PPV accumulates at a lower level in wild-type scions of the
highly resistant transgenic rootstocks
As shown in Figure 1, depending on the cycle taken into consideration
and the transgenic rootstock line, a certain number of wt scions were
infected by the virus. RT-qPCR analysis was conducted on a random subset
of PPV-positive wt scions from the four transgenic rootstocks. The PPV
titer of the apricot scions grafted onto the resistant plum rootstocks
St5’-1 and St5’-9 was significantly lower than those found in apricot
scions grafted onto the susceptible St5’-7 line (Figure 2). In addition,
apricots grafted onto the tolerant St5’-6 line had a lower virus titer
than St5’-7, although differences were not significant according to a
one-tail Dunnett’s test (Figure 2). The above data, together with those
reported in Figure 1 and Table 2, pointed out that
the RNA silencing mechanism
reduces the virus titer progressively till eliminating the virus from
the wt scions grafted on the transgenic resistant PPV plants.