Black rot on orchids

Last updated

Black rot on orchids is caused by Pythium and Phytophthora species. [1] Black rot targets a variety of orchids but Cattleya orchids are especially susceptible. [1] Pythium ultimum and Phytophthora cactorum are known to cause black rot in orchids. [1]

Contents

Pythium ultimum is a pathogen that causes damping-off and root rot on plants. [2] Symptoms of this pathogen include stunting and chlorosis. [2] Identifying Pythium ultimum has traditionally been done by examining oogonia, antheridia, and sporangium structure. [2] Now, PCR (polymerase chain reaction) technology can identify the pathogen using DNA fragments. [2]

Phytophthora cactorum is a pathogen that causes root rot on many plant species. [3] Symptoms of this pathogen include necrosis in the roots, chlorosis, and wilting. [3] Phytophthora cactorum can be identified by examining oogonia, antheridium, oospore, and sporangia structure. [4]

Disease cycle


Pythium ultimum

P. ultimum requires moist conditions to germinate. [2] When conditions are favorable, surviving oospores in the soil produce a sporangia and zoospores which facilitate infection via germ tube. [2] From there, mycelium will grow throughout all plant tissues. [2] The disease is primarily a root rot that causes symptoms of foliar blight. Sporangia are produced on the mycelium and can produce zoospores for asexual reproduction or an oogonium and antheridium for sexual reproduction. [2] Once the oogonium is fertilized, the oospore either infects via germ tube or produces sporangia and zoospores. [2]

Phytophthora cactorum

P. cactorum requires free water to reproduce. [1] Zoospores are released from sporangium and blown via wind or rain splash and use free water on the leaf to germinate. [1] An appressorium is formed and a penetration peg penetrates the leaf surface. [1] From there, hyphae grow throughout the leaf and infects all plant tissues. [1] While this pathogen enters through the leaf, the disease is caused by root rot that causes symptoms of foliar blight. The mycelium gives rise to chlamydospores and oospores. [1] Oospores produce mycelium that produce sporangia. [1] Oospores are the survival structure of P. cactorum. [1] Chlamydospores produce mycelium that continues to infect the plant. [1]

Environmental conditions


Pythium ultimum

Pythium species rely on moist soils and cool conditions. [5] Moist conditions allow the movement of zoospores which infect the plant. [2] From here, the fungus penetrates the leaf surface and mycelial growth takes over the plant. [2]

Phytophthora cactorum

Phytophthora species thrive in moist soils. When there is free water in the soil, conditions are met for sporangia to be produced. [6] As the disease cycle mentioned, sporangia produce zoospores which are infectious. Spring and autumn also produce temperatures that are most favorable for zoospore production. [6]

Control and management

Avoiding black rot in orchids is challenging. Avoiding symptomatic plants and isolating new plants from larger populations is helpful. [7] In addition, decontaminating pots, tools, and work surfaces ensures that there are no contamination that could infect healthy plants. Potting media should also be sterilized as spores and hyphae can survive in dust or free water. [3] Being careful not to over water, providing good drainage, air circulation, and proper potting media are helpful to prevent zoospores from having an optimal environment to move and infect. [7] Fungicides are also used. The primary fungicide treatments to control black rot are metalaxyl, fosetyl-AI, and etridiazole that are sprayed onto the plant. [7] Poultices such as copper sulfate and lime or cinnamon can also be useful fungicides. [7]

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.

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.

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

Phytophthora palmivora is an oomycete that causes bud-rot of palms, fruit-rot or kole-roga of coconut and areca nut. These are among the most serious diseases caused by fungi and moulds in South India. It occurs almost every year in Malnad, Mysore, North & South Kanara, Malabar and other areas. Similar diseases of palms are also known to occur in Sri Lanka, Mauritius, and Sumatra. The causative organism was first identified as P. palmivora by Edwin John Butler in 1917.

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.

<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 Peronosprales 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.

Pythium ultimum is a plant pathogen. It causes damping off and root rot diseases of hundreds of diverse plant hosts including corn, soybean, potato, wheat, fir, and many ornamental species. P. ultimum belongs to the peronosporalean lineage of oomycetes, along with other important plant pathogens such as Phytophthora spp. and many genera of downy mildews. P. ultimum is a frequent inhabitant of fields, freshwater ponds, and decomposing vegetation in most areas of the world. Contributing to the widespread distribution and persistence of P. ultimum is its ability to grow saprotrophically in soil and plant residue. This trait is also exhibited by most Pythium spp. but not by the related Phytophthora spp., which can only colonize living plant hosts.

Phytophthora erythroseptica—also known as pink rot along with several other species of Phytophthora—is a plant pathogen. It infects potatoes causing their tubers to turn pink and damages leaves. It also infects tulips (Tulipa) damaging their leaves and shoots.

Pythium aphanidermatum is a soil borne plant pathogen. Pythium is a genus in the class Oomycetes, which are also known as water molds. Oomycetes are not true fungi, as their cell walls are made of cellulose instead of chitin, they are diploid in their vegetative state, and they form coenocytic hyphae. Also, they reproduce asexually with motile biflagelette zoospores that require water to move towards and infect a host. Sexually, they reproduce with structures called antheridia, oogonia, and oospores.

Pythium aristosporum is a species of pythium under the class oomycota that causes root dysfunction in creeping bentgrass.

Pythium graminicola is a plant pathogen infecting cereals.

Pythium myriotylum is a soil-borne oomycete necrotroph that has a broad host range, this means that it can infect a wide range of plants.

Pythium volutum is a plant pathogen infecting wheat, barley, and turfgrass. It is known to be sensitive to some of the compounds typically present in selective media commonly used for isolating Pythium spp., so isolation may require alternative methods.

Sclerophthora macrospora is a protist plant pathogen of the class Oomycota. It causes downy mildew on a vast number of cereal crops including oats, rice, maize, and wheat as well as varieties of turf grass. The common names of the diseases associated with Sclerophthora macrospora include “crazy top disease” on maize and yellow tuft disease on turf grass. The disease is present all over the world, but it is especially persistent in Europe.

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

Phytophthora capsici is an oomycete plant pathogen that causes blight and fruit rot of peppers and other important commercial crops. It was first described by L. Leonian at the New Mexico State University Agricultural Experiment Station in Las Cruces in 1922 on a crop of chili peppers. In 1967, a study by M. M. Satour and E. E. Butler found 45 species of cultivated plants and weeds susceptible to P. capsici In Greek, Phytophthora capsici means "plant destroyer of capsicums". P. capsici has a wide range of hosts including members of the families Solanaceae and Cucurbitaceae as well as Fabaceae.

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.

Globisporangium sylvaticum is a plant pathogen, an oomycete known to cause root rot and damping off in a multitude of species. These species include apples, carrot, cherry laurel, cress, cucumber, garlic, lettuce, pea, rhododendron, and spinach. Symptoms of infection include stunting, wilt, chlorosis, and browning and eventual necrosis of roots. The pathogen can by identified by the presence of thick, microscopic, round spores within the cells of the root.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 "Black Rot". www.aos.org. 31 March 2016. Retrieved 21 December 2019.
  2. 1 2 3 4 5 6 7 8 9 10 11 Cheng, L (2007). "Pythium ultimum". projects.ncsu.edu.
  3. 1 2 3 "UC IPM: UC Management Guidelines for Pythium Root Rot on Floriculture and Ornamental Nurseries". ipm.ucanr.edu. Retrieved 21 December 2019.
  4. ↑ Rivard, C. "Phytophthora cactorum". projects.ncsu.edu. Retrieved 21 December 2019.
  5. ↑ "Disease Caused by Pythium (Pythium)". Pythium (Penn State University).
  6. 1 2 Wilcox, W. F. (1992), "Phytophthora root and crown rots. Phytophthora spp.(deBary)", Tree Fruit Crops-Cornell Cooperative Extension
  7. 1 2 3 4 Hudelson, B. D. "Common Diseases of Orchids and Management" (PDF). WISC. Retrieved 21 December 2019.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.