Résumé
Studies have been conducted on rice yellow mottle virus (RYMV). RYMV diversity was investigated in Côte d'Ivoire and compared to other countries in Africa using immunological and molecular markers. Several strains of RYMV were identified. Two were found in Côte d'Ivoire (SI and S2), one numerically dominant in the south and the centre of the country (SI), the other in the north (S2). In mixed inoculation, there was a consistent dominance of S2 isolates over S1 isolates. Quantitative trait loci (QTL) of partial resistance in 0. sativa japonica were found on chromosome 12 with epistasic interaction with a QTL of chromosome 7 and involvement of QTLs linked to developmental genes such as the semi-dwarf gene. Partial resistance was expressed as a delay in virus accumulation, probably reflecting slower vascular and cell-to-cell virus movement in 0. japonica linked to the slower growth of that sub-species. The mestome peri-vascular cell layer may act as a further barrier to virus spread. Tolerance was also involved in the response of O. japonica to RYMV infection. Experiments in growth chambers indicated that there was no biological deterrent to abiotic transmission of the virus, but effective transmission through soil or water remains to be proved in the field. Studies have also been completed on other viruses such as African cassava mosaic virus, tomato yellow leaf curl and its transmission by thewhitefly Bemisia tabaci. (Résumé d'auteur)