| Peronospora trifoliorum | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Stramenopiles |
| Phylum: | Oomycota |
| Order: | Peronosporales |
| Family: | Peronosporaceae |
| Genus: | Peronospora |
| Species: | P. trifoliorum |
| Binomial name | |
| Peronospora trifoliorum de Bary, (1863) | |
| Synonyms | |
Peronospora fulva Contents | |
Peronospora trifoliorum, commonly known as downy mildew of alfalfa, is an oomycete plant pathogen infecting alfalfa.
Peronospora trifoliorum commonly infects numerous strains and varieties of alfalfa. On alfalfa, the primary symptoms of Peronospora trifoliorum are chlorotic leaf blotches that range from light green to yellow-green to gray-green; rolled or downturned leaves; and thickened, stunted stems ending in rosette-like growths. The main method of identifying the disease is by the moldy, downy growth on the underside of leaves that appears white, gray, or light purple as this is a diagnostic sign of downy mildew of alfalfa [1] (Davis, Frate, and Putnam, 2017). Only seedlings and young tissue are susceptible to infection which, with proper cultural controls, can limit the development and progression of the disease. There is also the potential for secondary infection, which can occur every five days during ideal conditions [2] (Goldberg, 2000).
Peronospora trifoliorum has been reported from Trifolium repens but it is uncommon. [3]
Peronospora trifoliorum prefers high humidity and moderate to warm temperatures. Peak spore production and infection occurs around 65 °F, though the pathogen is active in temperatures between 40 and 85 °F [2] (Goldberg, 2000). This means that Peronospora trifoliorum is primarily seen during cool, wet periods in the summer or warmer, dry periods in the spring and fall, and is usually found in the midwestern and southern United States [4] (UW-Extension, 2006). Since Peronospora trifoliorum is an oomycete, free moisture is needed for the disease to spread as well as to infect tissue [2] (Goldberg, 2000). The disease may overwinter in dead leaf debris, in crown buds, or in seeds [4] [5] (UW-Extension, 2006: Pacific Northwest Extension, 2019).
Growing resistant varieties of alfalfa is the most common form of control used against Peronospora trifoliorum [6] (Samac, Rhodes, and Lamp, 2015). A form of cultural control, resistant varieties limit the ability of the disease to infect and survive in the plant. Another cultural control is to cut the alfalfa crop early, which removes the infectious conidia [6] (Samac, Rhodes, and Lamp, 2015) while limiting the amount of foliage lost, removing the infected tissue, and decreasing the moisture and humidity through increased air circulation [5] (Pacific Northwest Extension, 2019). While cultural controls are believed to be the most effective form of control against Peronospora trifoliorum, the use of chemical control in the form of metalaxyl and mefenoxam is common and effective for alfalfa seedlings [6] (Samac, Rhodes, and Lamp, 2015). These systemic fungicides are used to suppress the infectious stage of the disease. Additionally, there have been attempts to find alternative methods to control Peronospora trifoliorum: a 2011 study used various biotic and abiotic compounds to test the use of bio- and chemical controls on different alfalfa diseases. The study found that to some degree, salicylic acid, potassium phosphite, neem oil, Bio-Arec, and Bio-Zaid betaine all protect against downy mildew and numerous other alfalfa diseases [7] (Mohamed Morsy, Fawzy Abdel-Monaim, and Mamoud Mazen, 2011).
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.
A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions often have a centre of necrosis. Symptoms can overlap across causal agents, however differing signs and symptoms of certain pathogens can lead to the diagnosis of the type of leaf spot disease. Prolonged wet and humid conditions promote leaf spot disease and most pathogens are spread by wind, splashing rain or irrigation that carry the disease to other leaves.
Grape black rot is a fungal disease caused by an ascomycetous fungus, Guignardia bidwellii, that attacks grape vines during hot and humid weather. “Grape black rot originated in eastern North America, but now occurs in portions of Europe, South America, and Asia. It can cause complete crop loss in warm, humid climates, but is virtually unknown in regions with arid summers.” The name comes from the black fringe that borders growing brown patches on the leaves. The disease also attacks other parts of the plant, “all green parts of the vine: the shoots, leaf and fruit stems, tendrils, and fruit. The most damaging effect is to the fruit”.
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.
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.
Pseudopeziza medicaginis is a fungal pathogen of alfalfa.
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.
Sclerophthora macrospora is a protist plant pathogen of the class Oomycota. It causes downy mildew on a vast number of cereal crops including oats, rice, maize, and wheat as well as varieties of turf grass. The common names of the diseases associated with Sclerophthora macrospora include "crazy top disease" on maize and yellow tuft disease on turf grass. The disease is present all over the world, but it is especially persistent in Europe.
Bremia lactucae is a plant pathogen. This microorganism causes a disease of lettuce denominated as downy mildew. Some other strains can be found on 36 genera of Asteraceae including Senecio and Sonchus. Experiments using sporangia from hosts do not infect lettuce and it is concluded that the fungus exists as a quantity of host-specific strains. Wild species, such as Lactuca serriola, or varieties of Lactuca can hold strains that infect lettuce, but these pathogens are not sufficiently common to seriously infect the plant.
Peronospora farinosa is a species name that has been widely applied to downy mildew on leaves of wild and cultivated Amaranthaceae: Amaranthus, Atriplex, Bassia, Beta, Chenopodium, Halimione, Salsola, Spinacia, etc. However, the species name has been taxonomically rejected as the original description contained reference to multiple species and could not unequivocally be attributed to a species of Peronospora. In the past, some of the species on important crop plants have been given names as formae speciales, notably f.sp. betae on sugar beet and f.sp. spinaciae on spinach. However, phylogentic reconstructions have revealed that these "forms" of Peronospora on different genera and their subdivisions, are distinct species, most of which already have previously published scientific names. Such host specialization possibly also exists with respect to the various wild amaranthaceous species given as hosts of P. farinosa.
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.
Podosphaera fuliginea is a plant pathogen that causes powdery mildew on cucurbits. Podosphaera fuliginea and Erysiphe cichoracearum are the two most commonly recorded fungi causing cucurbit powdery mildew. In the past, Erysiphe cichoracearum was considered to be the primary causal organism throughout most of the world. Today, Podosphaera fuliginea is more commonly reported.
Peronospora hyoscyami f.sp. tabacina is a plant pathogen infecting tobacco that causes blue mold. It is an oomycete 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. 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. Each year, Peronospora hyoscyami is introduced as blue mold as windblown spores from outside the region by infected transplants.
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.
Spring Black Stem is a common fungal, foliar disease caused by Ascochyta medicaginicola. Spring Black Stem is most commonly found in alfalfa, but also attacks certain clovers. The fungus survives in stubble from previous cuttings and spreads easily by rain splash, running water, and equipment. The disease is present in numerous alfalfa fields throughout the Northeast United States.
Clavibacter insidiosus is a species of Clavibacter. It causes bacterial wilt, with its most notable host being Medicago sativa (alfalfa). Other species in the Medicago genus are also known to be hosts such as Medicago falcata. Additionally, Lotus corniculatus, Melilotus alba, Onobrychis viciifolia, and Trifolium sp. are known hosts.
Peronospora aquilegiicola is a species of oomycete in the family Peronosporaceae, first described in 2019. It is a plant pathogen: it can infect susceptible plants belonging to the genus Aquilegia, causing the plant disease Aquilegia downy mildew, as well as plants belonging to the genus Semiaquilegia. Peronospora aquilegiicola is native to East Asia, however it has a widespread distribution in the United Kingdom, and has since been detected in the German states of Lower Saxony, North Rhine-Westphalia, and Bavaria.