The potato murrain on the European continent and the revolutions of 1848

The tale of the Irish Famine, 1845¿1849, following the outbreak of potato late blight, has been told repeatedly, but the parallel story of the Continental Famine, 1845¿1847, has not yet been recorded. The Continental Famine was caused by poor harvests of potatoes, due to the same late blight, but also of grain, due to frost, drought, rust, voles, inopportune rains, floods and hailstorms. The Continental Famine was enhanced by hoarding, speculation, and poor governance. Hunger was followed by infectious diseases. The demographic effects of hunger and diseases are difficult to disentangle. The number of excess deaths due to the Continental Famine cannot yet be determined with any precision, but clearly it approaches that of the Irish Famine. The harvest failures of 1845 and 1846 and the resulting famines came on top of rural pauperisation and urban discontent, and thus contributed to the revolutions of 1848 on the European Continent. The statement `an epidemic of potato late blight caused an epidemic of revolutions¿ is, perhaps, exaggerated but it contains a grain of truth

The integrated concept of disease resistance; a new view including horizontal and vertical resistance in plants

Horizontal, uniform, race-non-specific or stable resistance can be discerned according to Van der Plank, from vertical, differential, race-specific or unstable resistance by a test in which a number of host genotypes (cultivars or clones) are tested against a number of pathogen genetypes traces of isolatest. If the total non-environmental variance in levels of resistance is due to main effects only differences between cultivars and differences between isolates) the resistance and the pathogen many (in the broad sense) are horizontal in nature. Vertical resistance and pathogenicity are characterized by the interaction between host and pathogen showing up as a variance compenent in this test due to interaction between cultivars and isolates. A host and pathogen model was made in which resistance and pathogenicity are governed by live polygenic loci. Within the host the resistance genes show additivity. Two models were investigated in model I resistance and pathogenicity genes operate in an additive way as envisaged by Van der Plank in his horizontal resistance. Model II is characterized by a gene-for-gene action between the polygenes of the host and those of the pathogen. The cultivar isolate test in model I showed only main effect variance. Surprisingly, the variance in model II was also largely due to main effects. The contribution of the interaction to the variance uppeared so small, that it would be difficult to discern it from a normal error variance. So-called horizontal resistance can therefore be explained by a polygenic resistance, where the individual genes are vertical and operating on a gene-for-gene basis with virulence genes in the pathogen. The data reported so far support the idea that model II rather than model I is the realistic one. The two models also revealed that populations with a polygenic resistance based on the gene-for-gene action have an increased level of resistance compared with the addition model, while its stability as far as mutability of the pathogen is concerned, is higher compared to those with an additive gene action. Mathematical studies of Mode too support the gene-for-gene concept. The operation of all resistance and virulence genes in a natural population is therefore seen as one integrated system. All genes for true resistance in the host population, whether they are major or minor genes are considered to interact in a gene-for-gene way with virulence genes either major or minor, in the pathogen population. The models revealed other important aspects. Populations with a polygenic resistance based on a gene-for-gene action have an increased level of resistance compared to populations following the addition model. The stability, as far as mutability of the pathogen is concerned, is higher in the interaction model than in the addition model. The effect of a resistance gene on the level of resistance of the population consists of its effect on a single plant times its gene frequency in the population. Due to the adaptive forces in both the host and the pathogen population and the gene-for-gene nature of the gene action an equilibrium develops that allows all resistance genes to remain effective although their corresponding virulence genes are present. The frequencies of the resistance and virulence genes are such that the effective frequencies of resistance genes tend to be negatively related to the magnitude of the gene effect. This explains why major genes often occur at low frequencies, while minor genes appear to be frequent. It is in this way that the host and the pathogen, both as extremely variable and vigorous populations, can co-exist. Horizontal and vertical resistance as meant by Van der Plank therefore do not represent different kinds of resistances, they represent merely polygenic and oligogenic resistances resp. In both situations the individual host genes interact specifically with virulence genes in the pathogen. Van der Plank's test for horizontal resistance appears to be a simple and sound way to test for polygenic inheritance of resistance. The practical considerations have been discussed. The agro-ecosystems should be made as diverse as possible. Multilines, polygenic resistance, tolerance, gene deployment and other measures should be employed, if possible in combination

Multilocus sequence typing of a global collection of pasteurella multocida isolates from cattle and other host species demonstrates niche association

Background- Pasteurella multocida causes disease in many host species throughout the world. In bovids, it contributes to bovine respiratory disease (BRD) and causes haemorrhagic septicaemia (HS). Previous studies have suggested that BRD-associated P. multocida isolates are of limited diversity. A multilocus sequence typing (MLST) scheme for P. multocida was used to determine whether the low levels of diversity reported are due to the limited discriminatory power of the typing method used, restricted sample selection or true niche association. Bovine respiratory isolates of P. multocida (n = 133) from the UK, the USA and France, collected between 1984 and 2008 from both healthy and clinically affected animals, were typed using MLST. Isolates of P. multocida from cases of HS, isolates from other host species and data from the MLST database were used as comparison. Results - Bovine respiratory isolates were found to be clonal (ISA 0.45) with 105/128 belonging to clonal complex 13 (CC13). HS isolates were not related to bovine respiratory isolates. Of the host species studied, the majority had their own unique sequence types (STs), with few STs being shared across host species, although there was some cross over between porcine and bovine respiratory isolates. Avian, ovine and porcine isolates showed greater levels of diversity compared to cattle respiratory isolates, despite more limited geographic origins. Conclusions - The homogeneity of STs of bovine respiratory P. multocida observed, and the differences between these and P. multocida subpopulations from bovine non-respiratory isolates and non-bovine hosts may indicate niche association

2000

Ontstaan van internationaal in gebruik zijnde decimale code voor het vastleggen van de groeistadia van granen, in het bijzonder tarwe. Gebaseerd op de schaal van Feekes en geschikt voor computergebrui

Hoeveel schade doen ziekten en plagen nu eigenlijk?

Kritische kanttekeningen op gedocumenteerde berekingen over biotische schade aan gewassen over de gehele wereld. De kritiek richt zich vooral op de gekozen locaties voor het gewasbeschermingsmiddelenonderzoek. De gekozen locaties vertegenwoordigen allerminst een neutrale beginsituatie, maar zij kenmerken een beschadigd agro-ecosysteem waar de natuurlijke vijanden weggespoten zij

Lamsoor-roest-meeldauw; een zoutbestendig pathosysteem

Algemene beschouwing van onderzoek naar Lamsoorvelden (Limonium vulgare) op de Boschplaat op Terschellin