''Puccinia porri'' (previously known as ''Puccinia allii'') is a species of

rust fungus Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales (previously known as Uredinales). An estimated 168 rust genera and approximately 7,000 species, more than half of which belong to the genus ''Puccinia'', are currently ...

that causes leek rust. It affects

leek The leek is a vegetable, a cultivar of ''Allium ampeloprasum'', the broadleaf wild leek ( syn. ''Allium porrum''). The edible part of the plant is a bundle of leaf sheaths that is sometimes erroneously called a stem or stalk. The genus ''Alli ...

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...

onion An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus ''Allium''. The shallot is a botanical variety of the onion ...

, and

chives Chives, scientific name ''Allium schoenoprasum'', is a species of flowering plant in the family Amaryllidaceae that produces edible leaves and flowers. Their close relatives include the common onions, garlic, shallot, leek, scallion, and ...

, and usually appears as bright orange spots on infected plants.

Fungus

''Puccinia porri'' is

autoecious 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 cycl ...

, meaning that all stages of its life cycle occur on the host plant. While ''P. porri'' and ''P. mixta'' were originally thought to be separate species, by 1984 they were all generally categorized under ''P. allii''. The fungus causes leek rust, but it also affects

, and

. In 2016, Alistair McTaggart and colleagues used

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

analysis to sort out collections of fungi labeled as ''Puccinia allii'' occurring in Australia, and placed this name in

synonymy A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

with ''Puccinia porri''.

Conditions for growth

Leek rust appears seasonally, starting in the middle of August. It develops more quickly in warmer weather, so conversely, cold spells can reduce the onset of symptoms. If a leek reaches maturation closer to winter, it is more susceptible to infection, whereas a leek that matures earlier in the fall must be wet to endure a heavy attack. According to the

Royal Horticultural Society The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at Wisley (Surrey), Hyde Hall (Essex), Harlow Carr (Nort ...

, there are no

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

s approved for use by amateur gardeners to combat leek rust. However, in practice there are different fungicides that are recommended for use in different countries, depending on the ''Allium'' crop. For example, in Ethiopia, the fungicides

mancozeb Mancozeb is a dithiocarbamate non-systemic agricultural fungicide with multi-site, protective action on contact. It is a combination of two other dithiocarbamates: maneb and zineb. The mixture controls many fungal diseases in a wide range of f ...

propiconazole Propiconazole is a triazole fungicide, also known as a DMI, or demethylation inhibiting fungicide due to its binding with and inhibiting the 14-alpha demethylase enzyme from demethylating a precursor to ergosterol. Without this demethylation st ...

tebuconazole Tebuconazole is a triazole fungicide used agriculturally to treat plant pathogenic fungi. Environmental Hazards Though the U.S. Food and Drug Administration considers this fungicide to be safe for humans, it may still pose a risk. It is listed ...

azoxystrobin Azoxystrobin is the ISO common name for an organic compound that is used as a fungicide. It is a broad spectrum systemic active ingredient widely used in agriculture to protect crops from fungal diseases. It was first marketed in 1996 using the ...

are approved for use to control the fungus. They will control the rust if sprayed on the plant at 10-day intervals.

Symptoms of infection

On leeks, ''P. porri'' manifests as bright orange or yellow pustules on the upper parts of the leaves, usually between veins. Sometimes, the pustules grow to network with each other and spread to the base of the leaf. The

aeciospores 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 pl ...

are between 19 and 28

micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...

s in diameter, with yellow walls 1 to 2 micrometers in length. The urediniospores are more elliptical in shape, with a major axis diameter of 22–32 micrometers and a minor axis diameter of 20–26 micrometers. The

teliospores Teliospore (sometimes called teleutospore) is the thick-walled resting spore of some fungi ( rusts and smuts), from which the basidium arises. Development They develop in '' telia'' (sing. ''telium'' or ''teliosorus''). The telial host is the p ...

are also elliptical, with a major axis diameter of 28–45 micrometers and a minor axis diameter of 20–26 micrometers.

Economic damage

An infected leek's discolouring can cause it to lose market value, as there is an expectation the vegetables do not have visual defects or flaws. The infection can also slow and reduce the growth of the plant. In addition, Uma (1984) writes that ''P. porri'' has caused significant losses for garlic farmers in

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, Israel, South Africa, and Brazil.

References

{{Taxonbar, from=Q1422236 porri Fungi described in 1809 Fungal plant pathogens and diseases Fungi of Africa Fungi of North America Fungi of South America Taxa named by James Sowerby