DYNAMIC CONSERVATION OF VARIABILITY - RESPONSES OF WHEAT POPULATIONS TO DIFFERENT SELECTIVE FORCES INCLUDING POWDERY MILDEW

A programme of dynamic conservation of genetic resources has been conducted on winter wheat in France since 1984. One allogamous and 2 preferential selfing populations, with a large genetic base, made up the initial gene pools. Seed samples of these pools were distributed throughout a multi-site experimental network. The populations obtained were multiplied each year in each site. Populations developed significantly after 8 years of multiplication: plant height had increased, the proportion of viable pollen grains had increased in male-fertile plants of allogamous populations and a north-south gradient for precocity was observed for autogamous populations. Resistance to powdery mildew had developed in local populations, both for adult-plant resistance and the frequency of specific resistance genes to Erysiphe graminis f sp tritici. The differentiation depended on the gene pool of the host populations. Virulence frequencies of the parasite populations varied according to the site and the year. There was no clear relationship between virulence frequencies and resistance gene frequencies. The proportion of plants without specific resistance genes seems to correlate with adult-plant susceptibility in local autogamous populations. Most of the variability was maintained through propagation under various natural selection forces.