| Chrysanthemum white rust | |
|---|---|
 | |
| Pustules caused by chrysanthemum white rust | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Basidiomycota |
| Class: | Pucciniomycetes |
| Order: | Pucciniales |
| Family: | Pucciniaceae |
| Genus: | Puccinia |
| Species: | P. horiana |
| Binomial name | |
| Puccinia horiana | |
Puccinia horiana is a species of fungus that causes chrysanthemum white rust, is a disease of plant species of the genus Chrysanthemum .
Chrysanthemum white rust (CWR) was first identified in Japan in 1895. [2] The fungus Puccinia horiana was first described and published by German mycologist Paul Christoph Hennings (1841–1908), when found on the leaves of Chrysanthemum sinense in Honshu, Japan. [3]
It is now established throughout Asia, Europe, Australia, and South America. [4] It has been found in the United States on several occasions, but early detection and eradication efforts have prevented the disease from becoming established. [5]
Plants infected by chrysanthemum white rust exhibit spots on the upper surfaces of leaves. These spots are initially pale-green to yellow in color and up to 5mm in diameter, but may turn brown as the tissue becomes necrotic. On the underside of the leaf, stems, and flower, spots develop into pink or white waxy telial clusters/pustules where teliospores develop. [5] Pustules are able to form on any green tissue of the plant, but are most common on young leaves and flower bracts. [2]
Puccinia horiana is a microcyclic, autoecious rust, meaning that the fungus has two known spore stages: teliospores and basidiospores, as well as no known alternate host. [6] Similar to other microcyclic rusts, two-celled teliospores produce unicellular basidiospores which are then dispersed via air currents. Basidiospores are disseminated 3-6 hours after development through wind and/or water. [6] Under a laboratory setting, it has been shown to both spores need high humidity (50-90% RH) and no less than 5 hours of constant leaf wetness to germinate. [6] Reports have shown that basidiospores can travel over 700 meters by wind. [6] Spores of P. horiana are susceptible to desiccation at RH levels less than 90%. Due to this trait, chrysanthemum white rust is more likely to be spread via greenhouse contamination than by air, such as by human contact, improper sanitation techniques, or by keeping a constant high humidity to keep the spores viable. [7] Symptoms begin to occur 7-10 days after penetration into the epidermis. Shortly after leaf spots appear, telial clusters will begin to form on the stems, flowers, and abaxial leaf surfaces. This is where teliospores develop. These teliospores will produce basidiospores initiating a new cycle.
Similar to most rusts, CWR has 4 stages of infection: [8]
(i) Basidospore lands on susceptible plant. Development of germ tube and infection peg begins.
(ii) Formation of small vesicles inside the host epidermis.
(iii) Formation of elongated fungal vesicles inside the host epidermis
(iv) Formation of septate fungal vesicles with branching hyphae. Here the fungus will move to infect the rest of the plant.
Due to the popularity of chrysanthemums as an ornamental flower, there has been a large effort in preventing spread of CWR. In the United States, Phytosanitary Quarantine against CWR have been established. This means that all imports of known and/or suspected hosts of P. horiana must be inspected upon entering the country. [6] If CWR is detected through various methods of detection, the plants are immediately eradicated. While eradication prevents significant economic loss if the pathogen were to become established, U.S. growers who receive infected plants suffer substantial losses. From 1990 - 1999, CWR was present in California from plants imported from Asia and Mexico. The average cost of eradication ranged from $5,000 - $7,000 per site, depending on size of lot and success of first eradication attempt. The costs of eradication in 2014 were estimated to be $788 - $11,000 respectively. Direct and indirect financial losses from CWR infestations in the U.S. from 1992 - 1997 were estimated to be $2 million dollars. Establishment of CWR may have devastating consequences, it has been shown that Turkey and Poland experience anywhere from 80% to 100% crop loss, which is significant as they are the top producers of Chrysanthemums. [9]
Infection of CWR is systemic. By creating such a systemic infection, P. horiana has the potential to overwinter in plants as a form of protection. [10] The best form of prevention for CWR is to purchase plants, seeds, and materials from reputable sources to avoid P. horiana from ever entering the facility. [2] Proper sanitation of greenhouse or garden equipment and materials is also an important preventative measure.
Propiconazole has been shown to be an effective fungistatic. Propiconazole's mode of action blocks the biosynthesis of ergosterols, which is critical to the formation of cell walls of fungi. This stops the growth of the fungus, effectively preventing further infection and/or invasion of host tissues [11]
APHIS outlines management practices in three different categories for CWR. [12]
Rusts are fungal plant pathogens of the order Pucciniales causing plant fungal diseases.
Karnal bunt is a fungal disease of wheat, durum wheat, and triticale. The smut fungus Tilletia indica, a basidiomycete, invades the kernels and obtains nutrients from the endosperm, leaving behind waste products with a disagreeable odor that makes bunted kernels too unpalatable for use in flour or pasta. While Karnal bunt generally does not lead to devastating crop losses, it has the potential to dramatically decrease yield, and poses additional economic concerns through quarantines which limit the export of suspected infectious wheat products from certain areas, including the U.S. Several chemical control methods exist for Karnal bunt of wheat, but much work remains to be done in identifying resistant host varieties.
Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by K.C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.
Gymnosporangium juniperi-virginianae is a plant pathogen that causes cedar-apple rust. In virtually any location where apples or crabapples (Malus) and eastern red cedar coexist, cedar apple rust can be a destructive or disfiguring disease on both the apples and cedars. Apples, crabapples, and eastern red cedar are the most common hosts for this disease. Similar diseases can be found on quince and hawthorn and many species of juniper can substitute for the eastern red cedars.
Puccinia schedonnardii is a basidiomycete fungus that affects cotton. More commonly known as a “rust,” this pathogen typically affects cotton leaves, which can decrease the quality of the boll at time of harvest. As large percentages of cotton in the United States are resistant to various rust varieties, there is little economic importance to this disease. In places where rust is prevalent, however, growers could see up to a 50% reduction in yield due to rust infection.
Urocystis agropyri is a fungal plant pathogen that causes flag smut on wheat.
Puccinia asparagi is the causative agent of asparagus rust. It is an autoecious fungus, meaning that all stages of its life cycle – pycniospores, aeciospores, and teliospores – all develop upon the same host plant . Rust diseases are among the most destructive plant diseases, known to cause famine following destruction of grains, vegetables, and legumes. Asparagus rust occurs wherever the plant is grown and attacks asparagus plants during and after the cutting season. Asparagus spears are usually harvested before extensive rust symptoms appear. Symptoms are first noticeable on the growing shoots in early summer as light green, oval lesions, followed by tan blister spots and black, protruding blisters later in the season. The lesions are symptoms of Puccinia asparagi during early spring, mid-summer and later summer to fall, respectively. Severe rust infections stunt or kill young asparagus shoots, causing foliage to fall prematurely, and reduce the ability of the plant to store food reserves. The Puccinia asparagi fungus accomplishes this by rust lowering the amounts of root storage metabolites. The infected plant has reduced plant vigor and yield, often leading to death in severe cases. Most rust diseases have several stages, some of which may occur on different hosts; however, in asparagus rust all the life stages occur on asparagus. Because of this, many observers mistake the different stages of the Puccinia asparagi life cycle as the presence of different diseases. The effects of Puccinia asparagi are present worldwide wherever asparagus is being grown. Asparagus rust is a serious threat to the asparagus industry.
Puccinia coronata is a plant pathogen and causal agent of oat and barley crown rust. The pathogen occurs worldwide, infecting both wild and cultivated oats. Crown rust poses a threat to barley production, because the first infections in barley occur early in the season from local inoculum. Crown rusts have evolved many different physiological races within different species in response to host resistance. Each pathogenic race can attack a specific line of plants within the species typical host. For example, there are over 290 races of P. coronata. Crops with resistant phenotypes are often released, but within a few years virulent races have arisen and P. coronata can infect them.
Puccinia menthae is a fungal plant pathogen that causes rust on mint plants. It was originally found on the leaves of Mentha aquatica.
Uromyces viciae-fabae var. viciae-fabae is a plant pathogen commonly known as faba-bean rust. The rust is distinguished by the typical rust-like marks on the stem and leaves, causing defoliation and loss of photosynthetic surface along with reduction in yield. The disease is fungal and is autoecious meaning it has one plant host. The rust of faba beans is macrocyclic, or contains 5 spores during its life cycle.
Puccinia thaliae is the causal agent of canna rust, a fungal disease of Canna. Symptoms include yellow to tan spots on the plant's leaves and stems. Initial disease symptoms will result in scattered sori, eventually covering the entirety of the leaf with coalescing postulates. Both leaf surfaces, although more predominant on the underside (abaxial) of the leaf, will show yellow to brownish spore-producing these pustulate structures, and these are the signs of the disease. Spots on the upper leaf-surface coalesce and turn to brown-to-black as the disease progresses. Infection spots will become necrotic with time, with small holes developing in older leaves. These infected leaves eventually become dry and prematurely fall.
Austropuccinia is a monotypic genus of rust native to South America with the only species Austropuccinia psidii, commonly known as myrtle rust, guava rust, or ʻōhiʻa rust. It affects plants in the family Myrtaceae. It is a member of the fungal complex called the guava rust group. The spores 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.
Telium, plural telia, are structures produced by rust fungi as part of the reproductive cycle. They are typically yellow or orange drying to brown or black and are exclusively a mechanism for the release of teliospores which are released by wind or water to infect the alternate host in the rust life-cycle. The telial stage provides an overwintering strategy in the life cycle of a parasitic heteroecious fungus by producing teliospores; this occurs on cedar trees. A primary aecial stage is spent parasitizing a separate host plant which is a precursor in the life cycle of heteroecious fungi. Teliospores are released from the telia in the spring. The spores can spread many kilometers through the air, however most are spread near the host plant.
Pine-pine gall rust, also known as western gall rust, is a fungal disease of pine trees. It is caused by Endocronartium harknessii, an autoecious, endocyclic, rust fungus that grows in the vascular cambium of the host. The disease is found on pine trees with two or three needles, such as ponderosa pine, jack pine and scots pine. It is very similar to pine-oak gall rust, but its second host is another Pinus species. The fungal infection results in gall formation on branches or trunks of infected hosts. Gall formation is typically not detrimental to old trees, but has been known to kill younger, less stable saplings. Galls can vary from small growths on branch extremities to grapefruit-sized galls on trunks.
Spruce broom rust or yellow witches' broom rust is a fungal plant disease caused by the basidiomycete fungus known as Chrysomyxa arctostaphyli. It occurs exclusively in North America, with the most concentrated outbreaks occurring in northern Arizona and southern Colorado on blue and Engelmann spruce, as well as in Alaska on black and white spruce. This disease alternates its life cycle between two hosts, with the spruce serving as the primary host and bearberry serving as the secondary or alternate host. The name for the disease comes from the distinctive “witches broom”, commonly yellow in color, which forms on the spruce after young needles have been infected. Management must be carried out through physical or mechanical methods, such as the pruning of brooms or the removal of the secondary host from the area, because no chemical control measures have yet been determined to be economically effective. Generally, spruce broom rust is seen as a mostly cosmetic issue, and it is very rarely the direct cause of tree death; however, research has shown a reduction in overall productivity and health of infected trees, making it an important issue for logging and timber companies.
Chrysomyxa weirii, is a fungus that causes a disease, commonly known as Weir's cushion rust, of spruce trees. It is mostly a cosmetic problem, causing yellowish spotting and banding on spruce needles, but in some cases can cause severe premature defoliation. Weir’s cushion rust can also disfigure and reduce growth of spruce trees by targeting the tender needles of newly emerging shoots. This pathogen's spores are spread by wind and water splash and germinate to infect newly developing needles on the same spruce, or neighboring spruce trees. Unlike many other rust disease pathogens, C. weirii is autoecious, only infecting spruce trees. C. weirii is also microcyclic, producing only two of the five possible spore stages common in rust fungi. Trees affected by Weir's cushion rust usually have obvious symptoms, but if treated correctly, the disease can be managed.
Phakopsora euvitis is a rust fungus that causes disease of grape leaves. This rust fungus has been seen in regions including: Eastern Asia, Southern Asia, Southwestern Brazil, the Americas, and northern Australia. It is widely distributed in eastern and southern Asia but was first discovered on grapevines in Darwin, Australia in 2001 and was identified as Asian grapevine leaf rust by July 2007.
Puccinia sorghi, or common rust of maize, is a species of rust fungus that infects corn and species from the plant genus Oxalis.
Puccinia porri is a species of rust fungus that causes leek rust. It affects leek, garlic, onion, and chives, and usually appears as bright orange spots on infected plants.
Cronartium quercuum, also known as pine-oak gall rust is a fungal disease of pine and oak trees. Similar to pine-pine gall rust, this disease is found on pine trees but its second host is an oak tree rather than another pine.