Preliminary evaluation of the competitiveness of PPV-Rec and PPV-D under field conditions

PPV-D, PPV-M and PPV-Rec are the three main strains of Plum pox virus (PPV), the most detrimental viral pathogen of stone fruits (Prunus sp.). While different experimental results reported that PPV-M is more aggressive than PPV-D, limited information are available about the competitiveness of PPV-Rec relatively to PPV-D or PPV-M. To provide this information, we monitored the PPV-Rec and PPV-D spreading in an experimental plum orchard (577 trees) located in Bistrita, Romania. The dynamic of spread of the two strains was monitored during four vegetative periods (2008-2011). The sanitary status of the trees was assessed visually and by ELISA testing each year. In 2008, the strain status of each PPV isolate was determined by IC- RT-PCR using strain specific primers located in the (Cter) CP, (Cter) NIb – (Nter) CP and the 6K1-CIP coding regions. From 2009 to 2011, strain typing was performed for every new disease case and for all single strain infections detected in the previous years, in order to check for possible over infection with the other strain. Disease incidence increased from 57 % (328/577) in 2008 to 72 % (414/577) in 2011. From a total of 328 infected trees in 2008, 58% of the trees were infected by PPV-Rec, 13 % by PPV-D and 29% were co-infected by PPV-D and PPV-Rec. The results on the rate of progression of PPV-D and PPV-Rec as well as the frequency of co-infections will be presented and a preliminary conclusion upon the competitiveness of PPV-Rec and PPV-D in our conditions will be discussed.