Differential Transmission of Closely Related Strains of Potato Virus Y by the Green Peach Aphid and the Potato Aphid

Abstract

Comparative transmission trials were made with 2 strains of potato virus Y (MPVY and RPVY) using the green peach aphid, Myzus persicae (Sulzer). and the aphid, Macrosiphum euphorbiae (Thomas). RPVY inoculated by green peach aphids caused both mild and sever symptoms in ‘California Wonder’ pepper (CW) whereas inoculation by potato aphids and by sap of RPVY consistently caused severe symptoms in CW pepper. Symptoms of MPVY in CW pepper were always severe regardless of type of inoculation used. The mild syndrome of RPVY could be restored to the severe syndrome by serial sap inoculation in pepper. Fourteen days after inoculation, titrations by sap inoculation indicated concentrations of mild and severe symptom RPVY to be similar; whereas titrations by green peach aphid transmissions indicated concentration of the mild symptom RPVY to be significantly lower than concentration of the severe symptom type. Thirty-nine days after inoculation, titrations of these same plants by green peach aphid transmissions showed equal concentrations of both mild and severe symptom RPVY. MPVY was transmitted very efficiently by green peach and potato aphids in only 10–12 days after inoculation of virus source plants, irrespective of whether aphid-or sap-inoculated plants were used. Titrations by sap inoculation of MPVY correlated well with titrations by green peach aphid transmissions. In CW plants infected for 18–40 days, potato aphids transmitted both mild and severe symptom RPVY (both sap-inoculated and aphid-inoculated) with equal efficiency. Green peach aphids initially had difficulty in transmitting mild symptom RPVY where aphid-inoculated (either green peach or potato) virus inoculum source plants were used, but after 40 days these plants were equal as inocula to sap-inoculated plants. Rates of postacquisition feeding loss of RPVY in green peach aphids and potato aphids were determined for mild and severe symptom types of virus using both sap-inoculated RPVY. MPVY was tested similarly but only with green peach aphids. The half-life life of severe symptom RPVY (for both sap-and aphid-inoculated virus) was about 40 min in green peach and potato aphids. However, the half-life of mild symptom RPVY inoculated by green peach aphids was less (10 minutes) than when inoculated by sap or potao aphids (40–75 minutes). This was true for both green peach and potato aphids. The half-life of MPVY as determined for green peach aphids was (1) similar for both sap- and aphid-inoculated virus, and (2) was much longer than for RPVY (150–180 minutes). When vector efficiency was plotted against the half-life of virus, a linear relationship seemed evident.