1,376,990 research outputs found
Biocontrol of fire blight with the bacterial antagonist Rhanella aquatilis Ra39 in combination with aromatic compounds
No full textThe bacterial strain Ra39 of Rahnella aquatilis significantly reduced fire blight incidence on blossom in the field. However, efficacy of Ra39 in reducing the disease was lower than that of streptomycin and was not high enough for commercial purposes. To increase the efficiency of control, Ra39 was combined with different aromatic compounds, which inhibited the fire blight pathogen in vitro. In the laboratory, on petri dishes Ra 39, in contrast to Erwinia amylovora, showed no sensitivity to aromatic compounds like benzoate and vanillate and was able to degrade these compounds. In the field, a combination of Ra 39 and benzoate reduced fire blight on blossoms to levels (68%) nearly similar to that of streptomycin (77%) and higher to that obtained with Ra39 by itself. In conclusion, the combination of Ra39 and benzoate represents an effective alternative to chemicals for control of fire blight
Regional spore dispersal as a factor in disease risk warnings for potato late blight: a proof of concept
No full textThis study develops and tests novel approaches that significantly reduce the fungicide input necessary for potato late blight control while maintaining the required high level of disease control. The central premise is that fungicide inputs can be reduced by reducing dose rates on more resistant cultivars, by omitting applications on days when conditions are unsuitable for atmospheric transport of viable sporangia and by adapting the dose rate to the length of the predicted critical period. These concepts were implemented and tested in field experiments in 2007 and 2008 in the North Eastern potato growing region in the Netherlands which is known for its high potato late blight disease pressure. Field experiments contained three starch potato cultivars, representing a range in resistance to potato late blight from susceptible to highly resistant, and a series of decision rules determining spray timing and incorporating an increasing number of variables such as: remaining fungicide protection level, critical weather, atmospheric capacity for viable transport of sporangia and the length of the predicted critical period. The level of cultivar resistance was used to reduce the dose rate of the preventive fungicide Shirlan (a.i. fluazinam) by default. A 50% – 75% reduction of the fungicide input proved possible in both years without adverse consequences to the crop or yield. The principles can be used in many decision contexts, but further work is needed to test and refine the methods before it can be used in practic
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
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
Control of Fire Blight with a Lysozyme from the Erwinia amylovora Phage ɸEa1h
No full textA lysozyme gene from Erwinia amylovora phage Ea1h was cloned and expressed in Escherichia coli, and the protein activity compared with lysozyme from E. coli phage T4. Ea1h lysozyme lysates strongly affected E. amylovora cells. The protein displayed enzymatic and antibacterial activities. The lytic function could be destroyed by heat treatment of lysates, which still formed inhibition zones after boiling on agar plates and showed enhanced growth inhibition of bacterial cultures. According to recent data, the antibacterial activity of lysates with Ea1h lysozyme can be explained with kanamycin bound to high molecular weight cell components. This agrees with findings that growth of bacterial strains carrying kanamycin-resistance was not inhibited, in contrast to all other tested E. amylovora strains and other Gram-negative bacteria, which were highly sensitive to lysates with Ea1h lysozyme. Similarly, pear slices soaked in Ea1h lysozyme-containing cell lysates showed reduced fire blight symptoms after inoculation with E. amylovora. The T4 lysozyme mainly affected the growth of Gram-positive bacteria. The Ea1h lysozyme gene has been expressed not only in tobacco but also in an apple cultivar with the aim to enhance the resistance against fire blight
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
Epiphytic Erwinias to control fire blight
No full textSeveral epiphytic bacteria isolated from healthy apple and pear flowers were characterized by their phenotypic properties and by DNA sequence comparisons. Selected epiphytes from Australia and South Africa induced hypersensitive response (HR) on tobacco leaves and produced the exopolysaccharide levan. Sequence comparison of 16S rRNA and the housekeeping genes recA and gapDH showed a close relationship of these epiphytes to Erwinia amylovora and to other plant pathogenic bacteria of the genus Erwinia, however, the epiphytes form a separate group and are not pathogenic to apple and pear. Another close relative of E. amylovora, the epiphyte Erwinia billingiae did not produce levan and HR on tobacco, but it synthesized an acyl-homoserine lactone (AHL). The epiphytic strains from Australia and South Africa were antagonists against E. amylovora in assays on immature pear slices and on apple flowers. E. billingiae also showed significantly antagonism against E. amylovora. Using Real-Time PCR and plating samples on selective agar, we demonstrated that the epiphytic isolates provided effective growth suppression of the pathogen when apple flowers were co-inoculated with a high concentration of the epiphytes and low concentrations of E. amylovora. These epiphytes could possibly be used for biological control of fire blight
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
Accelerated introgression of fire blight resistance from Malus xrobusta 5 and other wild germplasm into elite apples
No full textIntrogression of fire blight resistances from wild apples to develop high quality apple cultivars is an important breeding strategy of the Agroscope apple breeding programme. In order to obtain parental material suitable for cultivar breeding several pseudo-backcrosses with high quality parents are required. On F2 progeny plants of Malus ×robusta 5 a low-input fast-track breeding approach was applied to accelerate the generation cycle. Seedlings were screened with molecular markers for FB_MR5 fire blight resistance QTL and Rvi6 scab resistance. Selected seedlings were grown on their own roots under optimal growing conditions to enhance flowering, including non-limiting fertilization, regular prohexadione-Ca and ethephon treatments followed by winter simulation. From flowering plants carrying the FB_MR5 QTL, pollen was collected for crosses with high quality Malus ×domestica cultivars and flowers were pollinated with elite apple germplasm. Parents for new introgression cycles carrying the FB_MR5 QTL were selected based on fruit evaluations and on results of artificial shoot inoculation tests with a Swiss strain of Erwinia amylovora.
In order to include new sources of fire blight resistance into the breeding programme, additional Malus crabapples, described as fire blight resistant, were inoculated by shoot injection. In this paper we report on the progress of the introgression of the fire blight resistance FB_MR5 using a fast-track breeding approach and present results of fire blight shoot inoculation tests in wild and pre-breeding germplasm
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