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Wheat yellow dwarf virus disease
Symptoms of the disease primarily include yellowing leaves and stunted growth. The most characteristic symptom appears on the leaf blade, where the infection spreads gradually from the tip toward the base, turning part of the leaf yellow. The yellow portion typically covers 1/3 to 1/2 of the leaf, while the base remains green for a long time, sometimes running parallel to the veins. However, the yellowing is not restricted by the vein patterns. Affected leaves remain smooth. Severe stunting occurs early in the infection, though the extent varies depending on the plant species. Winter wheat often shows no visible symptoms but is vulnerable to cold stress, leading to freezing and reduced survival in late spring. Infected plants are severely stunted, with poor or very small heads. At the jointing and booting stages, plants are slightly shorter with underdeveloped roots. During the heading stage, only the flag leaf turns yellow, and the overall stunting may be less noticeable, although panicle size and grain weight are reduced. Unlike physiological yellowing, which starts from the lower leaves and affects the entire leaf uniformly, yellow dwarf disease begins at the tip of new leaves, with the flag leaf showing heavy symptoms. The disease typically starts at the center of the plant and spreads outward.
Barley Yellow Dwarf Virus (BYDV) is a viral pathogen that belongs to the Luteoviridae family. It includes several strains such as DAV, GAV, GDV, RMV, and others. The virus particles are icosahedral, measuring approximately 24 nm in diameter. Electron microscopy reveals that the virus is present in the phloem tissue of infected leaves, with single-stranded RNA as its genetic material. The virus is inactivated at temperatures above 65–70°C. It can infect a wide range of hosts, including wheat, barley, oats, rye, corn, bromegrass, chloris, teff, and yellow foxtail.
The virus is transmitted exclusively through aphid vectors, such as Schizaphis graminum, Rhopalosiphum padi, Sitobion avenae, Metopolophium dirhodum, and R. maidis. These aphids transmit the virus persistently, meaning they carry it for life. The virus cannot spread through seeds, soil, or sap. Transmission occurs when aphids feed on infected plants and then move to healthy ones. Optimal transmission occurs between 16–20°C, with an incubation period of 15–20 days. At higher temperatures (above 25°C), the virus becomes less active, and at 30°C or more, symptoms are rarely observed. Aphids can acquire the virus after feeding on diseased leaves for 30 minutes and transmit it to healthy plants within 5–10 minutes. The highest transmission rate occurs 3–8 days after the aphid acquires the virus, and the ability to transmit decreases over time but does not disappear entirely.
In winter wheat regions, the disease centers around the overwintering host plants. A peak occurs during the rejoining phase, and the virus spreads as aphid populations increase, reaching 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, the aphids return to wheat fields, completing their life cycle. Some populations overwinter in the base of wheat seedlings, while others survive in weedy areas. In some regions, winter and spring wheat coexist, allowing aphids to migrate between them. Late wheat, barnyard grass, and self-generated wheat seedlings serve as important summer hosts for the virus. The presence of these hosts significantly influences the spread of the disease.
Factors affecting disease incidence include sowing time, slope orientation, irrigation, and management practices. Early sowing increases the risk, while sunny slopes are more affected than shady ones. Dry land tends to have higher incidence compared to irrigated areas. Extensive farming methods lead to higher disease rates, while intensive cultivation reduces it. The severity of the disease is closely related to the population density of aphids. Warmer conditions favor both aphid reproduction and virus transmission, shortening the incubation period. The spread of the virus is most active in early spring in winter wheat areas. Cold stress during the jointing and booting stages weakens plant resistance, making them more susceptible to yellow dwarf disease. The prevalence of the disease is strongly linked to the availability of virus sources, such as volunteer wheat and other large host plants. High aphid populations can quickly lead to outbreaks.
Control strategies include using resistant varieties, timely aphid control, cultural practices, and protective measures. Selecting local varieties with good resistance is an effective approach. Seed treatments with phosphorus solutions, dimethoate, or other insecticides can protect young plants. Spraying insecticides like 40% dimethoate, 50% quinalphos, or cypermethrin helps reduce aphid populations. Soil application of insecticides around the base of wheat plants can also help manage overwintering pests. Improving field management, removing weeds, and adjusting planting dates can enhance plant resistance. Covering winter wheat with plastic film has been shown to significantly reduce disease occurrence.
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Wheat yellow dwarf virus disease