Yield potential of spring turnip rape synthetics and composite hybrids compared with open-pollinated commercial cultivars

Yield potentials of spring turnip rape (Brassica rapa L.) synthetics and composite hybrids were compared with those of open-pollinated commercial cultivars during a 3-yr period (2000-2002). The trials included 16 synthetics and 25 composite hybrids derived from 22 different parent lines, as well as five open-pollinated commercial cultivars. All of the material tested had low erucic acid and glucosinolate contents and was well adapted for cultivation in southern Finland. The composite hybrids, which were tested for the first time in turnip rape, exhibited significantly higher seed yields than open-pollinated cultivars. The maximum commercial heterosis in seed yield was 18% in synthetics and 23% in composite hybrids. Both synthetics and composite hybrids showed better resistance to lodging than commercial cultivars. When studying the effect of commercial heterosis on seed yield, a high degree of variation was observed both within the synthetics and the composite hybrids. This result highlights the importance of testing parental combinations in turnip rape in order to find combinations that give the strongest heterotic effect.