The tobacco mosaic virus is named from how its infection manifests on the leaves. It looks like a mosaic of different colored (usually shades of yellow and green and possibly brown if the disease is advanced) leaf tissues. It is spread via an insect vector that "bites" into the leaf. The virus would then spread from that "bite". If you see a line of brown tissue I would think it's something else. Are the lines of brown leaf tissue along the margins of the leaves? If they are along the margins, or outside layer, of the leaves, I would think that you actually have a salt toxicity. (in other words, too much fertilizer) When plants absorb nutrients, they move from the roots, up the stems and into the leaves. If there is too much of a certain nutrient and it doesn't get used immediately, it will accumulate along the margins of the leaf. If the concentration gets too high, the plant tissue won't survive, and you will see a line of brown tissue along the edge. If the line of brown tissue is not along the edge of the leaf let me know, but I assume what I just wrote out is the problem. I hope this is helpful. :) Robby
