Pythium Aristosporum
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''Pythium aristosporum'' is a species of pythium under the class oomycota (often referred to as water molds) that causes root dysfunction in creeping bentgrass.


Hosts and symptoms

''Pythium aristosporum'' causes root dysfunction in creeping bentgrass. Creeping bentgrass is a cool season grass that is found mainly on the putting greens, fairways, and tees of
golf course A golf course is the grounds on which the sport of golf is played. It consists of a series of holes, each consisting of a teeing ground, tee box, a #Fairway and rough, fairway, the #Fairway and rough, rough and other hazard (golf), hazards, and ...
s in the Northern United States due to its ability to be cut at very low heights (an eighth of an inch) and survive winters relatively unharmed. It is ideal for golf courses because it grows stoloniferously (with above ground shoots). This allows the grass grow laterally relatively quickly and form dense ground covers, making it ideal for golf courses. Like the disease name suggests, ''Pythium aristosporum'' affects the roots of creeping bentgrass. While there are no macroscopic signs, there are a few above and belowground symptoms that plants infected with this disease will exhibit. Aboveground, there will be dieback on the tip of the grass blade and the grass will turn from the lush green to a yellow/brown color typically in circular patches. Symptoms aboveground are secondary, and a result of the necrosis of the roots. Belowground, the roots will die back, turn a pale tan color, and lose their root hairs. These symptoms are systemic, as they involve the whole plant, and the mass of root tissue that is lost is a primary symptom because it is a direct result of the pythium. Listed are all macroscopic symptoms, or ones that can be seen without the use of magnification. Microscopically,
hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...
e are visible. The primary survival structures of pythium are oospores and
sporangia A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...
. Oospores and sporangia are circular in shape. Antheridia and
oogonia An oogonium (: oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in lar ...
would also be present on hyphal cells. The oogonium is in the shape of a circle that is connected to the hyphae and the antheridium looks like a branch of hyphae that connects to the oogonium to produce oospores.


Disease cycle

''Pythium aristosporum'' infects plants in a variety of ways such as through wind, water, overwintering in soil, equipment, and infected plants. For the sake of this cycle, the overwintered oospore will be the starting point. Oospores on a plant can use a
germ tube A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination. The germ tube differentiates, grows, and develops by mitosis to create somatic hyphae.C.J. Alexopolous, Charles W. Mims, M. Blackwell, ''Introductory My ...
to get into the cell of a plant. If not already on a plant cell, the oospore will release a zoosporangium that releases zoospores.
Zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...
s have two flagella (one tinselated and one whiplash) and are motile, needing water to move and spread. They then encyst on a cell and develop haustoria as a way to leach nutrients from the cell. Once established in the cell,
mycelium Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...
spread throughout the plant. Sporangia are then able to arise from the mycelia and either directly infect a cell or release zoospores to infect. From there, mycelia are able to spread and the cycle repeats. Because this is able to happen more than once per crop cycle, it is a polycyclic disease. After conditions are no longer conducive to growth and survival (very dry or cold conditions) or the plant has died,
haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...
antheridia and oogonia from the hyphae fertilize together to create
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
oospores.


Environment

Environment plays a key role on whether the disease develops in a plant or not. While the host plant and
microbe A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...
may be present, if the environment is not conducive, then there will not be
disease A disease is a particular abnormal condition that adversely affects the structure or function (biology), function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical condi ...
. Pythium root dysfunction develops in the roots of creeping bentgrass in the fall, winter, and spring when mean soil temperatures are between 50-70°F. This pathogen reduces the ability of roots to absorb water and nutrients from the soil, which makes the disease much more harmful during times of stress, such as low fertility, low soil oxygen levels, and especially drought. Because of this, symptoms are most common during warm periods in the summer when soil temperature is within key range. Due to the disease impacting the roots so heavily, creeping bentgrass in sand-heavy soils fare even worse as sandy soils have excellent infiltration and
percolation In physics, chemistry, and materials science, percolation () refers to the movement and filtration, filtering of fluids through porous materials. It is described by Darcy's law. Broader applications have since been developed that cover connecti ...
.
Turf Sod is the upper layer of turf that is harvested for transplanting. Turf consists of a variable thickness of a soil medium that supports a community of turfgrasses. In British and Australian English, sod is more commonly known as ''turf'', ...
in soils that are high in organic matter content fares better (once infected) because of the soils ability to retain nutrients and moisture, which allows the hindered roots to be able to absorb them better than if in a very well drained soil. While the soils that retain a higher plant available moisture content allow the plant to survive better once infected with the disease, the best way to prevent it is just the opposite-having soils that allow water to drain well and prevent long periods of pooling. Saturated conditions allow zoospores to spread and infect turf root cells, so it is ideal to prevent the ground from being saturated for too long. Insects, like billbugs, can also act as vectors by transferring spores or by feeding on roots and creating openings-allowing the oomycete to enter more easily.


References

{{Taxonbar, from=Q7263875 Water mould plant pathogens and diseases Wheat diseases aristosporum Oomycete species Protists described in 1938