Phytophthora kernoviae

from Wikipedia, the free encyclopedia
Phytophthora kernoviae
Necrotic bark of an infected beech tree

Necrotic bark of an infected beech tree

Systematics
Department : Egg mushrooms (Oomycota)
Class : Oomycetes
Order : Peronosporales
Family : Peronosporaceae
Genre : Phytophthora
Type : Phytophthora kernoviae
Scientific name
Phytophthora kernoviae
Brasier, 2005

Phytophthora kernoviae is a phytopathogen that mainlyaffects red beech ( Fagus sylvatica ) and the Pontic rhododendron ( Rhododendron ponticum ). It was firstidentifiedin Cornwall ( UK )in 2003when scientists tried to produce evidence of Phytophthora ramorum . It was the third newly described Phytophthora species in Great Britain in a decade. The specific epithet kernoviae is derived from the ancient name "Kernow" for Cornwall. It causes extensive trunk lesions on beeches and necroses on the shoots and leaves of Rhododendron ponticum . The species is self-fertile . It has also beenisolatedfrom English oak ( Quercus robur ) and tulip trees ( Liriodendron tulipifera ). The original description also states that infections occur in magnolias and camellias , Pieris formosa , Chilean hazelnut ( Gevuina avellana ), magnolia doltsopa and stone oak ( Quercus ilex ). Since then, many other plant species have been identified as hosts. Molecular biological analyzes have shown that an infection in a Monterey pine ( Pinus radiata ), which wasdocumentedin New Zealand in 1950, was caused by P. kernoviae .

Symptoms

Because Phytophthora kernoviae can cause such severe symptoms, it should be viewed as a serious threat to trees and shrubs. In rhododendron bushes, a disease begins with the blackening of the leaf stalk , which occasionally spreads to the base of the leaf and affects both old and young leaves equally. In addition to this blackening, there are lesions of the stem axis. The leaves can become lesions so severe that they become necrotic and die off completely. These lesions begin with a progression of blackening of the leaf tissue that spreads over the entire leaf. In some cases, these necroses cause tree cancer and the death of the infected plant. Although the symptoms are similar for trees, there are some differences. Red beeches ( Fagus sylvatica ) include dark brown to blue-black lesions on the trunk, which vary in size and shape depending on the severity of the infection. Tulip trees ( Liriodendron tulipifera ) are also susceptible hosts. The trees infected by the pathogens show many smaller "bleeding" lesions on the trunk and also lesions on the leaf tips. Both shrubs and trees show the same leaf necrosis and shoot lesions, which underlines the severity of the disease.

Diagnosing the disease can be difficult because the symptoms of Phytophthora ramorum and Phytophthora kernoviae infections are very similar. Test samples from DNA extracts from plant tissue should be tested against conventional PCR and real-time PCR approaches. If any of these tests prove negative, there is no P. kernoviae infection , while positive tests show their presence. In addition, isolations and morphological identifications can take place.

ecology

Phytophthora kernoviae spreads fastest and with the greatest harmful effect in a damp environment, i.e. directly after rainfall or in high humidity. Rain and strong winds contribute to the spread of the spores and further infections. The species thrives best at temperatures of 16… 26 ° C. This optimum suggests that the species originally came from a temperate climate zone, possibly China before it was introduced to the UK. In other species of the genus, such as P. ramorum , transport via running water from the outbreak sites was observed. This has not yet been observed for P. kernoviae . While there are no known carriers of disease among insects, the spores can be spread by humans via agricultural equipment, shoe soles, and infected plants. These factors are considered to be the most important for its spread.

management

Since the disease was only recently discovered, appropriate management measures are still under development. For successful management, it is extremely important to remove the spore-producing plants in the infected area. Along with this, attempts were made to stop the spread of the disease by clearing trees or completely removing the shrub layer and leaf litter. The elimination of standing water and an adapted irrigation regime help limit the spread of spores through water. In areas with severe infections, the removal of the hosts and leaves can be ordered. In addition, orders can be made on hiking trails to prevent the transport of spores by humans. Anti Phytophthora - fungicides can be used in some cases, these fungicides do not kill the pathogens, but only prevent her setting, or her continued growth. Another currently practiced method is the removal of rhododendrons in infected areas. An infected Pontic Rhododendron was found in Ireland in 2008 . More research into the spread and reproduction of the pathogen is needed before more advanced chemical methods of control can be made available.

Life cycle

Phytophthora kernoviae can survive as an oospore - a thick-walled resting form - and was found as such in infected plant tissues and in the soil. Chlamydospores - dormant forms that survive for a long time - are known from Phytophthora ramorum and other Phytophthora species, but have not been detected in Phytophthora kernoviae . In P. kernoviae the production of sporangia , oospores and zoospores has been observed. Sporangia are only formed in hosts with sensitive foliage, while tree cancer does not show any sporangia formation on the shoot axes and does not contribute to the spread of the disease. This results in a simple life cycle in Phytophthora kernoviae . Oospores can "germinate" and form mouse-shaped sporangia. These serve as structures for spreading and create zoospores - mobile infectious spores that they also release. Once released, the oospores "germinate" on the host and infect the target tissues. If conditions are right after infection, Phytophthora kernoviae produces sporangia that are removed naturally and spread into the surrounding tissue. Under laboratory conditions, the sporangia production was observed within one week, the sporangia appearing six days after infection and the disease could be documented in the plant tissue. The sporangia of Phytophthora kernoviae are spread locally by wind and water and infect neighboring sensitive tissues. Large-scale distribution occurs through the transport of infected plant material and through soil particles that are carried off with vehicles, animals and shoes.

Course of disease

Infection with Phytophthora kernoviae is triggered by the release of zoospores and its spread by the wind. Existing wounds on the host are quickly exploited, but are not absolutely necessary for infection. One interesting aspect of P. kernoviae , according to research, is that only two thirds of infections are symptomatic , so an actual infection often goes undetected by visual inspection. Before infection of the inner bark of red beeches, the pathogen causes leaf necrosis and the death of the saplings in the undergrowth of forests and ornamental plants. This is where the release of spores takes place on the infected saplings and their leaves, so that the surrounding trees are also infected, which in turn can have "bleeding" wounds. The adaptation of the pathogen to airborne distribution is a key factor in the transmission of ornamental plants to trees.

Once infected, the beech phloem will exhibit “bleeding” lesions and discoloration. The color varies with the amount of oxygen present and the time since infection. Often the lesions have pink or orange fluid-filled cavities called lagoons in the phloem below. The pathogen then invades the underlying xylem , allowing further spread throughout the plant and causing further phloem lesions. In addition, the presence of the pathogen in the xylem leads to local dysfunction, which progressively damages the plant tissue and allows it to penetrate the previously healthy bark. Once P. kernoviae has invaded the xylem, this can continue for up to 24 months. The tree then dies within a few years of the initial infection.

meaning

Since 2003, Phytophthora kernoviae has caused some damage to ornamental plants and trees in the south west of the UK. The pathogen was first discovered in the 1990s, but only gained widespread attention when it was identified, along with P. ramorum, as one of the causes of "sudden oak death". Although the greatest concentration of the pathogens is observed in south west England , the range has extended to south Wales , Cheshire and even north to Scotland . It is currently found on the stems and leaves of rhododendrons , mainly on the Pontic rhododendron. Additionally , the aggressive nature of Phytophthora kernoviae makes it a significant threat to the fragile ecosystems of the main part of Britain. From a rhododendron host, the pathogen can easily be airborne to the bark of neighboring trees such as red beech ( Fagus sylvatica) , which are particularly sensitive. The disease was confined to a relatively small area of ​​Cornwall until 2005, but has also been found in Wales and Cheshire, so it suggests that it was spread through the garden plant trade. Due to the national and international demand for such plant products, Phytophthora kernoviae has attracted attention with detection of blueberries ( Vaccinium myrtillus ). The disease causes pronounced necrosis on leaves, bleeding lesions on the shoot axes and their death as primary symptoms, which appear very quickly and extensively. Countless species such as blueberries, cranberries ( Vaccinium vitis-idaea ), bearberries ( Arctostaphylos uva-ursi ) and Pontic rhododendrons ( Rhododendron ponticum ) are especially endangered by P. kernoviae .

Individual evidence

  1. ↑ a b c C. Brasier, PA Beales, SA Kirk, S. Denman, J. Rose: Phytophthora kernoviae sp. Nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK . In: Mycological Research . 109, No. Pt 8, 2005, pp. 853-9. doi : 10.1017 / S0953756205003357 .
  2. ^ Forestry Commission - Plant Health - New Phytophthora . Forestry.gov.uk. Retrieved July 15, 2010.
  3. ↑ a b Plants recorded as natural hosts of Phytophthora kernoviae . FERA. February 26, 2009. Retrieved July 15, 2010.
  4. ^ Forestry Commission, GB: Symptoms of Phytophthora kernoviae . Retrieved October 19, 2015.
  5. ↑ Shouhua Wang: Phytophthora kernoviae , a new threat to our trees and woodlands . Nevada Department of Agriculture. Retrieved October 19, 2015.
  6. ↑ PM 7/112 (1) Phytophthora kernoviae . In: EPPO Bulletin . 43, 2013, pp. 81-93. doi : 10.1111 / epp.12022 .
  7. ↑ a b c Phytophthora ramorum and P. kernoviae . RHS Gardening. Retrieved October 19, 2015.
  8. ↑ a b Clive M. Brasier, Paul A. Beales, Susan A. Kirk, Sandra Denman, Joan Rose: Phytophthora kernoviae sp. nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK . In: Mycological Research . 109, No. 8, August 1, 2005, ISSN  1469-8102 , pp. 853-859. doi : 10.1017 / S0953756205003357 .
  9. ↑ Keith Walters: Phytophthora ramorum and Phytophthora kernoviae in England and Wales - Public Consultation and New Program . US Forest Service. Retrieved October 19, 2015.
  10. ↑ Elliot Mathew: Phytophthora . Botanical Society of Scotland. Retrieved October 19, 2015.
  11. ↑ Consultation on future management of risks from Phytophthora ramorum and Phytophthora kernoviae . Department for Environment, Food and Rural Affairs. July 15, 2008. Retrieved October 19, 2015.
  12. ↑ Mike Benson: Recovery Plan for Phytophthora kernoviae . United States Department of Agriculture. November 2008. Retrieved October 19, 2015.
  13. ↑ a b A threat to our woodlands, heathlands and historic gardens Phytophthora kernoviae . Retrieved October 20, 2015.
  14. ↑ a b c d e E.J. Fichtner, DM Rizzo, SA Kirk, JF Webber: Infectivity and sporulation potential of Phytophthora kernoviae to select North American native plants . In: Plant Pathology . 61, No. 2, August 24, 2011, pp. 224-233. doi : 10.1111 / j.1365-3059.2011.02506.x .
  15. ^ Frank Martin: Phylogenetic relationships of Phytophthora ramorum , P. nemorosa , and P. pseudosyringae , three species recovered from areas in California with sudden oak death . In: The British Mycological Society . 107, No. 12, December 2003, pp. 1379-1391. doi : 10.1017 / S0953756203008785 . Retrieved May 20, 2019.
  16. ^ A b S. Denman, SA Kirk, E. Moralejo, JF Webber: Phytophthora ramorum and Phytophthora kernoviae on naturally infected asymptomatic foliage . In: EPPO Bulletin . 39, No. 1, April 1, 2009, ISSN  1365-2338 , pp. 105-111. doi : 10.1111 / j.1365-2338.2009.02243.x .
  17. ^ A b S. Denman: Phytophthora kernoviae and P. ramorum : host susceptibility and sporulation potential on foliage of susceptible trees 1 . In: EPPO Bulletin . 36, No. 2, 2006, pp. 373-376. doi : 10.1111 / j.1365-2338.2006.01014.x .
  18. ↑ a b A. V. Brown, CM Brasier: Colonization of tree xylem by Phytophthora ramorum , P. kernoviae and other Phytophthora species . In: Plant Pathology . 56, No. 2, April 1, 2007, ISSN  1365-3059 , pp. 227-241. doi : 10.1111 / j.1365-3059.2006.01511.x .
  19. ↑ a b Clive Brasier, Joan Rose, Susan Kirk, Sandra Denman, Joan Webber: Comparative Host Range and Aggressiveness of Phytophthora ramorum and Phytophthora kernoviae sp. nov. on North American and European Trees . In: Proceedings of the Second Sudden Oak Death Science Symposium: The state of our knowledge . 2005.
  20. ^ PA Beales, PG Giltrap, A. Payne, N. Ingram: A new threat to UK heathland from Phytophthora kernoviae on Vaccinium myrtillus in the wild . In: Plant Pathology . 58, No. 2, April 1, 2009, ISSN  1365-3059 , p. 393. doi : 10.1111 / j.1365-3059.2008.01961.x .