USING BULKED EXTREMES AND RECESSIVE CLASS TO MAP GENES FOR PHOTOPERIOD-SENSITIVE GENIC MALE-STERILITY IN RICE

Photoperiod-sensitive genic male sterile (PSGMS) rice has a number of desirable characteristics for hybrid rice production. In this study we made use of a published rice genetic linkage map to determine the loc ations of PSGMS genes and we have characterized the effects of these g enes on sterility by using molecular markers. A two step approach was designed for mapping the genes: (i) identifying possible PSGMS gene-co ntaining chromosome regions with bulked DNA from extreme fertile and e xtreme sterile plants of a very large F-2 population and (ii) determin ing the map locations of the genes in extreme sterile individuals. We show that this mapping method is much more cost effective and statisti cally efficient than using a random sample of an F-2 population We ide ntified two chromosomal regions each containing a PSGMS locus, one des ignated pms1 on chromosome 7 and one designated pms2 on chromosome 3. The existence of these two loci was confirmed by a large sample assay and with data on ratooning progenies of the F-2 plants. A marker based analysis shows that the effect of pms1 is 2-3 times larger than that of pms2 and that dominance is almost complete at both loci. Implicatio ns in the breeding of PSGMS rice lines are discussed.