Abstract
1) In recent years, a mosaic disease of lettuce has been recognized in the vicinity of Tokyo as one of the most destructive diseases of lettuce. Symptoms on crisp-head type varieties, Imperial 847 and Great Lakes, are conspicuous, leaves becoming distorted and frequently developing mosaic or vein-clearing. In butter-head type variety, Wayahead, very faint mosaic or vein-clearing, and in some individuals, necrotic flecks are observed.
2) Twenty-three collections of mosaic lettuce plants were tested for the causal viruses by inoculating with carborundum to several indicator plants. As a result, 4 samples yielded cucumber mosaic virus, while the other 19 samples were found to contain a virus hitherto unreported from Japan.
3) This virus was readily transmitted either by mechanical inoculation or by aphids, Myzus persicae and Hyperomyzus sp. It infected plants belonging to three of the eight families tested, including lettuce, zinnia, aster, Chenopodium album, C. anthelminticum, and Gomphrena globosa. The last three plants developed only local lesions. Cucumber, tobacco, tomato, petunia, bean, broad bean, cowpea, turnip, corn, etc., were not infected.
4) The virus was found to be carried over in the seed of lettuce. Seed-borne infection occured at a rate of 1 to 6per cent, in varieties Imperial 847, Great Lakes, and Wayahead.
5) The virus activity was lost when juice of diseased lettuce was diluted 1:500, when exposed to 60°C for 10 minutes, or when subjected to aging in vitro for 2 days.
6) From these results, it has been concluded that this virus is to be identified with the lettuce mosaic virus (Marmor lactucae), known from U. S. A. and other countries.
