Divergent evolution of wheat populations conducted under recurrent selection and dynamic management

The effects of artificial selection in a recurrent selection programme (RS) and natural selection in a dynamic management programme (DM) were studied in a wheat composite population. The initial population, populations of different cycles of RS and four populations of DM were compared for agromorphological traits. It is shown that DM and RS led to divergent evolution of the populations that could be sharply distinguished by fen traits: plant height, earliness, frequency of bearded plants and susceptibility to powdery mildew and leaf rust. Except for plant height, genetic variability was maintained in the DM system either within the populations or through the differentiation between populations. Variability was also preserved in the RS programme except for leaf rust resistance for which the strong increase of resistance level led to a loss of genetic variability. Compared with RS, DM could have selected more multigenic resistances and conserved a larger diversity of resistance genes. Conditions for the possible use of the DM populations as a source of variability for the RS programme are discussed. We suggest the introduction of artificial selection in some DM populations in order to preserve their 'cultivated' phenotype. In DM, the benefit of multiplication sites with high and contrasting parasitic pressures is emphasized. ((C) Inra/Elsevier, Paris.).