ABSTRACT
Deployment of strategies for integrated crop protection against cereal rusts in France is prevented by a lack of information on wheat resistance genes and rust agent virulence factors. Accordingly, a study consisting of a survey of yellow rust virulences (Puccinia striiformis Westend) on wheat and a comparison of mixtures and pure cultivars having different resistance factors was initiated. The comparison concerned the increase of disease over time and the efficiency of fungicide treatments. In a first experiment a varietal mixture (Clement, Joss Cambier, Talent) inoculated with a yellow rust race (232 E 137) had lower disease intensity (area under the disease progress curve) and slower disease progress (apparent infection rate) than the means of the three components cultivated in pure stands. However, the apparent increase in yield of the mixture compared with pure cultivars could be explained by the evolution of the cultivar tiller proportion during the season because the resistant variety was dominant. In a second experiment, where initial inoculum was higher and epidemic duration shorter, no advantage of four three-component mixtures over the means of pure cultivars was encountered. Nevertheless, at the end of the season the proportion of cultivars in the mixtures had evolved significantly from the initial 1:1:1 ratio. Fungicide treatment efficiency was different between varietal mixtures and pure varieties. The same yield was obtained with two of the three mixtures (1 susceptible, 2 resistant) when sprayed once as was obtained with the susceptible cultivar sprayed three times.
