Podosphaera macularis: Difference between revisions
m →Management: Misc. fixes |
m →Disease cycle: Misc. fixes |
||
| Line 31: | Line 31: | ||
plants. Spots may fade to gray or white as the season progresses. Signs include white clusters of hyphae, which are often present on the leaves, and in some cases can infect the cone itself. If this infection occurs, a brown, necrotic lesion may develop. Occasionally, chleistothecia are visible as small, black dots on the undersides of leaves. |
plants. Spots may fade to gray or white as the season progresses. Signs include white clusters of hyphae, which are often present on the leaves, and in some cases can infect the cone itself. If this infection occurs, a brown, necrotic lesion may develop. Occasionally, chleistothecia are visible as small, black dots on the undersides of leaves. |
||
== Disease |
== Disease cycle == |
||
Podosphaera macularis overwinters in the soil as fungal survival structures (chasmothecia) or as mycelia in plant buds.<ref name=":0" /> These chasmothecia are formed closer to the end of the growing season. In addition, the morphology of chasmothecia are spherical black structures with spiked appendages. When the chasmothecia encounter favorable conditions during early |
''Podosphaera macularis'' overwinters in the soil as fungal survival structures ([[chasmothecia]]) or as [[mycelia]] in plant buds.<ref name=":0" /> These chasmothecia are formed closer to the end of the growing season. In addition, the morphology of chasmothecia are spherical black structures with spiked appendages. When the chasmothecia encounter favorable conditions during early spring, they will rupture and release asci (sac-like structures), which contain [[ascospore]]s. Favorable conditions for ascospore release include low light, excess fertility, and high soil moisture.<ref name=":0">{{cite web |url=http://www.plantpath.wisc.edu/wivegdis/pdf/2015/Hop%20PM%20A4053-02.pdf |title=Hop Powdery Mildew |date=December 2014 |accessdate=October 19, 2015 |website=University of Wisconsin-Extension |publisher=University of Wisconsin |last=Marks |first=Michelle |last2=Gevens |first2=Amanda}}</ref> Optimal infection is observed when the temperature is between 64 and 70 degrees Fahrenheit.<ref name=":1">{{cite web |url=http://www.uvm.edu/extension/cropsoil/wp-content/uploads/PowderyMildew.pdf |title=Managing Powdery Mildew of Hops in the Northeast |date=July 2011 |accessdate=October 19, 2015 |website=University of Vermont-Extension |publisher=University of Vermont |last=Madden |first=Rosalie |last2=Darby |first2=Heather}}</ref> These ascospores are sexual spores produced by [[meiosis]]. Furthermore, the ascospores act as the primary inoculum and are dispersed by wind and rain splash. Upon encountering a susceptible host plant, the ascospores will germinate and cause infection. Following infection, masses of asexual spores ([[conidia]]) will be produced during the season.<ref name=":0" /> It is these masses of conidia that contribute to the characteristic white, powdery appearance of infected plants. The lower leaves are the most affected, but the disease can appear on any part of the plant that is above the ground.<ref name=":1" /> Conidia are dispersed through wind, rain splash, insects, tractors, other farming equipment, and humans. Thus, ''Podosphaera macularis'' is a polycyclic pathogen as conidia are produced/dispersed during the growing season and can further infect additional host plants. Particularly, the disease will be noticeable as the hop shoots start to emerge. These shoots that emerge from infected buds are called “flag shoots,” which will covered with spores.<ref name=":1" /> Additionally, these flag shoots will be stunted with distorted leaves. Periods of rapid plant growth are the most favorable for infection. Also, the time in which lateral branch development takes place is also very vulnerable to the development of the disease.<ref name=":1" /> Due to ''Podosphaera macularis'' causing local infection, only the location of the host plant tissue where spores have landed will develop the disease. |
||
== Management == |
== Management == |
||
Revision as of 22:47, 20 October 2015
| Podosphaera macularis | |
|---|---|
| |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Subclass: | |
| Order: | |
| Family: | |
| Genus: | |
| Species: | P. macularis
|
| Binomial name | |
| Podosphaera macularis (Wallr.) U. Braun & S. Takam., (2000)
| |
| Synonyms | |
|
Alphitomorpha macularis | |
Podosphaera macularis (formerly Sphaerotheca macularis) is a plant pathogen infecting several hosts including chamomile, caneberrie, strawberries, hop, hemp and Cineraria. It causes powdery mildew of hops.
Host range and symptoms of Podosphaera macularis
The pathogen that causes powdery mildew of hops was once considered to be Sphaerotheca macularis, which is capable of infecting many plants; however, in recent years, the pathogen that causes powdery mildew of hops has been taxonomically classified as Podosphaera macularis.[1] This ascomycete is only pathogenic on hop plants, including both ornamental and wild hops. The host range of many Podosphaera macularis strains is restricted by the existence of resistant hop varieties, such as the “Nugget” variety of Washington state and Oregon, although in recent years, resistance within this hop variety has been overcome in the laboratory. [2] When disease does occur, early symptoms include chlorotic spots on the leaves of hop plants. Spots may fade to gray or white as the season progresses. Signs include white clusters of hyphae, which are often present on the leaves, and in some cases can infect the cone itself. If this infection occurs, a brown, necrotic lesion may develop. Occasionally, chleistothecia are visible as small, black dots on the undersides of leaves.
Disease cycle
Podosphaera macularis overwinters in the soil as fungal survival structures (chasmothecia) or as mycelia in plant buds.[3] These chasmothecia are formed closer to the end of the growing season. In addition, the morphology of chasmothecia are spherical black structures with spiked appendages. When the chasmothecia encounter favorable conditions during early spring, they will rupture and release asci (sac-like structures), which contain ascospores. Favorable conditions for ascospore release include low light, excess fertility, and high soil moisture.[3] Optimal infection is observed when the temperature is between 64 and 70 degrees Fahrenheit.[4] These ascospores are sexual spores produced by meiosis. Furthermore, the ascospores act as the primary inoculum and are dispersed by wind and rain splash. Upon encountering a susceptible host plant, the ascospores will germinate and cause infection. Following infection, masses of asexual spores (conidia) will be produced during the season.[3] It is these masses of conidia that contribute to the characteristic white, powdery appearance of infected plants. The lower leaves are the most affected, but the disease can appear on any part of the plant that is above the ground.[4] Conidia are dispersed through wind, rain splash, insects, tractors, other farming equipment, and humans. Thus, Podosphaera macularis is a polycyclic pathogen as conidia are produced/dispersed during the growing season and can further infect additional host plants. Particularly, the disease will be noticeable as the hop shoots start to emerge. These shoots that emerge from infected buds are called “flag shoots,” which will covered with spores.[4] Additionally, these flag shoots will be stunted with distorted leaves. Periods of rapid plant growth are the most favorable for infection. Also, the time in which lateral branch development takes place is also very vulnerable to the development of the disease.[4] Due to Podosphaera macularis causing local infection, only the location of the host plant tissue where spores have landed will develop the disease.
Management
The three primary ways to control Podosphaera macularis are cultural, chemical, and mechanical control. The most effective way to manage hop powdery mildew is through preventative measures. Cultural/mechanical control of the disease include growing powdery-mildew tolerant/resistant varieties of the host plant.[4] Cultural practices that can help prevent the disease include carefully monitoring water and nutrient, reducing initial inoculum, and removing basal growth. Furthermore, pruning, crowning, and/or scratching will aid in further reduction of the disease.[4] Pruning consists of removing shoots before training. Crowning refers to the process of the top 1–2 inches of the crown are removed before budbreak. Scratching is done through disturbing the soil surface to remove the top 1–2 inches of buds.[4] All of these methods disturb the overwintering stage of the life cycle of Podosphaera macularis. Likewise, chemical control primarily consists of spraying fungicides in hopes of preventing the disease through the use of early, continuous spraying during the growing season. Thus, prophylactic fungicide programs can be a very effective way in preventing the disease.[3] Since the fungicides are a preventative measure, they are not very useful to use during a full-blown infection. Therefore, the use of fungicides disturbs release of spores and further infection within the disease cycle of Podosphaera macularis. As there are several fungicides that are effective against powdery mildew, it is important to apply the fungicides at specific times. If it is known that powdery mildew is present, spray programs should be started as soon as the shoots emerge. As powdery mildew is quick to develop resistance to fungicides, it is important to rotate the fungicides that are used.[5] Few or no fungicide applications should be used during burr development as these burrs have increased vulnerability to damage.[3] In this case, removing basal growth before flowering and applying a protectant fungicide with long-term residual action should be employed.
Pathogenesis of Podosphaera macularis
In order for pathogenesis to occur, a viable pathogen, susceptible host, and conducive environment must simultaneously be present. The germ tube of P. macularis plays an important role in determining the pathogen’s viability, because it can penetrate its host in approximately 15 hours. The germ tube begins branching, leading to as many as three potentially conidia-forming germ tubes. As the pathogen invades host tissue, it establishes a haustorium to facilitate the collection of nutrients from the host cells. Despite this invasion, only certain hosts are susceptible, because there are seven R genes in hop varieties that can be activated in response to infection. Many of them operate by either causing the initial haustorium to lyse, or by preventing the pathogen from spreading. The spread is slowed by a hypersensitive response, which is often associated with the establishment of large callose and lignin deposits surrounding infected cells. Although susceptible plants can increase callose and lignin deposits in response to infection, the hypersensitive response is only found in resistant varieties. Finally, although powdery mildew can grow in a relatively hot and dry environment compared to downy mildew, conidia production peaks at temperatures of approximately 25oC. Conidia can be produced at temperatures above 25oC, but their infectivity is often reduced.[6]
External links
References
- ^ Darby, P (1998). "The symptoms and biology of hop powdery mildew". Hop Powdery Mildew Electronic Symposium, (Proceedings, 1998 US Hop Industry Joint Meeting, Yakima, Washington, 19-23 January 1998).
- ^ Smith, J (2005). "Powdery Mildew (Podosphaera macularis Braun & Takamatsu) Resistance in Wild Hop Genetic Resources". Unpublished Master's Thesis.
- ^ a b c d e Marks, Michelle; Gevens, Amanda (December 2014). "Hop Powdery Mildew" (PDF). University of Wisconsin-Extension. University of Wisconsin. Retrieved October 19, 2015.
- ^ a b c d e f g Madden, Rosalie; Darby, Heather (July 2011). "Managing Powdery Mildew of Hops in the Northeast" (PDF). University of Vermont-Extension. University of Vermont. Retrieved October 19, 2015.
- ^ Eyck, Laura; Gehring, Dietrich (2015). The Hop Grower's Handbook: The Essential Guide for Sustainable, Small-Scale Production for Home and Market. Chelsea Green Publishing. pp. 156–161. ISBN 978-1-60358-555-2.
- ^ Peetz, Amy B.; Mahaffee, Walter F.; Gent, David H. "Effect of Temperature on Sporulation and Infectivity of Podosphaera macularis on Humulus lupulus". Plant Disease. 93 (3): 281–286. doi:10.1094/PDIS-93-3-0281.
 | This plant disease article is a stub. You can help Wikipedia by expanding it. |