|Scientific Name||Barley yellow dwarf luteoviruses (Acronym BYDV)|
|Synonyms||Maize leaf fleck virus, cereal yellow dwarf virus, Hordeum virus nanescens, oat red leaf virus, rice giallume virus.|
|Common Names||English: Barley yellow dwarf; Spanish: Virus del enanismo amarillo de la cebada; German: Gelbverzwegungsvirus; French: Jaunisse nanisante de l'Orge|
Barley yellow dwarf is caused by a group of luteoviruses named barley yellow dwarf luteoviruses. The different viruses causing barley yellow dwarf were originally characterized based on their transmission by the species of aphid that most efficiently transmitted that strain; MAV by Sitobion avenae, PAV by Rhopalosiphum padi, S. avenae and others, RMV by R. maidis, RPV by R. padi and SGV by Schizaphis graminum. The Chinese strains GPV, DAV and GPDAV have serological relation to MAV and PAV, but differ in the aphid transmission pattern. The BYDVs are divided in two subgroups; group 1 includes PAV, MAV and SGV, group 2 RPV and RMV. Group 2 is more closely related to other luteoviruses than to group 1 BYDVs.
BYDV particles are isometric with a diameter of 24-28 nm and sediment as a single component at 104-118 S (density in CsCl 1.40 g cm-3). The protein capsid is composed of one polypeptide (MW 23.5-24.4 x 10³), the genome consists of a single molecule of +sRNA (MW 1.85 - 2.0 x 106).
Symptoms caused by BYDVs differ with host species and cultivar, age and physiological state of the host plant at the time of infection, the strain and the environmental conditions and can be easily confused with nutritional and abiotic disorders. Symptoms include leaf discoloration from tip to base and from margin to centre. In wheat, the infected leaves are generally yellow, sometimes red. Other leaf symptoms include serrations along leaf borders and corkscrew symptoms. Plants are often stunted, with a decrease in tiller number and biomass and a reduced root system. Symptoms occur usually as yellow or red patches of stunted plants. Disease severity depends on the strain of viruses which are transmitted by various aphid species.
Aphids acquire and transmit BYDVs while feeding on the phloem sieve tube elements of host plants (minimum feeding access times 0.1 - 4.0 h). The latent period (time from the start of acquisition until the aphid becomes able to infect plants) is between 12 and 24 h.
After acquisition from the phloem, virions are transported to the aphid gut, cross the hindgut epithelium and are transported in the hemocoel in coated vesicles. The virions reach the salivary canals via the accessory salivary gland basal lamina and plasmalemma, from where they are excreted while the aphid is feeding. As vector transmission pattern often corresponds to serotypes, the specificity of transmission is high.
BYDVs are transmitted to a new crop by alate aphids from infected sources. Under favorable weather conditions for aphid development and spread, the virus is spread in the crop. The primary infection depends on the number of aphids and their ability to transmit the virus. Reservoirs of primary inoculum may be infected maize crops, volunteers or other grass species.
BYDVs are transmitted by aphids in a persistent, circulative but non-propagative manner; they are not mechanically or seed transmissible.
Many species of aphids infest cereal crops; more than twenty have been reported as vectors of BYDVs. The most important include Rhopalosiphum padi, R. maidis, R. rufiabdominalis, Sitobion avenae, Metopolophium dirhodum and Schizaphis graminum. In general, BYDV-PAV causes severe symptoms, MAV moderately severe and RPV, RMV and SGV produce mild symptoms. However, as there is high variability among the isolates from the same BYDV strain an RPV isolate may cause more severe symptoms than a PAV isolate.
Additional Crop Information
Barley, oats, rice, other grass species
Due to the wide host range and the widespread occurrence of their vectors, BYDVs are the economically most important virus disease of cereals. Yield losses may be serious but vary with BYDV strain, host plant variety, growth stage at infection, and environmental conditions. Losses may reach more than 10 %, however, are considerably lower in general.
Integrated Crop Management
Cultural practices to reduce the incidence of BYDVs include delayed sowing dates in order to avoid primary infection, removal of cereal regrowths and stubble as a reservoir of virus and vectors. Incorporating resistance or tolerance to BYDVs into wheat is one of the most promising control options. Various sources of tolerance have been reported. Resistance to virus multiplication may be introgressed from wheat relatives like Aegilops, Elymus and Agropyron.
Biological control has been reported to be successful in South America, where S. avenae and M. dirhodum were controlled through the introduction of Coccinellid predators and Aphelinid and Aphidiid parasites and in New Zealand with the introduction of Aphidius rhopalosiphi. In most areas, natural enemies limit aphid populations and it is important to integrate chemical and natural control methods.
Chemical control of barley yellow dwarf relies on the control of its aphids vectors, especially at early growth stages. Insecticides may be applied prophylactic or based on forecasting systems. The most commonly used active ingredients include organophosphates and synthetic pyrethroids. Neonicotinoids such as imidacloprid are also effective when applied as a systemic seed treatment.
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