Six genotypes derived from a high and low yielding selection within each of the 3 chromosome classes 27, 28 (euploid) and 29 were grown as pure stands and in all possible binary mixture combinations in a tray experiment carried out at Aberystwyth and Newcastle over a two year period. Dry matter yield, tiller number and plant height were recorded for each of several harvests each season. The results showed that:1)(i) the euploids were of high yield and average competitive ability, (ii) the hypoploids were of average yield and low competitive ability, (iii) the hyperploids were of lower than average yield and of high competitive ability;2)Insome cases significant differences were found between selections within a chromosome class;3)Mixture performance was intermediate to that of the component pure stands;4)When high yielding selections were grown in a mixture with a selection of superior competitive ability they tended to produce more tillers per unit dry weight than in pure stands. It was concluded that, until more is known of the relative performance of euploids and aneuploids, marketed seed should contain as high a proportion of euploids as possible.
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