Genetic and Pathogenic Diversity within RYMV Pathotypes S2 and S1 Isolated in Côte d’Ivoire

Rice yellow mottle (RYMV) is the most well-known viral disease of rice fields that causes significant economic loss.However, the high resistant rice genotypes that are available can be circumvented by emergent virulent pathotypes.In order to develop sustainable rice breeding strategies against RYMV in Cte d'Ivoire, both resistance spectra and intraspecific viral pathogenecity have to be taken into account.For this purpose, RYMV 95 strains were sampled from infected leaves within the 7 rice growing regions in Cte d'Ivoire and were confirmed serologically as S2 (98%) and S1 (2%).The phylogeny of the Cp protein amplified by RT-PCR revealed that while the S1 pathotype represented one clade, an intrapathotype diversity was observed within S2 in Cte d'Ivoire.An extended resistance spectrum analysis of 22 strains representing S1 and S2 pathotypes was carried out using the promising resistant rice varieties Gigante, TOG 5674, TOG 5672, TOG 5681 that carry four different alleles rymv 1-2, rymv 1.5, rymv 1-4, rymv 1-3 and the sensitive check Bouak 189.Whithin the S2 pathotypes, a group of viruses could circumvent the resistance by giving symptoms (SRB) while the second group could bypass resistance without giving symptoms (nSRB).While the resistance genes Rymv1-5, Rymv 1-3 and Rymv 1-4/Rymv2 could be bypassed by 81%, 9% and 22.7% of S2 pathotype, no S2 pathotype bypassed the gene Rymv1-Moreover, the two S1 that were genetically identical showed a pathogenic variation and a divergence within the Vp region.