We confirmed these observations by crossing
Del/Ros1 plants to the aw mutant of tomato in the Ailsa Craig
genetic background, which lacks DFR activity and cannot
make anthocyanins [19]. In the F2, the plants that contained
Del/Ros1 but lacked DFR activity (aw2/2) produced orange
fruit due to high levels of flavonols. Like the VIGS-SlDFRsilenced
sectors, the aw2/2, Del/Ros1 fruit were no less susceptible
to B. cinerea than were red tomatoes (Figure 3D).
The orange fruit had 2-fold higher hydrophilic antioxidant capacity
than the parental aw2/2 line (Figure 3E) and they could
be kept longer postharvest, although not as long as purple
tomatoes (Figure 3F). Consequently, the delay in overripening
and the enhanced pathogen resistance of purple tomatoes are
not due to off-targets of the Del and Ros1 transcription factors.
Resistance to B. cinerea is specifically the result of the accumulation
of anthocyanins, whereas the delay in overripening
is most likely associated with the increased hydrophilic antioxidant
capacity of the fruit