Heterosis and genetic distance in rapeseed (Brassica napus L.): use of kinship coefficient

Different agronomic characters have been measured on F1 rapeseeds from inbred lines that are more or less related and on their parents, in Rennes (France). Two different experiments were conducted over a 2-year period. A study of the relationship between heterosis and genetic distance, measured here by a function of kinship coefficient (1–ψ), was carried out in two steps. First, four classes of increasing 1–ψ values were defined and related to heterosis value and F1 performance. The results point out a significant effect of the class, whatever the character and the year. Moreover, the best heterotic hybrids were always obtained with lines unrelated and coming from two different geographic pools. Then, the efficiency of 1–ψ for predicting heterosis or cross values was tested: it varies with year and character. For example, in the first experiment average relationship between lines was high, about 50% of seed yield variation owing to mean parent heterosis was explained with the 1–ψ distance. Key words: heterosis, cross prediction, genetic distance, kinship coefficient, Brassica napus L.