Abstract
Understanding linkage block size and molecular mechanisms of recombination suppression is important for plant breeding.
Previously large linkage blocks ranging from 14 megabases to 27 megabases were observed around the rice blast resistance
gene Pi-ta in rice cultivars and backcross progeny involving an indica and japonica cross. In the present study, the same
linkage block was further examined in 456 random recombinant individuals of rice involving 5 crosses ranging from F2 to F10
generation, with and without Pi-ta containing genomic indica regions with both indica and japonica germplasm. Simple
sequence repeat markers spanning the entire chromosome 12 were used to detect recombination break points and to
delimit physical size of linkage blocks. Large linkage blocks ranging from 4.1 megabases to 10 megabases were predicted
from recombinant individuals involving genomic regions of indica and japonica. However, a significantly reduced block from
less than 800 kb to 2.1megabases was identified from crosses of indica with indica rice regardless of the existence of Pi-ta.
These findings suggest that crosses of indica and japonica rice have significant recombination suppression near the
centromere on chromosome 12.