The effects of azadirachtin on the acquisition and inoculation of potato leafroll virus by Myzus persicae

The roots of Nicotiana clevelandii (Gray) seedlings infected with potato leafroll virus (PLRV) were immersed in 0, 50, 100 or 150 ppm azadirachtin solutions for 84 h. Adult apterous peach-potato aphids, Myzus persicae (Sulzer), were placed onto the seedlings for an acquisition access period (AAP) of 72 h starting 12 h after root immersion or 2 days after the seedlings had been re-potted in compost. The aphids were then placed onto indicator plants to assess PLRV acquisition. Although azadirachtin did not affect aphid survival, PLRV infection of the indicator plants was recorded less frequently when inoculated by aphids which had spent the AAP on azadirachtin-treated plants. The ability to produce viable nymphs on indicator plants was severely reduced when the aphids had spent the AAP on seedlings with their roots immersed in azadirachtin. This effect was also detected after the aphids had spent the AAP on azadirachtin-treated seedlings re-potted after treatment. The concentrations required to prevent PLRV acquisition from infected seedlngs were not visibly phytotoxic, but a higher concentration of azadirachtin (500 ppm) caused short-term (wilting) and long-term (deformation) phytotoxicity. Immersing the roots of uninfected N. clevelandii seedlings in 500 ppm azadirachtin solution did not prevent them becoming infected with PLRV after exposure to viruliferous aphids in 'choice' and 'no-choice' experiments.