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Crown rust is a world-wide disease on wild and on cultivated species of oat. In Morocco, this disease is considered as a major cause of yield reduction, which must be controlled by genetic resistance of the host. This work focused on the study of these problems at the level of three different Moroccan regions : Tangier, Gharb and Doukkala. The analysis of the rust isolates collected in these regions revealed a large number of biotypes, which do not differ meaningfully by their virulence whatever the region. The presence of complex biotypes (having 3 genes of virulence or more), their abundance (close to 70 % of biotypes analysed) and the sexuality of the parasite confirm that a high genetic variability must be taken into account in the strategy of improvement and the subsequent deployment of selected varieties. The analysis of 450 collected accessions showed that resistant genotypes were especially abundant in regions where the disease pressure is very high (Northern Morocco). Six genotypes belonging to the species Avena maroccana and one genotype belonging to the species Avena sterilis were selected for their resistance in the field and were analysed in controlled conditions of inoculation by four isolates carrying a large number of virulence genes. Among the basic parameters of the infection cycle (infection types, period of latency, production of spores and germination of spores), it appears that the production of spores differentiates the oat genotypes according to their resistance.

Avena --- Avena --- Puccinia --- Puccinia --- Disease resistance --- Disease resistance --- Epidemiology --- Epidemiology