Virus of curly top disease was introduced, through one cotyledon, into seedlings of a highly susceptible sugar beet strain. The inoculated cotyledon developed phloem hyperplasia—abnormal multiplication of cells—characteristic of the curly top disease. This symptom was observed in the main vein and some small veins on the third day after inoculation. In many samples, the main vascular bundle also showed pronounced necrotic obliteration in the older part of the phloem tissue, a symptom not previously described for curly top infection.
