Inheritance And Genetic Relationships Of The D8 And D2-2 Restorer Genes For Cotton Cytoplasmic Male Sterility

In cotton, cytoplasmic male sterility conditioned by the D-8 alloplasm (CMS DI) is independently restored to fertility by its specific D-8 restorer (D8R) and by the D-2 restorer (D2R) that was developed for the D, cytoplasmic male sterile alloplasm (CMS-D2). However, knowledge of the relationship between the two restorer genes is lacking. The objectives of these studies were to determine the inheritance and genetic relationship between D2R and D8R. A series of intercrosses and test crosses were used to determine the inheritance and relationships. CMS-D8 lines crossed with D8R resulted in all sterile F-1 plants, confirming that the D8 restorer gene does not suppress D-2 cytoplasmic dysfunction. A segregation ratio of one fertile to one sterile in three testcross combinations revealed that D2R contained one restorer gene, Rf, for both CMS-DI and CMS-D2. The Rf gene functioned sporophytically, whereas the D8R gene is known to function gametophytically. However, Rf pollen with the D-80 or D-2 cytoplasm was preferentially effective in fertilization based on the low number of sterile plants obtained when alloplasmic F-1 plants were Self-pollinated or used as the pollen-parent in crosses with CMS-D8. In tests for allelism only g sterile plants out of 1921 were obtained in two testcrosses of (D8R x D2R)F-1 x normal cotton. Thus, the two restorer loci are not allelic but are tightly linked with an average genetic distance of 0.93 cM. The D-2 gene Rf is redesignated Rfi, and Rf(2) is assigned to the Dg restorer gene.