175,237 research outputs found
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
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
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
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
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
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
ECONOMIC IMPACTS OF FUSARIUM HEAD BLIGHT IN WHEAT AND BARLEY: 1993-2001
No full textFusarium Head Blight (FHB), commonly known as scab, has been a severe problem for wheat and barley producers since 1993. This study provides an update of economic losses suffered by wheat and barley producers in scab-affected regions in the United States. Emphasis is placed on estimating direct and secondary economic impacts of yield and price losses suffered by wheat and barley producers from 1993 to 2001. Nine states are included in the analysis for three wheat classes. Three of the nine states were also used for the analysis of malting and feed barley. The cumulative direct economic losses from FHB in hard red spring (HRS) wheat, soft red winter (SRW) wheat, durum wheat, and barley are estimated at 7.7 billion. Two states, North Dakota and Minnesota, account for about 68 percent of the total dollar losses.Fusarium Head Blight, scab, vomitoxin, crop losses, wheat, barley, Crop Production/Industries,
Bacterial blight (Pseudomonas pisi Sackett) of peas in South Africa, with special reference to frost as a predisposing factor
No full textIn the beginning of the nineteen fifties bacterial blight caused much damage to pea crops in South Africa, particularly to those grown for seed production. A study has been made of the causal organism and the conditioning factors of the disease, special attention being paid to frost as a predisposing factor.The symptoms of the disease vary according to weather conditions during and after infection. In dry weather with occasional frost they usually start on the stem near the soil and extend upwards to stipules and leaflets, where a characteristic fan- like pattern develops. In rainy weather they appear as scattered spots on the stems and leaves. The bacterium that causes the disease was identified as Pseudomonas pisi Sackett.Although frost is not essential to infection, the susceptibility of pea plants increased considerably when they were frosted before inoculation. There was no correlation between the increase in susceptibility and the amount of permanent frost injury. In freezing experiments with pods alone, it was confirmed that frost is a predisposing factor for infection, but frost cracks in the tissue were not a prerequisite. A second effect of frost is that the disease spreads more rapidly in tissue that has been frosted. Stem lesions did not spread far on the stems of plants in experimental fields as long as the temperature remained above freezing point. After a frost, however, the disease spread for a considerable distance on the stems and to the stipules, on which the typical fan-like symptoms developed. These results were confirmed in experiments with artificially frosted plants. A possible explanation is that the pathogen spreads in the temporarily enlarged, water-filled intercellular spaces of the stems and leaves that have been exposed to frost.Because frost is a predisposing factor and because the optimum temperature for the development of symptoms is relatively high (about 25°-30°C), the winter climate in the seed producing areas of South Africa where frost in the early winter morning is followed by high day temperatures, is very conducive to the disease.The time of planting had a considerable effect on the occurrence of the disease; it was much more severe in crops planted in April than in those planted in the second half of May or later. The difference in susceptibility between crops planted at different times is probably caused by the fact that early planted peas are more sensitive to frost than those that are planted later. Furthermore it was found in glasshouse experiments that pea plants that were grown at high temperatures were more susceptible to blight than those grown at low temperatures. The differences in susceptibility were correlated with the stomatal frequency. These results may also partially explain the differences in susceptibility between early and late plantings. Varietal resistance investigated in cultivar trials was not consistent over the years. Pea plants suffering from lack of water were more sensitive to frost than plants that were regularly irrigated, but not much difference in the occurrence of blight was found between peas grown at different irrigation levels.Bacterial blight is a seed-borne disease and the pathogen remains viable in infected seed from one season to the next. Only if moderate frost occurs when the seeds are swelling in the pods and if there is a source of inoculum nearby, the pods and seeds may become infected in normal dry winters. Because the South African isolates of the pathogen do not easily move in the wood vessels, it is unlikely that seeds from apparently healthy pods will be infected, even if they are borne on diseased plants.In South Africa no other natural host plant for Ps. pisi was found. In a pea field the spread of the disease was erratic, no obvious connection was found between new and already existing infections.The following preventive measures are recommended: (a) plant at the right time of the year, (b) avoid frost pockets and (c) plant government certified seed.Experiments were done to investigate how frost renders the plants more susceptible to infection. One of the effects of frost is that the plant tissue becomes water-soaked on thawing. Water-soaking, induced either by injecting the stems with sterile water or by bruising the leaflets, rendered pea plants considerably more susceptible to infection, probably because the pathogen penetrated the water- soaked tissue more easily. In experiments to study the effect of frost on the establishment of the pathogen it was found that the growth rate of Ps. pisi in pea plants, that had been exposed to frost, did not differ much from the growth rate in non-frosted plants. Neither did prolonged watersoaking of plant tissue have a favourable effect on the multiplication of Ps. pisi . Saprophytes did, however, multiply rapidly in water-soaked leaves while they remained stationary in normal plant tissue. During the first day of incubation the growth of Ps. pisi in intercellular fluid from non-frosted pea plants, which had been infiltrated with distilled water, showed a lag phase, even though the fluid was inoculated with actively dividing bacteria. In one case a decrease in the concentration of Ps. pisi was observed. In intercellular fluid from plants which had been frosted, the lag was less distinct than in fluid from infiltrated plants of the same planting, or it was entirely absent. After the lag phase little difference was observed between the growth rate of Ps. pisi in intercellular fluid from plants that had been frosted and that in intercellular fluid from infiltrated, non-frosted plants.The results described above show that the effect of frost on infection is primarily, that by inducing water congestion of the tissue it facilitates the invasion of the plants by the pathogen; and in the second place compounds, exuding into the intercellular spaces from cells which have been exposed to frost, favour the establishment of the bacteria.The Ps. pisi strain tested did not produce polygalacturonase, pectinlyase or the cellulolytic Cx enzyme in artificial media or in intercellular fluid. Ps. pisi did, however, produce caseinolytic enzymes, but it is doubtful whether they are important as a virulence factor, because they were also found in sterile intercellular fluid
Toxicity induced by Solanapyrone A in Chickpea shoots and its metabolism through Glutathione/Glutathione-S-Transferase system
No full textSolanapyrone A and C were isolated from a Pakistani isolate of Ascochyta rabiei, Pk-1. Two experiments were conducted to investigate the phytotoxic effects of the most potent toxin, solanapyrone A on chickpea cultivars and its subsequent detoxification through glutathion/glutathion-s-transferase(GST) system. When the shoots of cultivars were fed solanapyrone A, symptoms mimicking to Ascochyta blight appeared and extent of manifestation of symptoms varied with the cultivar. In the first experiment, the effect of three different plant ages of 2 cultivars with different levels of resistance to toxin was determined in terms of GST activity unit. GST activity in Balkasar-2000 (a resistant cultivar) increased 1.92 times, 1.72 and 1.65 times in two-week-old seedling, eight-week-old and adult plants (all treated) respectively as compared to their respective controls. In the highly susceptible cultivar, AUG-424, a slight increase (1.14 times) over control was noticed in GST activity at all the three ages. In the second experiment, where shoots of three cultivars were tested against 2 doses of the toxin, an increase in GST activity in Noor-91 (a moderately susceptible cultivar) and AUG-424 was significantly less than resistant cultivar, Balkasar-2000 showing direct relationship between resistance and activity of the enzyme. It may be concluded that it is a reason for difference in response of cultivars to the disease
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