Concentration of virus and ultrastructural changes in oats at various stages of barley yellow dwarf virus infection

Enzyme-linked immunosorbent assay was used to monitor the concentration of barley yellow dwarf virus (BYDV) in roots and leaves of oats inoculated at the 1 - 2 leaf stage and at the 4 - 5 leaf stage, respectively. Virus was detectable 20 h after inoculation in the roots and after 48 h in the leaves of plants inoculated at the 1 - 2 leaf stage. The virus concentration reached a plateau in the roots after 7–8 days, and was 3–4 times higher than in the leaves. In plants inoculated at the 4 - 5 leaf stage virus was detectable in roots and leaves after 3 and 5 days, respectively. The concentration reached a maximum after 10 days in the roots and after 18 days in the leaves; the concentration in the leaves was 2–3 times higher than in the roots. Virus was readily detectable in seeds from infected plants, both fresh and old dried seeds. However, seed transmission could not be demonstrated. Virus-like particles were first observed in phloem cells of roots 4 days after inoculation, but no ultrastructural changes were detected at this stage. After 5–6 days, disintegrated nuclei and virus-induced vesicles were observed in many cells and abnormal production of callose was found after 10 days. Necrotic phloem cells were observed from day 13, shortly after the appearance of external symptoms.