Control of cucumber mosaic virus (CMV) disease of tomato by application of an attenuate strain of CMV

In Japan, tomato plants are cultivated in the fields from spring to autumn. Mosaic disease of tomato caused by cucumber mosaic virus (CMV) is one of the most important virus diseases in these fields. A strain of CMV (CMV-SR) isolated from spinach plants showing rugose symptoms did not induce any symptoms in systemically infected tomato plants. CMV-SR was tested in the glasshouse and fields for assessing the possibility of using it as an attenuate virus in order to control the occurrence of CMV causing mosaic symptoms on tomato plants. In the glasshouse, the pre-inoculation of crude juice prepared from Nicotiana debneyi leaves infected with CMV-SR protected effectively the infection of tomato plants performed through sap inoculation of virulent CMV. The pre-inoculation of purified CMV-SR (3, 6, 30, 100 μg/ml) also controlled effectively the infection of tomato plants performed through sap inoculation and aphid transmission of virulent CMV, especially CMV-SR at a concentration of 100 μg/ml controlled nearly completely the infection. In the field experiments carried out in spring to autumn, the pre-inoculation of purified CMV-SR (100 μg/ml) markedly reduced the rate of occurrence of mosaic disease, disease index, and the rate of abnormally colored tomato fruits caused by CMV infection. The inoculation of CMV-SR did not adversely affect the growth of the tomato plants. These results indicated that CMV-SR could be used practically as an attenuate virus to control the mosaic disease caused by CMV on tomato plants.