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.
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.
Erysiphe cruciferarum is a plant pathogen of the family Erysiphaceae, which causes the main powdery mildew of crucifers, including on Brassica crops, such as cauliflower, cabbage, broccoli, and Brussels sprouts. E. cruciferarum is distributed worldwide, and is of particular concentration in continental Europe and the Indian subcontinent. E. cruciferarum is an ascomycete fungus that has both sexual and asexual stages. It is also an obligate parasite that appears to have host specificity; for example, isolates from turnip will not infect Brussels sprout, and vice versa. While being a part of the family Erysiphaceae, it belongs to those members in which the conidia are formed singly and whose haustoria are multilobed.
Leveillula taurica is an obligate fungal pathogen, from the phylum Ascomycota, which causes powdery mildew on onion. This disease prefers warm, dry environments. It is rare in the United States, and is currently restricted to western states. Globally, it is also a minor problem with limited occurrences in the Middle East, Europe, and South America. L. taurica causes powdery mildew of onions, but is also known to infect other allium, solanaceous, and cucurbit species. The disease has appeared in parts of the Middle East, the Mediterranean, and South and North America. Currently, it is not a cause for major concern in the U.S. and throughout the world, as its geographic extent is sparse. In addition, it is relatively easy to control through basic sanitation and reducing water stress.
Peronospora trifoliorum, commonly known as downy mildew of alfalfa, is an oomycete plant pathogen infecting alfalfa.
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.
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.
Oidium mangiferae is a plant pathogen that infects mango trees causing powdery mildew. Powdery mildew of mango is an Ascomycete pathogen of the Erysiphales family that was initially described by Berthet in 1914, using samples collected from Brazil. O. mangiferae is found in all areas where mangoes have been raised long term, but is particularly widespread in India where both the host and the pathogen are native. Currently no teleomorph stage has been identified, but due to certain morphological characteristics it has been suggested that O. mangiferae belongs in the Erysiphe polygony group. Mango is the only known host for this pathogen, though O. mangiferae appears to be identical to fungi responsible for powdery mildew diseases on various other plant species, particularly oak, though some differences may be observed. In particular, the number of cells in conidiophores varies from 2 on mango to 3-5 on oak. O. mangiferae has been known to infect oak leaves in the laboratory, however due to the lack of a known teleomorph stage O. mangiferae is still considered to only be a pathogen of mango. Recent analysis of its ribosomal DNA suggests it is conspecific with Erysiphe alphitoides, the causative agent of powdery mildew in European oaks.
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.
Cercospora sojina is a fungal plant pathogen which causes frogeye leaf spot of soybeans. Frog eye leaf spot is a major disease on soybeans in the southern U.S. and has recently started to expand into the northern U.S. where soybeans are grown. The disease is also found in other soybean production areas of the world.
Botrytis fabae is a plant pathogen, a fungus that causes chocolate spot disease of broad or fava bean plants, Vicia faba. It was described scientifically by Mexican-born Galician microbiologist Juan Rodríguez Sardiña in 1929.
Pseudoperonospora cubensis is a species of water mould known for causing downy mildew on cucurbits such as cantaloupe, cucumber, pumpkin, squash and watermelon. This water mould is an important pathogen of all these crops, especially in areas with high humidity and rainfall, such as the eastern United States. In most years the disease is an annual, late-season problem on squash and pumpkin in the eastern and central United States, however, since 2004 it has become one of the most important diseases in cucumber production. Considered a highly destructive foliar disease of cucurbits, successful breeding in the mid-twentieth century provided adequate control of downy mildew in cucumber without the use of fungicides. The resurgence in virulence has caused growers great concern and substantial economic losses, while downy mildew in other cucurbit crops continues to be a yearly hindrance.
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 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.
This article summarizes different crops, what common fungal problems they have, and how fungicide should be used in order to mitigate damage and crop loss. This page also covers how specific fungal infections affect crops present in the United States.
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.
Peronosclerospora philippinensis, commonly known as Philippine downy mildew, is a species of mildew of the fungal-like protist class Oomycetes. It is related to Phytophthora infestans, which caused the potato blight that led to the Great Irish famine.
Alternaria black spot of canola or grey leaf spot is an ascomycete fungal disease caused by a group of pathogens including: Alternaria brassicae, A. alternata and A. raphani. This pathogen is characterized by dark, sunken lesions of various size on all parts of the plant, including the leaves, stem, and pods. Its primary economic host is canola. In its early stages it only affects the plants slightly by reducing photosynthesis, however as the plant matures it can cause damage to the seeds and more, reducing oil yield as well.
