A comparison of methods for hybrid seed production using self-incompatibility in swedes (Brassica napus ssp napobrassica)

Procedures for producing seed of hybrid swedes using self-incompatibility w ere examined. Single-cross, double-cross and modified double-cross hybrids were compared in isolation plots using natural pollinators and in polythene tunnels using blow-flies. With good coincidence of flowering and the same flower colour, nearly 100% hybrid seed was produced by natural pollinators with the single-crosses, the double-cross and one of the two modified doubl e-cross hybrids; the other modified double-cross hybrid produced 87% hybrid seed. With poor coincidence of flowering and different flower colours the proportion of hybrids dropped to 61%. Using different flower colours and bl ow-flies as pollinators in polythene tunnels, higher levels of outcrossing were produced than in isolation plots with natural pollinators; the opposit e result was obtained when the same flower colour was used.