This commentary relates to the work by M. Borja et al, (M. Borja, T. Rubio,
H. B. Scholthof, and A. O. Jackson, MPMI 12:153-162, 1999) that shows that
wild-type virus can be restored frequently by double recombination events
between a tomato bushy stunt virus mutant with deletions inactivating the c
oat protein gene and a coat protein transgene. Here, we focus on evidence s
uggesting that new viruses might evolve via recombination with transgenes u
sed for disease resistance, and discuss the potential effects of widespread
use of these sources of resistance on virus evolution. We argue that the b
enefits arising from using transgenic sources of resistance for virus disea
se control outweigh potential negative consequences of evolution of novel h
ybrid viruses with destructive disease potential.