Interpopulational and intervarietal F1 hybrids in Lolium perenne: performance in field sward conditions

Fifteen intervarietal F1hybrids and their parents were evaluated in two field sward trials, representing three levels of management intensity each maintained over a 2-year harvest period. The trials were sown in different years and at different sites. Several hybrids exhibited significant levels of heterosis for total annual dry-matter yield – up to 5–5 % mid-parent and up to 3–6 % higher-parent heterosis. Within individual trials mid-parent heterosis up to 8% was found, while at particular harvests over 25% heterosis was not uncommon. Comparisons made of performance in swards, simulated swards and spaced-plant conditions showed that genetic differences found maximum expression in non-competitive conditions. This was greatly reduced in simulated swards and further suppressed in sown swards in the field. Expression of heterosis was highly specific to the conditions in which it was tested, although the two hybrids most heterotic as spaced plants were also significantly heterotic in field swards.