Puccinia xanthii is a fungal pathogen of plants in the Asteraceae, and can infect hosts from at least 42 genera within that family, most notably species in the Xanthium and Ambrosia genera. This pathogen was discovered growing on Xanthium strumarium in North Carolina, United States in 1822. Common names of P. xanthii include Summer Rust and Cocklebur Rust.
Distribution Puccinia xanthii is native to the continental United States, Canada, Mexico, Hawaii, Cuba, Haiti, the Dominican Republic, Puerto Rico, and the Bahamas. This fungus has been reported in several countries throughout Europe, Asia, Africa and Australia; often following the introduction of invasive host plants from North America or intentional release as a biocontrol agent.
Europe Researchers have detected P. xanthii in Bulgaria, southern France, Hungary, northern Italy, Romania, Spain, and the former Yugoslavia (Bosnia, Serbia, Slovenia, Montenegro, Macedonia, Herzegovina, and Croatia). Puccinia xanthii was found growing on Xanthium orientale subsp. italicum in eastern Hungary in December 2002.
Asia Puccinia xanthii has been detected in India, Indonesia, Japan, Pakistan, and Korea. Puccinia xanthii was found growing in lesions on leaves of Xanthium orientale in Okcheon-gun, Korea in October 2021 and from Xanthium orientale subsp. italicum in the Liaoning Province of China in August 2013. Xanthium orientale subsp. italicum was first found in Beijing, China in 1991 and has been shown to decrease the biodiversity of native flora and cause human health hazards from allergenic pollen. As a result of this, the P. xanthii is considered beneficial in this area as it may decrease the vigor of this weed. Puccinia xanthii was also found on Xanthium strumarium in Parachinar, Pakistan in 2018.
Australia Puccinia xanthii was observed on Xanthium occidentale in Australia in 1975.
Africa Puccinia xanthii was found growing on Helianthus annous in the Northwest Province of South Africa in February 2000.
Taxonomy Puccinia xanthii is a rust in the phylum Basidiomycota, subphylum Pucciniomycotina, class Pucciniomycetes, order Pucciniales, and family Pucciniaceae. Its full scientific name is Puccinia xanthii Schwein., Schriften der Naturforschenden Gesellschaft zu Leipzig 1:73. Using data from ITS (internal transcribed spacer) and TEF (translation elongation factor) phylogenetic analyses, the closest relative of P. xanthii is P. melampodii, and these species are a sister group to the fungus Dietelia portoricensis. In 2005, Hennen et. al proposed that P. xanthii, P. melampodii, and 51 other microcyclic rusts from the Americas and Eurasia that infect members of the Asteraceae should be grouped under the single morphospecies name Puccinia cnici-oleracei. This complex is based on morphology and needs further proof to be considered valid, however, P. xanthii and P. melampodii could not be easily separated at the species level using phylogenetic data from the ITS and TEF regions. This fungus has a high level of intraspecies variation, resulting in many different strains that specialize on one or a few hosts in the Asteraceae. Studies on the pathogenicity of Puccinia xanthii vary considerably based on where the isolate (which cannot be grown in culture) was taken. This high level of genetic variation is created through sexual recombination during karyogamy, somatic hybridization, mutations, and genes introduced from closely related species or other strains of P. xanthii. For example, an Australian strain of P. xanthii was able to infect Calendula offinalis and some cultivars of Helianthus annus while an American strain was able to infect only Ambrosia trifida in cross inoculation tests. Index Fungorum recognizes three classifications of P. xanthii below the species level: Puccinia xanthii var. ambrosiae-trifidae, Puccinia xanthii var. parthenii-hysterophorae, and Puccinia xanthii var. xanthii. This pathogen requires more study as the number of reported host species of Puccinia xanthii comprises more species than those infected by these subclassifications.
Puccinia xanthii var. ambrosiae-trifidae This is an obligate pathogen of Ambrosia trifida, commonly known as the giant ragweed. Studies in the Liaoning Province of China show that P. xanthii var. ambrosiae-trifidae is a suitable biocontrol for this plant, which is highly allergenic and invasive throughout Asia, Europe, and Australia. There is controversy over whether P. xanthii var. ambrosiae-trifidae is considered a forma specialis, as it was originally named in 1981, or a variety. Genetic evidence considering the degree or similarity between P. xanthii morphospecies suggests that the term variety is more accurate to distinguish between populations of P. xanthii, but literature varies in the use of f. sp. or var.
Puccinia xanthii var. parthenii-hysterophorae This variation is native to Mexico and specializes in infecting the plant Parthenium hysterophorus. Outside of its native range, this North American weed has caused issues in agriculture via allopathic chemicals, decreased biodiversity, and its pollen is a human health hazard. P. xanthii var. parthenii-hysterophorae has been intentionally introduced to north and central Queensland, Australia in 2000 as a biocontrol for this invasive plant. It was also introduced in South Africa as a biocontrol in 2010 as part of an effort to contain this weed from spreading through sub-Saharan Africa.
Puccinia xanthii var. xanthii This variation specializes on plants in the Xanthium genus.
Synonyms Leptopuccinia xanthii Micropuccinia xanthii Dasyspora xanthii
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