Abstract
Reproductive barriers are often observed in progenies derived from crosses between relatively distant species, such as cultivated varieties and their wild relatives. Such barriers hinder the transfer of agronomically important genes from one species to another. In the process of constructing a series of introgression lines (ILs) between Oryza sativa japonica cv. Koshihikari and wild species O. nivara, we observed the occurrence of hybrid breakdown, a reproductive barrier observed in F2 and later generations. Plants affected by this hybrid breakdown show extremely weak growth and die before heading. Linkage analysis and construction of ILs indicated that the locus -hbd1(t), located on the short arm of chromosome 2 of O. nivara, induces hybrid breakdown in the Koshihikari genetic background. hbd1(t) is identical to hbd1, which was previously identified in a cross between Koshihikari and Nona Bokra (indica) cultivars of O. sativa. We present genetic evidence that hbd1(t) regulates hybrid breakdown and its location within 50 kb. Possible reasons for this locus being responsible for hybrid breakdown in inter- and intraspecific crosses are discussed.
