The Movement of Tobacco Mosaic Virus Within the Plant

Abstract

Summary. By means of extensive cutting‐up test's on tomato plants inoculated with tobacco mosaic the following points have been determined: 1. Confirming the work of Holmes, there is no movement of virus from the inoculated leaf for the first 3 or 4 days. This period is slightly less or considerably more according to the greater or less activity of growth of the plant. 2. When the virus passes out from the inoculated leaf it travels first to the roots of the plant with such speed that it can seldom be intercepted at intervening positions. 3. Usually about a day later it travels with equal rapidity to the top of the plant. 4. In the earliest stages of entering the stem virus particles may be separated by considerable distances (at least several centimetres), since successive samples taken from the stem may yield lengths of 2 1 / 2 cm. (the length of the cuttings) free from infection. interspersed irregularly between portions containing the infection. 5. The presence of developing fruit trusses on the stem may cause part of the virus to travel upwards as far as these trusses at the same time that the initial downward movement is occurring. 6. The virus enters developing fruits at the same time as it travels through the stem, whereas adjacent leaves remain uninfected for days or weeks. 7. In pot plants, after the initial rapid infection of the developing leaves at the top of the plant. the more mature leaves become successively invaded from the top downwards and from the bottom upwards until the plant is completely invaded by the virus. Complete invasion occurs very quickly in small vigorously growing plants; it may take 3 weeks or more in medium sized plants (Text‐fig. 2); and as much as 2 months in large fruiting plants (Text‐fig. 3). 8. Complete invasion never occurs when large field plants of tobacco or tomato bearing a number of mature leaves are inoculated. The mature leaves remain free from virus, apart from a limited movement along the mid‐ribs, for periods of more than 3 months following inoculation (Text‐fig. 4).