Barley yellow mosaic virus. Coloured transmission electron micrograph (TEM) of virus particles (virions) of the barley yellow mosaic virus (BaYMV). This plant virus is a bymovirus, and has an RNA (ribonucleic acid) genome. It was first identified in 1940 in barley (Hordeum) plants in Japan. Barley is one of the world's major cereal crops. Symptoms are yellow streaks on the leaves. The virus is transmitted by the fungus Polymyxa graminis. It is found in Japan, China and Europe. Magnification: x67,000 when printed 10cm high.