Chromosome behaviour in autotetraploid cereals and grasses

Abstract

The cytological behaviour, with emphasis on quadrivalent and bivalent formation at metaphase, was studied in four autotetraploid cereals: wheat, oats, barley, and rye, and in two grasses: Hordeum bulbosum, and Arrhenatherum elatius. 1. Chiasma frequency of the autotetraploids was less than twice that of diploids. No definite correlation relating chiasma frequency to the number of quadrivalents could be established. 2. In flax and maize, plants with small chromosomes, over 70% of the chromosomes were associated as quadrivalents. This value is slightly higher than the average for the cereals and grasses. 3. The effect of the environment, compared for two different growing seasons and one trial in a growth cabinet, was not found to be significant on chromosome associations. 4. With one exception in H. bulbosum, no differences in pairing behaviour within a species were demonstrated. The strains had different origins, and the colchicine-induced autotetraploids, differed in number of generations that had been grown since the time of their production. 5. A mean of 4.3 quadrivalents per cell was found for the six species and no species differed significantly from this value. There were, therefore, no major differences between the natural and the artificially produced autotetraploids. There was no evidence to indicate a trend towards bivalent formation in any of the autotetraploids. 6. Autotetraploids of some species had more seed set than others. Lines of T. monococcum with high and low fertility were selected. Because the amount of quadrivalent formation was the same in all lines it was concluded that genetical control and the impact of the environment affected the fertility more than irregularities of meiosis.