Heterodera avenae
Encyclopedia
Heterodera avenae, the cereal cyst nematode or Ustinov cyst nematode, is a plant pathogen and an obligate parasite
of cereal crops including barley
, oats
, wheat
and rye
. Cereal crops infected with this nematode are more prone to infection by fungal diseases such as rhizoctonia
root rot.
exhibits sexual dimorphism
. The female is rounded and white and measures 680 by 930 micrometres. The male is vermiform and transparent and measures 40 by 1300 micrometres. The eggs
are oval and the vermiform larvae
moult four times. The second instar
larvae are mobile and can travel distances of up to thirty centimetres, looking for and invading roots of suitable host species. Here they develop, growing into sedentary bottle-shaped third instar larvae and rounded fourth instar ones. These then develop into either females or males and mating takes place. The female retains the majority of the several hundred eggs she produces inside her body. She turns into a brown cyst
by the end of plant growth season, as her external surface hardens and her internal parts die. The larvae may remain in anabiosis within this cyst for several years until suitable host plants become available. The cysts can withstand harsh conditions and can be spread in soil, by agricultural machinery, by animals, by wind, by dust storms or other means.
When nematode populations are high, significant losses in yield can occur. All wheat varieties are susceptible but some cultivars do not support cyst formation.
It was found in trials that direct-drilling that did not disturb the soil below seeding depth reduced the incidence of cereal cyst nematode but did not have the same effect on the other serious cereal seedling diseases of rhizoctonia root rot and take-all
. Control is by crop rotation, fallowing and the use of less susceptible varieties.
Obligate parasite
An obligate parasite is a parasitic organism that cannot complete its life cycle without dependence on its host.-See also:*Obligate intracellular parasite*Parasitism*Parasitic plant*Facultative parasite...
of cereal crops including barley
Barley
Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...
, oats
OATS
OATS - Open Source Assistive Technology Software - is a source code repository or "forge" for assistive technology software. It was launched in 2006 with the goal to provide a one-stop “shop” for end users, clinicians and open-source developers to promote and develop open source assistive...
, wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
and rye
Rye
Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...
. Cereal crops infected with this nematode are more prone to infection by fungal diseases such as rhizoctonia
Rhizoctonia
Rhizoctonia is a genus of anamorphic fungi in the order Cantharellales. Species do not produce spores, but are composed of hyphae and sclerotia and are asexual states of fungi in the genus Thanatephorus. Rhizoctonia species are saprotrophic, but are also facultative plant pathogens, causing...
root rot.
Life cycle
This microscopic nematodeNematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
exhibits sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. The female is rounded and white and measures 680 by 930 micrometres. The male is vermiform and transparent and measures 40 by 1300 micrometres. The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are oval and the vermiform larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
moult four times. The second instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
larvae are mobile and can travel distances of up to thirty centimetres, looking for and invading roots of suitable host species. Here they develop, growing into sedentary bottle-shaped third instar larvae and rounded fourth instar ones. These then develop into either females or males and mating takes place. The female retains the majority of the several hundred eggs she produces inside her body. She turns into a brown cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
by the end of plant growth season, as her external surface hardens and her internal parts die. The larvae may remain in anabiosis within this cyst for several years until suitable host plants become available. The cysts can withstand harsh conditions and can be spread in soil, by agricultural machinery, by animals, by wind, by dust storms or other means.
Economic significance
Infection with cereal cyst nematode is associated with a reduction in grain yield which may be of significant proportions. Thresholds of harmfulness depend on the population density of the nematode and differ among various cultivars and varieties. The weather conditions and soil types are also an important factor, with infections being increased in damp, warm growing seasons. The symptoms of infection include stunting and yellowing of the visible parts of the plant which may give the crop an uneven appearance. The presence of the disease can be established by inspecting the root system of plants and looking for abnormal development. The roots of infested plants develop a tangle of branches and swellings which are white when young but turn dark brown with age. It is the seedlings of cereals that are most readily infected with this nematode and damaged roots are often invaded by soil-borne pathogens such as root and crown rots.When nematode populations are high, significant losses in yield can occur. All wheat varieties are susceptible but some cultivars do not support cyst formation.
It was found in trials that direct-drilling that did not disturb the soil below seeding depth reduced the incidence of cereal cyst nematode but did not have the same effect on the other serious cereal seedling diseases of rhizoctonia root rot and take-all
Take-all
Take-all is a plant disease affecting the roots of cereal plants in temperate climates caused by the fungus Gaeumannomyces graminis var. tritici. All varieties of wheat and barley are susceptible...
. Control is by crop rotation, fallowing and the use of less susceptible varieties.