Genetic relationships in an international collection of Puccinia horiana isolates based on newly identified molecular markers and demonstration of recombination.

Authors: DEBACKER, MATHIAS - Ghent University; BONANTS, PETER - Plant Research International - Netherlands; Pedley, Kerry; MAES, MARTINE - Ghent University; ROLDAN-RUIZ, ISABEL - Ghent University; VAN BOCKSTAELE, ERIK - Ghent University; HEUGENS, KURT - Ghent University; VAN DER LEE, THEO - Plant Research International - Netherlands

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2013
Publication Date: 10/8/2013
Citation: Debacker, M., Bonants, P., Pedley, K.F., Maes, M., Roldan-Ruiz, I., Van Bockstaele, E., Heugens, K., Van Der Lee, T. 2013. Genetic relationships in an international collection of Puccinia horiana isolates based on newly identified molecular markers and demonstration of recombination. Phytopathology.103:1169-1179. https://doi.org/10.1094/PHYTO-01-13-0007-R.
DOI: https://doi.org/10.1094/PHYTO-01-13-0007-R

Interpretive Summary: The fungal pathogen Puccinia horiana is the causal agent of chrysanthemum white rust. Although the pathogen is a quarantine organism in Europe, Africa and America, it was able to spread to most chrysanthemum producing regions in the world since the 1960’s. However, the migration routes are largely obscure. A set of thirty-three molecular markers were developed to measure levels of diversity in 45 isolates of P. horiana originating from North and South America, Asia and Europe. Based upon the presence or absence of these markers, clustering for the isolates was in most cases related to geographic origin, indicating local establishment of this quarantine organism. In addition, evidence of recent migration was observed, including migration events between Europe and South America and between South-East Asia and Europe. The European isolates mostly grouped in two major clusters that may relate to the two historic introductions previously reported. A correlation between the marker analysis data and previously obtained pathogenicity data was observed, and one marker was associated with the most virulent isolates. These markers will be helpful tools to further elucidate the migration pathways of this pathogen as well as help guide future quarantine measures.

Technical Abstract: The obligate biotrophic pathogen Puccinia horiana is the causal agent of chrysanthemum white rust. Although the pathogen is a quarantine organism in Europe, Africa and America, it was able to spread to most chrysanthemum producing regions in the world since the 1960’s, however; the migration routes are largely obscure. An extremely low level of allelic diversity was observed in a geographically diverse set of eight isolates using CRoPS™ technology. Only 184 of the 16196 contigs (1.1 percent) showed one or more SNPs. For this study 32 SNPs and one SSR were translated into molecular markers. These were used to genotype a total of 45 isolates originating from North and South America, Asia and Europe. Phylogenetic clustering was in most cases related to geographic origin, indicating local establishment of this quarantine organism. The European isolates mostly grouped in two major populations that may relate to the two historic introductions previously reported. However, evidence of recent migration was also observed, including migration events between Europe and South America and between South-East Asia and Europe. In contrast with the presumed clonal propagation of this microcyclic rust, strong indications of marker recombination were observed, presumably as a result of anastomosis, karyogamy and somatic meiosis. Recombination and migration also explain the geographical dispersal of specific markers. A near-to-significant correlation between the genotypic data and previously obtained pathotype data was observed and one marker was associated with the most virulent pathotype group. In combination with a fast SNP detection method, the markers will be helpful tools to further elucidate the migration pathways and local survival of this pathogen as well as help guide future quarantine measures.