Cytoplasmic-nuclear male sterility in pearl millet: comparative RFLP and transcript analyses of isonuclear male-sterile lines

The identification of diagnostic cytoplasmic molecular markers is of prime interest to pearl millet breeders wishing to identify sources of cytoplasmic-nuclear male sterility (CMS) which can be used as an alternative to the single source currently used in the production of F-1 hybrid seed. Here, we report the classification of five pearl millet CMS sources based on RFLP analysis of isonuclear lines carried out using mitochondrial gene-specific DNA probes in combination with eight restriction endonucleases. On the basis of RFLP data, the five CMS cytoplasms can be distinguished from each other and from the isonuclear fertile cytoplasm. In addition, based on cox1, cox3, atp6 and atp9 polymorphisms, these lines can be classified into two major groups: one corresponds to A(5), A(egp), A(v) and A(1) cytoplasms, and the other consists of the A(4) cytoplasm. Our results suggest that a rearrangement involving the cox1 gene might be related to CMS in the first group (A(5), A(egp), A(v) and A(1)), whereas a rearrangement within the atp6/cox3 cluster region might be related to CMS in the second group (A(4)).