Genetic linkage maps of the chromosomal regions associated with apomictic and sexual modes of reproduction in Cenchrus ciliaris

Cenchrus ciliaris reproduces by apomixis, an asexual mode of reproduction through seeds. Genetic analysis of apomixis in this species revealed that this trait is dominant and that a chromosomal region of more than 11 Mb controls this trait, which is hemizygous, heterochromatic and recombinationally suppressed. A novel F2 mapping population comprising 86 individuals segregating for apomictic and sexual modes of reproduction, generated after crossing a new set of obligate apomictic and sexual parents (IG-96-3108 and IG-96-443), was used in this study to identify a large number of amplified fragment length polymorphism (AFLP) and sequence characterized amplified region (SCAR) markers linked to these traits. Out of 180 polymorphic AFLP markers, 42 and 29 markers associated with apomixis and sexuality were mapped around Apo and Sexual loci, respectively. Markers 20G, 18G and 19G showed close linkage to Apo locus at map distance of only 1.1 cM, while 12FS, 4HS and 12b showed tight linkage to Sexual locus at map distance of 1.7 cM. Markers clustered around Apo and Sexual loci on either side. A large number of recombining AFLP markers were mapped around both loci, indicating a minor role of suppression of recombination. Four anchor markers from earlier studies also clustered around Apo locus, validating the present genetic linkage map. In addition, seven and one SCAR markers closely linked to Apo and Sexual loci were also developed, which could be used for fine mapping of the loci.