Genetic Relationships in an International Collection of Puccinia horiana Isolates Based on Newly Identified Molecular Markers and Demonstration of Recombination

Abstract

The obligate biotrophic pathogen Puccinia horiana is the causal agent of chrysanthemum white rust. Although P. horiana is a quarantine organism, it has been able to spread to most chrysanthemum-producing regions in the world since the 1960s; however, the transfer routes are largely obscure. An extremely low level of allelic diversity was observed in a geographically diverse set of eight isolates using complexity reduction of polymorphic sequences (CRoPS) technology. Only 184 of the 16,196 contigs (1.1%) showed one or more single-nucleotide polymorphisms (SNPs). Thirty-two SNPs and one simple-sequence repeat were translated into molecular markers and used to genotype 45 isolates originating from North and South America, Asia, and Europe. In most cases, phylogenetic clustering was related to geographic origin, indicating local establishment. The European isolates mostly grouped in two major populations that may relate to the two historic introductions previously reported. However, evidence of recent geographic transfer was also observed, including transfer events between Europe and South America and between Southeast 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 transfer also explain the geographic 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 presented here will be helpful tools to further elucidate the transfer pathways and local survival of this pathogen.

Cladosporium cladosporioides and Cladosporium pseudocladosporioides as potential new fungal antagonists of Puccinia horiana Henn., the causal agent of chrysanthemum white rust

“…Due to its economic importance to floriculture, it is classed as a quarantine disease by the European and Mediterranean Plant Protection Organization (EPPO), Inter-African Phytosanitary Council (IAPSC), Andean Community (CAN) and North American Plant Protection Organization (NAPPO), and is also listed as a regulated pest by the International Plant Protection Convention (IPPC). Currently it is present in most chrysanthemum producing areas throughout the world and can cause important losses [ 3 , 4 , 5 ].…”

Evidence that Austropuccinia psidii may complete its sexual life cycle on Myrtaceae

“…De Backer et al . () observed recombination followed by karyogamy in a microcyclic rust, Puccinia horiana , and suggested this took place after anastomoses of germ tubes produced by basidiospores. This life cycle strategy was described by Ono () as the ‘anastomosis of vegetative mycelia at an early stage of basidiospore infection’.…”

In vitro and in planta investigation of succinate dehydrogenase inhibitor resistance conferred by target‐site amino acid substitutions in Puccinia horiana, chrysanthemum white rust

“…13 Notably, this rust pathogen does not produce uredospores, although it always forms teliospores, which easily generate basidiospores under laboratory conditions. 10,14 Germination of basidiospores, unlike uredospores, shows high sensitivity to SDHIs. 12,13 Furthermore, basidiospores in this species are always homozygous, 14 making it easier to analyze the relationship between gene mutations and sensitivity to fungicides.…”

“…10,14 Germination of basidiospores, unlike uredospores, shows high sensitivity to SDHIs. 12,13 Furthermore, basidiospores in this species are always homozygous, 14 making it easier to analyze the relationship between gene mutations and sensitivity to fungicides. The EC 50 values for oxycarboxin upon basidiospore germination were very close for eight isolates with the same SdhC-I88F substitution (range 30.2 to 59.8 mg L −1 ), indicating the stability of the test system measuring the inhibition of basidiospore germination.…”