Meiotic behaviour of telo-tertiary compensating trisomics of rye: evaluation for use in hybrid varieties.

Meiosis of four telocentric-tertiary compensating trisomics of rye (Secale cereale L.) was studied with the purpose of evaluating their suitability for use in maintaining genic male-sterile lines applied in hybrid varieties. They had been constructed from four different reciprocal translocations and three different telocentrics. In one trisomic a slight, but significant tendency was demonstrated for preferential pairing of the two normal chromosomes associated with the compensating complex. This promotes the desired segregation into one normal and one compensating karyotype. In all trisomies, however, too high a frequency of failure of chiasma formation in a critical segment of the complex was evident. This is correlated with the ease of recovery of the trisomics, but results in undesired segregational products. Interstitial chiasmata leading to the formation of branched configurations were also present, more in some trisomics than in others. These also result in undesired segregations. The behaviour at meiosis was so closely correlated with the length of the chromosome segments involved that a prediction of the most favourable combination of telocentric and translocation can be made. The telocentric should be large, the corresponding translocated segment large and the interstitial segment small. The non-translocated arm of the translocated chromosome should be large and the second translocated segment small. The combinations of translocations and telocentrics had not been selected for these criteria and did not meet the requirements for practical application.