Editing Rust (fungus) (section)

==Life cycle==
All rusts are obligate or biotrophic [[parasite]]s, meaning that they require a living host to complete their life cycle. They generally do not kill the host plant but can severely reduce growth and yield.<ref name="csldiagnostics.co.uk">Central Science Laboratory. (2006). Plant Healthcare: Rusts [Fact Sheet]. Retrieved from www.csldiagnostics.co.uk</ref> [[Cereal crops]] can be devastated in one season; oak trees infected in the main stem within their first five years by the rust ''[[Cronartium quercuum]]'' often die.<ref>{{cite web|url=http://www.backyardnature.net/f/rusts.htm|title=Rust Fungi|website=www.backyardnature.net|access-date=2010-08-06|archive-date=2010-09-17|archive-url=https://web.archive.org/web/20100917143359/http://backyardnature.net/f/rusts.htm|url-status=live}}</ref>

[[File:Modell von Puccinia graminis (Getreiderost) -Osterloh- -Brendel 10 h, 2-.jpg|thumb|Germinating urediniospore of ''[[Puccinia graminis]]'', model from the late 19th century, [[Botanical Museum Greifswald]]]]

Rust fungi can produce up to five spore types from corresponding fruiting body types during their life cycle, depending on the species. Roman numerals have traditionally been used to refer to these morphological types.

*0-'''[[Pycniospores]]''' ([[Spermatia]]) from [[Pycnidia]]. These serve mainly as [[haploid]] [[gamete]]s in [[heterothallic]] rusts.
*I-'''[[Aeciospores]]''' from Aecia. These serve mainly as non-repeating, [[dikaryotic]], asexual spores, and go on to infect the primary host.
*II-'''[[Urediniospores]]''' from [[Uredia]] ([[Uredinia]]). These serve as repeating dikaryotic vegetative spores. These spores are referred to as the repeating stage because they can cause auto-infection on the primary host, re-infecting the same host on which the spores were produced. They are often profuse, red/orange, and a prominent sign of rust disease.
*III-'''[[Teliospores]]''' from Telia. These dikaryotic spores are often the survival/[[overwintering]] stage of the life cycle. They usually do not infect a plant directly; instead they germinate to produce basidia and basidiospores. 
*IV-'''[[Basidiospores]]''' from [[Teliospores]]. These windborne haploid spores often infect the alternate host in Spring.<ref name="Schumann, G. 2010">Schumann, G. & D'Arcy, C. (2010). Essential plant pathology. APS Press</ref><ref>Scott, K.J, & Chakravorty, A.K., (1982), The Rust fungi. Academic Press.</ref> They are rarely observed outside of the [[laboratory]].

Rust fungi are often categorized by their life cycle. Three basic types of life cycles are recognized based on the number of spore types as '''macrocyclic''', '''demicyclic''', and '''microcyclic'''.<ref name="How many rust species exist?"/> The macrocyclic life cycle has all spore states, the demicyclic lacks the uredinial state, and the microcyclic cycle lacks the basidial, [[pycnia]]l, and the aecial states, thus possess only uredinia and telia.  Spermagonia may be absent from each type but especially the microcyclic life cycle.  In macrocyclic and demicyclic life cycles, the rust may be either host alternating ([[heteroecious]]) (i.e., the aecial stage is on one kind of plant but the [[telial stage]] on a different and unrelated plant), or single-host ([[autoecious]]) (i.e., the aecial and telial states on the same plant host).<ref name="How many rust species exist?"/> [[Heteroecious]] rust fungi require two unrelated hosts to complete their life cycle, with the primary host being infected by aeciospores and the alternate host being infected by basidiospores. This can be contrasted with an autoecious fungus, such as ''[[Puccinia porri]]'', which can complete all parts of its life cycle on a single host species.<ref name="Schumann, G. 2010"/> Understanding the life cycles of rust fungi allows for proper disease management.<ref name="Peterson, R. 1974">Peterson, R., (1974). The Rust Fungus Life Cycle. The Botanical Review. 40(4), 453-513.</ref>