To gain an understanding of the molecular
basis for resistance to rice blast (Magnaporthe grisea),
we have initiated a project to clone Pi5(t), a locus associated
with broad-spectrum resistance to diverse blast
isolates. AFLP-derived markers linked to Pi5(t)-mediated
resistance were isolated using bulked segregant
analysis of F2 populations generated by crossing three
recombinant inbred lines (RILs), RIL125, RIL249, and
RIL260 with the susceptible line CO39. The most tightly
linked AFLP marker, S04G03, was positioned on
chromosome 9 of the fingerprint-based physical map of
Nipponbare, a well-characterized rice genotype. Flanking
BAC-based Nipponbare markers were generated for
saturation mapping using four populations, the three
initial RILs and an additional one derived from a cross
between M202 and RIL260. A BIBAC (binary BAC)
library was constructed from RIL260. Using these resources
Pi5(t) was mapped to a 170-kb interval, and a
contiguous set of BIBAC clones spanning this region was constructed. It had previously been suggested that
Pi3(t) and Pi5(t) might be allelic, due to their identical
resistance spectrum and tight linkage. We therefore
compared genomic regions for lines containing Pi3(t)
using the Pi5(t)-linked markers. DNA gel-blot analyses
indicated that the region around Pi3(t) is identical to
that of Pi5(t), suggesting that Pi3(t) and Pi5(t) are
the same resistance gene.