Although 48 R genes were molecularly characterized from
plant species, most were from Arabidopsis, followed by tomato
and rice (Martin et al. 2003, Wang 2003), allele-specific DNA
markers for disease resistance based on R genes are still very
limited. An additional allele-specific marker for blast is the
dominant marker for the Pi-b gene (Pi-b dom). However, in
contrast to Pi-ta, which is a single-copy gene in the rice
genome, Pi-b is a member of a small gene family. Thus Pi-b
dom may not detect the Pi-b gene (Fjellstrom et al. 2004). This
is the first report on the application of the perfect markers
derived from portions of an R gene. As more agronomically
important R genes are cloned, more allele-specific DNA
markers will be available for accelerating the incorporation
of durable, broad-spectrum R genes into high-yielding, good
quality advanced breeding lines.