SERIOUSNESS OF COFFEE LEAF RUST AND FACTO RS INVOLVED IN COFFEA-CANEPHORA FIELD-RESISTANCE IN THE COTE-DIVOIRE

The seriousness of leaf rust (Hemileia vastatrix) was assessed on Coff ea canephora planting material either extended or undergoing selection in the Cote-d'Ivoire. The impact of the disease can be considerable o n susceptible genotypes. In a fungicide trial, 60 % defoliation was ob served on the untreated susceptible control, compared to a mere 20 % o n the same control when treated. Observations of the degree of attack in breeding plots revealed strong interactions between genotypes, site s and years. The susceptibility of plants of the same genotype planted in a totally randomized design in clonal trials also proved to be var iable. These results show heterogeneous distribution of pathogen races with different virulence genes. It can be assumed that races other th an race II, which is the only one to be inventoried so far in the Cote -d'Ivoire, are present. Despite this pathogen variability, a large num ber of genotypes have revealed substantial resistance throughout the o bservation years, which will enable effective selection. The consequen ces of these results for Coffea canephora breeding methods are discuss ed.