Different helper factors associated with aphid transmission of some potyviruses.

Myzus persicae transmitted watermelon mosaic virus (WMV) after acquiring it through artificial membranes from a solution of purified virus mixed with the soluble fraction from infected leaf extracts or by prefeeding on the soluble fraction before acquiring purified virus. WMV-induced helper factor assisted M. persicae in transmitting purified turnip mosaic virus (TuMV) but not potato virus Y (PVY). TuMV-induced helper factor from infected leaves was ineffective for the transmission of purified WMV or PVY. PVY-induced helper factor from infected leaves was capable of helping the transmission of TuMV but not that of WMV. The results indicate that there are at least three distinct helper factors with different specificity associated with potyviruses.