Viral diseases of grain crops

There are more than 8 thousand pathogens worldwide that cause significant damage to agricultural crops. Every agricultural producer knows how important it is to take timely preventive measures to limit the development and spread of various diseases of grain crops.
The causative agents may be fungi,bacteria , viruses and flowering plant parasites. Among agricultural crop diseases, viral and mycoplasma diseases occupy one of the leading places in terms of economic damage.

Viral diseases of cereals have been known since the end of the last century, but their etiology was attributed mainly to non-infectious factors. Currently available information about the nature of viruses, methods of their spread, range of host plants, as well as the emergence of more advanced diagnostic methods make it possible to determine the area of ​​viral diseases with high accuracy. Such studies are carried out by qualified specialists from the testing laboratories of the Federal State Budgetary Institution “Center for Grain Quality Assessment”.

The causative agents of these diseases are viruses - non-cellular prokaryotes containing only one ribonucleic acid (RNA), which is coated with a protein coat. As is known, viruses cannot independently penetrate the cell of a host plant, since they do not have any adaptations for this, nor for exiting it into the environment. Their distribution in nature occurs, as a rule, in a vectorial manner with the participation of insect vectors such as aphids, cicadas, beetles, thrips, as well as mites, nematodes, and soil fungi. Viruses are divided into non-persistent (stylet) and persistent (circulative). Non-persistent viruses acquire infectivity very quickly - within 30...120 seconds of the vector's feeding. Immediately after feeding, vectors are able to transmit viruses to healthy plants and soon lose their ability to transmit (virophority). Such transmission is typical, for example, for aphids.
Persistent viruses have a much more complex relationship with vectors. After feeding, the vector needs a certain latent period (from several days to several weeks), and only after that it acquires the ability to infect healthy plants with viruses. This ability persists for a long period, sometimes throughout life. In the body of carriers, persistent viruses actively multiply and are deposited in the form of crystalline or amorphous inclusions.

— Currently, almost 100 viral diseases developing on grain crops have been identified. The following examples of viral diseases affect not only all types of grains, but also many weeds. Viruses cause profound, irreversible changes in diseased plants. At the same time, carbohydrate and nitrogen metabolism are disrupted, the activity of many enzymes decreases, as a result, growth processes are suppressed, yields are reduced, and plant death often occurs, say specialists from the Altai branch of the FSBI Center for Grain Quality Assessment.
Typically, agricultural producers have great difficulty diagnosing the cause of grain diseases, and their harmful effects are often associated with factors of abiotic and other origin. To prevent the spread of viral diseases of grain crops, preventive control measures are used based on knowledge of the patterns of spread of viruses in nature. It is possible to limit a massive outbreak of the disease by weakening or completely breaking one or more links in the chain that determine the circulation of viruses. In simple words, we need to fight the vectors, not the symptoms. In this case, a significant role is given to the agrotechnical method of control, which can compete on equal terms with chemical protection.

Taking this into account, we present a description of the most common viral diseases of grain crops and their pathogens, which will help to correctly diagnose viruses and timely carry out reasonable preventive measures on a particular crop.

Russian mosaic of winter wheat
Etiology: causative agent of the disease Russian winter wheat mosaic virus ( Russian mosaic virus of winter wheat). The disease is observed everywhere. The virus is spread by leafhoppers and is not transmitted mechanically. The infection persists on winter crops, cereal weeds and in the body of the vector. Sick plants are stunted, bushy heavily, and often do not form productive stems.
The virus affects spring wheat, millet, barley and winter rye, and among wild cereals – bristle grass (Setaria glauca Beauv., S. viridis Beauv.), as well as ground reed grass (Calamagrostis epigeios).
Symptoms: in autumn, mosaic or light green (lemon yellow) spots, streaks and stripes appear on the leaves and sheaths, which subsequently become chlorotic.

Striped mosaic
Etiology: causative agent – ​​Wheat striate mosaic virus, transmitted by a gall-forming mite, does not spread through seeds or through soil. Mites are easily carried by wind and on the body of aphids from plant to plant. The vector becomes virophoric after 30 minutes of feeding on the affected plant. The pathogen overwinters on winter crops and cereal weeds. The virus persists on winter wheat; in the spring, vectors transfer it to spring wheat; millet, winter rye, oats, bristleweed and bromegrass species are affected.
Symptoms: Light green streaks or stripes appear on the leaves. Plants are stunted and do not produce productive stems. When plants are severely damaged, grain does not form.

Pupation of oats
Etiology: causative agent – ​​a highly specialized virus Siberian oats mosaic virus. The pathogen is carried by the dark leafhopper. The infection persists in the perennial organs of wild cereals and in the body of the leafhopper.
Symptoms depend on the timing of infection. When seedlings are damaged, plant development stops and mosaic patterns are observed; if infection occurs before tillering, the affected plants bush heavily, forming up to 200 shoots. Panicles are not formed, or spikelets do not produce seeds.

Source: Altai branch of the Federal State Budgetary Institution “Grain Quality Assessment Center”