Plant Pathogen Populations Research Articles

Books on Soil Science recently received

Beek, K. J., Burrough, P. A. & Mccormack, D. E. (eds) Quantified Land Evaluation Procedures.Brady, N. C. (ed.) Advances in Agronomy, Volume 40.Bruehl, G. W. Soilborne Plant Pathogens.Dokuchaev institute of Soil Science. Classification and Diagnostics of Soils of the USSR.Dunsmore, J. R. KHARDEP; Rural Development in the Hills of Nepal.Fairchild, D. M. Ground Water Quality and Agricultural Practices.Fitzpatrick, E. A. An Introduction to Soil Science.Follett, R. F. (ed.) Soil Fertility and Organic Matter as Critical Components of Production Systems.Greenhalgh, R. & Roberts, T. R. (eds) Pesticide Science and Biotechnology.Hallsworth, E. G. Anatomy, Physiology and Psychology of Erosion.Lof, P. Soils of the World. Methods of Soil Analysis. Klute, A. (ed.). Physical and Mineralogical Methods. Page, A. L., Miller, R. H. & Keeney, D. R. (eds) Chemical and Microbiological Properties. Morgan, R. P. C. Soil Erosion and Conservation.Newman, A. C. D. (ed.). Chemistry of Clays and Clay Minerals.Runge, E. C. A., et al. (eds) Utilization, Treatment, and Disposal of Waste on Land.Tabatabai, M. A. (ed.) Sulfur in Agriculture.Tate, R. L., Soil Organic Matter; Biological and Ecological Effects.Tate, R. L. (ed.) Microbial Autecology; a Method for Environmental Studies.Vaughan, D. & Malcolm, R. E. (eds) Soil Organic Matter and Biological Activity.West, S. H. (ed.) Physiological‐Pathological Interactions Affecting Seed Deterioration.White, R. E. Introduction to the Principles and Practice of Soil Science.Wilcox, J. R. (ed.) Soybeans: Improvement, Production and Uses.Wilson, M. J. (ed.) A Handbook of Determinative Methods in Clay Mineralogy.Wolfe, M. S. & Caten, C. E. (eds) Populations of Plant Pathogens; their Dynamics and Genetics.

Estimating relative fitness in asexually reproducing plant pathogen populations

A mathematical model is presented and analysed to find the conditions under which changes in gene frequencies can be used in asexually reproducing populations for estimating fitness of single genes, for example, for estimating the fitnesses of unnecessary virulence genes relative to their corresponding avirulence genes. It is concluded that the underlying distribution of relative fitness of clones (genotypes) has to be unimodal and that many populations consisting of a mixture of distinguishable clones then provide the best experimental data for estimating relative fitness of single genes. An improved statistical test procedure, i.e. generalized logistic regression, is suggested for analysing changes in gene frequencies in population experiments with a mixture of distinguishable clones. A population study of Erysiphe graminis f.sp. hordei (Klug-Andersen 1980) provides data to illustrate the procedure in the case where the population consists of a large number of genotypes. A bimodal distribution of "genotypes" possessing the virulence gene is indicated here.

A Simple Model of Selection for Fungicide Resistance in Plant Pathogen Populations

A Simple Model of Selection for Fungicide Resistance in Plant Pathogen Populations

Two different processes for the selection of fungicide‐resistant sub‐populations1

Plant pathogen populations subjected to selection for fungicide resistance have responded either qualitatively through the establishment of a new highly resistant population or quantitatively through a gradual loss of sensitivity. The type of response seems to be dictated by the toxicant rather than by the target organism. The qualitative response is better understood, proceeds faster, and leads usually to a sudden and complete loss of disease control in the field. The quantitative response is less well understood, proceeds slower, and loss of disease control associated with it is gradual and frequently incomplete. It seems that the same strategies, fungicide mixtures and alternations, can be used to delay both responses; however, substantially more direct experimental evidence is needed to support and better quantify the effects of these strategies.

Populations of plant pathogens: some constraints on analysis of variation in pathogenicity

Population surveys of plant pathogens can be used to determine the frequencies of particular pathogenicity genes and of changes in frequency with time. Such data can also be used to search for linkage disequilibrium (the non‐random association of alleles) which is of particular interest if it is due to selection. However, a linkage disequilibrium may arise for several other reasons which may be confounded with the effects of selection. Two principal reasons, often overlooked, are the lack of recombination between pathogen genotypes in the population, and the failure to define the boundaries of the sampled population. Examples from the literature illustrate some of these limitations. Recommendations are made for the conduct of surveys for particular objectives.

Stabilizing Racial Populations of Plant Pathogens by Use of Resistance Genes

AbstractVertical resistance (VR) genes in plants function by restricting the infection site and the infection process of parasites. Such genes are effective against certain races and ineffective against others. Horizontal resistance (HR) genes in plants function by reducing the amount of disease by reducing disease increase. Horizontal resistance is effective to some extent against all races. The use of resistance genes to curb population shifts is examined herein. It is probable that HR curbs population shifts by virtue of its polygenic inheritance which requires that the parasite obtain and accumulate a number of new virulence genes. The use of VR genes in multilines holds some promise, deployment of VR genes probably does not, and pyramiding of VR genes seems most worthy. The concept of stabilizing selection is presented, discussed, evaluated, and deemed of doubtful validity as a means of curbing racial shifts.

The Direct Assay of Plant Pathogen Populations in Soil

The Direct Assay of Plant Pathogen Populations in Soil