Puccinia xanthii

Puccinia xanthii is native to the continental United States, Canada, Mexico, Hawaii, Cuba, Haiti, the Dominican Republic, Puerto Rico, and the Bahamas. Puccinia xanthii was found growing on Xanthium orientale subsp. italicum in eastern Hungary in December 2002. Puccinia xanthii was found growing in lesions on leaves of Xanthium orientale in Okcheon-gun, Korea in October 2021 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. 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. 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. Puccinia xanthii var. xanthii This variation specializes on plants in the Xanthium genus. == Synonyms ==

Leptopuccinia xanthii Micropuccinia xanthii Dasyspora xanthii == Disease Cycle ==

Puccinia xanthii is a microcyclic, autoecious obligate biotroph. These telia will bore teliospores that can either germinate immediately if conditions are favorable or act as a survival structure for the fungus. The teliospores are darker or lighter yellowish-brown, smooth, 42-58 μm x 12-21 μm and thicker near the conical apex. They are two-celled and have a constricted septum. Teliospores also have a persistent yellowish-brown pedicel that is 22-70 μm long. The teliospores will germinate to form a tube-shaped basidium with three septations. This basidium then forms four white, thin-walled, binucleate, single-celled basidiospores. The basidiospores are binucleate due to a mitotic division of the initial nucleus while the infective mycelium is monokaryotic. These basidiospores break off of the basidium (usually attached to the teliospore and telia) and continue the infection cycle. == Signs and symptoms ==

Puccinia xanthii forms dark brown pustules (raised spots) with a chlorotic halo on the adaxial, and sometimes abaxial leaf surface. == Application as a Biocontrol ==

For information on where this species is being used as a biocontrol, please refer to the section on distribution. There are mixed results on the use of P. xanthii as a biocontrol, while it can cause significant damage on some host plants, it requires suitable environmental conditions to hinder plant growth. For example, while P. xanthii was able to infect and kill invasive cocklebur species in Hungary if infection starts when the plant is a cotyledon, natural infections that begin during the second part of the growing season and are seldom lethal. The Australian Department of Agriculture, Water and the Environment has put out an extension document on using P. xanthii var. parthenii-hysterophorae as a biocontrol agent. They advocate for people to intentionally spread summer rust onto invasive Parthenium spp. by collecting symptomatic leaves and pinning them to uninfected plants. This strategy has been used in Australia to contain the spread of Parthenium. Kassai-Jager et al. has also recommended the use of this pathogen as a classical biocontrol agent in Australia against another invasive member of the Asteraceae from North America, Ambrosia artemisifolia. Puccinia xanthii from Ambrosia artemisifolia growing in the wild in Texas was "highly virulent on A. artemisifolia plants from Australia". Natural infections of Puccinia xanthii var. ambrosia-trifidae on Ambrosia trifida in Maryland caused severe decline on A. trifida and reduced its propagative potential. Batra performed pathogenicity tests on this variation and recommended using P. xanthii var. ambrosia-trifidae as a biocontrol in Eurasia where this plant is an invasive species. == Pathogenicity on Sunflowers ==

Puccinia xanthii may also pose a potential threat to the ornamental plant trade. Puccinia xanthii could infect and cause foliar damage to Helianthus annus and Calendula offiinalis in pathogenicity tests using strains from C. officinalis in Queensland. This is likely an undescribed variety of P. xanthii. More taxonomic research is needed to distinguish between the varieties of P. xanthii by host-pathogen interaction. ==See also==