Naturally occurring strains of the potato leaf roll virus

Summary

Results of these studies of isolates of the potato leaf roll virus from 56 various seed potato areas of the United States and Canada, covering a wide geographical range, substantiate the existence of distinct strains of the virus. In addition to the 3 strains from Wisconsin previously reported, one additional very severe strain, designated as strain 4, exists in at least one area in South Dakota. The strains are distinguished most readily by the initial symptom type and relative disease severity onP. floridana. The response ofP. floridana infected with strain 4 at 24° and 28° C, is directly opposite to that of the other 3 strains at the same temperatures.

The four strains produced a wide range of symptoms onP. floridana, varying from severe defoliation and death of plants with strain 4, to moderate initial symptoms and subsequently rapid recovery with strain 1.

A temperature of 24° C. was found to be optimum for symptom expression and development. Distinct strain differences, however, are shown at 16° and 28° C.

Strains 1, 2 and 3 seem to be coexistent in most potato growing areas of the United States and Canada.

Further experiments are being conducted to study the 4 leaf roll strains under controlled conditions on a number of potato varieties.