THE UTILIZATION OF HETEROSIS FOR SEED YIELD IN HYBRID AND SYNTHETIC CULTIVARS OF SUMMER TURNIP RAPE

Hybrids of summer turnip rape (Brassica rapa L. syn. B. campestris L.) have been shown to exhibit high levels of heterosis. This study was u ndertaken to determine whether the heterosis for seed yield observed i n hybrids could be captured by synthetic cultivars of turnip rape. The agronomic performance of reciprocal inter-cultivar hybrids and their corresponding two-component synthetics was studied using four turnip r ape cultivars. Hybrid seed was produced by hand pollination in the gre enhouse and Syn(1) seed was produced by mixing equal proportions of ea ch parent to form the base seed (Syn(0)) of each synthetic, and planti ng these in isolation in the field. The seed yield of hybrids, synthet ics and parents were similar in 1985 while in 1986, hybrids yielded 25 % and synthetics 23% more than parents. Actual versus predicted synthe tic yields were similar except for one synthetic, Echo-Torch in 1986, where the actual yield exceeded the predicted value. Hybrid yields may have been underestimated by the chosen prediction method and therefor e the yield potential of hybrids would be greater than for synthetics in turnip rape. However, until a suitable pollination control system i s developed in this species, synthetic cultivars are a viable alternat ive to hybrids.