Isolation of telotertiary compensating trisomics from telocentric translocation trisomics and telo-substituted translocation heterozygotes of rye (Secale cereale L.)

Telotertiary compensating trisomics (CTs) of rye (Secale cereale L.), in which the absence of one normal chromosome is compensated by the presence of a telocentric and a translocation chromosome, were isolated in progenies of telocentric translocation trisomics, and telo-substituted translocation heterozygotes, respectively. These two sources were obtained from crosses between five interchanges of the Wageningen translocation tester set, and telocentric normal trisomics (for IRS, IRL and 5RS), or telocentric substitutions (for IR and 3R), respectively. In test crosses with normal male plants, CTs were identified using either critical meiotic configurations, the segregation of karyotypes in selfed trisomic progenies, or the segregation of a marker located on the compensated chromosome. CT yields ranged from 0.0–6.3%. These frequencies were concluded to be determined mainly by the frequency of the exchanged segment of the translocation chromosome involved in the CT complex being associated at first meiotic metaphase (MI) in the source plants. The lower association frequencies result in the higher CT yields. The correlation between high association frequency of this segment and low CT yield suggests that infrequent adjacent orientation of one critical segment is also responsible for the origin of CTs. This agrees with cytogenetic theory.