Barley yellow dwarf (BYD) is a plant disease caused by the ''barley yellow dwarf virus'' (BYDV), and is the most widely distributed viral disease of cereals. It affects the economically important crop species

barley Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikele ...

oat The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural). Oats appear to have been domesticated as a secondary crop, as their seeds ...

wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

triticale Triticale (; × ''Triticosecale'') is a hybrid of wheat (''Triticum'') and rye (''Secale'') first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation ...

and

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

Virus

Barley yellow dwarf is caused by barley yellow dwarf viruses. They contain genomes made of ribonucleic acid (RNA). Seven species of barley yellow dwarf virus are recognized, classified as follows: * Kingdom: ''

Orthornavirae ''Orthornavirae'' is a kingdom of viruses that have genomes made of ribonucleic acid (RNA), including genes which encode an RNA-dependent RNA polymerase (RdRp). The RdRp is used to transcribe the viral RNA genome into messenger RNA (mRNA) and t ...

'' ** Phylum: '' Kitrinoviricota'' *** Class: '' Tolucaviricetes'' **** Order: '' Tolivirales'' ***** Family: ''

Tombusviridae ''Tombusviridae'' is a family of single-stranded positive sense RNA plant viruses. The family contains 18 genera in 3 subfamilies. The name is derived from Tomato bushy stunt virus (TBSV). Genome All viruses in the family have a non-segmente ...

'' ****** Genus: '' Luteovirus'' ******* ''Barley yellow dwarf virus kerII'' ******* ''Barley yellow dwarf virus kerIII'' ******* ''Barley yellow dwarf virus MAV'' ******* ''Barley yellow dwarf virus PAS'' ******* ''Barley yellow dwarf virus SGV'' ** Phylum: '' Pisuviricota'' *** Class: '' Pisoniviricetes'' **** Order: '' Sobelivirales'' ***** Family: '' Solemoviridae'' ****** Genus: ''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' ******* ''Barley yellow dwarf virus GPV'' ******* ''Barley yellow dwarf virus SGV''

Pathology

When aphids feed on the

phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is ...

of the leaf, the virus is transmitted to the phloem cells. Once inside the plant, the virus begins to replicate and assemble new virions. This process requires significant metabolic input from the plant, and causes the symptoms of barley yellow dwarf disease. The symptoms of barley yellow dwarf vary with the affected crop

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

, the age of the plant at the time of infection, the strain of the virus, and environmental conditions, and can be confused with other disease or physiological disorders. Symptoms appear approximately 14 days after infection. Affected plants show a yellowing or reddening of leaves (on oats and some wheats), stunting, an upright posture of thickened stiff leaves, reduced root growth, delayed (or no) heading, and a reduction in yield. The heads of affected plants tend to remain erect and become black and discoloured during ripening due to colonization by

saprotrophic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...

fungi. Young plants are the most susceptible. Barley Yellow Dwarf Virus in wheat

The virus is transmitted from the phloem when the aphid feeds. When the aphid feeds, virions go to the aphid's hind gut, the coat protein of the virus is recognised by the hindgut epithelium, and the virion is allowed to pass into the insect's

hemolymph Hemolymph, or haemolymph, is a fluid, similar to the blood in invertebrates, that circulates in the inside of the arthropod's body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph c ...

, where it can remain indefinitely, but the virus cannot reproduce inside the aphid.Gray, S. and Gildow, F.E. 2003. Luteovirus-aphid interactions ''Annual Review of Phytopathology'' 41:539-566 The virus is actively transported into the accessory

salivary gland The salivary glands in many vertebrates including mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of min ...

to be released into salivary canals and ducts. The virus is then excreted in the aphid saliva during its next feeding. The host range of BYDVs consists of more than 150 species in the

Poaceae Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and species cultivate ...

; a large number of grasses both annual and perennial are alternate hosts to BYVD and can serve as reservoirs of the virus.

Sources and spread

There are two main sources by which a cereal crop might be infected 1. By non-migrant wingless aphids already present in the field and which colonise newly emerging crops. This is known as "green-bridge transfer". 2. By winged aphids migrating into crops from elsewhere. These then reproduce and the offspring spread to neighbouring plants. One aphid species in particular, ''

Rhopalosiphum rufiabdominale ''Rhopalosiphum rufiabdominale'', the rice root aphid or red rice root aphid, is a sap-sucking insect pest with a wide host range and a global distribution. As a member of the superfamily Aphidoidea, it is one of 16 species of the genus ''Rhopalo ...

'', known as the rice root aphid, is commonly known to vector the virus to a range of cereal crops.

Effect on yield

This is variable since it depends on viral strain, time of infection and rate of spread. Most severe losses are from early infections and can be as high as 50%.

Control

"Green bridge" sources must be ploughed in as early as possible. Alternatively, a desiccant herbicide should be applied 10 days prior to cultivation.

Insecticide Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, i ...

sprays may be used at crop emergence. Drilling dates prior to mid-October favors attacks from winged migrant aphids. However, yield penalties may be experienced from late drilling. Insecticide sprays in this instance are therefore aimed at killing the aphids before significant spread can occur.

Products used

Synthetic

pyrethroid A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums (''Chrysanthemum cinerariaefolium'' and ''Chrysanthemum coccineum, C. coccineum''). Pyrethroids are used as commercial and hou ...

insecticides

References

{{DEFAULTSORT:Barley Yellow Dwarf Viral plant pathogens and diseases