Transgenic plant material used in the study
Four transgenic plum (Prunus domestica  L.) lines St5’-1, St5’-6, St5’-7, and St5’-9, obtained after transforming ’Stanley’ hypocotyls and with different resistance levels to PPV (García-Almodovar et al. , 2015), were used in the study. Lines St5’-1 and St5’-9 are highly PPV resistant since the virus was never found in any plant. Line St5’-6 is considered tolerant because the virus was detected early after graft-mediated PPV inoculation but was undetectable later. Transgenic line St5’-7 is PPV-susceptible since most of the challenged plants were infected with the virus (García-Almodovar et al. , 2015).
In vitro  transgenic plum shoots were multiplicated, rooted, and acclimatized in the greenhouse and successively transplanted to 5L forestall pots to allow for a good root system development.