Abstract
An attempt was made to distinguish the isolates of turnip mosaic virus into two strains: the one designated the ordinary strain that produces mild symptoms on Brassica oleracea capitata and Nicotiana glutinosa, and the other the cabbage strain that causes severe necrotic ring spot disease on B. oleracea capitata and severe mosaic on N. glutinosa.
Turnip mosaic virus isolates which had hitherto been reported by various workers were separated into either of the two strains according to the disease symptoms appearing on the plants mentioned above.
An examination was made on geographical distribution of the virus isolates of each of the two strains to see if there was any pattern in the strain distribution.
The isolates of the ordinary strain were found in large numbers in India, China, and Japan, but no isolates belonging to the cabbage strain were reported from this area. This led us to assume that the ordinary strain of turnip mosaic virus has its origin in this area.
Further, the cabbage strain is indigenous to the area of origin of B. oleracea or its native associates, viz. England or other western Europe.
In North America, it was assumed that the two strains were introduced from Europe at about the same time, and that there was also introduction of the ordinary strain from Oriental countries.
