Changes in variety composition in spring barley mixtures over years

Summary

In a variety mixture, competition between component varieties as well as differences in performance of the components may lead to changes in the proportion of component varieties between seed sown and seed harvested. This will imply that farm saved seeds of variety mixtures will constitute an evolving population. How much changes are found over a short period of years and in different environments?
In 2002, six 3-component variety mixtures of spring barley were constructed based on altogether 14 mostly high-yielding varieties. The six mixtures and derivatives of these were included in the large Danish BAR-OF variety trials in the years 2002-2005 (Østergård et al. 2005). Here, a subset of this material is considered: only trials from 2003 and 2004 at the sites Flakkebjerg, Foulum and Jyndevad with organic growing conditions. In 2003, the mixtures were composed of seeds from conventional multiplication of the component varieties in equal weight proportions taking into account differences in seed germination. Seeds harvested from the mixtures were in 2004 sown at the same location, resembling the use of farm saved seeds. The smallest seeds were removed before sowing to descrease the load of seed borne diseses. By means of DNA markers, changes in the proportions of the different components in each mixture were estimated.
Four of the six mixtures could be successfully described by the markers chosen. In all cases, changes from the 1:1:1 proportions were found after two years of natural selection and competition between the components of each mixture. For one mixture, changes between locations were revealed whereas for the remaining three mixtures, changes in similar direction were found for all locations. The latter may to some extend be a consequence of the removal of small seeds before sowing; this would give a disadvantage to components with the low TGW which also was indicated by the results. In conclusion, among the four mixtures considered, only in one mixture an interaction with the environment was observed indicating local adaptation of this mixture. In this mixture one of the varieties had very high weed suppression ability and at the same time being very susceptible to netblotch. The environment where the decrease in that component was pronounced had much netbloch and the component increased slightly in frequency in the two other environments. Further analyses of the relation between changes in frequencies of components and characteristics of the components and the environments are in progress.