Strong selection in wheat populations during ten generations of dynamic management

Abstract

Temporal evolution of genetic variability in a Dynamic Management programme of wheat populations was assessed for fitness-related traits and for 29 RFLP markers. Populations of the 1st, 5th and 10th generations were studied. Genetic correlation between plant height (PH) and kernel number (KN) or kernel weight (KW) per plant was high and positive in each population, due to an advantage for the taller plants in intergenotypic competition conditions. This led to a linear increase in PH over generations. On the other hand, KN and KW linearly decreased over generations certainly due to re-allocation of reproductive resources to vegetative functions in the taller plants. On the basis of temporal variation of allelic frequencies of RFLP markers, very low effective sizes (Ne) were estimated: 216 between the 1st and 5th generation, and 157 between the 5th and 10th. These values, much lower than expected from census sizes (= 2650) demonstrated that selection strongly influenced the evolution of neutral loci either by direct hitch-hiking effects and/or by increasing variance of progeny size. The non-significantly different Ne estimates for both periods of time suggested that selection remained constant over the 10 generations. This result is consistent with the continuous evolution of the quantitative traits. A great heterogeneity of temporal variations was observed among loci, showing the heterogeneity of selective pressures over the genome. Detection of selected loci using genetic markers is discussed.