References
Department of Plant Breeding, 252 Emerson Hall, Cornell University, Ithaca, NY 14853-1902, USA
We have recently developed the first version of a rice RFLP (restriction
fragment length polymorphism) map (McCouch et al. 1988). The purpose of this
report is to provide rice geneticists and breeders with an updated knowledge on
this research.
The objective of the project has been to construct a "saturated" linkage map of rice chromosomes based on cloned single copy DNA sequences. The source of clones was a PstI sized-selected (1-2Kb) genomic library. At high stringency, we found 85% of the clones to be single copy and proceeded to use them as hybridization probes for genetic mapping in an F\2\ population derived from the cross IR 34583-19-3-3 (Indica from the Philippines) X Bulu Dalam (Javanica from Indonesia). Thus far we have mapped 144 loci. Chromosomal positions of markers were determined by dosage analysis using primary and hybrid trisomics provided by Dr. G.S. Khush (IRRI). The map derived from these segregation data is shown in the previous page.
While all chromosomes now have at least one RFLP marker, some chromosomes are underrepresented (e.g. chromosomes 8 and 10) and oters are comprised of more than one linkage group (e.g. chromosomes 1,5-10). We know the linkage groups are on the same chromosome based on trisomic analysis, yet we can detect no genetic linkage between them. It is expected that as new clones are mapped it will be possible to fill in the gaps and eventually tie these linkage groups together.
Currently, we are investigating the possibility of using doubled haploid lines from anther culture (provided by Dr. E. Guiderdoni, IRRI) to establish a permanent mapping population that can be propagated as inbred lines. Recombinant inbred lines are also being constructed at IRRI for this same purpose by Dr. Khush and associates.
Amount of polymorphism within O. sativa. One use of the RFLP map will be to facilitate certain aspects of rice breeding. For this to happen it is necessary that there be sufficient polymorphism for the RFLP markers among rice varieites. Z. Wang of this laboratory has recently completed a pilot study which involved surveying a number of rice varieites with 10 RFLP markers (including Japonica and Indica types). Using these probes, he was able to differentiate 96% of the 70 varieites. These results look encouraging regarding potential use of the rice map in breeding.
Researchers interested in obtaining mapped rice clones should write to us at the address given in this note. We are also interested in interacting with other rice researchers to map cloned genes. This research is supported by a grant from the Rockefeller Foudation.
Fig. 1. RFLP map of rice chromosomes. Asterisks indicate chromosomal
location verified by trisomic dosage analysis. Orders where the confidence level
is below 99% are bracketed.
References
McCouch, S.R., G. Kochert, Z.H. Yu, Z.Y. Wang, G.S. Khush, W.R. Coffman and S.D. Tanksley, 1988. Molecular mapping of rice chromosomes. Theor. Appl. Genet. 76: 815-829.