New article: Origin, Migration Routes and Worldwide Population Genetic Structure of the Wheat Yellow Rust Pathogen Puccinia striiformis f.sp. tritici

Origin, Migration Routes and Worldwide Population Genetic Structure of the Wheat Yellow Rust Pathogen Puccinia striiformis f.sp. tritici / Sajid Ali, Pierre Gladieux, Marc Leconte, Angelique Gautier,  Annemarie F. Justesen, Mogens  S. Hovmøller, Jerome Enjalbert, Claude de Vallavieille-Pope

In: PLoS Pathog 2014, 10(1): e1003903.

doi: 10.1371/journal.ppat.1003903

Abstract

Analyses  of  large-scale  population structure of  pathogens enable the identification of  migration patterns, diversity reservoirs or longevity of populations, the understanding of current evolutionary trajectories and the anticipation of future ones. This is particularly  important for long-distance migrating fungal pathogens  such as Puccinia striiformis f.sp. tritici (PST), capable of rapid spread to new regions and crop varieties. Although a range of recent PST invasions at continental scales are well documented, the worldwide population structure and the center of origin of the pathogen were still unknown. In this study, we used multilocus microsatellite genotyping to infer worldwide population structure of PST and the origin of new invasions based on 409 isolates representative of distribution of the fungus on six continents.  Bayesian and multivariate clustering methods partitioned the set of multilocus genotypes into six distinct genetic groups associated with their geographical origin. Analyses of linkage disequilibrium and genotypic diversity indicated a strong regional heterogeneity in levels of recombination, with clear signatures of recombination in the Himalayan (Nepal and Pakistan) and near-Himalayan regions (China) and a predominant clonal population  structure in  other  regions. The higher genotypic diversity, recombinant population structure and high sexual reproduction  ability in the Himalayan and neighboring regions suggests this area as the putative center of origin of PST. We used clustering methods and approximate  Bayesian computation (ABC) to compare different competing scenarios describing ancestral relationship among ancestral populations  and more recently founded populations. Our analyses confirmed the Middle East-East Africa as the most likely source of newly spreading, high- temperature-adapted  strains; Europe as the source of South American, North American and Australian populations; and Mediterranean-Central Asian populations as the origin of South African populations. Although most geographic populations are not markedly affected by recent dispersal events, this study emphasizes the influence of human activities on recent long-distance spread of the pathogen.