Investigating resistance toBarley mild mosaic virus

Abstract

There are claims that at least 11 genes confer resistance in barley (Hordeum vulgaris) to one or more components of the soilborne barley mosaic virus complex but, apart from the immunity conferred by the widely used generym4, little is known about their mode of action. This study used mechanical (sap) and plasmodiophorid vector‐inoculation techniques combined with ELISA, RT‐PCR, symptom development and virus transmission to investigate the response of different genotypes toBarley mild mosaic virus(BaMMV). Barley genotypes were grown at 20 and 12°C to test for temperature sensitivity. Plants with the genesrym3orrym6were fully susceptible to the virus, whereas those with genesrym1,Rym2,rym5orrym11appeared to be immune, as BaMMV was never detected in any tissue type nor was the virus transmitted from them to susceptible genotypes. The remaining genotypes could all be infected to some extent by BaMMV using one or both inoculation methods, and virus could be transmitted from their roots by the plasmodiophorid vectorPolymyxa graminis. Plants with therym7gene had delayed symptoms compared to susceptible controls at 12°C. Plants with therym8gene could be infected by both inoculation methods, but there was no virus in the leaves at 12°C. Plants with therym9gene could be infected only by vector inoculation, and virus remained localized in the roots. Plants with therym10gene appeared susceptible by mechanical inoculation at both temperatures, but after vector inoculation virus moved to leaves only at 20°C. This suggests the operation of translocation resistance in plants with therym8,rym9orrym10genes, which is temperature‐sensitive inrym8andrym10and perhaps tissue‐specific inrym9. No resistance toP. graminiswas observed in any of the genotypes.