Peronospora hyoscyami f.sp. tabacina | |
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Scientific classification | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Stramenopiles |
Phylum: | Oomycota |
Order: | Peronosporales |
Family: | Peronosporaceae |
Genus: | Peronospora |
Species: | P. hyoscyami |
Forma specialis: | P. h. f.sp. tabacina |
Trionomial name | |
Peronospora hyoscyami f.sp. tabacina Skalický, (1964) | |
Synonyms | |
Peronospora hyoscyami f.sp. tabacina is a plant pathogen infecting tobacco that causes blue mold. It is an oomycete (a fungus-like organism) that is highly destructive toward seed plants. It is very prevalent in humid farming zones, like the southeastern and Eastern U.S., Canada, and countries bordering the Caribbean. The disease was first identified in 1921 in Florida and Georgia. [1] Ten years later the same disease was found once again in the same region of the U.S. The disease began to spread into Virginia, Maryland, and North Carolina. A few years later, the disease reached Kentucky and Tennessee. In 1960, a blue mold epidemic spread in approximately eleven countries. There was approximately twenty five million dollars in losses which is nearly thirty percent of tobacco plants at the time. [1] Each year, Peronospora hyoscyami is introduced as blue mold as windblown spores from outside the region by infected transplants.
Tobacco plants with an upright position of small patches of the seed bed are typically early signs of blue mold. These leaves are usually 2–4 centimetres (0.79–1.57 in) in diameter, and normally spotted with yellow, gray, or a bluish mold in the lower surface. Younger plants that are up to four weeks old and are affected by the disease are easily killed by the oomycete. Older plants become deformed and dark, indicating that parts of the plant are dead. In more severe cases the stem and root become infected and turn to a brownish color. The observation of downy mold in the lower surface of the leaf is the most reliable symptom of blue mold. Downy mold carries thousands of small reproductive units called conidia [2] If conidia forms at different spots in the seedbed an outbreak is more than likely to occur. The symptoms usually take place before it's obvious. The symptoms evolve rapidly and are typically noticeable over night.
The oomycete frequently takes place when the vein of the leaves reaches vascular tissue of the stem, causing weakness and lodging. This infection is called "systemic infection". The infection causes a stunt in growth and the leaves become narrow and short. The vascular system of the plants usually turns brown in color and the weakened stalk usually causing the stalk to fall over.
The mould is highly weather sensitive. During the time when the weather is cool, wet, or overcast the disease can evolve in a greenhouse or field. The disease spreads rapidly because of the pathogen. The rate of continental spread is based on the potential for high levels of inoculum and effective wind spores. When the weather is clear, dry, and hot the disease usually stops spreading and more than likely stops all together.
A major way blue mold spreads is by the distribution of infected transplants. Even though they may appear to be healthy, they can still harbor the infection. Farmers generally buy transplants from other growers, and take risks of possibly buying diseased plants. If these plants are diseased they are risking their other plants' getting blue mold.
A plant may remain symptom-free for five to seven days, before the first appearance of disease. When weather conditions are reasonable, a second set of spores evolves in seven to ten days. If these plants are not chemically treated, the cycle may be repeated several times during the growing season. This can cause a huge epidemic causing many plants to be infected. Blue mold has been found to appear three times each week from March to August. [3]
After the germination of conidia, the initial penetration of the host depends on the formation of appressoria near the stomata. This is largely due to a response of P. hyoscyami f.sp. tabacina to topographical cues of the host such as stomatal openings. [4] Upon entry of an infection peg through a stomatal opening, hyphae grow and develop between plant cells. When hyphae reach a photosynthetic mesophyll cell a peg penetrates the cell and establishes a haustorium which the oomycete uses to absorb the necessary nutrients for its own growth. [5] Through the establishment of haustoria the pathogen develops an intimate relationship with the host. In doing so P. hyoscyami f.sp. tabacina efficiently redirects the nutrients of the host and delivers effector proteins into the host cytoplasm that suppress the host defense response. [5]
The activation of systemic acquired resistance (SAR) has shown to be an effective management strategy for P. hyoscyami f.sp. tabacina. It has been documented that an accumulation of pathogenesis-related proteins (PR proteins) and increased activities of peroxidase, β-1, 3-glucanase, and chitinases have been shown to be associated with induced resistance in tobacco to P. hyoscyami f.sp. tabacina. [6] In addition, PR proteins have been shown to have antifungal activities in vitro and thus are thought to be a key component in the resistance of tobacco to blue mold. [6] Of the tobacco defense responses to P. hyoscyami f.sp. tabacina SAR has been characterized as the best activated response to blue mold.
In addition to SAR, tobacco plants have been found to secrete β–ionone and T-phylloplanin which both inhibit the sporulation and growth of P. hyoscyami f.sp. tabacina. [5] T-phylloplanin proteins are secreted by tall glandular trichomes on the aerial surface of tobacco leaves and may be a novel leaf surface defense molecule in tobacco. [7]
The disease is getting harder to manage and is becoming a problem. [8] The way to prevent the disease is to manage crops and protect plants with fungicides when they are most vulnerable while taking control of the crops early on. Making the environment less favorable for the pathogen to survive and protect the tobacco will prevent its growth and spread and it is imperative to always keep the pathogen out of tobacco and the area for as long as possible. Farmers are also always able to grow their own plants rather than purchase them from others which should reduce the chance of planting diseased plants.
Fusarium wilt is a common vascular wilt fungal disease, exhibiting symptoms similar to Verticillium wilt. This disease has been investigated extensively since the early years of this century. The pathogen that causes Fusarium wilt is Fusarium oxysporum. The species is further divided into formae speciales based on host plant.
Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to the Peronosporaceae family. In commercial agriculture, they are a particular problem for growers of crucifers, grapes and vegetables that grow on vines. The prime example is Peronospora farinosa featured in NCBI-Taxonomy and HYP3. This pathogen does not produce survival structures in the northern states of the United States, and overwinters as live mildew colonies in Gulf Coast states. It progresses northward with cucurbit production each spring. Yield loss associated with downy mildew is most likely related to soft rots that occur after plant canopies collapse and sunburn occurs on fruit. Cucurbit downy mildew only affects leaves of cucurbit plants.
White onion or Allium cepa are a cultivar of dry onion which have a distinct light and mild flavour profile. Much like red onions, they have a high sugar and low sulphur content, and thus have a relatively short shelf life. White onions are used in a variety of dishes, such as those of Mexican and European origin. Their uses in dishes often relate to their mild nature, they are often included in dishes to provide a light, fresh and sour taste to dishes and are often added uncooked to dishes such as salads.
Peronosporaceae are a family of water moulds that contains 21 genera, comprising more than 600 species. Most of them are called downy mildews.
This is a glossary of some of the terms used in phytopathology.
Hyaloperonospora is a genus of oomycete, obligate, plant pathogens that was originally considered to be part of Peronospora. Species in this group produce a disease called downy mildew and can infect many important crops. From the 19 downy mildew producing genera, Hyaloperonospora has been grouped with Perofascia in the brassicolous downy mildews. In the group of downy mildews, Hyaloperonospora is the third biggest genus. The most famous species in the genus is the Hyaloperonospora parasitica, or also known as Hyaloperonospora arabidopsis. This species has become a model organism from its ability to infect the model plant Arabidopsis thaliana. It is used to study plant-pathogen interactions, and is currently the only Hyaloperonospora species that has an assembled genome.
Hyaloperonospora parasitica is an oomycete from the family Peronosporaceae. It has been considered for a long time to cause downy mildew of a variety of species within the Brassicaceae, on which the disease can cause economically important damage by killing seedlings or affecting the quality of produce intended for freezing. Hyaloperonospora parasitica causes downy mildew on a wide range of many different plants. It belongs to the Kingdom Chromista, the phylum Oomycota, and the family Peronosporaceae. The former name for H. parasitica was Peronospora parasitica until it was reclassified and put in the genus Hyaloperonospora. It is an especially vicious disease on crops of the family Brassicaceae. It is most famous for being a model pathogen of Arabidopsis thaliana which is a model organism used for experimental purposes. Accordingly, the former Hyaloperonospora parasitica has been split into a large number of species. For instance, the taxonomically correct name of the parasite of the well-known model organism Arabidopsis thaliana is Hyaloperonospora arabidopsidis, not H. parasitica, whereas the pathogen of Brassica has to be called Hyaloperonospora brassicae.
Phytophthora nicotianae or black shank is an oomycete belonging to the order Peronosporales and family Peronosporaceae.
Peronospora sparsa is an oomycete plant pathogen that causes downy mildew in berry producing plants; especially in the genus's Rubus and Rosa. Downy mildew plant pathogens are often host specific and cause problems in cloudberries, blackberries, boysenberries, strawberries, and arctic bramble. Since they are host specific, Peronospora sparsa will not cause downy mildew in grapes because a different plant pathogen causes downy mildew in grapes; Plasmopara viticola. Although it depends on the cultivar, symptoms do not normally start until later stages of disease and can look different on different plants. The most common symptoms include red lesions in the veins of leaves, with dry and deformed berries.
Peronospora trifoliorum, commonly known as downy mildew of alfalfa, is an oomycete plant pathogen infecting alfalfa.
Albugo is a genus of plant-parasitic oomycetes. Those are not true fungi (Eumycota), although many discussions of this organism still treat it as a fungus. The taxonomy of this genus is incomplete, but several species are plant pathogens. Albugo is one of three genera currently described in the family Albuginaceae, the taxonomy of many species is still in flux.
Peronospora manshurica is a plant pathogen. It is a widespread disease on the leaves of soybeans and other crop plants. The fungi is commonly referred to as downy mildew, "leafspot", or "leaf-spot".
Plasmopara halstedii is a plant pathogen infecting sunflowers. The species is one of many pathogens commonly referred to as downy mildew. P. halstedii originated in North America.
Plasmopara viticola, the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition release zoospores. Zoospores are splashed by rain into the canopy, where they swim to and infect through stomata. After 7–10 days, yellow lesions appear on foliage. During favorable weather the lesions sporulate and new secondary infections occur.
Pseudoperonospora humuli is a plant pathogen that causes downy mildew on hops.
Peronosclerospora sorghi is a plant pathogen. It is the causal agent of sorghum downy mildew. The pathogen is a fungal-like protist in the oomycota, or water mold, class. Peronosclerospora sorghi infects susceptible plants though sexual oospores, which survive in the soil, and asexual sporangia which are disseminated by wind. Symptoms of sorghum downy mildew include chlorosis, shredding of leaves, and death. Peronosclerospora sorghi infects maize and sorghum around the world, but causes the most severe yield reductions in Africa. The disease is controlled mainly through genetic resistance, chemical control, crop rotation, and strategic timing of planting.
Peronospora is a genus of oomycetes that are obligate plant pathogens of many eudicots. Most species in this group produce a downy mildew disease, which can cause severe damage to many different cultivated crops, as well as wild and ornamental plants. There are 19 genera that produce downy mildew, and Peronospora has been placed alongside Pseudoperonospora in the group of downy mildews with coloured conidia. Peronospora has far more species than any other genus of the downy mildews. However, many species have been moved from this genus to be reclassified to other or new genera. Among these was the most famous Peronospora species, formerly known as Peronospora parasitica, and now known as Hyaloperonospora parasitica. Now, the Peronospora species of most importance is likely the Peronospora tabacina. Peronospora tabacina causes blue mold on tobacco plants and can severely reduce yields of this economically important crop to the point where it has been classified as a bioweapon.
Peronospora destructor is a plant pathogen. It causes downy mildew on leaves of cultivated and wild Allium. Allium cepa is most often affected, while Allium schoenoprasum (chives) and Allium porrum (leek) are only occasionally affected.
Commonly known as Philippine downy mildew, this disease is caused by the species Peronosclerospora philippinensis of the fungal-like protist class Oomycetes, which also has members such as water molds and Phytophthora infestans, which caused the potato blight that led to the Great Irish famine.
Cladosporium fulvum is an Ascomycete called Passalora fulva, a non-obligate pathogen that causes the disease on tomatoes known as the tomato leaf mold. P. fulva only attacks tomato plants, especially the foliage, and it is a common disease in greenhouses, but can also occur in the field. The pathogen is likely to grow in humid and cool conditions. In greenhouses, this disease causes big problems during the fall, in the early winter and spring, due to the high relative humidity of air and the temperature, that are propitious for the leaf mold development. This disease was first described in the North Carolina, by Mordecai Cubitt Cooke (1883), on cultivated tomato, although it is originally from South and Central America. The causal fungus of tomato leaf mold may also be referred to as Cladosporium fulvum, a former name.