Male Sterilities and F1 Hybrids in Brassica

Abstract

Many Brassica species are economically important as vegetables (B. oleracea, B. campestris, B. juncea), condiments (B. nigra, B. juncea), forages (B. oleracea, B. campestris, B. napus) and as sources of edible or industrial oil and meal (B. campestris, B. napus, B. juncea, B. carinata). Reports for significant heterosis for some agronomic characters such as plant height, leaf area and yield in B. napus (Lefort-Buson et al., 1987) and the possibility of homogeneous production (mechanical harvesting) in B. oleracea have stimulated interest in the development of hybrid cultivars. But to exploit the advantages of heterosis on a commercial scale, an effective pollination control system to produce F1 hybrid seeds is essential. In diploid species (B. oleracea and B. campestris), hybrid cultivars were mostly produced by using self-incompatibility genes. The complexity of sporophytic incompatibility lead to a reduced number of lines convenient for seed production (genetic background effect). It required also bud pollination (very time-consuming) to reach homozygosity of lines and to produce isogenic lines for the establishment of the parents of hybrids. Incompatibility is scarcely complete and inbreds originated from self pollination are often present in hybrid seed lots. Numerous controls are therefore necessary to check about the good genetic quality of seeds. This leads to high seed costs to the growers. In allotetraploid species (B. napus, B. juncea) hybrid seed production is impeded by the preferential autogamous character of these crops. Thus an effective system of cross-pollination is necessary for hybrid rapeseed breeding.