32,430 research outputs found
Identification of markers associated with bacterial blight resistance loci in cowpea (Vigna unguiculata (L.) Walp.)
No full textCowpea bacterial blight (CoBB), caused by Xanthomonas axonopodis pv. vignicola (Xav), is a worldwide major disease of cowpea [Vigna unguiculata (L.) Walp.]. Among different strategies to control the disease including cultural practices, intercropping, application of chemicals, and sowing pathogen-free seeds, planting of cowpea genotypes with resistance to the pathogen would be the most attractive option to the resource poor cowpea farmers in sub-Saharan Africa. Breeding resistance cultivars would be facilitated by marker-assisted selection (MAS). In order to identify loci with effects on resistance to this pathogen and map QTLs controlling resistance to CoBB, eleven cowpea genotypes were screened for resistance to bacterial blight using 2 virulent Xav18 and Xav19 strains isolated from Kano (Nigeria). Two cowpea genotypes Danila and Tvu7778 were identified to contrast in their responses to foliar disease expression following leaf infection with pathogen. A set of recombinant inbred lines (RILs) comprising 113 individuals derived from Danila (resistant parent) and Tvu7778 (susceptible parent) were infected with CoBB using leaf inoculation method. The experiments were conducted under greenhouse conditions (2007 and 2008) and disease severity was visually assessed using a scale where 0 = no disease and 4 = maximum susceptibility with leaf drop. A single nucleotide polymorphism (SNP) genetic map with 282 SNP markers constructed from the same RIL population was used to perform QTL analysis. Using Kruskall-Wallis and Multiple-QTL model of MapQTL 5, three QTLs, CoBB-1, CoBB-2 and CoBB-3 were identified on linkage group LG3, LG5 and LG9 respectively showing that potential resistance candidate genes cosegregated with CoBB resistance phenotypes. Two of the QTLs CoBB-1, CoBB-2 were consistently confirmed in the two experiments accounting for up to 22.1 and to 17.4% respectively for the first and second experiments. Whereas CoBB-3 was only discovered for the first experiment (2007) with less phenotypic variation explained of about 10%. Our results represent a resource for molecular marker development that can be used for marker assisted selection of bacterial blight resistance in cowpe
Can Physiology Help Us to Combat Late Blight in Potato?
No full textLate blight is a devastating disease in potato production world-wide. Breeding for resistance is complex because of the versatile and aggressive population of Phytophthora infestans, which overcomes any new genetic source of resistance very rapidly. There are reliable fungicides available to control the disease, but chemical control is costly and harmful to the environment. There are no cultural practices reducing the infestation, which are reliable enough to cope with the disease in a non-chemical way. Given the close link between the physiological condition of the crop and its resistance to late blight, this paper addresses the question whether crop physiology can help to combat the disease. Although there are possibilities to (partly) escape to the late blight by advancing the crop cycle or the tuber bulking, it is concluded that crop physiology can do little to reliably reduce the susceptibility to late blight. Breeding for resistance remains the best option
Partial resistance of tomatoes against Phytophthora infestans, the late blight fungus
No full textIn the Netherlands, the source of inoculum of the late blight fungus on tomatoes is the late blight fungus on potato crops. In regions of Europe mentioned, where tomatoes are grown in the open, P. infestans on tomatoes is the main source of inoculum. Especially in Bulgaria and Hungary, the effect of year-round cropping of tomatoes on prevalence and severity of the disease is obvious.In field and laboratory experiments, the pathogenicity to tomatoes of P. infestans originating from potatoes can be increased by serial passages through tomato foliage. In Europe, no other hosts than potatoes and tomatoes played a role in the tomato late blight epidemidogy. Phacelia tanacetifolia is added to the host list of the fungus. For the purpose of genetics classification, two laboratory methods, probit - log dosage analysis and components analysis, and one field method have been developed to assess the resistance of tomatoes against P.infestans.In particular the components infection ratio, lesion extension and sporulation intensity were studied. In the field method, the 'apparent infection rate' r was used. For breeding purposes, a simplified field method was indicated. A comparison of the three methods was made.The resistance of tomatoes increased considerably until at least 8 weeks after seeding. Partial resistance of W.Va 700 against the 1-t-pathotype of P.infestans is based on a single gene, here named Ph 2
Complete genome sequence of the fire blight pathogen Erwinia pyrifoliae DSM 12163(T) and comparative genomic insights into plant pathogenicity
No full textSmits THM, Jaenicke S, Rezzonico F, et al. Complete genome sequence of the fire blight pathogen Erwinia pyrifoliae DSM 12163(T) and comparative genomic insights into plant pathogenicity. BMC Genomics. 2010;11(1): 2.Background: Erwinia pyrifoliae is a newly described necrotrophic pathogen, which causes fire blight on Asian (Nashi) pear and is geographically restricted to Eastern Asia. Relatively little is known about its genetics compared to the closely related main fire blight pathogen E. amylovora. Results: The genome of the type strain of E. pyrifoliae strain DSM 12163(T), was sequenced using both 454 and Solexa pyrosequencing and annotated. The genome contains a circular chromosome of 4.026 Mb and four small plasmids. Based on their respective role in virulence in E. amylovora or related organisms, we identified several putative virulence factors, including type III and type VI secretion systems and their effectors, flagellar genes, sorbitol metabolism, iron uptake determinants, and quorum-sensing components. A deletion in the rpoS gene covering the most conserved region of the protein was identified which may contribute to the difference in virulence/host-range compared to E. amylovora. Comparative genomics with the pome fruit epiphyte Erwinia tasmaniensis Et1/99 showed that both species are overall highly similar, although specific differences were identified, for example the presence of some phage gene-containing regions and a high number of putative genomic islands containing transposases in the E. pyrifoliae DSM 12163T genome. Conclusions: The E. pyrifoliae genome is an important addition to the published genome of E. tasmaniensis and the unfinished genome of E. amylovora providing a foundation for re-sequencing additional strains that may shed light on the evolution of the host-range and virulence/pathogenicity of this important group of plant-associated bacteria
Epidemiology and integrated control of Potato Late Blight in Europe
No full textPhytophthora infestans, the causal agent of late blight, is a major threat to potato production in northwestern Europe. Before 1980, the worldwide population of P. infestans outside Mexico appeared to be asexual and to consist of a single clonal lineage of A1 mating type characterized by a single genotype. It is widely believed that new strains migrated into Europe in 1976 and that this led to subsequent population changes including the introduction of the A2 mating type. The population characteristics of recently collected isolates in NW Europe show a diverse population including both mating types, sexual reproduction and oospores, although differences are observed between regions. Although it is difficult to find direct evidence that new strains are more aggressive, there are several indications from experiments and field epidemics that the aggressiveness of P. infestans has increased in the past 20 years. The relative importance of the different primary inoculum sources and specific measures for reducing their role, such as covering dumps with plastic and preventing seed tubers from becoming infected, is described for the different regions. In NW Europe, varieties with greater resistance tend not to be grown on a large scale. From the grower’s perspective, the savings in fungicide input that can be achieved with these varieties are not compensated by the higher (perceived) risk of blight. Fungicides play a crucial role in the integrated control of late blight. The spray strategies in NW Europe and a table of the specific attributes of the most important fungicides in Europe are presented. The development and use of decision support systems (DSSs) in NW Europe are described. In The Netherlands, it is estimated that almost 40% of potato growers use recommendations based on commercially available DSS. In the Nordic countries, a new DSS concept with a fixed 7-day spray interval and a variable dose rate is being tested. In the UK, commercially available DSSs are used for c. 8% of the area. The validity of Smith Periods for the new population of P. infestans in the UK is currently being evaluated
Boosting potato defence against late blight
No full textFor more than one century efforts has been made to obtain potato (Solanum tuberosum) cultivars resistant to late blight. However, introduced resistance has repeatedly been overcome by Phytophthora infestans (Mont) de Bary. Today late blight control is dependent on the frequent use of fungicides, but development of fungicide resistance and increasing fungicide restrictions by EU are of major concern. Methods with less fungicide requirement is therefore of crucial importance for a more environmentally sound and sustainable late blight control in the future.
In this study the potential of integrating BABA-induced resistance in existing late blight management with fungicides was investigated in field. The fungicide dose could be lowered with up to 25% when combined with BABA, without any decrease in late blight control or metabolic cost in terms of tuber yield. BABA was shown to directly activate basal defence responses and hormone signaling in potato. The BABA-induced hypersensitive-like lesions and major changes in the amino acid balance indicate that BABA induces resistance by stress imprinting.
Furthermore the potential of using a biosurfactant, produced by Psuedomonas koreensis strain 2.74, to control late blight in greenhouse was demonstrated. The biosurfactant was shown to have a direct effect on zoospores and also to induce PR-1 accumulation in the apoplast of potato leaves. Future experiments will reveal if the biosurfactant induces other defence mechanisms in potato.
This study demonstrated how integration of different control methods could lead to unchanged or even improved late blight control despite the decrease in fungicide dose
QTLs for fire blight (Erwinia amylovora) resistance in Pyrus ussuriensis.
No full textFire blight is the most devastating bacterial disease of apples and pears. The need for highly disease-resistant cultivars is more pressing than ever. Genetic disease immunity or resistance is recognized as an important feature of integrated pest management (IPM). In this study, we used an F1 progeny of Pyrus communis ‘Doyenne du Comice’ × Pyrus ussuriensis to build parental genetic maps and to identify quantitative trait loci (QTLs) related to fire blight resistance. Linkage maps were constructed using a set of microsatellites and enriched with amplified fragment length polymorphism (AFLP) markers. For the first time QTLs for fire blight resistance in P. ussuriensis were identified by the Kruskal-Wallis test in its LGs U9, U_a, U_e, Ug, and U11. QTLs identified in LGs U_e and U_g are linked to AFLP-RGA markers that additionally confirms the presence of resistance genes in these LGs. Despite the high susceptibility of P. communis ‘Doyenne du Comice’, four QTLs for fire blight resistance in this cultivar were localized in LG K3, K4, K11, and K_a. These data confirm the existence of the interspecific transgression phenomenon, also previously observed on the basis of infection level evaluation of seedlings belonging to the studied hybrid family
Fusarium in wheat. Effects of soil fertility strategies and nitrogen levels on mycotoxins and seedling blight.
No full textIn a two-year field experiment in the Netherlands the relation between three soil fertility strategies, additional nitrogen levels and Fusarium Head Blight in wheat are explored. There was a substantial year-effect, as could be expected. The soil fertility strategies showed differences, but were party coinciding with location. Although not consistent over the years and strategies, a significant relation was found between additional nitrogen applications around anthesis and FHB, expressed as presence of mycotoxines (DON) and Total Root Rot from the Blotter test. Higher nitrogen levels from fertilizer applications at anthesis give a higher chance on FHB, with other so far unknown factors playing a role
Broad spectrum late blight resistance in potato differential set plants MaR8 and MaR9 is conferred by multiple stacked R genes
No full textPhytophthora infestans is the causal agent of late blight in potato. The Mexican species Solanum demissum is well known as a good resistance source. Among the 11 R gene differentials, which were introgressed from S. demissum, especially R8 and R9 differentials showed broad spectrum resistance both under laboratory and under field conditions. In order to gather more information about the resistance of the R8 and R9 differentials, F1 and BC1 populations were made by crossing Mastenbroek (Ma) R8 and R9 clones to susceptible plants. Parents and offspring plants were examined for their pathogen recognition specificities using agroinfiltration with known Avr genes, detached leaf assays (DLA) with selected isolates, and gene-specific markers. An important observation was the discrepancy between DLA and field trial results for Pi isolate IPO-C in all F1 and BC1 populations, so therefore also field trial results were included in our characterization. It was shown that in MaR8 and MaR9, respectively, at least four (R3a, R3b, R4, and R8) and seven (R1, Rpi-abpt1, R3a, R3b, R4, R8, R9) R genes were present. Analysis of MaR8 and MaR9 offspring plants, that contained different combinations of multiple resistance genes, showed that R gene stacking contributed to the Pi recognition spectrum. Also, using a Pi virulence monitoring system in the field, it was shown that stacking of multiple R genes strongly delayed the onset of late blight symptoms. The contribution of R8 to this delay was remarkable since a plant that contained only the R8 resistance gene still conferred a delay similar to plants with multiple resistance genes, like, e.g., cv Sarpo Mira. Using this “de-stacking” approach, many R gene combinations can be made and tested in order to select broad spectrum R gene stacks that potentially provide enhanced durability for future application in new late blight resistant varietie
Epidemiology of Alternaria blight of Paulownia
No full textPaulownia trees are indigenous to China, where they are found in all regions from the sub-tropical south, to the plains and mountainous areas in the north. In Australia, a number of Paulownia plantations have been established in recent years as the timber is a valuable resource with strong export potential. The main species grown are P. fortunei and P. tomentosa.
In Western Australia, major plantations have been established to the north of Perth, in a Mediterranean environment with irrigation and fertigation over the summer months. At some sites the trees are subject to strong winds that can cause significant physical damage to the large leaves, and sunscald also has a major impact on tree growth.
In addition to abiotic factors affecting the health of the trees, foliar diseases are also present. Alternaria blight (1) and a phytoplasma-associated disease (2) have been reported, and other pathogens are regularly being identified. Here we outline some of the major findings from research being conducted on Alternaria blight of Paulownia in Western Australia
- …
