Assessment of transmission ability of barley yellow dwarf virus-PAV isolates by different populations of Rhopalosiphum padi and Sitobion avenae

Populations of two aphid species from different geographic regions of Moroc co were tested for their ability to transmit five barley yellow dwarf virus -PAV (BYDV-PAV) type isolates using Clintland 64 oat as the test plant. Tra nsmission efficiencies were determined for 10 sub-populations of Rhopalosip hum padi and 12 sub-populations of Sitobion avenae. After a short acquisiti on access period (AAP) of 4 h, all populations transmitted the virus but wi th different efficiencies. R. padi (Rp-S) and S. avenae (Sa-S) collected in the Settat region were the most efficient vectors, with transmission rates of 38% and 27%, respectively. R. padi (Rp-C) collected at Chaouen and S. a venae (Sa-B) at Berkane, were poor transmitters with respective vectoring a bilities of 20% and 16%. These four sub-populations were chosen to study th e acquisition of BYDV-PAV and the retention of virus within aphids in more detail. The transmission after two AAPs of 4 h and 48 h were compared. Star ved aphids given a 4 h AAP had significantly higher transmission efficienci es than non-starved aphids. However, after a 48 h AAP, no difference was ob served in the transmission between starved and non-starved aphids. Intraspe cific variability was also detected by means of serial transfers of individ ual aphids after the given AAP. Following the first day of serial transfers , no differences were observed in transmission efficiency and virus titers for sub-populations within each species acquiring the virus during 48 h, bu t there was significant variation when the virus was acquired in 4 h. The l evels of PAV antigen retained by aphids fed on healthy plants declined rapi dly during the first day after acquisition, but remained fairly constant du ring the next 5-7 days depending on the length of the AAP. Virus antigen co uld be detected by ELISA in Rp-S and Sa-S for up to 11 days of serial trans fer, but it was shown that aphids could retain and transmit BYDV-PAV for at least 3 weeks.