Abstract
1) Potato plants (variety Wheeler) showing yellow blotching of the leaves (Fig. 1 and 2) were found at Yatsugatake National Potato Foundation Seed Farm, Chino, Nagano Prefecture, in August 1962. There was no apparent tuber necrosis.
2) By mechanical inoculation from these potato plants, a virus was transmitted to potato, broad bean, bean, cowpea, tomato, cucumber, tobacco, etc. From the host range and symptoms on these plants, the virus was identified with alfalfa mosaic virus.
3) The virus was tuber-perpetuated and graft-transmissible; also readily transmitted by Myzus persicae or Aphis gossypii from diseased broad bean or tobacco to healthy broad bean or tobacco. There was no transmission from diseased ladino clover or potato to healthy potato plants by Myzus persicae, Aphis gossypii, Macrosiphum euphorbiae and Aulacorthum solani.
4) The thermal inactivation point of the virus was 55∼60°C; dilution end point, 5, 000∼10, 000; and longevity in vitro, 1∼2 days.
5) In order to determine whether potato plants carry the virus without symptom, leaf extract from each of 130 apparently healthy potato plants (var. Wheeler) was mechanically inoculated to bean, broad bean or cowpea. There was no indication of the presence of virus.
6) In the vicinity of the potato fields, there were many ladino clover plants with yellow-patch symptom. The virus isolated from yellow-patch ladino clover was found to be same or closely related to the potato strain in respect to host range and physical properties.
