Cherry X Disease | |
---|---|
Causal agents | Phytoplasma |
Hosts | Sweet/sour cherries |
Vectors | mountain leafhopper (Colladonus montanus) |
Cherry X disease also known as Cherry Buckskin disease is caused by a plant pathogenic phytoplasma. Phytoplasmas are obligate parasites of plants and insects. They are specialized bacteria, characterized by their lack of a cell wall, often transmitted through insects, and are responsible for large losses in crops, fruit trees, and ornamentals. [1] The phytoplasma causing Cherry X disease has a fairly limited host range mostly of stone fruit trees. Hosts of the pathogen include sweet cherry, sour cherry, choke cherry, peaches, nectarines, almonds, clover, and dandelion. Most commonly the pathogen is introduced into economical fruit orchards from wild choke cherry and herbaceous weed hosts. The pathogen is vectored by mountain and cherry leafhoppers. The mountain leafhopper ( Colladonus montanus ) vectors the pathogen from wild hosts to cherry orchards but does not feed on the other hosts. The cherry leafhopper (Fieberiella florii) feeds on cherry trees and can transmit the disease from cherry orchards to peach, nectarine, and other economic crops. The Saddled Leafhopper (Colladonus clitellarius) is a vector of the disease in peaches. Control of Cherry X disease is limited to controlling the spread, vectors, and weed hosts of the pathogen. Once the pathogen has infected a tree it is fatal and removal is necessary to stop it from becoming a reservoir for vectors.
For Cherry X disease there are two types of hosts for the phytoplasma, reservoir and non-reservoir hosts. Reservoir hosts can survive for long periods while being infected with the disease. This allows them to be a constant food source for the leafhoppers which act to vector the phytoplasma from these hosts to other hosts in the area. Choke cherry is the most common reservoir host and a favorite food for the cherry leafhoppers. Other reservoir hosts include clovers and dandelions. [2] Sweet/sour cherries, as well as almonds and Japanese plums are all fruit tree reservoir hosts for the Cherry X disease. All of these, once infected, can act as a source for the disease to be vectored from to other hosts. While non-cherry hosts can become infected they are not the preferred host of the phytoplasma. Because of the vectors preference for cherry trees, choke cherry which is a wild growing cherry species is the most common host of the disease. The range that Cherry X disease is distributed over is directly linked to the distribution of wild choke cherry populations. [3]
Non-reservoir hosts are hosts that once infected do not allow for the disease to be spread. Peach and nectarine trees can be infected but they do not allow for the spread of the disease. This process which causes them to halt the spread of the pathogen is still not well understood. Peaches are commonly infected when near cherry orchards. Non-reservoir hosts are infected when cherry leafhoppers that are carrying the phytoplasma feed on non-reservoir hosts that are near a cherry orchard that has the pathogen. [2]
The symptoms of Cherry X disease vary greatly depending on the host. On cherry hosts symptoms can usually first be seen on the fruits, causing them to be smaller in size with a leathery skin. Pale fruit is common at harvest time. It is common for symptoms to first be seen in a single branch. The branch may lose its older leaves, and the leaves tend to be smaller with a bronzed complexion. [4]
The rootstock that the cherry is grafted onto can play a significant role in the disease symptoms seen. Rootstocks of Mahaleb cherry exhibit different symptoms from stocks of Colt, Mazzard, or Stockton Morello. When the scion is grafted onto Mahaleb, symptoms consistent with Phytophthora root rot can be seen. To distinguish between root rot and x-disease the wood under the bark at the graft union should be examined. If it is x-disease the wood at the union will have grooves and pits this causes a browning of the phloem and shows the cells in decline. This rapid decline is caused by the rootstock cells near the graft union dying in large quantities. Foliage begins to turn yellow and the curl upward and inward toward the leaf midrib. Trees infected with Mahaleb rootstock die by late summer or early the following year.[ citation needed ]
When Cherries are grafted onto Colt, Mazzard, or Stockton Morello rootstocks, there is a different range of symptoms. Affected leaves are smaller than normal and the foliage may be sparse. Dieback of shoot tips is common as the disease progresses. Fruit on branches are smaller, lighter, pointed, low sugar content, poor flavor, and a bitter taste. [2]
Peaches are the next most common economic fruit host of the X-disease. Symptoms can be seen after about two months single branches will begin to show symptoms of their individual leaves. These leaves curl up and inward with irregular yellow to reddish-purple spots. These spots can drop out leaving “shotholes”. Leaves that are affected by the disease will fall prematurely. After 2–3 years the entire tree will show symptoms. [5]
The mountain leafhopper (Colladonus montanus) overwinters on winter annual weeds, particularly near streams and canals. Adults can be plentiful on sugarbeet during late winter/spring and migrate to favored weed hosts such as curly dock or burclovers in orchards. The Mountain leafhopper is most abundant vector found on cherry but does not reproduce on cherry. The mountain leafhopper (Colladonus montanus) spreads the disease from wild herbaceous hosts to woody hosts. It is believed that it is more responsible for the introduction of the disease into cherry trees, then in transferring them from cherry tree to cherry tree in an orchard. The cherry leafhopper (Fieberiella florii) reproduces on a broad range of woody hosts. The cherry leafhopper is more important in vectoring the disease from tree to tree within an orchard, since cherry is a favored host. After a leafhopper feeds on an infected host the pathogen has to undergo a latent period. During the latent period the pathogen spreads and multiplies inside the vector. Depending on temperature and the vector, the average latent period for the cherry x disease is about a month or longer. The phytoplasma is then transmitted from the leafhopper to the tree when the leafhopper is feeding on the trees phloem. It's then spread throughout the tree becoming systemic. July through October is when the highest concentrations of pathogen are present in leaves of infected trees. [2]
The disease is fatal and will always yield damaged fruit (choke cherries) as well as a dying/dead tree. If left unattended to, the leafhoppers can become life-time transmitters/vectors for the disease following about a 1-month latent period. The disease can take as quickly as 2–3 months to develop symptoms but more commonly 6–9 months, but the symptoms are usually first seen in the next growing season after the infection, with the rare exception that the infection and first symptoms occur both in the same spring season. In high cherry producing areas, such as California, Washington, and Oregon, this disease could be devastating if left unchecked. For instance in 2002, 57,000 tons of cherries were harvested from 24,000 acres in California. The year grossed a total of over $152 million. [6] If, in 2002, this disease was allowed to incubate, the results would show a drastic decline of production and huge loss of revenue as early as 2003. This disease does not take long to develop and since fatality is always the endgame, high producing areas such as these would see results of epidemic proportions.[ citation needed ]
Leafhoppers are the only known vectors that can carry the X-disease from a wild host into peach and cherry orchards. Orchard trees are most often infected by insect vectors. In California where it was first noted, the two most important vectors were the mountain leafhopper ( Colladonus montanus ) and the cherry leafhopper ( Fieberiella florii). [7] [8] [2]
There are seven known vectors that transmit the disease in western United States. These leafhoppers are Colladonus geminatus, Fieberiella florii, Keonolla confluens, Scaphytopius delongi, Osbornellus borealis, Colladonus montanus and Euscelidius variegatus . Other possible leafhopper vectors are Scaphytopius aculus, Paraphlepsius irroratus, Colladonus clitellarius and Norvellina seminude . [7] [9] Not a lot of information is available for ideal environmental conditions for the disease. However, conditions conducive to leafhoppers is most likely the key for the greatest spread of disease.[ citation needed ]
The mountain leafhopper ( Colladonus montanus ) survives on winter annual weeds during winter, usually near stream banks or canals. In late winter or spring, adults can be found in sugar beet fields and can then migrate to favored weed hosts (curly dock, burclovers) in orchards. The mountain leafhopper is most often the abundant vector found on cherry, however, cherry is not the preferred host and the leafhopper does not reproduce on cherry. Preferred hosts for the mountain leafhopper are; alfalfa, California burclover, clovers, curly dock, and sweet clovers. Of the preferred hosts alfalfa and curly dock cannot become infected with the disease itself but are just a host for the leafhopper. Occasional hosts are; vetches (in legume family) and sweet cherry. It’s believed that the role of this leafhopper is introducing the disease into cherry orchards rather than spreading the disease between cherry trees within an orchard. [2]
The cherry leafhopper (Fieberiella florii) has a more significant role in spreading the disease between cherry trees because cherry is a favored host. The leafhopper feeds and reproduces on a wide range of woody hosts. Preferred hosts for the cherry leafhopper are; box wood, lilac, myrtle, privet, pyracantha, sweet cherry, and viburnum. Of these preferred hosts only sweet cherry can become infected with the pathogen itself. Occasional hosts are almond, apple and crabapple, apricot, bitter cherry, ceanothus, chokecherry, hawthorn, peach, pear, Japanese plum, and prune. Of these occasional hosts, only chokecherry and bitter cherry and occasionally almond, peach and Japanese plum can become infected with the disease itself. [2]
There are numerous steps one has to take to try to manage the disease as best as possible. The aim is at prevention because once the pathogen reaches the cherry trees, disease will surely ensue and there is no cure or remedy to prevent the loss of fruit production as well as the ultimate death of the tree.[ citation needed ]
The first approach, which is the best approach at an effective management practice would be to eradicate or severely damage the mountain and cherry leafhopper population because the leafhoppers are the number one vectors for this pathogen. To do this, pesticides (i.e. acephate, bifenthrin, cyfluthrin) [10] could be applied or biological control (predators of the leafhopper) could be used. There should be a pre-season application of control measures as well as a post-season application. This is to maximize the effort at controlling both types of leafhoppers (Cherry and Mountain), thus cutting down the starting inoculum at both stages in the life cycle.[ citation needed ]
Some herbaceous hosts naturally have the Cherry X Disease. Once the spreads to the cherry hosts, with the help of the mountain leafhoppers, the cherry leafhoppers can spread the disease around to other woody hosts.[ citation needed ] Here are some approaches at management with each host type:
The herbaceous hosts are common weeds (i.e. clovers, dandelions, alfalfa) that serve as a feeding ground for the mountain leafhoppers. The herbaceous hosts are the source of the X Disease, which is picked up and transmitted to the cherry hosts by the mountain leafhopper. (See Environment) For a control, conventional herbicides are effective. There exists a common herbaceous host, curly dock, which serves as the mountain leafhopper's main breeding ground. Getting rid of curly dock with an herbicide would be key to limit the population, thus limiting the spread of the X Disease to the cherry hosts.[ citation needed ]
After the disease moves on from the herbaceous host with the help of the mountain leafhoppers, it moves to the cherry hosts (i.e. bitter cherry and chokecherry). Once there, the infected trees should be destroyed and removed, along with all infected fruits. This is to prevent further spreading into other woody hosts such as peach, plum, apple etc., because once a tree is infected, it cannot be saved and it will become a source of the X Disease which the cherry leafhoppers can pick up and spread to the other woody hosts. In conclusion, all infected woody hosts should be removed and destroyed along with all infected fruits. [3]
Phytoplasmas are obligate intracellular parasites of plant phloem tissue and of the insect vectors that are involved in their plant-to-plant transmission. Phytoplasmas were discovered in 1967 by Japanese scientists who termed them mycoplasma-like organisms. Since their discovery, phytoplasmas have resisted all attempts at in vitro culture in any cell-free medium; routine cultivation in an artificial medium thus remains a major challenge. Phytoplasmas are characterized by the lack of a cell wall, a pleiomorphic or filamentous shape, a diameter normally less than 1 μm, and a very small genome.
Plum pox, also known as sharka, is the most devastating viral disease of stone fruit from the genus Prunus. The disease is caused by the plum pox virus (PPV), and the different strains may infect a variety of stone fruit species including peaches, apricots, plums, nectarine, almonds, and sweet and tart cherries. Wild and ornamental species of Prunus may also become infected by some strains of the virus.
Xylella fastidiosa is an aerobic, Gram-negative bacterium of the genus Xylella. It is a plant pathogen, that grows in the water transport tissues of plants and is transmitted exclusively by xylem sap-feeding insects such as sharpshooters and spittlebugs. Many plant diseases are due to infections of X. fastidiosa, including bacterial leaf scorch, oleander leaf scorch, coffee leaf scorch (CLS), alfalfa dwarf, phony peach disease, and the economically important Pierce's disease of grapes (PD), olive quick decline syndrome (OQDS), and citrus variegated chlorosis (CVC). While the largest outbreaks of X. fastidiosa–related diseases have occurred in the Americas and Europe, this pathogen has also been found in Taiwan, Israel, and a few other countries worldwide.
Aster yellows is a chronic, systemic plant disease caused by several bacteria called phytoplasma. The aster yellows phytoplasma (AYP) affects 300 species in 38 families of broad-leaf herbaceous plants, primarily in the aster family, as well as important cereal crops such as wheat and barley. Symptoms are variable and can include phyllody, virescence, chlorosis, stunting, and sterility of flowers. The aster leafhopper vector, Macrosteles quadrilineatus, moves the aster yellows phytoplasma from plant to plant. Its economic burden is primarily felt in the carrot crop industry, as well as the nursery industry. No cure is known for plants infected with aster yellows. Infected plants should be removed immediately to limit the continued spread of the phytoplasma to other susceptible plants. However, in agricultural settings such as carrot fields, some application of chemical insecticides has proven to minimize the rate of infection by killing the vector.
Curly top is a viral disease that affects many crops. This disease causes plants to become smaller in size, have shriveled petals and leaves, and are twisted and pulled out of shape. They are often caused by curtoviruses, members of the virus family Geminiviridae. This disease is important in western United States, such as California, Utah, Washington, and Idaho.
Monilinia fructigena is a plant pathogen in the fungus kingdom causing a fruit rot of apples, pears, plums, peaches and cherries.
Prune dwarf virus (PDV) is an economically important plant pathogenic virus affecting Prunus species globally. PDV is found worldwide due to easy transmission through seed, pollen, and vegetative propagation. The virus is in the family Bromoviridae an important family of plant RNA viruses containing six genera, including Alfamovirus, Ilarvirus, Bromovirus, Amularvirus, Oleavirus, and Cucumovirus. PDV belongs to the genera Ilarvirus. It can cause dwarfism of leaves on certain prune and plum plants. It will also cause yellows in sour cherry, especially when present with Prunus necrotic ringspot virus. There are no known transmission vectors, though the pollen of infected cherry trees has been found to infect other cherry trees a small percent of the time.
Prunus necrotic ringspot virus (PNRSV) is a plant pathogenic virus causing ring spot diseases affecting species of the genus Prunus, as well as other species such as rose and hops. PNRSV is found worldwide due to easy transmission through plant propagation methods and infected seed. The virus is in the family Bromoviridae and genus Ilarvirus. Synonyms of PNRSV include European plum line pattern virus, hop B virus, hop C virus, plum line pattern virus, sour cherry necrotic ringspot virus, and peach ringspot virus.
Elm yellows is a plant disease of elm trees that is spread by leafhoppers or by root grafts. Elm yellows, also known as elm phloem necrosis, is very aggressive, with no known cure. Elm yellows occurs in the eastern United States, and southern Ontario in Canada. It is caused by phytoplasmas which infect the phloem of the tree. Similar phytoplasmas, also known confusingly as 'Elm yellows', also occur in Europe. Infection and death of the phloem effectively girdles the tree and stops the flow of water and nutrients. The disease affects both wild-growing and cultivated trees.
Flavescence dorée is one of the most important and damaging phytoplasma diseases of the vine with the potential to threaten vineyards. The bacterial agent has recently been named Candidatus Phytoplasma vitis, and its vector is the leafhopper, Scaphoideus titanus. Infection may kill young vines and greatly reduce the productivity of old vines. It is classified as a phytoplasma disease belonging to the group generically termed grapevine yellows. Occurrences are in sporadic epidemics, and varieties vary in their sensitivity to it.
Texas Phoenix palm decline, or lethal bronzing, is a plant disease caused by a phytoplasma, Candidatus Phytoplasma palmae. It takes its name from the state it was first identified in and the palm genus, Phoenix, upon which it was first identified. It is currently found in parts of Florida and Texas.
Sugarcane grassy shoot disease (SCGS), is associated with 'Candidatus Phytoplasma sacchari' which are small, pleomorphic, pathogenic mycoplasma that contribute to yield losses from 5% up to 20% in sugarcane. These losses are higher in the ratoon crop. A higher incidence of SCGS has been recorded in some parts of Southeast Asia and India, resulting in 100% loss in cane yield and sugar production.
The Citrus stubborn disease is a plant disease affecting species in the genus Citrus. Spiroplasma citri, a Mollicute bacterium species, is the causative agent of the disease. It is present in the phloem of the affected plant. Originally discovered transmitted by several leafhoppers including Circulifer tenellus and Scaphytopius nitridus in citrus-growing regions of California, it is now spread by the same hoppers in Arizona and Circulifer haematoceps in the Mediterranean region.
Leucostoma canker is a fungal disease that can kill stone fruit. The disease is caused by the plant pathogens Leucostoma persoonii and Leucostoma cinctum (teleomorph) and Cytospora leucostoma and Cytospora cincta (anamorphs). The disease can have a variety of signs and symptoms depending on the part of the tree infected. One of the most lethal symptoms of the disease are the Leucostoma cankers. The severity of the Leucostoma cankers is dependent on the part of the plant infected. The fungus infects through injured, dying or dead tissues of the trees. Disease management can consist of cultural management practices such as pruning, late season fertilizers or chemical management through measures such as insect control. Leucostoma canker of stone fruit can cause significant economic losses due to reduced fruit production or disease management practices. It is one of the most important diseases of stone fruit tree all over the world.
Peach scab, also known as peach freckles, is a disease of stone fruits caused by the fungi Cladosporium carpophilum. The disease is most prevalent in wet and warm areas especially southern part of the U.S. as the fungi require rain and wind for dispersal. The fungus causes scabbing, lesions, and defoliating on twig, fruit, and leaf resulting in downgrade of peach quality or loss of fruits due to rotting in severe cases.
Little cherry disease or LChD, sometimes referred to as little cherry, K & S little cherry or sour cherry decline, is a viral infectious disease that affects cherry trees, most notably sweet cherries and sour cherries . Little cherry disease should not be confused with cherry buckskin disease, which is caused by Phytoplasma. Note that both diseases are among the diseases referred to as cherry decline.
CandidatusPhytoplasma fraxini is a species of phytoplasma, a specialized group of bacteria which lack a cell wall and attack the phloem of plants. This phytoplasma causes the diseases ash yellows and lilac witches' broom.
Papaya Bunchy Top Disease was first discovered in 1931 in Puerto Rico. Early on, the identity of the pathogen was highly contested due to the inability of isolating it; thus Koch’s postulates could not be fulfilled. Scientists have previously believed that Papaya Bunchy Top Disease was caused by a virus, a mycoplasma-like organism (MLO), or a phytoplasma, but these possible pathogens have since been disproven. Since the identity of the pathogen was unknown, all diagnoses were given solely based on a list of commonly associated symptoms. Through sequencing and microscopy, scientists identified the pathogen to be a part of the genus Rickettsia in 1996. The bacterium is described as being rod-shaped, small, gram-negative, and laticifer-inhibiting. Rickettsia causes diseases in animals, such as typhus and spotted fever, as well as in other plants, such as phony disease of peach and almond leaf scorch. Papaya Bunchy Top is found throughout the American tropics and has been economically important due to its major impact on fruit production. There is little information about the current economic impact.
Pecan bacterial leaf scorch is a disease of the pecan tree that is common throughout the production regions of the United States caused by the pathogenic bacterium Xylella fastidiosa subsp. multiplex. The pathogen was initially discovered to be coincidentally associated with symptoms of pecan fungal leaf scorch in 1998 and has subsequently been found to be endemic in the southeastern United States, as well as Arizona, California, and New Mexico.
Candidatus Phytoplasma pruni is a species of phytoplasma in the class Mollicutes, a class of bacteria distinguished by the absence of a cell wall. The specific epithet pruni means "living on Prunus", emphasizing the fact that the phytoplasma is a parasite of various Prunus species, otherwise known as stone fruits. The phytoplasma is commonly called the X-disease phytoplasma.