SATURATED MOLECULAR MAP OF THE RICE GENOME BASED ON AN INTERSPECIFIC BACKCROSS POPULATION

A molecular map has been constructed for the rice genome comprised of 726 markers (mainly restriction fragment length polymorphisms; RFLPs). The mapping population was derived from a backcross between cultivate d rice, Oryza sativa, and its wild African relative, Oryza longistamin ata. The very high level of polymorphism between these species, combin ed with the use of polymerase chain reaction-amplified cDNA libraries, contributed to mapping efficiency. A subset of the probes used in thi s study was previously used to construct an RFLP map derived from an i nter subspecific cross, providing a basis for comparison of the two ma ps and of the relative mapping efficiencies in the two crosses. In add ition to the previously described PstI genomic rice library, three cDN A libraries from rice (Oryza), oat (Avena) and barley (Hordeum) were u sed in this mapping project. Levels of polymorphism detected by each a nd the frequency of identifying heterologous sequences for use in rice mapping are discussed. Though strong reproductive barriers isolate O. sativa from O. longistaminata, the percentage of markers showing dist orted segregation in this backcross population was not significantly d ifferent than that observed in an intraspecific F-2 population previou sly used for mapping. The map contains 1491 cM with an average interva l size of 4.0 cM on the framework map, and 2.0 cM overall. A total of 238 markers from the previously described PstI genomic rice library, 2 50 markers from a cDNA library of rice (Oryza), 112 cDNA markers from oat (Avena), and 20 cDNA markers from a barley (Hordeum) library, two genomic clones from maize (Zea), 11 microsatellite markers, three telo mere markers, eleven isozymes, 26 cloned genes, six RAPD, and 47 mutan t phenotypes were used in this mapping project. Applications of a mole cular map for plant improvement are discussed.