Cytogenetics of Ditelosomic Alien Addition Lines in rice (Oryza sativa L.) Each Carrying an Extra Pair of Telocentric Chromosomes of O. punctata Kotschy

Ditelosomic alien addition lines (DtAALs: 2n=2x + 2t) of rice each carrying a pair of telocentric chromosomes of Oryza punctata were isolated at low frequencies (2.5-11.1%) from the progenies of respective monotelosomic alien addition lines (MtAALs: 2n=2x + 1t) 7, 11 and one unidentified MtAAL. During the meiosis, the alien telocentric chromosomes of three DtAALs completely paired at the pachytene and usually separated to each daughter cell at anaphase I, giving rise to viable gametes with an alien telocentric chromosome at high frequencies. These DtAALs were characterized by stable transmission of the alien telocentric chromosome in the progenies. The transmission rates of the alien chromosome were considerably high in the DtAALs, and most plants of their self-pollinated progeny carried at least one alien telocentric chromosome. The pollen and seed fertility were different among three DtAALs. DtAAL 11 carrying a short telocentric chromosome of O. punctata showed high pollen and seed fertility similar to the disomics. The DtAALs showed relatively stable transmission of alien telocentric chromosome(s), where gametes with an extra telocentric chromosome are functional in both female and male germ cells. These suggest that small chromosome fragment with functional centromere, that is a telocentric chromosome, can be transmitted to the progenies and be stable in the next generation. High transmission rates of the alien telocentric chromosome in these DtAALs assure the efficient changes in genetic background of any recipient cultivars by backcrossing.