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Wheat yellow dwarf virus disease
Symptoms of the disease typically include yellowing leaves and stunted growth. A characteristic feature is that the new leaves show a gradual yellowing from the tip toward the base, with the yellowed portion covering about one-third to one-half of the leaf blade. The base of the leaf remains green for a long time, sometimes even parallel to the veins. However, this yellowing is not restricted by the vein patterns. Affected leaves are smooth in texture. Severe dwarfing occurs early in the infection, though the severity varies depending on the plant species. In winter wheat, symptoms may be less obvious, but the plants are more susceptible to cold damage during winter, reducing their survival rate in late spring. Infected plants are significantly stunted, often fail to head or produce very small heads. At the jointing and booting stages, plants are slightly shorter with poor root development. During the heading stage, only the flag leaf turns yellow, while the overall stunting is less noticeable. However, panicle size and grain weight are reduced. Unlike physiological yellowing, which starts from the lower leaves and spreads uniformly across the field, yellow dwarf disease begins at the leaf tips and progresses outward, with the flag leaf showing heavy infection. The disease usually originates from the center of the infected plant and spreads to surrounding areas.
The pathogen responsible is the Barley Yellow Dwarf Virus (BYDV), which belongs to the Luteoviridae family. It has several strains, including DAV, GAV, GDV, RMV, and others. Viral particles are spherical, icosahedral, and measure approximately 24 nm in diameter. They contain single-stranded RNA and can be observed under an electron microscope in the phloem tissue of infected leaves. The virus is inactivated at temperatures above 65–70°C. It infects a wide range of crops, such as wheat, barley, oats, rye, corn, bromegrass, chloris, teff, and yellow foxtail.
Transmission occurs through persistent aphid vectors, including Schizaphis graminum, Rhopalosiphum padi, Sitobion avenae, Metopolophium dirhodum, and R. maidis. The virus cannot be transmitted through seeds, soil, or sap. The incubation period is 15–20 days at 16–20°C, while higher temperatures (over 25°C) shorten the incubation period, and above 30°C, symptoms may not appear. Aphids can transmit the virus after feeding on infected plants for 5–10 minutes, with the highest transmission rate occurring 3–8 days post-infection. Transmission decreases over time but does not last for the entire life of the aphid.
In winter wheat regions, the disease is most severe during the rejoining phase when aphid populations increase, leading to a second peak at the heading stage. After the spring harvest, winged aphids migrate to summer crops like rice, millet, sorghum, and weeds. When autumn wheat emerges, they return to wheat fields, overwintering at the base of seedlings. Some populations may survive the winter in certain areas. In regions where winter and spring wheat coexist, aphids migrate from winter wheat to spring wheat in early May. Late wheat, barnyardgrass, and self-sown wheat serve as important hosts for the virus during summer, and winter wheat aphids return to spread the virus again.
Factors influencing disease incidence include sowing date, slope exposure, irrigation, and management practices. Early sowing of winter wheat increases disease risk, while sunny slopes tend to have higher incidence than shaded ones. Dry soils are more prone to infection than irrigated areas. Extensive farming practices lead to higher disease rates compared to intensive cultivation. Soil fertility also plays a role, with barren land being more susceptible. The density of aphid populations directly affects the spread of the virus, as higher aphid numbers increase both their breeding and the likelihood of virus transmission. Low temperatures during the jointing and booting stages reduce plant resistance, making them more vulnerable to yellow dwarf disease. High numbers of virus sources, such as self-sown seedlings, contribute to outbreaks. Large aphid populations can lead to widespread epidemics.
Control measures include using resistant varieties, which have been developed in recent years to suit local conditions. Preventing aphid infestations is crucial in controlling the spread of the disease. Seed treatments with phosphorus solutions, dimethoate, or other insecticides can help protect young plants. Spraying insecticides like 40% Dimethoate EC, 50% Quercus Pine EC, or Cypermethrin EC at appropriate dilutions can effectively manage aphid populations. Additionally, dusting with parathion or dimethoate powder provides further control. Applying 40% Dimethoate emulsion mixed with fine soil around the base of wheat seedlings helps reduce overwintering aphid populations. Cultural practices such as weed control, proper sowing dates, and balanced fertilization improve plant health and resistance. Covering winter wheat with plastic film has also shown effectiveness in preventing the disease.
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Wheat yellow dwarf virus disease