Variation between and within Trifolium repens L. populations collected from sown swards in Uruguay

Nineteen Trifolium repens L. (white clover) populations were collected in different parts of Uruguay (where conditions are marginal for the species) from swards sown 2–15 years earlier. Twenty five genotypes of each population were grown as spaced plants on a single site. Leaflet length and width, petiole length, plant height, plant diameter and internode length were recorded. In a second experiment, ten of the populations were studied in a similar way. Large genetic correlations were obtained among leaflet length, leaflet width, petiole length and plant height as one group, and among major plant diameter, minor plant diameter and internode length as another group, in both experiments. Collection site characteristics that tended to result in relatively short, small-leaved plants were: the sowing of cv. Bayucuá or Santa Fé (rather than Zapicán orYi); a relatively old sward; relatively high available soil P; overgrazing; and dry conditions. There was an indication that, in some respects, there was less variation within a population in older than in younger swards. Overall and within populations heritabilities were relatively high for leaflet length, leaflet width and petiole length and relatively low for plant diameter, with plant height intermediate. Genotypes from populations (such as that from Romero) that survived for 15 years in unfavourable conditions could be useful in a plant breeding programme. Selection for rather smaller-leaved types might enhance persistence.