Identification of peanut (Arachis hypogaea) chromosomes usinga fluorescence insitu hybridization system reveals multiplehybridization events during tetraploid peanut formation

The cultivated peanut Arachis hypogaea (AABB) is thought to have originated from the hybridization of Arachisduranensis (AA) and Arachisipaensis (BB) followed by spontaneous chromosome doubling. In this study, we cloned and analyzed chromosome markers from cultivated peanut and its wild relatives. A fluorescence insitu hybridization (FISH)-based karyotyping cocktail was developed with which to study the karyotypes and chromosome evolution of peanut and its wild relatives. Karyotypes were constructed in cultivated peanut and its two putative progenitors using our FISH-based karyotyping system. Comparative karyotyping analysis revealed that chromosome organization was highly conserved in cultivated peanut and its two putative progenitors, especially in the B genome chromosomes. However, variations existed between A.duranensis and the A genome chromosomes in cultivated peanut, especially for the distribution of the interstitial telomere repeats (ITRs). A search of additional A.duranensis varieties from different geographic regions revealed both numeric and positional variations of ITRs, which were similar to the variations in tetraploid peanut varieties. The results provide evidence for the origin of cultivated peanut from the two diploid ancestors, and also suggest that multiple hybridization events of A.ipaensis with different varieties of A. duranensis may have occurred during the origination of peanut.