Choice of methods and indices for identifying the best parentals for synthetic varieties in faba bean

The aim of this study was to determine the efficiency of different evaluati on methods and indices for the prediction of the best parentals for the dev elopment of a synthetic variety of the faba bean. Our work compared top-cro ss and poly-cross methods in two modalities (1 and 3 seed per hill) using f our different indices, one of which was developed by us. Indices were evalu ated for seed number and yield per plant. Outcrossing rates were estimated by using seven isozyme markers, the mixed mating model and the multilocus m ethod. Indices were compared in terms of similarity in their ranking of par ental genotypes, assuming that the most consistent index is that which give s the highest similarity in ranking over all the designs. There were no dif ferences among the designs in terms of outcrossing rate. However, there wer e differences among parental lines and the level of outcrossing of a partic ular parental line depended on the spatial arrangement in the field. Rankin g of parental lines based on both modalities of the poly-cross design was s imilar for all the indices used suggesting that the evaluation of outcrossi ng in poly-cross designs might be unnecessary. However, indices that take i nto account variability in outcrossing gave similar ranking of parental lin es over both methods and modalities. Our results underline the importance o f taking into account the variability in outcrossing rate when developing s ynthetic varieties in partially allogamous crops. (C) 1999 Inra/Editions sc ientifiques et medicales Elsevier SAS.