Breeding for cabbage root fly (<i>Delia radicum</i>) resistance in cauliflower

Selection of parental lines was continued according to biannual cycles bringing the plant material in the odd years cycle up to F₄ in 1991 and in the even years cycle to the same stage in 1992. The greatest difference between the lines with the lowest (1.3) and the highest mean number of eggs per plant (28.7) was found in 1990 (or 22 fold). Steady progress of level of resistance from one generation to the other is difficult to achieve. Seggregation of high and low egg numbers within descendants of the same parent was first observed in F₄ in 1991. Some 1991 lines showing levels of resistance were grown in an area of higher fly population. The root damage index confirms the results of the eggcounts