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 pota to leafroll virus (PLRV) were immersed in 0, 50, 100 or 150 ppm azadir achtin solutions for 84 h. Adult apterous peach-potato aphids, Myzus p ersicae (Sulzer), were placed onto the seedlings for an acquisition ac cess 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 th en placed onto indicator plants to assess PLRV acquisition. Although a zadirachtin did not affect aphid survival, PLRV infection of the indic ator plants was recorded less frequently when inoculated by aphids whi ch had spent the AAP on azadirachtin-treated plants. The ability to pr oduce viable nymphs on indicator plants was severely reduced when the aphids had spent the AAP on seedlings with their roots immersed in aza dirachtin. This effect was also detected after the aphids had spent th e AAP on azadirachtin-treated seedlings re-potted after treatment. The concentrations required to prevent PLRV acquisition from infected see dlngs were not visibly phytotoxic, but a higher concentration of azadi rachtin (500 ppm) caused short-term (wilting) and long-term (deformati on) phytotoxicity. Immersing the roots of uninfected N. clevelandii se edlings in 500 ppm azadirachtin solution did not prevent them becoming infected with PLRV after exposure to viruliferous aphids in 'choice' and 'no-choice' experiments.