Phytophthora kernoviae

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Phytophthora kernoviae
Phytophthora kernoviae - Beech tree infection cropped.jpg
Necrotic bark on an infected beech tree
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Oomycota
Order: Peronosporales
Family: Peronosporaceae
Genus: Phytophthora
Species:
P. kernoviae
Binomial name
Phytophthora kernoviae
Brasier, (2005)

Phytophthora kernoviae is a plant pathogen that mainly infects European beech ( Fagus sylvatica ) and Rhododendron ponticum . It was first identified in 2003 in Cornwall, UK when scientists were surveying for the presence of Phytophthora ramorum . This made it the third new Phytophthora species to be found in the UK in a decade. [1] It was named Phytophthora kernoviae after the ancient name for Cornwall, Kernow. [2] It causes large stem lesions on beech and necrosis of stems and leaves of Rhododendron ponticum. It is self-fertile. It has also been isolated from Quercus robur and Liriodendron tulipifera . The original paper describing the species, stated it can infect Magnolia and Camellia species, Pieris formosa , Gevuina avellana , Michelia doltsopa and Quercus ilex . [1] Since then many other plants have been identified as natural hosts of the pathogen. Molecular analysis has revealed that an infection on Pinus radiata , recorded in New Zealand in 1950, was caused by P. kernoviae. [3] The pathogen was also noted on Drimys winteri, Gevuina avellana, Ilex aquifolium, Quercus ilex, Vaccinium myrtillus, Hedera helix, Podocarpus salignas. [4]

Contents

Symptoms

Since Phytophthora kernoviae has such serious symptoms it should be seen as a serious threat to both trees and shrubs. On the shrubs of Rhododendron , the disease starts with the blackening of the leaf petiole sometimes extending to the base of the leaf, affecting old and young leaves equally. [5] In addition to this darkening lesion on the stem, leaves can get severe enough lesions to become necrotic and cause entire leaf death. These lesions begin as a progressive blackening of the leaf tissue and spread across the leaf surface. In some cases this necrosis causes dieback and cankers on the infected plant. While symptoms for trees hosts are similar they have a few distinct differences. For the European beech (Fagus sylvatica) host symptoms include dark brown to blue black lesions on the trunk ranging in size and shape depending on severity of the infection. Tulip trees Liriodendron tulipifera are another susceptible host. The pathogen infects and causes many smaller bleeding lesions along the trunk and can even cause lesions on leaf tips. [6] Both shrubs and trees share the characteristic symptoms of leaf necrosis with lesions on the stem and trunk proving the severity of this disease.[ citation needed ]

Diagnosis of the disease can be difficult as symptoms for Phytophthora ramorum and Phytophthora kernoviae can be very similar. One should test samples with DNA extraction of the plant tissue tested against conventional PCR and real-time PCR. If either of these tests come back negative you have a negative sample for P. kernoviae. While positive samples indicate the presence of this pathogen. In addition to this you can use isolation followed by morphological identification. [7]

Environment

Phytophthora kernoviae spreads most quickly and detrimentally in moist conditions such as direct rainfall and also those of heavy humidity. [8] Rain and heavy winds help in the dispersal of spores for further infection. This disease has an optimal growing range of 26–16 °C (79–61 °F). [9] This range suggests that it may have originated in a temperate climate, possibly China, Taiwan, the Himalayas, or even New Zealand before being introduced to the UK. 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. [8]

Management

Since this disease has more recently been identified management practices are still developing. For best management it is most important to remove the sporulating plants in the area of infection. [10] Along with this the clear cutting of trees or complete removal of shrub growth and thorough sanitation including removal of plant debris and leaves in infected area have been attempted to control the spread of the disease. [11] Removal of standing water, properly timed watering and proper irrigation help to prevent the spread of spores through water. In areas of large infection bans can be placed on the removal of host plants and foliage from them. In addition to this bans on hiking trails can be enforced to manage spore transport through human activity. [12] Anti-Phytophthora fungicides may be used in some cases, while these fungicides do not actually kill the organism but prevent it from becoming established or continued growth. Another method currently being used is controlling by culling Rhododendrons within diseased regions. [1] In 2008, an infected Rhododendron ponticum was found in Ireland. [3] More studies will need to be conducted in the spread and reproduction of this disease before more advanced chemical management methods become available. [13]

Life cycle

Phytophthora kernoviae can survive as an oospore, a thick walled resting structure and has been found to survive on infected plant tissues and in soil. Chlamydospores, long term resting structures that are seen in Phytophthora ramorum and other Phytophthora species are not observed in Phytophthora kernoviae. [14] Production of sporangia, oospores, and zoospores were observed on Phytophthora kernoviae. [15] Sporangia are only formed on hosts with susceptible foliage, trunk cankers have not exhibited sporulation and do not spread disease. [15] This creates a simple life cycle for Phytophthora kernoviae. Oospores can germinate and create mouse-shaped sporangia. Sporangia serve as dispersal structures and create and release Zoospores, motile infectious spores. Once released, oospores germinate on the host and infect target host tissues. After infection if the conditions are correct, Phytophthora kernoviae produce sporangia that are dislodged by natural occurrences and spread to nearby plant tissue. [15] In lab settings the production of these sporangia are documented within one week, with the sproangia present six days after inoculation causing documented disease in new plant tissues. [15] The sporangia of Phytophthora kernoviae are spread locally through wind and water dispersion, infecting nearby susceptible tissues, long distance travel is occurs through the movement of infected plant tissues and in soil carried on vehicles, animals and footwear. [14]

Importance

Since 2003, Phytophthora kernoviae has caused marked damage to ornamentals and species of trees in the Southwest United Kingdom. The oomycete pathogen was first discovered in the 1990s, yet only gained widespread attention when it was identified as one of the causal agents, along with P. ramorum, of sudden oak death. [16] Although the main concentration of this pathogen is primarily in South West England, its reach has extended to South Wales, Cheshire, and even further north into Scotland. Recently, this pathogen has been found on the stems and foliage of Rhododendron, most significantly on R. ponticum. [17] Furthermore, the aggressive nature of Phytophthora kernoviae makes it an even more significant concern considering that the mainland of the UK has diverse ecosystems that are susceptible to the impact of this plant pathogen. From the Rhododendron host, infection is able to spread via the air to the bark of tree species, with the European beech tree (Fagus sylvatica) being especially susceptible. [17] As of 2005, it was confined to a relatively small area of Cornwall but has also been found in Wales and Cheshire suggesting that the pathogen may be being spread by the horticultural trade. Due to the national and international demand of these plant products, Phytophthora kernoviae has initiated recent concern after being found Vaccinium myrtillus , commonly called Bilberry. [18] This pathogen causes significant necrosis on leaves, bleeding stem lesions, and stem dieback as the primary symptoms, which occur at an impressive rate. Countless species including V. myrtillus, V. vitis-idaea , Arctostaphylos uva-ursi , and Rhododendron ponticum are all especially vulnerable to P. kernoviae. [9]

Pathogenesis

Phytophthora kernoviae infect through release and wind dispersal of zoospores. It is quick to take advantage of wounds already present on its host, but does not require the host to be injured. [19] One interesting aspect of P. kernoviae is that in one study, only two thirds of typical infections were symptomatic, making it easy for this pathogen and infection to go unnoticed from typical visual inspection. [20] Before infecting the inner bark of European Beech trees, the pathogen causes leaf necrosis and the dieback of shoots in the under-foliage of the forest along with ornamental species. It is here where the sporulation occurs on the infected shoots and foliage, and is able to cause infection of the surrounding trees, giving rise to bleeding cankers on the stems. [20] This pathogen's adaption for aerial dispersal is a key factor in its transmission from initial ornamental host to tree species. [16]

Once on European beech trees, infected phloem will generally show bleeding lesions and discoloration. The color varies based on exposure to oxygen and elapsed time from infection. Often, these lesions will have pink or orange fluid-filled cavities called lagoons in the underlying phloem. The pathogen then occupies the xylem underneath the phloem lesions, which enables it to spread further throughout the vascular plant tissue and give rise to new phloem lesions. Furthermore, the pathogen present in the xylem leads to local dysfunction that furthers to damage the plant tissues, and move into previously healthy bark. [21] Once P. kernoviae has penetrated the xylem, it can continue penetrating for well over 24 months. [21] Tree mortality soon follows, in the matter of a few years from the initial time of infection. [15]

Related Research Articles

<i>Phytophthora</i> Genus of single-celled organisms

Phytophthora is a genus of plant-damaging oomycetes, whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The cell wall of Phytophthora is made up of cellulose. The genus was first described by Heinrich Anton de Bary in 1875. Approximately 210 species have been described, although 100–500 undiscovered Phytophthora species are estimated to exist.

<i>Phytophthora ramorum</i> Species of single-celled organism

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 leading to the death of the tree.

<i>Phytophthora cinnamomi</i> Species of single-celled organism

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.

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.

<i>Phytophthora cactorum</i> Species of single-celled organism

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 citrophthora, also known as brown rot of citrus, is a soil borne oomycete that infects several economically important citrus crops. A diagnostic symptom of P. citrophthora is gummosis, wherein lesions around the base of the tree exude sap. Other common symptoms include dark longitudinal lesions forming at the soil line, a sour smell, and eventual cracking of the bark. Advanced symptoms include yellowing and necrosis of the tree canopy. Girdling action caused by the pathogen around the trunk can often cause the collapse of the tree. Resistant lemon varieties have been developed and their implementation has been effective at controlling the spread of the disease. Fruits that have been infected with P. citrophthora exhibit symptoms of brown rot characterized by a distinct odor. This disease is most active in the moderate temperatures of spring, fall, and winter months, opposite of most other Phytophthora species.

<i>Phytophthora medicaginis</i> Species of single-celled organism

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.

Phytophthora nicotianae or black shank is an oomycete belonging to the order Peronosporales and family Peronosporaceae.

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.

Alternaria dauci is a plant pathogen. The English name of the disease it incites is "carrot leaf blight".

<i>Plasmopara viticola</i> Species of single-celled organism

Plasmopara viticola, the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition release zoospores. Zoospores are splashed by rain into the canopy, where they swim to and infect through stomata. After 7–10 days, yellow lesions appear on foliage. During favorable weather the lesions sporulate and new secondary infections occur.

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.

Peronosclerospora sorghi is a plant pathogen. It is the causal agent of sorghum downy mildew. The pathogen is a fungal-like protist in the oomycota, or water mold, class. Peronosclerospora sorghi infects susceptible plants though sexual oospores, which survive in the soil, and asexual sporangia which are disseminated by wind. Symptoms of sorghum downy mildew include chlorosis, shredding of leaves, and death. Peronosclerospora sorghi infects maize and sorghum around the world, but causes the most severe yield reductions in Africa. The disease is controlled mainly through genetic resistance, chemical control, crop rotation, and strategic timing of planting.

<i>Peronospora destructor</i> Species of single-celled organism

Peronospora destructor is a plant pathogen. It causes downy mildew on leaves of cultivated and wild Allium. Allium cepa is most often affected, while Allium schoenoprasum (chives) and Allium porrum (leek) are only occasionally affected.

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.

Phytophthora hydropathica is an oomycete plant pathogen that is found in aquatic environments such as irrigation and river water. The pathogen was previously classified as P. drechsleri Dre II before being categorized as its own distinct species. P. hydropathica has been primarily found in association with ornamental plant nurseries. The pathogen has been isolated throughout the Southern United States, as well as internationally in Mexico, Italy, and Spain.

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.

References

  1. 1 2 3 Brasier, C; Beales, PA; Kirk, SA; Denman, S; Rose, J (2005). "Phytophthora kernoviae sp. Nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK" (PDF). Mycological Research. 109 (Pt 8): 853–9. doi:10.1017/S0953756205003357. PMID   16175787. Archived from the original (PDF) on 15 March 2012. Retrieved 21 May 2009.
  2. ↑ "Forestry Commission - Plant Health - New Phytophthora". Forestry.gov.uk. Retrieved 15 July 2010.
  3. 1 2 "Plants recorded as natural hosts of Phytophthora kernoviae" (PDF). FERA. 26 February 2009. Archived from the original (PDF) on 8 December 2015. Retrieved 15 July 2010.
  4. ↑ Александров И.Н. (2012). "Phytophthora kernoviae – новый патоген декоративных и древесных культур". Современная микология в России. Том 3. Материалы 3-го съезда микологов России. М., Национальная академия микологии.
  5. ↑ GB, Forestry Commission. "Symptoms of Phytophthora kernoviae". www.forestry.gov.uk. Retrieved 19 October 2015.
  6. ↑ Wang, Shouhua. "Phytophthora kernoviae, a new threat to our trees and woodlands" (PDF). Nevada Department of Agriculture. Retrieved 19 October 2015.
  7. ↑ "PM 7/112 (1) Phytophthora kernoviae". EPPO Bulletin. 43: 81–93. 2013. doi: 10.1111/epp.12022 .
  8. 1 2 "Phytophthora ramorum and P. kernoviae/RHS Gardening". www.rhs.org.uk. Retrieved 19 October 2015.
  9. 1 2 Brasier, Clive M.; Beales, Paul A.; Kirk, Susan A.; Denman, Sandra; Rose, Joan (1 August 2005). "Phytophthora kernoviae sp. nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK". Mycological Research. 109 (8): 853–859. doi:10.1017/S0953756205003357. ISSN   1469-8102. PMID   16175787.
  10. ↑ Walters, Keith. "Phytophthora ramorum and Phytophthora kernoviae in England and Wales - Public Consultation and New Programme" (PDF). United States Department of Agriculture. US Forest Service. Retrieved 19 October 2015.
  11. ↑ Mathew, Elliot. "Phytophthora | Botanical Society of Scotland". www.botanical-society-scotland.org.uk. Retrieved 19 October 2015.
  12. ↑ "Consultation on future management of risks from Phytophthora ramorum and Phytophthora kernoviae" (PDF). Forestry Commission. Department for Environment, Food and Rural Affairs. 15 July 2008. Retrieved 19 October 2015.
  13. ↑ Benson, Mike (November 2008). "Recovery Plan for Phytophthora kernoviae" (PDF). Agriculture Research Service. United States Department of Agriculture. Retrieved 19 October 2015.
  14. 1 2 "A threat to our woodlands, heathlands and historic gardens Phytophthora kernoviae" (PDF). fera.co.uk. Archived from the original (PDF) on 8 December 2015. Retrieved 20 October 2015.
  15. 1 2 3 4 5 Fichtner, E.J.; Rizzo, D.M.; Kirk, S.A.; Webber, J.F. (24 August 2011). "Infectivity and sporulation potential of Phytophthora kernoviae to select North American native plants". Plant Pathology. 61 (2): 224–233. doi: 10.1111/j.1365-3059.2011.02506.x .
  16. 1 2 Denman, S.; et al. (2006). "Phytophthora kernoviae and P. ramorum: host susceptibility and sporulation potential on foliage of susceptible trees1". EPPO Bulletin. 36 (2): 373–376. doi:10.1111/j.1365-2338.2006.01014.x.
  17. 1 2 Brasier, C. M., et al. "Comparative host range and aggressiveness of Phytophthora ramorum and Phytophthora kernoviae sp. nov. on North American and European trees." Proceedings of the Second Sudden Oak Death Science Symposium: The state of our knowledge. 2005.
  18. ↑ Beales, P. A.; Giltrap, P. G.; Payne, A.; Ingram, N. (1 April 2009). "A new threat to UK heathland from Phytophthora kernoviae on Vaccinium myrtillus in the wild". Plant Pathology. 58 (2): 393. doi: 10.1111/j.1365-3059.2008.01961.x . ISSN   1365-3059.
  19. ↑ Martin, Frank (December 2003). "Phylogenetic relationships of Phytophthora ramorum, P. nemorosa, and P. pseudosyringae, three species recovered from areas in California with sudden oak death". The British Mycological Society. 107 (12): 1379–1391. doi:10.1017/S0953756203008785. PMID   15000239.
  20. 1 2 Denman, S.; Kirk, S. A.; Moralejo, E.; Webber, J. F. (1 April 2009). "Phytophthora ramorum and Phytophthora kernoviae on naturally infected asymptomatic foliage". EPPO Bulletin. 39 (1): 105–111. doi:10.1111/j.1365-2338.2009.02243.x. ISSN   1365-2338.
  21. 1 2 Brown, A. V.; Brasier, C. M. (1 April 2007). "Colonization of tree xylem by Phytophthora ramorum, P. kernoviae and other Phytophthora species". Plant Pathology. 56 (2): 227–241. doi: 10.1111/j.1365-3059.2006.01511.x . ISSN   1365-3059.
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