Instruct: Given a question, retrieve documents that answer the question.
Query: Is there treatment for phytophthora ramorum?
Early detection of P. ramorum is essential for its control. On an individual-tree basis, preventive treatments, which are more effective than therapeutic treatments,[39] depend on knowledge of the pathogen’s movement through the landscape to know when it is nearing prized trees. On the landscape level, P. ramorum’s fast and often undetectable movement means that any treatment hoping to slow its spread must happen very early in the development of an infestation. Since P. ramorum’s discovery, researchers have been working on the development of early detection methods on scales ranging from diagnosis in individual infected plants to landscape-level detection efforts involving large numbers of people.
P. ramorum produces both resting spores (chlamydospores) and zoospores, which have flagella enabling swimming. P. ramorum is spread by air;[16] one of the major mechanisms of dispersal is rainwater splashing spores onto other susceptible plants, and into watercourses to be carried for greater distances.[16] Chlamydospores can withstand harsh conditions and are able to overwinter.[16] The pathogen will take advantage of wounding, but it is not necessary for infection to occur.[17]
As mentioned above, P. ramorum does not kill every plant that can be used as a host, and these plants are most important in the epidemiology of the disease as they act as sources of inoculum.[18] In California, California bay laurel (Umbellularia californica) seems to be the main source of inoculum.[19] Green waste, such as leaf litter and tree stumps, are also capable of supporting P. ramorum as a saprotroph and acting as a source of inoculum. Because P. ramorum is able to infect many ornamental plants, it can be transmitted by ornamental plant movement.
Pseudomonas cichorii
In 1995, the bacteria "Pseudomonas cichorii" was discovered on container-grown rhododendrons in a nursery in Georgia, USA. The spots were at first very small, one to five millimeters in diameter, but soon grew into large, reddish brown blotches. (Uddin & McCarter, 1996).
Phytophthora ramorum
In 2002 and 2003, studies in nurseries throughout California and Oregon tested for "Phytophthora ramorum". The symptoms of the disease were large necrotic spots with water soaked outside borders and rust colored centers. Symptomatic plants were collected, and DNA was extracted from the spots. After amplifying it with a PCR assay, GenBank matched the DNA to that of "Phytophthora ramorum" and "P. lateralis". In 2004, Rhododendron leaves with similar symptoms were studied and showed the host range of P. hibernalis as well (Blomquist et al. 2005).
Early detection of P. ramorum on a landscape scale begins with the observation of symptoms on individual plants (and/or detecting P. ramorum propagules in watercourses; see below). Systematic ground-based monitoring has been difficult within the range of P. ramorum because most infected trees stand on a complex mosaic of lands with various ownerships. In some areas, targeted ground-based surveys have been conducted in areas of heavy recreation or visitor use such as parks, trailheads, and boat ramps. In California, when conducting ground-based detection, looking for symptoms on bay laurel is the most effective strategy, since P. ramorum infection of true oaks and tanoaks is almost always highly associated with bay laurel, the main epidemiological springboard for the pathogen.[42][43][44] Moreover, on many sites in California (though not all), P. ramorum can typically be detected from infected bay laurel tissues via culturing techniques year-round; this is not the case for most other hosts, nor is it the case in Oregon, where tanoak is the most reliable host.[45]
Phytophthora ramorum is the oomycete plant pathogen known to cause the disease sudden oak death (SOD). The disease kills oak and other species of trees and has had devastating effects on the oak populations in California and Oregon, as well as being present in Europe. Symptoms include bleeding cankers on the tree's trunk and dieback of the foliage, in many cases eventually leading to the death of the tree.
Canker pathogen, "Diplodia corticola," has become a major pathogen to the species over the last decade, causing leaf browning, bark cracking and bleeding, and high rates of tree mortality across the northeastern United States. The northern red oak is also characterized as one of the most susceptible species to plant fungi "Phytophthora cinnamomi" and "Phytophthora ramorum," which have caused severe, red-black cankers in the trunk region of the species. Both "P. cinnamomi" and "P. ramorum" grow under warmer temperature conditions; as a result, northern red oak trees found in California, France, and northern Spain all have higher incidences of fungal infection.
"Phytophthora kernoviae" spreads most quickly and detrimentally in moist conditions such as direct rainfall and also those of heavy humidity. Rain and heavy winds help in the dispersal of spores for further infection. This disease has an optimal growing range of . This range suggests that it may have originated in a temperate climate, possibly China, before being introduce to the UK. In some genus of the disease such as "P. ramorum" water transportation through the use of streams and rivers is seen from outbreak sites. This is a unique characteristic of the "P. ramorum" and has not been seen in the "kernoviae" species While there are no known insect vectors for the disease humans can transport spores via agricultural equipment, on shoe bottoms and direct plant movement. These are the most significant vectors for the disease.
Detection of P. ramorum in watercourses has emerged as the earliest of early detection methods. This technique employs pear or rhododendron baits suspended in the watercourse using ropes, buckets, mesh bags, or other similar devices. If plants in the watershed are infected with P. ramorum, zoospores of the pathogen (as well as other Phytophthora spp.) are likely present in adjacent waterways. Under conducive weather conditions, the zoospores are attracted to the baits and infect them, causing lesions that can be isolated to culture the pathogen or analyzed via PCR assay.[48][49] This method has detected P. ramorum at scales ranging from small, intermittent seasonal drainages to the Garcia, Chetco, and South Fork Eel Rivers in California and Oregon (144, 352, and 689 mi2 drainage areas, respectively). It can detect the existence of infected plants in watersheds before any mortality from the infections becomes evident. Of course, it cannot detect the exact locations of those infected plants: at the first sign of P. ramorum propagules in the stream, crews must scour the watershed using all available means to find symptomatic vegetation.
Several options exist for landowners who want to limit the impacts of SOD death on their properties. None of these options is foolproof, guaranteed to eradicate P. ramorum, or guaranteed to prevent a tree from becoming infected. Some are still in the initial stage of testing. Nevertheless, when used thoughtfully and thoroughly, some of the treatments do improve the likelihood of either slowing the spread of the pathogen or of limiting its impacts on trees or stands of trees. Assuming that the landowner has correctly identified the host tree(s) and symptom(s), has submitted a sample to a local authority to send to an approved laboratory for testing, and has received confirmation that the tree(s) are indeed infected with P. ramorum—or, alternatively, assuming that the landowner knows that P. ramorum-infected trees are nearby and wants to protect the resources on his or her property—he or she can attempt control by cultural (individual-tree), chemical, or silvicultural (stand-level) means.
Research on control of P. ramorum in nurseries has also focused on disinfesting irrigation water containing P. ramorum inoculum. Irrigation water can become infested from bay trees in the forest (if the irrigation source is a stream), from bay trees overhanging irrigation ponds, from runoff from infested forests,[59] or from recirculated irrigation water.[60] Experiments in Germany with three types of filters—slow sand filters, lava filters, and constructed wetlands—showed that the first two removed P. ramorum from the irrigation water completely, while 37% of the post-treatment water samples from the constructed wetland still contained P. ramorum.[61]
Detecting the presence of Phytophthora species requires laboratory confirmation. The traditional method of culturing is on a growth medium selective against fungi (and, in some cases, against other oomycetes such as Pythium species). Host material is removed from the leading edge of a plant tissue canker caused by the pathogen; resulting growth is examined under a microscope to confirm the unique morphology of P. ramorum. Successful isolation of the pathogen often depends on the type of host tissue and the time of year that detection is attempted.[40]
P. ramorum is a relatively new disease, and several debates have occurred about where it may have originated or how it evolved.
P. ramorum also infects a great number of other plant species, significantly woody ornamentals such as Rhododendron, Viburnum, and Pieris, causing foliar symptoms known as ramorum dieback or ramorum blight. Such plants can act as a source of inoculum for new infections, with the pathogen-producing spores that can be transmitted by rainsplash and rainwater.
Evidence suggests P. ramorum may be an introduced species, and these introductions occurred separately for the European and North American populations, hence why only one mating type exists on each continent– this is called a founder effect.[26] The differences between the two populations are thus caused by adaptation to separate climates. Evidence includes little genetic variability, as P. ramorum has not had time to diversify since being introduced. Existing variability may be explained by multiple introductions with a few individuals adapting best to their respective environments.[27] The behavior of the pathogen in California is also indicative of being introduced; it is assumed that such a high mortality rate of trees would have been noticed sooner if P. ramorum were native.
Trials of silvicultural methods for treating P. ramorum began in Humboldt County in northwest coastal California in 2006. The trials have taken place on a variety of infested properties both private and public and have generally focused on varying levels and kinds of host removal. The largest (50 acres (200,000m2)) and most replicated trials have involved removal of tanoak and bay laurel by chainsaw throughout the infested stand, both with and without subsequent underburning designed to eliminate small seedlings and infested leaf litter.[54] Other treatments included host removal in a modified “shaded fuelbreak” design in which all bay laurel is removed, but not all tanoaks; bay and tanoak removal using herbicides; and removal of bay laurel alone. The results of these treatments are still being monitored, but repeated sampling has so far detected only very small amounts of P. ramorum in the soil or on vegetation in the treated sites.
A promising treatment for preventing infection of individual oak and tanoak trees—not for curing an already established infection—is a phosphonate fungicide marketed under the trade name Agri-fos. Phosphonate is a neutralized form of phosphorous acid that works not by direct antagonism of Phytophthora, but by stimulating various kinds of immune responses on the part of the tree.[39] It is mostly environmentally benign if not applied to nontarget plants and can be applied either as an injection into the tree stem or as a spray to the bole. When applying Agri-fos as a spray, it must be combined with an organosilicate surfactant, Pentra-bark, to enable the product to adhere to the bole long enough to be absorbed by the tree. Agri-fos has been very effective in preventing tree infections, but it must be applied when visible symptoms of P. ramorum on other trees in the immediate neighborhood are still relatively distant; otherwise, the tree to be treated likely is already infected, but visible symptoms have not yet developed (especially true for tanoak).
Additionally, researchers have begun using features of the DNA sequence of P. ramorum to pinpoint the minuscule differences of separate P. ramorum isolates from each other. Two techniques for doing this are amplified fragment length polymorphism, which through comparing differences between various fragments in the sequence has enabled researchers to differentiate correctly between EU and U.S. isolates,[40] and the examination of microsatellites, which are areas on the sequence featuring repeating base pairs. When P. ramorum propagules arrive in a new geographic location and establish colonies, these microsatellites begin to display mutation in a relatively short time, and they mutate in a stepwise fashion. Based on this, researchers in California have been able to construct trees, based on microsatellite analyses of isolates collected from around the state, that trace the movement of P. ramorum from two likely initial points of establishment in Marin and Santa Cruz Counties and out to subsequent points.[41]
About the same time, a similar disease in continental Europe and the UK was also identified as Phytophthora ramorum.[3]
Research and development in managing P. ramorum in nursery settings extends from P. ramorum in the individual plant, to P. ramorum in the nursery environment, to the pathogen’s movement across state and national borders in infected plants.
One of the most important aspects of P. ramorum control involves interrupting the human-mediated movement of the pathogen by ensuring that infested materials do not move from location to location. While enforceable quarantines perform part of this function, basic cleanliness when working or recreating in infested areas is also important. In most cases, cleanliness practices involve ridding potentially infested surfaces—such as shoes, vehicles, and pets—of foliage and mud before leaving the infested area. The demands of implementing these practices become more complex when large numbers of people are working in infested areas, as in construction, timber harvesting, or wildfire suppression. The California Department of Forestry and Fire Protection and USDA Forest Service have implemented guidelines and mitigation requirements for the latter two situations; basic information about cleanliness in P. ramorum-infested areas can be found at the California Oak Mortality Task Force web site () under the “Treatment and Management” section (subsection “Sanitation and Reducing Spread”).
have also developed numerous molecular techniques for P. ramorum identification. These include amplifying DNA sequences in the internal transcribed spacer region of the P. ramorum genome (ITS polymerase chain reaction, or ITS PCR); real-time PCR, in which DNA abundance is measured in real time during the PCR reaction, using dyes or probes such as SBYR-Green or TaqMan; multiplex PCR, which amplifies more than one region of DNA at the same time; and single strand conformation polymorphism (SSCP), which uses the ITS DNA sequence amplified by the PCR reaction to differentiate Phytophthora species according to their differential movement through a gel.[40]
Where P. ramorum originated remains unclear, but most researchers feel Asia is the most likely, since many of the hosts of P. ramorum originated there.[28] Since certain climates are best suited to P. ramorum, the most likely sources are the southern Himalayas, Tibet, or Yunnan province.[29]
Because of these difficulties, researchers have developed some other approaches for identifying P. ramorum. The enzyme-linked immunosorbent assay test can be the first step in nonculture methods of identifying P. ramorum, but it can only be a first step, because it detects the presence of proteins that are produced by all Phytophthora species. In other words, it can identify to the genus level, but not to the species level. ELISA tests can process large numbers of samples at once, so researchers often use it to screen out likely positive samples from those that are not when the total number of samples is very large.[40] Some manufacturers produce small-scale ELISA “field kits” that the homeowner can use to determine if plant tissue is infected by Phytophthora.
The closely related Phytophthora kernoviae causes similar symptoms to P. ramorum, but infects the European beech (Fagus sylvatica).[15]