| Erysiphe alphitoides | |
|---|---|
 | |
| Powdery oak mildew on Quercus robur | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Leotiomycetes |
| Order: | Erysiphales |
| Family: | Erysiphaceae |
| Genus: | Erysiphe |
| Species: | E. alphitoides |
| Binomial name | |
| Erysiphe alphitoides (Griffon & Maubl.) U. Braun & S. Takam. | |
| Synonyms | |
Microsphaera alphitoidesGriffon & Maubl. | |
Erysiphe alphitoides is a species of fungus which causes powdery mildew on oak trees.
Today oak powdery mildew is one of the most common diseases in European forests but it is thought to not always have been present in these forests. The first reports of the disease were made in Paris and other regions of France, Spain, Luxembourg and the Netherlands in 1907. By 1908 the disease had spread into many other European countries, becoming an epidemic. By 1909 it had reached Russia and Turkey, followed by Brazil in 1912 and soon after was distributed around the world. The sudden outbreak of the disease puzzled mycologists as they were unsure about the origin of the pathogen. Its anamorph was easily distinguished from Phyllactinia guttata which had previously been reported to cause powdery mildew on oaks in Europe at low intensity. It did however share morphological similarities with Oïdium quercinum , Calocladia penicillata and Microsphaera penicillata which had previously been reported to cause powdery mildew on oaks in Europe. The sudden appearance and high incidence of the disease made it unlikely that it was caused by any of these species however and instead some authors hypothesised that it was caused by the introduction of a new species from outside Europe. Powdery mildew had already been reported from North America so it was thought that the new disease could have been imported on American oaks into Europe. The absence of the disease on American red oaks growing in France however, made this unlikely. Four years after the initial outbreak, a teleomorph was found in south-east France which Arnaud and Fox identified as an American species, Microsphaera quercina (now included in Microsphaera alni ). A detailed morphological study by Griffon and Maublanc in 1912 suggested that the species was different from all previously described species and proposed the name of Microsphaera alphitoides, referring to the floury appearance of the abundant white sporulation. This identification remained controversial until the 1940s. The origin of the disease was still uncertain however, in 1927, Raymond suggested that the disease may have been caused by a fungus identified in 1877 in Portugal that had been imported from Portuguese colonies. In 1980, Boesewinkel demonstrated that the same species was responsible for powdery mildew on Quercus robur and on a mango species from New Zealand, supporting the hypothesis that the fungus had shifted its host. [1]
Recently, molecular biology has provided new tools for identifying species and elucidating their relatedness. A study of ribosomal DNA from 33 samples of oak powdery mildew from Europe showed that E. alphitoides contains identical sequences to Oïdium mangiferae , a major disease of mango in several tropical regions and Oïdium heveae , an economically important pathogen of the para rubber tree. These results support the findings of Boesewinkel and suggest that E. alphitoides and O. mangiferae could be conspecific. The origin of the species is still uncertain but Mougou et al. (2008) reported that E. alphitoides likely originated from the tropics and expanded its range to oak after being introduced to Europe. [1]
Only young developing leaves are susceptible to colonisation by E. alphitoides. It only induces necrosis when infection occurs very early during leaf development. Because the pathogen develops late in spring, after the first leaves of oak seedlings have developed, it is more prevalent on the second and third flushes of leaves that develop in July and August. This habit also reduces the severity of the disease on mature trees. [2]
The disease can be very severe on Quercus robur and Quercus petraea in Europe, particularly on young trees. In mature trees the disease is generally less damaging, but in combination with other factors such as defoliation by insects can contribute to tree decline. A study of the effects of E. alphitoides on Quercus robur found it decreased stomatal conductance by 15–30%, did not affect the leaf mass to area ratio, decreased the nitrogen content of the leaf and increased dark respiration. Carbon fixation was also reduced in infected leaves by about 40–50% in fully infected leaves and those that were heavily infected were shed earlier than those not infected. Despite it affecting the ability of leaves to photosynthesise, the effect is low and this is thought to explain why the disease has only moderate consequences for tree health despite heavy infections. [2] Because the infection makes the plants less shade tolerant, it may lead to the death of seedlings growing in shade. [3]
An oak is a hardwood tree or shrub in the genus Quercus of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne in a cup. The genus is widely distributed in the Northern Hemisphere; it includes some 500 species, both deciduous and evergreen. Fossil oaks date back to the Middle Eocene. Molecular phylogeny shows that the genus is divided into Old World and New World clades, but many oak species hybridise freely, making the genus's history difficult to resolve.
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.
Uncinula necator is a fungus that causes powdery mildew of grape. It is a common pathogen of Vitis species, including the wine grape, Vitis vinifera. The fungus is believed to have originated in North America. European varieties of Vitis vinifera are more or less susceptible to this fungus. Uncinula necator infects all green tissue on the grapevine, including leaves and young berries. It can cause crop loss and poor wine quality if untreated. The sexual stage of this pathogen requires free moisture to release ascospores from its cleistothecia in the spring. However, free moisture is not needed for secondary spread via conidia; high atmospheric humidity is sufficient. Its anamorph is called Oidium tuckeri.
Oidium is a genus of Deuteromycetes, where traditionally most anamorphs of the order Erysiphales are included. Most of them are plant pathogens causing different forms of powdery mildew, for example:
Erysiphales are an order of ascomycete fungi. The order contains one family, Erysiphaceae. Many of them cause plant diseases called powdery mildew.
Blumeria graminis is a fungus that causes powdery mildew on grasses, including cereals. It is the only species in the genus Blumeria. It has also been called Erysiphe graminis and Oidium monilioides or Oidium tritici.
Powdery mildew is a fungal disease of barley caused by Blumeria graminis f. sp. hordei. The disease has a worldwide distribution and is most damaging in cool, wet climates. The host range of the form species hordei is restricted to barley and other Hordeum species.
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.
Erysiphe betae is a fungal plant pathogen. It is a form of powdery mildew that can affect crops of sugar beet, that could cause up to a 30% yield loss. The fungus occurs worldwide in all regions where sugar beet is grown and it also infects other edible crops, e.g. beetroot.
Podosphaera leucotricha is a plant pathogen that can cause powdery mildew of apples and pears.
Brasiliomyces malachrae is a species of fungus in the family Erysiphaceae. It is a plant pathogen that grows on Gossypium, Lavatera assurgentiflora, Malachra capitata, Malvastrum coromandelianum, and species of Malvaceae. It is found in South America.
Erysiphe heraclei is a plant pathogen that causes powdery mildew on several species including dill, carrot and parsley.
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.
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.
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.
Ampelomyces quisqualis is an anamorphic fungus that is a hyperparasite of powdery mildews. This parasitism reduces growth and may eventually kill the mildew. These mycoparasites can live up to 21 days on mildew-free host plant surfaces, attacking powdery mildew structures as soon as they appear. A. quisqualis is used as the active ingredient in a commercial fungicide.
Phytophthora quercina is a papillate homothallic soil-borne plant pathogen causing root rot of oak tree species in Europe. It is associated with necrotic fine roots.
Powdery mildew of lilac, or Erysiphe syringae is a fungal pathogen of lilacs.
Erysiphe azerbaijanica is a species of powdery mildew in the family Erysiphaceae. It is found in Azerbaijan, where it grows on the leaves of sweet chestnut trees.
Oak regeneration failure is a woodland phenomenon whereby insufficient seedling- and sapling-sized oak (Quercus) trees are recruited into the canopy to replace dead mature oaks. The result is a local population decline in oaks while other more shade-tolerant trees such as maple, lime, and ash may become more prominent. Oak regeneration failure has been observed across Eastern and Midwestern forests in the United States as well as in Europe.