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''Austropuccinia'' is a
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
genus of
rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...
(a type of
plant pathogen Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like orga ...
) native to
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
with the only species ''Austropuccinia psidii'', commonly known as myrtle rust, guava rust, or ʻōhiʻa rust. It affects plants in the family
Myrtaceae Myrtaceae (), the myrtle family, is a family of dicotyledonous plants placed within the order Myrtales. Myrtle, pōhutukawa, bay rum tree, clove, guava, acca (feijoa), allspice, and eucalyptus are some notable members of this group. All ...
. It is a member of the fungal complex called the guava rust (''Puccinia psidii'') group. The
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
s have a distinctive yellow to orange colour, occasionally encircled by a purple ring. They are found on lesions on new growth including shoots, leaves, buds and fruits. Leaves become twisted and may die. Infections in highly susceptible species may result in the death of the host plant. As of late 2013, it is infecting around 179 species in
New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...
and
Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
, from 41 genera (around 46% of genera in the Myrtaceae) in Australia.


Importance

''Austropuccinia psidii'', a myrtle rust or a rust fungus, has a large host range for infection, making disease control and prevention difficult. However, it has been seen to have biological uses. In Florida, the pathogen has been considered as a biological control agent for the invasive Australian plant, ''
Melaleuca quinquenervia ''Melaleuca quinquenervia'', commonly known as the broad-leaved paperbark, paper bark tea tree, punk tree or niaouli, is a small- to medium-sized tree of the myrtle Family (biology), family, Myrtaceae. It grows as a spreading tree up to tall, ...
''. ''Melaleuca quinquenervia'' is a weed tree that has invaded south Florida. If left unchecked, it will cause of the most serious threats to the integrity of the native ecosystem, turning marshes in the Everglades into swamps. With Autropuccinia psidii, the disease has the ability to disperse inoculum rapidly and attack healthy tissues, causing substantial damage to their hosts. This creates pustules and eventually leads to the death of the invasive species. ''Austropuccinia psidii'' can rapidly spread globally and can impact commercially and ecologically important species of Myrtaeceae such as '' Archirhodomyrtus beckleri'', '' Decaspermum humile'', '' Gossia hillii'' and ''
Rhodamnia maideniana ''Rhodamnia maideniana'', known as the smooth scrub turpentine, is a rare sub-tropical rainforest plant of eastern Australia. It is listed on ROTAP with a rarity factor of 2RC-. It occurs in coastal areas, north of the Richmond River, New Sout ...
,'' that are extremely important in Australia affecting their native forest ecosystems and causing extinctions. ''Austropuccinia psidii'' has also been found to also be an invasive species that infects young growing tissues of plants. It infects developed leaves, floral bud, fruits and Coppice. This fungus is a serious problem because of its ability to spread rapidly from its production of a large number of small spores that can be easily dispersed over long distances by wind. These spores can also be dispersed by vectors that include animals such as birds, bats, possums, and insects that have been in contact with the rust spores. ''Austropuccinia psidii'' has a potential to cause damage to natural ecosystems. In Australia, many ecosystems are dominated by ''
Eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
'' which is also the dominant tree in most of Hawaii's forests. Infection from ''Autropuccinia psidii'' results in significant changes to the structure, composition, and the function of forests trees on a landscape level. Thus, it greatly impacts biodiversity of other flora and fauna in these ecosystems.


Taxonomy

The fungus was first described scientifically in 1884 as ''Puccinia psidii'' by G. Winter, then described again in 2006 as ''Uredo rangelii'' by mycologists J.A. Simpson, K. Thomas, and Cheryl Grgurinovic. Finally in 2017 the names were synonymised by Beenken in a new genus as ''Austropuccinia psidii''''.''


Development and symptoms

Myrtle rust is typically characterised by the appearance of
urediniospore Urediniospores (or uredospores) are thin-walled spores produced by the uredium, a stage in the life-cycle of Rust (fungus), rusts. Development ''Urediniospores'' develop in the uredium, generally on a leaf's under surface. Morphology *Uredinio ...
s on the underside of the leaf, though urediniospores may also be found on the top of the leaf or on young stems. Initially, the disease appears as small purple or red brown flecks with a faint chlorotic halo on the leaf surface, which coalesce to form bright yellow pustules. As the rust develops, these pustules often fade to a grey brown colour. A high degree of pustule coalescence can result in distortion of the leaf. Myrtle rust also makes plants more susceptible to secondary infections, which may occur within days of the initial appearance of the pustules. Favourable conditions that increase the infection rate include: new tissue; high humidity; free water on plant surface for more than 6 hours; moderate temperatures, around 15–25 °C. Low light conditions (minimum of 8 hours) after spore contact can increase germination. The main ways in which myrtle rust can be spread are by: the movement of infected plant material, the movement of contaminated equipment, wind, water and gravity, animals, humans and/or vehicles. Myrtle rust may remain on a single host plant to complete its
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from conception to reproduction *Life-cycle hypothesis, in economics *Erikson's stages of psy ...
, which can be as short as 10–14 days.


As an invasive species

''Austropuccinia psidii'' can have very serious consequences to various species of plants in the Myrtaceae. This family includes
guava Guava ( ), also known as the 'guava-pear', is a common tropical fruit cultivated in many tropical and subtropical regions. The common guava '' Psidium guajava'' (lemon guava, apple guava) is a small tree in the myrtle family (Myrtaceae), nativ ...
(the original host of this rust in Brazil),
eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
,
melaleuca ''Melaleuca'' () is a genus of nearly 300 species of plants in the myrtle family, Myrtaceae, commonly known as paperbarks, honey-myrtles, bottlebrushes or tea-trees (although the last name is also applied to species of '' Leptospermum''). They ...
, and a number of species native to
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
, including some endemic species (found nowhere else on Earth) and at least one important native forest tree. There are numerous strains of the ''Austropuccinia psidii'' rust—some known to be established in
Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...
, and at least one reported from
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
and there is concern that strains may exist or develop that could be devastating to ʻōhiʻa (''
Metrosideros polymorpha ''Metrosideros polymorpha'', the ''ōhia lehua'',; is a species of flowering evergreen tree in the Myrtus, myrtle family, Myrtaceae, that is Endemism, endemic to the six largest Hawaiian Islands, islands of Hawaii, Hawaii. It is a member of the ...
''), one of Hawaii's dominant native trees, a foundation species for many remaining Hawaiian native
ecosystems An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...
. However currently, the major threat of Puccinia in Hawaii is the massive damage it is doing to ''
Eugenia koolauensis ''Eugenia koolauensis'', commonly known as Koolau eugenia or ''nioi'', is a species of flowering plant in the myrtle family, Myrtaceae. It is endemic to Hawaii, where it could previously be found on the islands of Molokai and Oahu; today populat ...
'', a federally listed endangered species. Myrtle rust was first recorded in
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
in mid-2010 and currently poses a major threat to the continent's ecosystem given that almost 80 per cent of Australian native trees are Mytraceae, most indigenous species rely on healthy trees for their survival. Additionally it poses a major threat to Australia's primary industry sector. Its current range includes much of the eastern coastal fringe of the Australian mainland. Initial detection was in April 2010 in
Gosford Gosford is a waterfront city at the northern end of Brisbane Water on the Central Coast in the state of New South Wales, Australia. The Gosford Waterfront is known for its boating and scenic views on the shores of Brisbane Water. Gosford is ...
in the Central Coast region of
New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...
. It was initially quarantined and eradication thought viable. The New South Wales government spent $5 million attempting to eradicate the disease. However, efforts to contain it failed and it spread rapidly north and south along the eastern coast. In response to the increasing threat, a Myrtle Rust National Management Group was formed on 2 July 2010 with the aim of eradication however due to the extent of its spread at that point of time, the group conceded that it had become impossible to eradicate. By December 2010, it had significantly spread north along the coast and recorded in
South East Queensland South East Queensland (SEQ) is a Bioregion, bio-geographical, Megalopolis, metropolitan and Statistics, statistical Regions of Queensland, region of the States and territories of Australia, state of Queensland in Australia, with a population of ...
with isolated cases in
Far North Queensland Far North Queensland (FNQ) is the northernmost part of the States and territories of Australia, Australian state of Queensland. Its largest city is Cairns, Queensland, Cairns and it is dominated geographically by Cape York Peninsula, which stret ...
cities of
Cairns Cairns (; ) is a city in the Cairns Region, Queensland, Australia, on the tropical north east coast of Far North Queensland. In the , Cairns had a population of 153,181 people. The city was founded in 1876 and named after William Cairns, Sir W ...
and
Townsville The City of Townsville is a city on the north-eastern coast of Queensland, Australia. With a population of 201,313 as of 2024, it is the largest settlement in North Queensland and Northern Australia (specifically, the parts of Australia north of ...
. In January 2012, an isolated myrtle rust outbreak was reported in
Victoria Victoria most commonly refers to: * Queen Victoria (1819–1901), Queen of the United Kingdom and Empress of India * Victoria (state), a state of Australia * Victoria, British Columbia, Canada, a provincial capital * Victoria, Seychelles, the capi ...
beginning in
Melbourne Melbourne ( , ; Boonwurrung language, Boonwurrung/ or ) is the List of Australian capital cities, capital and List of cities in Australia by population, most populous city of the States and territories of Australia, Australian state of Victori ...
's southern and eastern suburbs. Initial attempts to contain it were unsuccessful and by April, 2012 it had spread across much of the state via regional cities. By late 2015 myrtle rust was widespread in Queensland, NSW and Victoria. It has reached Tasmania, where it was detected in garden plants in the north-east in February 2015, and the Northern Territory, where it was detected on Melville Island in May 2015. The Tasmanian government is seeking to contain and eradicate myrtle rust from the state while the Northern Territory government has determined it is not possible to contain or eradicate the pathogen. In April 2017, New Zealand's Ministry for Primary Industries reported that myrtle rust had been detected on
Raoul Island Raoul Island (''Sunday Island''; ) is the largest and northernmost of the main Kermadec Islands, south south-west of 'Ata Island of Tonga and north north-east of New Zealand's North Island. It has been the source of vigorous volcanic activit ...
, off the New Zealand mainland; the following month, it was detected on the mainland, in
Kerikeri Kerikeri () is a town in the Bay of Islands, in the Far North District of the North Island of New Zealand. It lies at the head of Kerikeri Inlet, a northwestern arm of the Bay of Islands, where fresh water of the Kerikeri River enters the Paci ...
. As of 2020 it is spreading in New Zealand, and infecting pōhutukawa (''
Metrosideros excelsa ''Metrosideros'' is a genus of approximately 60 trees, shrubs, and vines in the family Myrtaceae, mostly found in the Pacific region. Most of the tree forms are small, but some are exceptionally large, the New Zealand species in particular. The ...
''), northern rātā (''
Metrosideros robusta ''Metrosideros robusta'', commonly known as the northern rātā, is a forest tree endemic to New Zealand. It grows up to or taller, and usually begins its life as a hemiepiphyte high in the branches of a mature forest tree; over centuries th ...
''), southern rātā (''
Metrosideros umbellata ''Metrosideros umbellata'', the southern rātā, is a tree endemic to New Zealand. It grows up to or more tall with a trunk up to or more in diameter. It produces masses of red flowers in summer. Unlike its relative, northern rātā, this sp ...
''), ramarama (''
Lophomyrtus bullata ''Lophomyrtus bullata'', also known by its Māori name of ramarama, is a species of evergreen myrtle shrub in the genus ''Lophomyrtus'', family Myrtaceae. It is endemic to New Zealand. ''Lophomyrtus bullata'' grows to a height of 8 metres, pr ...
'') and rohutu '' Lophomyrtus obcordata''.


Host genera

Species within the following plant genera have been recorded with the infection: *''
Acmena ''Acmena'' was formerly the name of a genus of shrubs and trees in the myrtle family Myrtaceae. The genus was first formally described in 1828 by Augustin Pyramus de Candolle in his '' Prodromus Systematis Naturalis Regni Vegetabilis''. The spec ...
'' *''
Agonis ''Agonis'' is a genus of flowering plants in the plant family Myrtaceae. All are endemic to Western Australia, growing near the coast in the south west. Plants in the genus ''Agonis'' are shrubs or trees with bisexual flowers arranged in hea ...
'' *''
Angophora ''Angophora'' is a genus of nine species of trees and shrubs in the myrtle family, Myrtaceae. Endemic to eastern Australia, they differ from other eucalypts in having juvenile and adult leaves arranged in opposite pairs, sepals reduced to projec ...
'' *'' Asteromyrtus'' *''
Austromyrtus ''Austromyrtus'' is a genus of shrubs in the myrtle family Myrtaceae. The genus was first described in 1893 by Franz Josef Niedenzu as a section of ''Myrtus'', but in 1941 it was elevated to a genus by Max Burret. Three species are found along t ...
'' *''
Backhousia ''Backhousia'' is a genus of thirteen currently known species of flowering plants in the family Myrtaceae. All the currently known species are endemic to Australia in the rainforests and seasonally dry forests of Queensland, New South Wales and ...
'' *''
Callistemon ''Callistemon'' is a genus of shrubs in the family Myrtaceae, first described as a genus in 1814. The entire genus is endemic to Australia but widely cultivated in many other regions and naturalised in scattered locations. Their status as a se ...
'' *''
Chamelaucium ''Chamelaucium'', also known as waxflower, is a genus of shrubs endemic to south western Western Australia. They belong to the myrtle family Myrtaceae and have flowers similar to those of the tea-trees (''Leptospermum''). The most well-known sp ...
'' *'' Choricarpia'' *'' Decaspermum'' *''
Eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...
'' *''
Eugenia ''Eugenia'' is a genus of flowering plants in the myrtle family Myrtaceae. It has a worldwide, although highly uneven, distribution in tropical and subtropical regions. The bulk of the approximately 1,100 species occur in the New World tropics, ...
'' *''
Gossia ''Gossia'' is a genus of rainforest trees in the Myrtaceae, myrtle family first described as a genus in 2003 by Neil Wilton Snow, Neil Snow and Gordon P. Guymer, Gordon Guymer. It is native to northeastern Australia (Queensland and New South Wal ...
'' *''
Lenwebbia ''Lenwebbia'' is a genus of shrubs or small trees in the myrtle family Myrtaceae. The type species is '' Lenwebbia lasioclada''. The genus is named to honour the Australian plant ecologist Dr. Leonard Webb. The genus occurs in mesic forests a ...
'' *''
Leptospermum ''Leptospermum'' is a genus of shrubs and small trees in the myrtle family Myrtaceae commonly known as tea trees, although this name is sometimes also used for some species of ''Melaleuca''. Most species are endemic to Australia, with the greate ...
'' *''
Lophomyrtus ''Lophomyrtus'' is a genus of the Myrtaceae, myrtle family described as a genus in 1941. The entire genus is endemic to New Zealand. It consists of evergreen shrubs or trees, noted for their colorful leaves, which are purple, chocolate, red or ...
'' *''
Melaleuca ''Melaleuca'' () is a genus of nearly 300 species of plants in the myrtle family, Myrtaceae, commonly known as paperbarks, honey-myrtles, bottlebrushes or tea-trees (although the last name is also applied to species of '' Leptospermum''). They ...
'' *''
Metrosideros ''Metrosideros'' is a genus of approximately 60 trees, shrubs, and vines in the family Myrtaceae, mostly found in the Pacific region. Most of the tree forms are small, but some are exceptionally large, the New Zealand species in particular. The ...
'' *''
Myrtus ''Myrtus'' (commonly called myrtle) is a genus of flowering plants in the family Myrtaceae. It was first described by Swedish botanist Linnaeus in 1753. Over 600 names have been proposed in the genus, but nearly all have either been moved ...
'' *'' Pilidiostigma'' *''
Rhodamnia ''Rhodamnia'' is a group of rainforest trees and shrubs in the myrtle family described as a genus in 1822.Govaerts, R., Sobral, N., Ashton, P., Barrie, F., Holst, B.K., Landrum, L.L., Matsumoto, K., Fernanda Mazine, F., Nic Lughadha, E., Proenç ...
'' *''
Rhodomyrtus ''Rhodomyrtus'' is a group of shrubs and trees in the family Myrtaceae, described as a genus in 1841 and native to southern China, the Indian subcontinent, Southeast Asia, Melanesia, and Australia. Its greatest levels of diversity are in New Gui ...
'' *''
Ristantia ''Ristantia'' is a genus of plants in the family Myrtaceae, first described in 1982. The entire genus is endemic to the state of Queensland, Australia. Species , Plants of the World Online accepts the following 3 species: # ''Ristantia gouldii ...
'' *''
Stockwellia ''Stockwellia'' is a monotypic genus in the flowering plant family Myrtaceae. The sole species in the genus, ''Stockwellia quadrifida'' (commonly known as Vic Stockwell's puzzle), is endemic to Queensland. Description ''Stockwellia quadrifida' ...
'' *''
Syncarpia ''Syncarpia'' is a small group of trees in the myrtle family (Myrtaceae) described as a genus in 1839. They are native to Queensland and New South Wales in Australia.Govaerts, R., Sobral, N., Ashton, P., Barrie, F., Holst, B.K., Landrum, L.L., ...
'' *''
Syzygium ''Syzygium'' () is a genus of flowering plants that belongs to the myrtle family, Myrtaceae. The genus comprises about 1200 species, and has a native range that extends from Africa and Madagascar through southern Asia east through the Pacific. I ...
'' *'' Tristania'' *''
Ugni ''Ugni'' is a genus of plants in the myrtle family Myrtaceae, described as a genus in 1848. It is native to western Latin America from the Valdivian temperate rain forests of southern Chile (including the Juan Fernández Islands) and adjacent r ...
'' *''
Uromyrtus ''Uromyrtus'' is a genus of plants in the myrtle family Myrtaceae described as a genus in 1941. The greatest diversity of species are found in New Caledonia and the remainder are found in Australia, New Guinea and Borneo.Govaerts, R., Sobral, N., ...
'' *''
Waterhousea ''Syzygium'' () is a genus of flowering plants that belongs to the myrtle family, Myrtaceae. The genus comprises about 1200 species, and has a native range that extends from Africa and Madagascar through southern Asia east through the Pacific. I ...
'' *''
Xanthostemon ''Xanthostemon'' is a genus of plants in the myrtle family Myrtaceae, first described in 1857 by the German–born Australian botanist Ferdinand von Mueller. The genus is distributed across Malesia, Papuasia and northern Australia. The genera '' ...
''


Environmental impacts

Since first being detected in 2010, myrtle rust has spread rapidly with entire plant species now under threat. In Australia, the family Myrtaceae - which includes eucalypts, melaleuca and lilly pilly - is diverse, widespread and important to many native ecosystems. The impact of myrtle rust has now been seen in a range of forest ecosystems including coastal heath, coastal and river wetlands, sand island ecosystems and subtropical and tropical rainforests. A number of plant species are now at risk of becoming extinct with about 40 plant species considered highly susceptible, such as the endangered ''Rhodamnia angustifolia''. Native animals are also likely to suffer significant impacts. Myrtle rust grows in shoots, fruits and flowers, destroying the food relied on by some species of flying foxes, lorikeets and honey eaters. There is the strong possibility that some of these species will become regionally extinct, and their loss could have serious flow-on effects.


Life cycle and disease cycle

Rust fungi typically have complex life cycles that include stages of sexual and asexual reproduction that occasionally occur on phylogenetically distinct host plants. ''Austropuccinia psidii''’s life cycle is quite controversial with one study showing that the rust is
autoecious A heteroecious parasite is one that requires at least two Host (biology), hosts. The ''primary host'' is the host in which the parasite spends its adult life; the other is the ''secondary host''. Both hosts are required for the parasite to compl ...
while another study finding it to be
heteroecious A heteroecious parasite is one that requires at least two hosts. The ''primary host'' is the host in which the parasite spends its adult life; the other is the ''secondary host''. Both hosts are required for the parasite to complete its life cy ...
but with an alternate host that has yet to be found. Looking at the fungus as a polycyclic pathogen, Stage I consists of
aeciospore Aeciospores are one of several different types of spores formed by rusts. They each have two nuclei and are typically seen in chain-like formations in the aecium An aecium (plural aecia) is a specialised reproductive structure found in some p ...
s inoculating young leaf/shoot/fruit/flower bud. Once infected, aeciospores germinate and penetrate the host by creating a
haustoria In botany and mycology, a haustorium (plural haustoria) is a rootlike structure that grows into or around another structure to absorb water or nutrients. For example, in mistletoe or members of the broomrape family, the structure penetrates th ...
. Colonies and urediniosori forms after penetration. In Stage II, the production of
urediniospore Urediniospores (or uredospores) are thin-walled spores produced by the uredium, a stage in the life-cycle of Rust (fungus), rusts. Development ''Urediniospores'' develop in the uredium, generally on a leaf's under surface. Morphology *Uredinio ...
s go back to inoculate young leaf/shoot/fruit/flower bud, important for secondary infection and contributing to the polycyclic nature of the pathogen. Stage II is also where urediniospores germinate, and penetration of the host occurs, resulting in the development of an uridiniosori. In Stage III, urediniospores germinate and the host is penetrated with the development of a haustoria. After penetration, colonies are formed and teliosori are developed. Teliosori produce
teliospore Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi (Rust (fungus), rusts and Smut (fungus), smuts), from which the basidium arises. Development They develop in ''telium, telia'' (sing. ''telium'' or ''telio ...
s which can further germinate. Once they're germinated,
basidiospore A basidiospore is a reproductive spore produced by basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid Ploidy () is the number of complete sets of chromos ...
s are developed. In Stage IV, basidiospores are spread, inoculating young leaf/shoot/fruit/flower bud. As a result, basidiospores germinate penetrating the host with the development of a haustorium. Aeciosori is formed with the production of aeciospores and the cycle repeats.


Infection pathway

Beginning with 1) extracellular pre-penetration processes (adhesion, germination, and
appressorium An appressorium is a specialized cell typical of many fungal plant pathogens that is used to infect host plants. It is a flattened, hyphal "pressing" organ, from which a minute infection peg grows and enters the host, using turgor pressure capable ...
formation 2) intercellular post-penetration processes (nutrient acquisition, ETS, ETI) and 3) dispersal of newly formed uredospores (reproduction and sporulation). To infect the plant, uredospores must adhere to the leaf surface which can be enhanced by the secretion of extracellular compounds. Both physical and chemical cues by neutralized spore germination inhibitors induces germination and break
dormancy Dormancy is a period in an organism's Biological life cycle, life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolism, metabolic activity and therefore helps an organism to conserv ...
. After the penetration of urediniospores by a combination of extracellular secretions and physical force, the
germ tube A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination. The germ tube differentiates, grows, and develops by mitosis to create somatic hyphae.C.J. Alexopolous, Charles W. Mims, M. Blackwell, ''Introductory My ...
is formed and elongated in a favorable area fueled by spore protein reserves from an appressorium. Once the hyphae is within the cell
apoplast The ''apoplast '' is the extracellular space outside of plant cell membranes, especially the fluid-filled cell walls of adjacent cells where water and dissolved material can flow and diffuse freely. Fluid and material flows occurring in any extr ...
, the hyphae penetrates a host
mesophyll cell A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, fl ...
to form a haustoria to acquire nutrients and suppress plant defenses. The hyphae and haustoria continually secrete effectors prevent plant resistance. Chemical signaling between plant and pathogen are continuously occurring to determine infection or any defense responses to the pathogen. Nutrient acquisition fuels pathogen growth by the accumulation of carbon from the host plant. This results in sporulation where the hyphae move toward plant surfaces to make urediniospores and to create a sori that ruptures through the dermal surface for penetration and infection.


Management

The original plan to eradicate myrtle rust from Australia was declared to be infeasible by the Myrtle Rust National Management Group in December 2010. The Myrtle Rust Response Plan was cancelled and focus was placed on minimising the spread and the impacts on myrtle rust. The Australian Government, through the Department of Agriculture Fisheries and Forestry, established the Myrtle Rust Coordination Group to manage the investment of $1.5 million of research funding. In 2016, The National Environmental Science Programme (http://www.environment.gov.au/science/nesp) hosted a national workshop on myrtle rust to discuss research findings and future management options. Participants included the Cooperative Research Centre for Plant Biosecurity, state and federal agencies, and botanical and plant conservation experts. Discussions centred around the impact on native species in Australia. A key outcome of the workshop included agreement that there is a need for a nationally coordinated approach through a long-term National Action Plan which aims to ensure that no species or ecosystems are lost to its impact. Practical measures to minimise the risk of increasing the distribution of myrtle rust include: not moving plant matter from one site to another; minimising pathogen spread by arriving and leaving each site clean of the pathogen, and avoiding areas that may contain myrtle rust-infected plant matter.


References


External links

*
'Beyond Myrtle Rust' New Zealand Research programme
* 2010. Loope, Lloyd L
A Summary of Information on the Rust ''Puccinia psidii'' Winter (Guava Rust) with Emphasis on Means to Prevent Introduction of Additional Strains to Hawaii
U.S. Geological Survey Open-File Report 2010–1082. * '
''Puccinia psidii'' species information
'' from th
Hawaiian Ecosystems at Risk project (HEAR)
* 2007. Eloise M. Killgore & Ronald A. He
Ohia Rust
{{Taxonbar, from1=Q95489807, from2=Q99219105, from3=Q7900369, from4=Q7258196 Pucciniales Monotypic fungus genera Taxa described in 2017