Small sections of necrotic bark pieces were placed on V8 juice or carrot agar medium selective for Phytophthora. ![]() Sampling was performed from infected alder trees that exhibited typical Phytophthora collar canker symptoms. For this study, surveys of Alnus glutinosa and Alnus incana stands were conducted over 10 years (from 1999 to 2009) across France, Belgium, and Hungary to collect P. Here we also considered the temporal dimension. This will minimize bias in the estimation of the diversity indices and deliver better approximations of the real population values. When the goal is to assess diversity in a population, as is the case here, the recommended strategy should be to sample along the whole distribution area of the target population, in order to attempt to collect more distinct and rare genotypes ( 23). × multiformis and/or its parental species are exotic or indigenous to Europe remains unknown.įor organisms with suspected low polymorphism, the choice of the sampling strategy is highly dependent on the objectives of the study. × multiformis could have emerged after an ancient interspecific hybridization of two currently undetermined Phytophthora species. × multiformis is a tetraploid organism, supporting the hypothesis raised by Ioos et al. This species is infrequently isolated, and only few individuals are available for analysis. Less is known about the origin of the other parental species, P. uniformis to Europe would have enabled its hybridization with the other parental species and could thus be a major factor in the emergence of P. uniformis is exotic to Europe and that North America could be its center of origin. uniformis populations revealed low diversity and a clonal structure, while North American populations were more diverse and exhibited signs of outcrossing ( 19). ×alni, is a diploid species and has been isolated both in Europe and in North America ( 18 – 20). uniformis, one of the parental species of P. uniformis, an invasive species in Europe, to the emergence of Phytophthora-induced alder decline. The study provides more insights on the contribution of P. Our detailed analyses point to a geographic structure that mirrors that observed for P. × alni originated from multiple hybridization events that involved different genotypes of the progenitors. Combined microsatellite and mtDNA results confirmed that P. The frequency of this dominant MLG increased after the disease emergence together with a decline in diversity, suggesting that it was favored by a genetic mechanism such as drift or selection. ![]() × alni were dominated by one multilocus genotype (MLG). × alni and the relationship with its parental species were investigated using 12 microsatellites and one mitochondrial DNA (mtDNA) marker on a European collection of 379 isolates. × alni should help us understand how reproductive mechanisms and historical processes shaped the population structure of this emerging hybrid pathogen. ![]() Describing the genetic characteristics of P. Phytophthora ×alni, a pathogen of alder, results from the homoploid hybridization of two related species, Phytophthora uniformis and Phytophthora × multiformis. Assessing the process that gives rise to hybrid pathogens is central to understanding the evolution of emerging plant diseases.
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