Genotypes homozygous for specific PGI2 alleles were selected from four existing cultivars of different maturities, Gremie, Aberystwyth S.321, Barlenna and Melle. Each of three groups of plants (early BB selected from Gremie, intermediate CC selected from Aberystwyth S.321 and Barlenna and late AA selected from Melle) was isolated and allowed to interpollinate producing three experimental seed lots or populations. These populations, screened for their electrophoretic purity, were found to exhibit only the selected parental PGI2 genotype.
The three labelled populations were sown in boxes in September 1982 as monocultures, as all possible 50:50 mixtures, and as a three-way mixture to produce miniswards. Following one harvest in the establishment year these were harvested and dry-matter yields determined on a monthly basis from April to October 1983, two horizons in the sward being examined separately at harvests 1–5. Changes in the proportions of populations in each mixture were monitored by random subsampling of the cut herbage and subsequent electrophoretic testing.
The ability to dominate productivity in the top horizon in mixtures was dependent on the timing of reproductive development of any particular population. The patterns of productivity in the bottom horizon and in both horizons combined showed the early population dominating the mixed swards briefly at the beginning of the harvest but the late population dominating from June–July onwards. The intermediate population, although the most productive in monoculture, did not reveal any tendency to dominate productivity in any of the mixtures.
The potential use of electrophoretically labelled cultivars to study complex aspects of plant competition is discussed, along with the possible application of results from these studies to agricultural practice.