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Identification of a hypervirulent pathotype of Rice yellow mottle virus: A threat to genetic resistance deployment in West-Central Africa

Eugénie Hébrard: IRD, Cirad, Univ Montpellier, IPME

<div><em>Rice yellow mottle virus</em> (RYMV) is a major biotic constraint on rice cultivation in Africa, causing high losses to rice production. Several sources of varietal high resistance are available but the emergence of virulent pathotypes that are able to overcome one or two resistance alleles can sometimes occur. Both resistance spectra and viral adaptability have to be taken into account to develop sustainable rice breeding strategies against RYMV. In this study, we assessed the adaptability of 20 viral isolates representative of the RYMV genetic and pathogenic diversity in Africa against high resistant rice accessions. Our results revealed a hypervirulent pathotype, named thereafter pathotype T’, that is able to overcome all known sources of high resistance. This pathotype, which is spatially localized in West-Central Africa, appears to be more abundant than previously suspected. To better understand the adaptive processes of pathotype T’, molecular determinants of resistance-breakdown were identified via Sanger sequencing and were validated through directed mutagenesis of an infectious clone. These analyses confirmed the key role of convergent non-synonymous substitutions in the central part of the VPg to overcome <em>RYMV1</em>-mediated resistance. In addition, deep-sequencing analyses revealed that virulence mutations present in a small proportion of the virus population can be sufficient for resistance-breakdown. Considering the spatial distribution of RYMV strains in Africa and their ability to overcome the RYMV resistance genes and alleles, we established a resistance-breaking risk map to optimize strategies for the deployment of sustainable and resistant rice lines in Africa.</div>

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