| Phytophthora nicotianae | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Stramenopiles |
| Phylum: | Oomycota |
| Order: | Peronosporales |
| Family: | Peronosporaceae |
| Genus: | Phytophthora |
| Species: | P. nicotianae |
| Binomial name | |
| Phytophthora nicotianae Breda de Haan, (1896) [1] | |
| Varieties [2] | |
| Synonyms | |
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Phytophthora nicotianae or black shank is an oomycete belonging to the order Peronosporales and family Peronosporaceae.
Phytophthora nicotianae has a broad host range comprising 255 genera from 90 families. [4] Hosts include tobacco, onion, tomato, ornamentals, cotton, pepper, and citrus plants. This pathogen can cause root rot, crown rot, fruit rot, leaf infection, and stem infection. Root rot symptoms are observed on tobacco, poinsettia, tomato, pineapple, watermelon, and as well as African violet. Fruit rots occur on tomato, papaya, and eggplant. Onion shows a leaf and stem infection. In tobacco black shank affects the roots and basal stem area, but all parts of the plant can become infected. [5] Damping off symptoms can be observed in young seedlings. The first above ground symptom that will be observed is the wilting of plants, which leads to stunting. Roots will be blackened and decayed. In final stages of the disease the stem begins to turn black, hence the name black shank. As this happens, tobacco leaves turn brown and become not marketable. Another symptom is disk-like appearance of the pith, although this is not a definitive symptom as it may also be the result of lightning strikes. [4] [6] On onion it causes the disease known as Phytophthora neck and bulb rot. Different stages of onion may be affected. Initially, tips of newly infected plants start to yellow and dry followed by softening of the "neck" of the plants that eventually fall over. Infected leaves may show grey lesions. Roots may become necrotic in late disease. [7]
Black shank is a polycyclic soil borne disease, with the possibility of multiple disease cycles per growing season occurring from May to October. There are important structures this pathogen uses in its disease cycle. Chlamydospores are produced asexually and serve as long lived resting structures, surviving from four to six years. [8] Chlamydospores are the primary survival structure, the primary inoculum, and are usually produced in abundance. [4] These spores germinate in warm and moist soil to produce a germ tube that infects plants or produces a sporangium. Another asexual structure and secondary inoculum, appearing ovoid, pear, or spherical in shape are called sporangium. These spores are produced and can either germinate directly or release motile zoospores within 24 hours of inoculation with the right conditions. Zoospores are kidney shaped with an anterior tinsel flagellum and a posterior whip like flagellum that helps to navigate toward root tips were infection occurs. Black shank needs water for germination and movement because zoospores swim through soil pores and standing water. Splashing water from rain or irrigation can infect healthy plant leaves leading to more repeating secondary cycles. [9] Zoospores move toward nutrient gradients around root tips and host wounds. Once the root surface is contacted, zoospores encyst and a germ tube will emerge penetrating the epidermis. Infection leads to systemic rotting of the root system and wilting and chlorosis in the leaves. Another structure called hyphae is colorless, transparent, and coenocytic, but colonies may yellow with age. Also, there is much morphological variation in colony type with different isolates of P. nicotianae and the growth may differ when grown on different media. The hyphae are heterothallic and require two mating types to produce oospores, the sexual survival structure. Many fields only contain one mating type, so the zoospores rarely germinate and rarely cause epidemics. [8]
This pathogen thrives in temperatures ranging from 84–90 °F (29–32 °C). Disease is prominent in many agricultural productive regions and therefore is a major host to many warm environment crops. [8] Black shank needs water for germination and movement. Saturated soil optimizes disease spread because water is used for dissemination of motile zoospores and sporangia. Low-lying areas of the soil that remain wet for prolonged periods of time will have more disease. Splashing water from rain or irrigation can infect healthy plant leaves leading to more repeating secondary cycles. Soils that are not saturated will lead to little to no disease development, so water management is important. Optimum soil pH for development is between 6 and 7. Levels of calcium and magnesium in the soils can affect disease progress. [6]
Several kinds of management exist for the prevention and suppression of disease. A cultural method that can be effective in preventing disease is sanitation. Equipment should be cleaned after use in infested fields so the disease does not spread into uninfested fields. To disrupt chlamydospore germination crops should be grown in drained disease free soil. Also, avoid transplanting without thorough knowledge of the transplant. To limit spread of structures limit traffic in infected fields and always clean after exposure. Disease is favored by pH values greater than 6.2, so lowering the pH is an effective method for preventing germination. pH management can be difficult because tobacco cannot survive in very low pH soils. Soil pH 5.5 to 6 allow successful growth of tobacco and control of disease. [8]
The cultural control, crop rotation, is very effective at limiting disease. The longer an infected field is planted in a crop other than the initial infected crop, the lower the population will become. A minimum three-year rotation is recommended. Crop rotation is recommended in combination with resistant varieties as genetic controls. Burley tobacco, burley tobacco hybrids, and dark tobacco are varieties of tobacco that are resistant to black shank. Resistance however is not reliable because a single variety has resistance to only a few races of black shank. Finding new lines of resistance is becoming increasingly important due to new discovered resistant races of the pathogen.
Chemical control is most successful if used with resistant varieties. Metalaxyl or mefenoxam are chemistries used to control Phytophthora nicotianae. Ridomil Gold is an example a systemic pesticide with a metalaxyl chemistry. [9] Mefenoxam is twice as active as metalaxyl, but they both have the same mode of action. Successful chemical control is difficult because we are limited to these two chemistries that are basically identical. A study by A. S. Csinos and P. F. Bertrand found out at a rate of 3.36 kg/ha would not inhibit many of the common races used in their study. Overall, from their study they observed that black shank severity was increasing in Georgia due to metalaxyl sensitivity and resistant races of black shank. [10]
Phytophthora nicotianae has a wide host range, affecting agriculture rich areas all over the world. In the United States this is a major pathogen of ornamentals, tobacco, and tomato. Black shank is one of the most damaging and far reaching diseases of tobacco. In 1896, black shank was first described in Indonesia by Van Breda de Haan. [8] Disease was observed near Georgia in 1915 and reached major tobacco growing areas of Kentucky and North Carolina in the 1930s and 1940s. In North Carolina black shank can be found in every county that grows flue-cured tobacco and currently causes statewide losses of 1 to 2.5 percent per year. [11] This pathogen thrives in warm climates, so it is destructive on crops grown in these areas. During favorable conditions, new generations of spores can be produced every 72 hours, so if this disease is not managed well it can be very destructive. Susceptible cultivars in the right conditions can reach losses of 100 percent, because infected plants do not recover. [8] Less than one propagule per gram of soil can lead to an epidemic. [6]
This pathogen causes secondary cycles of disease by mode of zoospores. Zoospores interact with the host by sensing and moving toward the nutrient gradients near the root tip and wounds of the plant. Without this means of sensing entry points there would be no secondary cycles of disease. [8] Zoospores, chlamydospores, and sporangia produce a germ tube that directly penetrates the epidermis of the plant. Without this penetration device the pathogen would not be able to infect the plant. The pathogen interferes with transport by infecting the roots. Typically hyphae can be seen in the pith and cause blackening and necrosis. [6] [9] Infection can proceed rapidly once the pathogen has made an entrance into the plant. Once established, further reproduction of both chlamydospores and sporangia will occur within host tissues, amplifying the spread of disease within the host plant and spreading out into nearby plants. Upon death of the host, the decomposing infected tissues will release the pathogen back into the soil, in the form of chlamydospores and zoospores. A resting spore, the chlamydospores are capable of surviving in the soil for years, but it has been noted that cold winters cause an inhibitory effect on the survival rate. This results in less black shank infections where tobacco is grown in cooler, more northern climates. [6]
The action of P. nicotianae is amplified by the presence of root-knot nematodes, which through their own feeding habits, assist the pathogen in finding an entrance to the host. This pathogen synergy with root-knot nematodes has the ability to overcome much of the resistance of cultivars especially bred for P. nicotianae resistance. [6]
Phytophthora cinnamomi, also known as cinnamon fungus, is a soil-borne water mould that produces an infection which causes a condition in plants variously called "dieback", "root rot", or, "ink disease".
Phytophthora sojae is an oomycete and a soil-borne plant pathogen that causes stem and root rot of soybean. This is a prevalent disease in most soybean growing regions, and a major cause of crop loss. In wet conditions the pathogen produces zoospores that move in water and are attracted to soybean roots. Zoospores can attach to roots, germinate, and infect the plant tissues. Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. Phytophthora sojae also produces oospores that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery.
Phytophthora palmivora is an oomycete that causes bud-rot of palms, fruit-rot or kole-roga of coconut and areca nut. These are among the most serious diseases caused by fungi and moulds in South India. It occurs almost every year in Malnad, Mysore, North & South Kanara, Malabar and other areas. Similar diseases of palms are also known to occur in Sri Lanka, Mauritius, and Sumatra. The causative organism was first identified as P. palmivora by Edwin John Butler in 1917.
Aphanomyces euteiches is a water mould, or oomycete, plant pathogen responsible for the disease Aphanomyces root rot. The species Aphanomyces euteiches can infect a variety of legumes. Symptoms of the disease can differ among hosts but generally include reduced root volume and function, leading to stunting and chlorotic foliage. Aphanomyces root rot is an important agricultural disease in the United States, Europe, Australia, New Zealand, and Japan. Management includes using resistant crop varieties and having good soil drainage, as well as testing soil for the pathogen to avoid infected fields.
Phytophthora cactorum is a fungal-like plant pathogen belonging to the Oomycota phylum. It is the causal agent of root rot on rhododendron and many other species, as well as leather rot of strawberries.
Phytophthora medicaginis is an oomycete plant pathogen that causes root rot in alfalfa and chickpea. It is a major disease of these plants and is found wherever they are grown. P. medicaginis causes failure of stand establishment because of seedling death. Phytophthora medicaginis is part of a species complex with Phytophthora megasperma.
Pythium irregulare is a soil borne oomycete plant pathogen. Oomycetes, also known as "water molds", are fungal-like protists. They are fungal-like because of their similar life cycles, but differ in that the resting stage is diploid, they have coenocytic hyphae, a larger genome, cellulose in their cell walls instead of chitin, and contain zoospores and oospores.
Phytophthora erythroseptica—also known as pink rot along with several other species of Phytophthora—is a plant pathogen. It infects potatoes causing their tubers to turn pink and damages leaves. It also infects tulips (Tulipa) damaging their leaves and shoots.
Pythium aphanidermatum is a soil borne plant pathogen. Pythium is a genus in the class Oomycetes, which are also known as water molds. Oomycetes are not true fungi, as their cell walls are made of cellulose instead of chitin, they are diploid in their vegetative state, and they form coenocytic hyphae. Also, they reproduce asexually with motile biflagelette zoospores that require water to move towards and infect a host. Sexually, they reproduce with structures called antheridia, oogonia, and oospores.
Pythium graminicola is a plant pathogen infecting cereals.
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.
Phytophthora capsici is an oomycete plant pathogen that causes blight and fruit rot of peppers and other important commercial crops. It was first described by L. Leonian at the New Mexico State University Agricultural Experiment Station in Las Cruces in 1922 on a crop of chili peppers. In 1967, a study by M. M. Satour and E. E. Butler found 45 species of cultivated plants and weeds susceptible to P. capsici In Greek, Phytophthora capsici means "plant destroyer of capsicums". P. capsici has a wide range of hosts including members of the families Solanaceae and Cucurbitaceae as well as Fabaceae.
Phytophthora fragariae is a fungus-like (oomycete) plant pathogen that causes red stele, otherwise known as Lanarkshire disease, in strawberries. Symptoms of red stele can include a red core in the roots, wilting of leaves, reduced flowering, stunting, and bitter fruit. The pathogen is spread via zoospores swimming through water present in the soil, released from sporangia.
Phytophthora megakarya is an oomycete plant pathogen that causes black pod disease in cocoa trees in west and central Africa. This pathogen can cause detrimental loss of yield in the economically important cocoa industry, worth approximately $70 billion annually. It can damage any part of the tree, causing total yield losses which can easily reach 20-25%. A mixture of chemical and cultural controls, as well as choosing resistant plant varieties, are often necessary to control this pathogen.
Phytophthora plurivora is a very aggressive soil-borne plant pathogen, with worldwide distribution and a wide variety of hosts.
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.
Buckeye rot of tomato is caused by three species of pathogens in the genus Phytophthora: P. nicotianae var. parasitica, P. capsici, and P. drechsleri. It is an oomycete that thrives in warm, wet conditions and lives in the soil. It is characterized by a bull’s eye pattern of dark brown rotting on the tomato fruit, and affects fruit that is close to, or lying on the soil. The easiest management is to keep the plant out of contact with the soil, although other chemical methods can be very effective. This disease commonly occurs in the southeast and south central areas of the United States. The disease has affected a large portion of crop yield in the United States as well as India. The relatively small genome size of Phytophthora parasitica compared to Phytophthora infestans gives researchers the unique ability to further examine its ability to cause disease.
Black rot on orchids is caused by Pythium and Phytophthora species. Black rot targets a variety of orchids but Cattleya orchids are especially susceptible. Pythium ultimum and Phytophthora cactorum are known to cause black rot in orchids.
Cranberry Root Rot (CRR) is a disease in cranberries that can cause a decline in yield.
| Authority control databases: National |
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