Physiologisch onderzoek met betrekking tot het virus der bladrolziekte van de aardappelplant, Solanum tuberosum L.

Starch accumulation was an important characteristic of a large group of virus diseases to which the potato leafroll disease belonged. There were two different conceptions about the cause of this phenomenon: a disturbance of the enzymic processes, and a disturbance of transport. Thung investigated which of the two viewpoints was correct for potato leafroll. His conclusion was that enzymic processes were not influenced by the virus, but that phloem transport was disturbed.

The disturbance in the transport in primarily infected leaves was confined to the lower part of the petiole. This was not so with the secondarily infected leaves. Consideration of the following facts supported the hypothesis that phloem in the primarily diseased leaves underwent its first disturbance in the lower part of the petiole. The virus was transmitted to the leaves by aphids; the young developing shoots were primarily infected by taking nutrients from older ones. The virus entered the young leaf with the nutrients. Consequently the lower portion of the petioles was reached first by the virus and there the disturbing action of the virus started. In the secondarily diseased plants the ways of transport were severely and uniformly diseased; transport took place in the same way as in healthy leaves but considerably slower.