Studies on soil-borne cereal mosaics

Abstract

Barley yellow mosaic is spread throughout Japan except Hokkaido, but there has been no published information on the occurrence of the disease in foreign countries. Barley yellow-mosaic virus (BYMV) is transmitted only to susceptible varieties of barley through the soil in the winter and produces mottling which resembles that in wheat caused by wheat yellow-mosaic virus (Marmor tritici var. fulvum McK.). BYMV does not attack wheat and rye. Intracellular inclusions (X-bodies) are present in the cells of the diseased plants.The writer has carried out experiments in order to learn about the mode of the disease and properties of BYMV. The experimental results are summarized as follows:(1) BYMV is transmitted, with difficulty, to healthy barley plants by the rubbing method of incoulation with pressed sap of diseased plants. The virus is not transmitted by insects and is not seed-borne.(2) Regarding the effect of the environmental conditions upon expression of symptoms, it is observed that the symptoms of plants were rendered less striking by rising temperature and by the addition of chemical fertilizer.(3) Fifteen cm. below the seeds was the greatest distance at which BYMV-infested soil caused the disease. Thermal inactivation point of the virus in soil was 50-60°C for 10 minutes.(4) When pregerminated seeds, which had already developed 2 or 3 roots, were planted in virus-infested soil in glass-house, the infection rate was 2-3 times higher than in the cases of planting seeds, which were presoaked but not yet developed roots.(5) Only a small number of plants were in fected when grown in soil composed of 10-50μ particle fraction or of nearly 50μ fraction separated from BYMV-infested soil.