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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

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In vitro culture --- Disease resistance --- Regeneration. --- Regeneration

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Isolates of Phaeoisariopsis griseola, collected for the most in Africa, were characterized according to their virulence properties and their molecular patterns. Differences in symptom intensities caused by the isolates on the inoculated plant genotypes revealed an important pathogenic variability and complexity. SSCP analysis on ITS sequence of the ribosomal DNA as well as RAPD analysis were used for molecular characterization of the isolates. It has been observed that some isolates with dissimilar patterns were collected within a same area. Simultaneously, similar molecular patterns have been found for isolates collected in different sites. However, the molecular similarity is higher among isolates collected within a same area. Analysis of the reactions observed on the plant genotypes after their inoculation revealed the existence of vertical resistance genes in Phaseolus vulgaris as well as in its secondary gene pool. Interspecific hybridization between the genotype NI666 (Phaseolus coccineus), resistant to all the isolates tested, and the genotype Aroana (P. vulgaris), susceptible to most of the isolates, gave F1 hybrid plants resistant to angular leaf spot disease.

Phaseolus vulgaris --- Phaseolus vulgaris --- Phaeoisariopsis --- Phaeoisariopsis --- Pathogenicity --- Pathogenicity --- Genetic polymorphism --- Genetic polymorphism --- Disease resistance --- Disease resistance

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Banana improvement programs aim at the creation of new varieties partially resistant to the black leaf disease. The principal objective of this study was to characterize the components of this resistance using the infectious life-cycle parameters, to judge their epidemiologic weight and to evaluate the variability of the aggressiveness. Significant differences were detected between partially resistant cultivars for some infectious life-cycle sequences either in natural than controlled conditions. Thus, some resistance components were suggested. The experimental devices used in the field did not, however, make it possible to judge the epidemiologic weight of some of them. Elsewhere, a low variability of M. fijiensis aggressiveness was detected and no "cultivar x isolate" specific interaction was highlighted. These results have an implication for the selection of effective and durable partial resistances.

Musa --- Musa --- Mycosphaerella --- Mycosphaerella --- Epidemiology --- Epidemiology --- Pathogenicity --- Pathogenicity --- Disease resistance --- Disease resistance --- Genetic control --- Genetic control

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Solanum tuberosum --- Solanum tuberosum --- Phytophthora infestans --- Phytophthora infestans --- Disease resistance --- Disease resistance --- genetic maps --- genetic maps