RELATIVE IMPORTANCE OF GENETIC-PARAMETERS FOR SELECTING BETWEEN OILSEED RAPE CROSSES

Limited resources constrain a breeder to evaluating either a few lines from many crosses or a large number of lines from only the best crosses. To identify crosses, we investigated the relative importance of genetic parameters for additive, dominance, additive by additive epistatic, and cytoplasmic effects in spring oilseed rape (Brassica napus). Three marketing varieties and three breeding lines of Swedish and French origin were used as parents. Parents, F2s and 16 randomly chosen F3 families from four crosses and their reciprocals were grown at Svalov in 1988. Generally, the dominance parameter was most important for explaining yield and maturity, whereas for oil content, only additive gene action was detected. In a few cases, epistatic effects were detected but cytoplasmic effects were of no importance. For the majority of cases, the ranking of crosses based on the expected performance of the best 10% of lines was similar to that based on the mean performance of the crosses.