The highly synchronous and reproducible symptom expression allowed the development of a disease scoring scheme that enabled us to analyse the effects of mutations in individual genes on plant resistance or on bacterial virulence in a simple and precise manner. This optimized Arabidopsis,Xcc pathosystem will be a robust tool for further genetic and post-genomic investigation of fundamental questions in plant pathology. [source] How will plant pathogens adapt to host plant resistance at elevated CO2 under a changing climate?NEW PHYTOLOGIST, Issue 3 2003Sukumar Chakraborty Summary , , To better understand evolution we have studied aggressiveness of the anthracnose pathogen, Colletotrichum gloeosporioides, collected from Stylosanthes scabra pastures between 1978 and 2000 and by inoculating two isolates onto two cultivars over 25 sequential infection cycles at ambient (350 ppm) and twice-ambient atmospheric CO2 in controlled environments. , , Regression analysis of the field population showed that aggressiveness increased towards a resistant cultivar, but not towards a susceptible cultivar, that is no longer grown commercially. , , Here we report for the first time that aggressiveness increased on both cultivars after a few initial infection cycles at twice-ambient CO2 as isolates adapted to combat enhanced host resistance, while at ambient CO2 this increased steadily for most cycles as both cultivars selected for increased aggressiveness. Genetic fingerprint and karyotype of isolates changed for some CO2 -cultivar combinations, but these were not related to changed aggressiveness. , , At 700 ppm fecundity increased for both isolates, and this increased population size, in combination with a conducive microclimate for anthracnose from an enlarged plant canopy under elevated CO2, could accelerate pathogen evolution. [source] Combating plant diseases,the Darwin connectionPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 11 2009Derek W Hollomon Abstract Although Darwin knew of plant diseases, he did not study them as part of his analysis of natural selection. Effective plant disease control has only been developed after his death. This article explores the relevance of Darwin's ideas to three problem areas with respect to diseases caused by fungi: emergence of new diseases, loss of disease resistance bred into plants and development of fungicide resistance. Darwin's concept of change through natural or artificial selection relied on selection of many small changes, but subsequent genetic research has shown that change can also occur through large steps. Appearance of new diseases can involve gene duplication, transfer or recombination, but all evidence points to both host plant resistance and fungicide susceptibility being overcome through point mutations. Because the population size of diseases such as rusts and powdery and downy mildews is so large, all possible point mutations are likely to occur daily, even during moderate epidemics. Overcoming control measures therefore reflects the overall fitness of these mutants, and much resource effort is being directed towards assessment of their fitness, both in the presence and in the absence of selection. While recent developments in comparative genomics have caused some revision of Darwin's ideas, experience in managing plant disease control measures clearly demonstrates the relevance of concepts he introduced 150 years ago. It also reveals the remarkable speed and the practical impact of adaptation in wild microorganism populations to changes in their environment, and the difficulty of stopping or delaying such adaptation. Copyright © 2009 Society of Chemical Industry [source] Epigenetic chromatin modifiers in barley: I. Cloning, mapping and expression analysis of the plant specific HD2 family of histone deacetylases from barley, during seed development and after hormonal treatmentPHYSIOLOGIA PLANTARUM, Issue 3 2009Kyproula Demetriou Epigenetic phenomena have been associated with modifications of chromatin structure. These are achieved, in part, by histone post-translational modifications including acetylations and deacetylations, the later being catalyzed by histone deacetylaces (HDACs). Eukaryotic HDACs are grouped into three major families, RPD3/HDA1, SIR2 and the plant-specific HD2. HDAC genes have been analyzed from model plants such as Arabidopsis, rice and maize and have been shown to be involved in various cellular processes including seed development, vegetative and reproductive growth and responses to abiotic and biotic stress, but reports on HDACs from other crops are limited. In this work two full-length cDNAs (HvHDAC2-1 and HvHDAC2-2) encoding two members of the plant-specific HD2 family, respectively, were isolated and characterized from barley (Hordeum vulgare), an agronomically important cereal crop. HvHDAC2-1 and HvHDAC2-2 were mapped on barley chromosomes 1H and 3H, respectively, which could prove useful in developing markers for marker-assisted selection in breeding programs. Expression analysis of the barley HD2 genes demonstrated that they are expressed in all tissues and seed developmental stages examined. Significant differences were observed among tissues and seed stages, and between cultivars with varying seed size, suggesting an association of these genes with seed development. Furthermore, the HD2 genes from barley were found to respond to treatments with plant stress-related hormones such as jasmonic acid (JA), abscisic acid (ABA) and salicylic acid (SA) implying an association of these genes with plant resistance to biotic and abiotic stress. The expression pattern of HD2 genes suggests a possible role for these genes in the epigenetic regulation of seed development and stress response. [source] Metabolomic analysis of host plant resistance to thrips in wild and cultivated tomatoes,PHYTOCHEMICAL ANALYSIS, Issue 1 2010Mohammad Mirnezhad Abstract Introduction , Western flower thrips (Frankliniella occidentalis) are among the most serious crop pests worldwide. Control of thrips mainly depends on pesticides, excessive use of which leads to human health risks and environmental contamination. As an alternative, we study host plant resistance to thrips. Objective , To apply nuclear magnetic resonance spectroscopy (NMR) metabolomics to study host plant resistance to thrips in wild and cultivated tomatoes. Methodology , Ten wild species and 10 cultivated tomato lines were compared. Five replicates of each species and lines were used for a thrips bioassay while another five replicates were used for the metabolomic analysis. The three most resistant and susceptible wild species, and cultivated lines, as identified by the thrips bioassay, were used for the metabolomics, performed by 1H NMR spectroscopy followed by principal component analysis. Results , Wild and cultivated tomatoes differed significantly in thrips resistance. Only wild tomatoes were thrips-resistant, among which Lycopersicon pennellii and L. hirsutum exhibited the lowest thrips damage. Their 1H NMR-based metabolomic profiles were significantly different from those of thrips-susceptible tomatoes. Thrips-resistant tomatoes contained acylsugars, which are known for their negative effect on herbivores. Conclusion , The identification of acylsugars as a resistance factor for thrips in tomato proves that NMR-based metabolomics an important tool to study plant defences, providing fundamental information for the development and realisation of herbivore resistance breeding programmes in agricultural crops. Copyright © 2009 John Wiley & Sons, Ltd. [source] Plant survival after freezing in wheat ,Cappelle Desprez' (,Bezostaya 1') intervarietal chromosome substitution linesPLANT BREEDING, Issue 2 2008G. Ganeva Abstract The effect of individual chromosomes of the wheat variety ,Bezostaya 1' on plant resistance to low temperatures was studied using the available set of intervarietal ,Cappelle Desprez' (,Bezostaya 1') chromosome substitution lines. The number of plants surviving after freezing at ,12, ,15 and ,17°C was determined for both parents and lines in trials in 2004/2005 and 2005/2006. Significant differences between the three temperature treatments and between lines were found, implying that two factors, the level of temperature stress and chromosome substitutions, were influencing plant survival. Improved frost resistance in both trials was associated with genes located on five chromosomes: 5A, 2D, 4A, 5D and 6A. An increase in the plant frost resistance because of the effects of 7A and 1A chromosomes was also observed in the 2005/2006 trial, when the overall autumn and winter (January) temperatures were lower than in 2004/2005. [source] Potential for effective marker-assisted selection of three quantitative trait loci conferring adult plant resistance to powdery mildew in elite wheat breeding populationsPLANT BREEDING, Issue 5 2006D. M. Tucker Abstract Three quantitative trait loci (QTL) associated with adult plant resistance (APR) to powdery mildew (Blumeria graminis) in wheat (Triticum aestivum) cultivar ,Massey' were mapped in a previous study. The three QTL were located on chromosomes 2A, 2B and 1B, and explained 50% of the total phenotypic variation. A 293 recombinant inbred line (RIL) breeding population (UJ) derived from the cross of ,USG 3209', a derivative of ,Massey', and ,Jaypee' was used to evaluate the potential effectiveness of marker-assisted selection (MAS) for APR. Powdery mildew severities of the 293 UJ RILs were evaluated in 2002 (F5 : 6) and 2003 (F6 : 7) under natural disease pressure in the field. The 293 RILs were also evaluated for disease severity in a 2004 (F7 : 8) greenhouse experiment using a composite of five different isolates of B. graminis. Selection of RILs possessing the QTL on chromosome 2A, and to a lesser extent, the one on chromosome 1B was effective in identifying powdery mildew resistance in both greenhouse and field experiments. Overall, selecting RILs with QTL on chromosomes 2A and 2B was most successful in identifying highly resistant RILs, which had mean mildew severities of 4.4% and 3.2% in 2002 and 2003 field experiments, respectively. Breeders implementing MAS programs for APR to powdery mildew via selection of RILs containing the two QTL on chromosomes 2A and 2B likely will obtain RILs having high levels of resistance in the field, however combining all three QTL may ensure greater durability. [source] Heterologous expression of Arabidopsis H+ -pyrophosphatase enhances salt tolerance in transgenic creeping bentgrass (Agrostis stolonifera L.)PLANT CELL & ENVIRONMENT, Issue 2 2010ZHIGANG LI ABSTRACT The Arabidopsis vacuolar H+ -pyrophosphatase (AVP1), when over-expressed in transgenic (TG) plants, regulates root and shoot development via facilitation of auxin flux, and enhances plant resistance to salt and drought stresses. Here, we report that TG perennial creeping bentgrass plants over-expressing AVP1 exhibited improved resistance to salinity than wild-type (WT) controls. Compared to WT plants, TGs grew well in the presence of 100 mm NaCl, and exhibited higher tolerance and faster recovery from damages from exposure to 200 and 300 mm NaCl. The improved performance of the TG plants was associated with higher relative water content (RWC), higher Na+ uptake and lower solute leakage in leaf tissues, and with higher concentrations of Na+, K+, Cl - and total phosphorus in root tissues. Under salt stress, proline content was increased in both WT and TG plants, but more significantly in TGs. Moreover, TG plants exhibited greater biomass production than WT controls under both normal and elevated salinity conditions. When subjected to salt stress, fresh (FW) and dry weights (DW) of both leaves and roots decreased more significantly in WT than in TG plants. Our results demonstrated the great potential of genetic manipulation of vacuolar H+ -pyrophosphatase expression in TG perennial species for improvement of plant abiotic stress resistance. [source] Evaluating different soil and plant hydraulic constraints on tree function using a model and sap flow data from ponderosa pinePLANT CELL & ENVIRONMENT, Issue 7 2001M. Williams Relationships between tree size and physiological processes such as transpiration may have important implications for plant and ecosystem function, but as yet are poorly understood. We used a process-based model of the soil,plant,atmosphere continuum to investigate patterns of whole-tree sap flow in ponderosa pine trees of different size and age (36 m and ,250 years versus 13 m and 10,50 years) over a developing summer drought. We examined three different hypothetical controls on hydraulic resistance, and found that size-related differences in sap flow could be best explained by absolute differences in plant resistance related to path length (hypothesis 1) rather than through different dynamic relationships between plant resistance and leaf water potential (hypothesis 2), or alterations in rates of cumulative inducement and repair of cavitation (hypothesis 3). Reductions in sap flow over time could be best explained by rising soil,root resistance (hypothesis 1), rather than by a combination of rising plant and soil,root resistance (hypothesis 2), or by rising plant resistance alone (hypothesis 3). Comparing hourly predictions with observed sap flow, we found that a direct relationship between plant resistance and leaf water potential (hypothesis 2) led to unrealistic bimodal patterns of sap flow within a day. Explaining seasonal reduction in sap flow purely through rising plant resistance (hypothesis 3) was effective but failed to explain the observed decline in pre-dawn leaf water potential for small trees. Thus, hypothesis 1 was best corroborated. A sensitivity analysis revealed a significant difference in the response to drought-relieving rains; precipitation induced a strong recovery in sap flow in the hypothetical case of limiting soil,root resistance (hypothesis 1), and an insignificant response in the case of limiting plant resistance (hypothesis 3). Longer term monitoring and manipulation experiments are thus likely to resolve the uncertainties in hydraulic constraints on plant function. [source] WRKY70 modulates the selection of signaling pathways in plant defenseTHE PLANT JOURNAL, Issue 3 2006Jing Li Summary Cross-talk between signal transduction pathways is a central feature of the tightly regulated plant defense signaling network. The potential synergism or antagonism between defense pathways is determined by recognition of the type of pathogen or pathogen-derived elicitor. Our studies have identified WRKY70 as a node of convergence for integrating salicylic acid (SA)- and jasmonic acid (JA)-mediated signaling events during plant response to bacterial pathogens. Here, we challenged transgenic plants altered in WRKY70 expression as well as WRKY70 knockout mutants of Arabidopsis with the fungal pathogens Alternaria brassicicola and Erysiphe cichoracearum to elucidate the role of WRKY70 in modulating the balance between distinct defense responses. Gain or loss of WRKY70 function causes opposite effects on JA-mediated resistance to A. brassicicola and the SA-mediated resistance to E. cichoracearum. While the up-regulation of WRKY70 caused enhanced resistance to E. cichoracearum, it compromised plant resistance to A. brassicicola. Conversely, down-regulation or insertional inactivation of WRKY70 impaired plant resistance to E. cichoracearum. Over-expression of WRKY70 resulted in the suppression of several JA responses including expression of a subset of JA- and A. brassicicola -responsive genes. We show that this WRKY70 -controlled suppression of JA-signaling is partly executed by NPR1. The results indicate that WRKY70 has a pivotal role in determining the balance between SA-dependent and JA-dependent defense pathways. [source] Silicon-augmented resistance of plants to herbivorous insects: a reviewANNALS OF APPLIED BIOLOGY, Issue 2 2009O.L. Reynolds Abstract Silicon (Si) is one of the most abundant elements in the earth's crust, although its essentiality in plant growth is not clearly established. However, the importance of Si as an element that is particularly beneficial for plants under a range of abiotic and biotic stresses is now beyond doubt. This paper reviews progress in exploring the benefits at two- and three-trophic levels and the underlying mechanism of Si in enhancing the resistance of host plants to herbivorous insects. Numerous studies have shown an enhanced resistance of plants to insect herbivores including folivores, borers, and phloem and xylem feeders. Silicon may act directly on insect herbivores leading to a reduction in insect performance and plant damage. Various indirect effects may also be caused, for example, by delaying herbivore establishment and thus an increased chance of exposure to natural enemies, adverse weather events or control measures that target exposed insects. A further indirect effect of Si may be to increase tolerance of plants to abiotic stresses, notably water stress, which can in turn lead to a reduction in insect numbers and plant damage. There are two mechanisms by which Si is likely to increase resistance to herbivore feeding. Increased physical resistance (constitutive), based on solid amorphous silica, has long been considered the major mechanism of Si-mediated defences of plants, although there is recent evidence for induced physical defence. Physical resistance involves reduced digestibility and/or increased hardness and abrasiveness of plant tissues because of silica deposition, mainly as opaline phytoliths, in various tissues, including epidermal silica cells. Further, there is now evidence that soluble Si is involved in induced chemical defences to insect herbivore attack through the enhanced production of defensive enzymes or possibly the enhanced release of plant volatiles. However, only two studies have tested for the effect of Si on an insect herbivore and third trophic level effects on the herbivore's predators and parasitoids. One study showed no effect of Si on natural enemies, but the methods used were not favourable for the detection of semiochemical-mediated effects. Work recently commenced in Australia is methodologically and conceptually more advanced and an effect of Si on the plants' ability to generate an induced response by acting at the third trophic level was observed. This paper provides the first overview of Si in insect herbivore resistance studies, and highlights novel, recent hypotheses and findings in this area of research. Finally, we make suggestions for future research efforts in the use of Si to enhance plant resistance to insect herbivores. [source] Establishment of an in vitro sciarid fly larvae assay to study plant resistanceANNALS OF APPLIED BIOLOGY, Issue 2 2009M. Chabannes Abstract Mechanisms underlying natural plant resistance to herbivorous invertebrates are still poorly understood in comparison with bacterial or fungal interactions. One reason is the difficulty in reliably and reproducibly assessing the effects under controlled conditions. This article describes a newly developed in vitro biological assay system that enables the interactions between sciarid larvae and plants, whose roots they feed on, to be studied under highly controlled conditions. The bioassay eliminates the problems created by the often variable environmental factors by providing an aseptic arena where experimental plants can be germinated and grown on agar within a Petri dish. Sciarid fly eggs are then collected, sterilised and added to the Petri dish. The system allows the eggs to hatch and the larvae to feed on the plant roots. A range of developmental parameters can then be recorded over time which can then be correlated with the experimental plant type. This assay system also allows a simultaneous comparison or ,choice chamber' between two (or more) different genotypes. The assay should greatly help to facilitate the identification of new components involved in insect resistance mediated pathway via the characterisation of mutant plants. [source] Quantitative trait locus mapping of resistance in apple to Cydia pomonella and Lyonetia clerkella and of two selected fruit traitsANNALS OF APPLIED BIOLOGY, Issue 3 2009S. Stoeckli Abstract Apple, Malus×domestica, is the most important fruit grown within the temperate zonobiome. It is attacked by both fruit-damaging and leaf-damaging lepidopteran pest insects, which require regular control such as the carpophagous codling moth, Cydia pomonella, or frequent control such as the phyllophagous apple leaf miner, Lyonetia clerkella. As many environmentally friendly pest control tactics are only effective at low levels of infestation, host plant resistance is a promising future component of integrated pest management systems, but knowledge is still lacking on such genetically based approaches against lepidopteran pests. The aim of the study was to identify molecular markers linked to C. pomonella and L. clerkella resistance or susceptibility in commercial apple as well as markers linked to selected fruit traits. The number of C. pomonella -infested fruits and the number of L. clerkella mines were quantified as measures of apple resistance or susceptibility to the studied moth species. Herbivore surveys on 160 apple genotypes, representing a segregating F1 cross of the apple cultivars ,Fiesta' and ,Discovery', were carried out during two consecutive years and at two sites in Switzerland. Broad-sense heritability was 29.9% (C. pomonella), 18.2% (L. clerkella), 21.9% (fruit number) and 16.6% (fruit diameter). A subsequent analysis identified a quantitative trait locus (QTL) associated to C. pomonella susceptibility on the Discovery linkage group 10. The closest marker to this QTL was the random amplified polymorphic marker Z19-350. No significant QTL was identified for resistance to L. clerkella. A putative QTL associated to fruit number was identified on Fiesta linkage group 12. The presented QTL associated with C. pomonella susceptibility and the putative QTL linked to fruit number may facilitate marker-assisted breeding of resistant apple cultivars with cropping traits desirable for optimal fruit production. [source] | ||||||||||||||||||||||||||||