Pythium dissotocum
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''Pythium dissotocum'' is a plant pathogen infecting strawberry and
rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...
.


Disease cycle

''Pythium dissotocum'' is a polycyclic
oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...
root rot capable of both
sexual Sex is the biological distinction of an organism between male and female. Sex or SEX may also refer to: Biology and behaviour *Animal sexual behaviour **Copulation (zoology) **Human sexual activity **Non-penetrative sex, or sexual outercourse ** ...
and asexual reproduction. In its mid-season asexual phase, ''P. dissotocum'' disperses by forming filamentous
sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...
, which produce vesicles housing 10-75 motile
zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or ...
s. Vesicles open, releasing zoospores which contact host roots, encyst, and produce a germ tube which infects the host root, and begins formation of mycelium. In sexual reproduction, if multiple mating types are present, hyphal
antheridium An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...
can contact each other and undergo
plasmogamy Plasmogamy is a stage in the sexual reproduction of fungi, in which the protoplasm of two parent cells (usually from the mycelia) fuse without the fusion of nuclei, effectively bringing two haploid nuclei close together in the same cell. This sta ...
, merging their membranes near the end of growing season. After several steps of differentiation and meiosis, an oospore, the primary survival structure, is formed. These thick-walled oospores can remain dormant for many months, and will eventually germinate through two methods. A sporangium can be produced, which generates a cyst and releases zoospores, or the oospore can create a germ tube which can directly penetrate and infect a host. This disease cycle is extremely dependent on water for dispersal, making greenhouses, irrigation systems, and hydroponics especially prone to spread of ''P. dissotocum.''


Importance

''P. dissotocum'' is primarily a water-borne pathogen, and as a result poses serious threats to plants managed via
hydroponics Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plant ...
and by
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...
.Bagnall, Roger Cuan. 2007. “Control of Pythium Wilt and Root Rot of Hydroponically Grown Lettuce by Means of Chemical Treatment of the Nutrient Solution.” Dissertation, University of Pretoria. https://repository.up.ac.za/handle/2263/24109. With motile spores that can move quickly, infection spreads rapidly in water-logged crops and hydroponic systems. ''P. dissotocum'' can infect a large range of hosts, including many agricultural and horticultural crops like lettuce, spinach, peppers, parsnip, parsley, tomato, sugar cane, and carrot and hydroponic ''
Cannabis sativa ''Cannabis sativa'' is an annual herbaceous flowering plant indigenous to Eastern Asia, but now of cosmopolitan distribution due to widespread cultivation. It has been cultivated throughout recorded history, used as a source of industrial fibe ...
''. Other economic products are threatened by the presence of ''P. dissotocum'', including tree nurseries, maize/corn, and
soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu a ...
s. Infection of ''P. dissotocum'' can lead to significant loss of crop yield due to necrosis of roots, root
lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classif ...
s,
chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...
, and
damping off Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions. Symptoms There ar ...
. This results in severe economic loss for farmers growing both sustenance crops, and commercial products. The organism is found in many regions across the Americas, Europe, and Asia, meaning that increasing globalization could cause introduction of the pathogen to potentially vulnerable crops and ecosystems.


Control

As a root rot, it tends to have more severe effects on young plants and seedlings, where it can damage and kill newly forming roots necessary for plant growth and nutrient acquisition. As a result, many control methods involve limiting the amount of exposure early in the season. Effective measure include application of fungicides like mefenoxam and
phosphonate In organic chemistry, phosphonates or phosphonic acids are organophosphorus compounds containing groups (where R = alkyl, aryl, or just hydrogen). Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly ...
s, often in conjunction. Additionally, inoculation with '' Pseudomonas chlororaphis,'' a common
biocontrol Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also in ...
inoculant used in
horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
, has potential to suppress symptoms of ''P. dissotocum'' infection, but is currently inconsistent in current trials, and doesn't block colonization. Like most root rots, ''P. dissotocum'' thrives in wet conditions. Preventing over-watering will help reduce infection in soil. Engaging in sanitation or fungicide treatment of tools and water can help reduce transmission and infection of ''P. dissotocum'' especially in irrigation or hydroponic systems. If infection has occurred, recovery can sometimes occur by trimming off damaged roots, and sterilizing those that are still white and healthy.


References


External links


USDA ARS Fungal Database
{{Taxonbar, from=Q7263879 dissotocum Water mould plant pathogens and diseases Water mould strawberry diseases Rice diseases