| Leptosphaeria lindquistii | |
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| Species: | L. lindquistii |
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| Leptosphaeria lindquistii Frezzi, (1968) | |
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Phoma macdonaldiiBoerema, (1970) Contents | |
Phoma macdonaldii (teleomorph: Leptosphaeria lindquistii) is a plant pathogenic fungus that is a major causal force for the disease Phoma Black Stem.
The primary host plant is a sunflower plant (Helianthus annuus L.) – a major oilseed crop. The plant has deep roots that prevent erosion linked damage, making for a highly adaptable crop. Helianthus is a large genus with 51 species, one of the largest plant families on Earth with a genome 3.5 billion letters long. Gene sequencing and current technological methods can be utilized to analyze the genome and potentially select for genes that may confer desirable traits such as disease resistance. [1] To date, sunflower genotypes with partial resistance to P. macdonaldii have been described, but no fully resistant genotypes are available.
Phoma black stem is one of the most common diseases affecting the sunflower plant in North and South America. Phoma Black stem has also been known to occur in regions of Europe and Asia. In most cases, small lesions are produced, however if the infection is caused early on in the season, the sunflower plant may become severely diseased. Phoma black stem typically results in a 10-30% yield loss in the United States. In the case of a more severe infection, which usually occurs if the infection takes root at the beginning of the growing season, smaller heads may be produced, which reduces seed yield and oil percentage to a higher degree. [2]
Many symptoms caused by the fungal pathogen can be observed post bloom or after flowering. The main identifying symptom is the production of black lesions along the stem which are usually 2 inches in length and 1 inch in height. Lesions are distinguishable from other similar diseases because they form at the petioles of the stem and are black in color. [3] Lesions can also develop on the leaves, flower bracts, back of the head, and crown or base of stalk. Leaf wilting will also be noticeable. Small, fruiting bodies (pycnidia) are produced on the stem. These structures are spore bearing and can be observed with a magnifying or other hand lens on the lesions themselves. [4] Phoma black stem can be distinguished from other diseases due to its black lesions and lack of lodging. The fungus also produces colonies that are gray-white in color and have a white mycelium that may resemble cotton. [2]
Phoma black stem infections can occur throughout the growing season, although the lesions are more noticeable during late summer. Phoma macdonaldii can be transmitted via rain splash or by stem weevil feeding. The fungus can either penetrate into the plants either directly via enzymatic degradation of the plant cell wall or by mechanical pressure. [5] The fungus overwinters in infected crop debris either inside of pycnidia or as mycelium. [6] Primary inoculum originates from overwintering fungal structures (perithecia, pycnidia, and mycelia). [5] Conidia (from pycnidia) and ascospores (from perithecia) are released from fruiting structures and subsequently dispersed by rain and wind. Disease development is favorable in wet conditions during flowering stage and immediately after flowering stage. Stem weevils transmit the fungus directly by their feeding behaviors. [2]
A supremely effective control measure has not been identified. However, a 4-year rotation to other crops minimizes Phoma fungus in the soil. Late seeding to delay the regular time schedule to adult plant formation has proven successful in reducing disease severity. [2] It's recommended to remove plant debris from the field after harvesting to prevent infections in the following season.
Nitrogen content in soil has been seen to affect pathogen ability to infect. The micro climate resulting from dense canopies, induced by high N fertilization, may have constituted a major climatic parameter in disease epidemiology and successful infection (within sunflower plants). [7]
A 2010 study attempted to identify the most crucial agronomic elements of the sunflower premature ripening disease induced by P. macdonaldii in south-western France. The combination of high nitrogen fertilization and heavy rain conditions resulted in high disease pressure every year. Additionally, differences in susceptibility of sunflower cultivars could be exploited as an additive research venue instead of sole focus developing fungicide protection. Cropping of resistant varieties in combination with appropriate nutrition and other cultural practices could reduce inoculum pressure and pre mature ripening. Promising cultivars should therefore be screened at high N supplies and under water-limited conditions, a procedure which could be used in resistance tests. [8]
The resulting symptoms of Phoma black stem are again stunted plants with thin stems, smaller heads, blackened pith. Yield losses of 30% may occur in Europe [9] and up to 70% losses have been reported in USA. [10]
In China, the first case was reported in Xinjiang in 2008 - it was believed to be introduced as a result of hybrid sunflower seeds being imported from abroad. The Chinese government included this fungus into its quarantine pathogen list in 2010. During 2010 and 2011 growing seasons, surveys were conducted in 37 commercial farms in five areas (Xinjiang, Inner Mongolia, Ningxia, Hebei, and Beijing). A total of 185 suspicious samples of sunflower black stem disease were collected and all were found from imported hybrid seed fields. The presence of P. macdonaldii was confirmed with pathogenic tests. [11]
In regards to host - pathogen interactions: to date, no genotypes (of sunflower plant) have been identified to be completely resistant but some lines are more resistant than others. The inheritance of sunflower resistance to Phoma black stem was reported to be quantitative under additive and dominant effects. It has been recognized that significant differences in pathogenicity exist among different Phoma macdonaldii isolates on the same genetic material. In one study, part of the partial resistance in partially compatible interactions was shown to have a possible association with the expression of genes encoding PAL2 and a thaumatin-like protein, which showed significantly different expression levels between compatible and partially compatible interactions in both sunflower lines contaminated with Phoma macdonaldii isolates. [12]
Leptosphaeria maculans is a fungal pathogen of the phylum Ascomycota that is the causal agent of blackleg disease on Brassica crops. Its genome has been sequenced, and L. maculans is a well-studied model phytopathogenic fungus. Symptoms of blackleg generally include basal stem cankers, small grey lesions on leaves, and root rot. The major yield loss is due to stem canker. The fungus is dispersed by the wind as ascospores or rain splash in the case of the conidia. L. maculans grows best in wet conditions and a temperature range of 5–20 degrees Celsius. Rotation of crops, removal of stubble, application of fungicide, and crop resistance are all used to manage blackleg. The fungus is an important pathogen of Brassica napus (canola) crops.
Ascochyta tarda or Phoma tarda is a fungal plant pathogen that causes dieback and leafspot on coffee and was first observed in Ethiopia in 1954. It poses a potentially serious threat to coffee crops, but climate change may reduce the prevalence of environmental conditions favorable to its spread.
Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.
Leptosphaeria sacchari is a plant pathogenic fungus which causes a disease called ring spot on Saccharum officinarum. This species was originally described in 1890 by Kruger and in 1892 by Van Breda de Haan after it was discovered in the Dominican Republic. L. sacchari is the applied name, whereas Epicoccum sorghinum is the accepted name.
Diaporthe helianthi is a fungal pathogen that causes Phomopsis stem canker of sunflowers. In sunflowers, Phomopsis helianthi is the causative agent behind stem canker. Its primary symptom is the production of large canker lesions on the stems of sunflower plants. These lesions can eventually lead to lodging and plant death. This disease has been shown to be particularly devastating in southern and eastern regions of Europe, although it can also be found in the United States and Australia. While cultural control practices are the primary method of controlling for Stem Canker, there have been a few resistant cultivars developed in regions of Europe where the disease is most severe.
Ascochyta is a genus of ascomycete fungi, containing several species that are pathogenic to plants, particularly cereal crops. The taxonomy of this genus is still incomplete. The genus was first described in 1830 by Marie-Anne Libert, who regarded the spores as minute asci and the cell contents as spherical spores. Numerous revisions to the members of the genus and its description were made for the next several years. Species that are plant pathogenic on cereals include, A. hordei, A. graminea, A. sorghi, A. tritici. Symptoms are usually elliptical spots that are initially chlorotic and later become a necrotic brown. Management includes fungicide applications and sanitation of diseased plant tissue debris.
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.
Stegophora ulmea is a foliar disease of elms commonly known as black spot of elm, twig blight, and elm leaf scab. It is characterized by yellow spots that become black spots on the leaves. The pathogen is an ascomycete fungus native to North America. Stegophora ulmea is its teleomorph name. It has two anamorph names, Gloeosporium ulmicolom referring to the macroconidia stage and Cylindrosporella ulmea referring to the microconidia stage. This pathogen was formerly known as Gnomonia ulmea.
Ascochyta pisi is a fungal plant pathogen that causes ascochyta blight on pea, causing lesions of stems, leaves, and pods. These same symptoms can also be caused by Ascochyta pinodes, and the two fungi are not easily distinguishable.
Didymella bryoniae, syn. Mycosphaerella melonis, is an ascomycete fungal plant pathogen that causes gummy stem blight on the family Cucurbitaceae, which includes cantaloupe, cucumber, muskmelon and watermelon plants. The anamorph/asexual stage for this fungus is called Phoma cucurbitacearum. When this pathogen infects the fruit of cucurbits it is called black rot.
Pyrenochaeta terrestris is a fungal plant pathogen that infects maize, sweet potatoes, and strawberries. This plant pathogen causes a disease in onion that is commonly called pink root. P. terrestris is also known to infect shallots, garlic, leeks, chives, cantaloupe, carrots, cauliflower, cowpea, cucumbers, eggplants, lima beans, millet, oats, peas, peppers, potatoes, spinach, sugarcane, and tomatoes.
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.
Alternaria helianthi is a fungal plant pathogen causing a disease in sunflowers known as Alternaria blight of sunflower.
Calophoma clematidina is a fungal plant pathogen and the most common cause of the disease clematis wilt affecting large-flowered varieties of Clematis. Symptoms of infection include leaf spotting, wilting of leaves, stems or the whole plant and internal blackening of the stem, often at soil level. Infected plants growing in containers may also develop root rot.
Raspberry spur blight is caused by the fungus Didymella applanata. This plant pathogen is more problematic on red raspberries (Rubus idaeus) than on black or purple raspberries. The fungus infects the leaves first and then spreads to the cane. It causes necrotic spots on the cane near the base of the petiole attachment. Raspberry spur blight can cause a significant reduction in yield, fruit blight, premature leaf drop, and weak bud and cane growth. The magnitude of damage is not clearly understood in the United States, however, studies from Scotland suggest damage to the cane itself is limited. The disease has minor economic impacts by reducing leaves in the summer or killing buds. Major economic damage occurs if the disease manages to kill the entire cane. In the United States, this disease is found in Oregon and Washington.
Ascochyta blights occur throughout the world and can be of significant economic importance. Three fungi contribute to the ascochyta blight disease complex of pea. Ascochyta pinodes causes Mycosphaerella blight. Ascochyta pinodella causes Ascochyta foot rot, and Ascochyta pisi causes Ascochyta blight and pod spot. Of the three fungi, Ascochyta pinodes is of the most importance. These diseases are conducive under wet and humid conditions and can cause a yield loss of up to fifty percent if left uncontrolled. The best method to control ascochyta blights of pea is to reduce the amount of primary inoculum through sanitation, crop-rotation, and altering the sowing date. Other methods—chemical control, biological control, and development of resistant varieties—may also be used to effectively control ascochyta diseases.
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.
Raspberry leaf spot is a plant disease caused by Sphaerulina rubi, an ascomycete fungus. Early symptoms of infection are dark green spots on young leaves. As the disease progresses, these spots turn tan or gray in color. Disease management strategies for raspberry leaf spots include the use of genetically resistant raspberry plant varieties, chemical fungicide sprays, and cultural practices such as pruning and thinning out canes.
Gummy stem blight is a cucurbit-rot disease caused by the fungal plant pathogen Didymella bryoniae. Gummy stem blight can affect a host at any stage of growth in its development and affects all parts of the host including leaves, stems and fruits. Symptoms generally consist of circular dark tan lesions that blight the leaf, water soaked leaves, stem cankers, and gummy brown ooze that exudes from cankers, giving it the name gummy stem blight. Gummy stem blight reduces yields of edible cucurbits by devastating the vines and leaves and rotting the fruits. There are various methods to control gummy stem blight, including use of treated seed, crop rotation, using preventative fungicides, eradication of diseased material, and deep plowing previous debris.
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