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) wer e studied in a wheat composite population. The initial population, pop ulations of different cycles of RS and four populations of DM were com pared for agromorphological traits. It is shown that DM and RS led to divergent evolution of the populations that could be sharply distingui shed by fen traits: plant height, earliness, frequency of bearded plan ts and susceptibility to powdery mildew and leaf rust. Except for plan t height, genetic variability was maintained in the DM system either w ithin the populations or through the differentiation between populatio ns. 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 sel ected more multigenic resistances and conserved a larger diversity of resistance genes. Conditions for the possible use of the DM population s as a source of variability for the RS programme are discussed. We su ggest 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.).