Relationship between competitive ability and yielding ability in mixtures and monocultures of populations of Dactylis glomerata L

Swards were developed from plants of contrasting populations of Dactylis glomerata L. selected for high and low dry‐matter (DM) production in monocultures and mixed cultures grown during 1970 and 1971. DM production of these mono‐genotype swards was assessed during 1974. Those swards developed from the divergent selections from monocultures maintained a significant difference between the high and low selections, whereas those developed from selections out of mixed cultures showed no significant difference in yield. These results are consistent with earlier reports that there is no positive relationship between competitive ability in mixed cultures and vigour in pure stands. The implications of the physiological basis of these responses in terms of grass breeding are discussed.