THE MEIOTIC BEHAVIOUR OF A NULLI-HAPLOID PLANT IN AVENA SATIVA L.

A nulli-haploid plant (2n = 20) was found in the progeny of an induced monosomic line of Avena sativa L. var. Rodney (2n = 6x = 42). At metaphase 1, the number of associations ranged from 1 to 6 with a mean frequency of 3.5. The pairing frequency can best be explained by the absence of a genetic system, similar to that of chromosome 5B in Triticum aestivum, which would control the diploidisation of hexaploid oats.Chromosomes were associated terminally with an occasional interstitial chiasma. Closed bivalents were rare, and the frequency of trivalent associations was low. This meiotic behaviour confirms the genetic evidence as to the homoeology of the three genomes of the hexaploid oats, but seems to indicate a great deal of structural divergence between them.It is suggested that the long sub-terminal chromosome 7 might carry the gene for diploidisation.