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 gene rym4, 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 to Barley mild mosaic virus (BaMMV). Barley genotypes were grown at 20 and 12°C to test for temperature sensitivity. Plants with the genes rym3 or rym6 were fully susceptible to the virus, whereas those with genes rym1, Rym2, rym5 or rym11 appeared 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 vector Polymyxa graminis. Plants with the rym7 gene had delayed symptoms compared to susceptible controls at 12°C. Plants with the rym8 gene could be infected by both inoculation methods, but there was no virus in the leaves at 12°C. Plants with the rym9 gene could be infected only by vector inoculation, and virus remained localized in the roots. Plants with the rym10 gene 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 the rym8, rym9 or rym10 genes, which is temperature‐sensitive in rym8 and rym10 and perhaps tissue‐specific in rym9. No resistance to P. graminis was observed in any of the genotypes.

A controlled environment test for resistance to Soil‐borne cereal mosaic virus (SBCMV) and its use to determine the mode of inheritance of resistance in wheat cv. Cadenza and for screening Triticum monococcum genotypes for sources of SBCMV resistance

“…Plant RNA viruses are known to have high rates of mutation, and new strains of viruses with altered pathogenicity have been reported to evolve frequently, especially when only one resistance gene source is employed extensively. This has happened recently in Europe with the P. graminis ‐transmitted bymoviruses Barley yellow mosaic virus and Barley mild mosaic virus , where pathotypes have emerged that overcome the resistance genes rym4 and rym5 (Hariri et al ., 1990; Huth, 1991; Adams, 2002; Hariri et al ., 2003; McGrann & Adams, 2004) that are used exclusively in all European barley breeding programmes. Therefore to ensure sustainable disease control via the deployment of resistant germplasms, other novel sources of SBCMV resistance will need to be identified.…”

Polymyxa graminis and the cereal viruses it transmits: a research challenge

“…It is not known whether the viruses are able to multiply inside P. graminis , but there is indirect evidence that suggests that they do not, at least for BaMMV. When viruliferous isolates of P. graminis have been grown in the roots of a virus‐resistant host, the released zoospores no longer contain or transmit virus (Adams et al ., 1987; McGrann and Adams, 2003).…”

Sharka: The Past, The Present and The Future

“…In addition, eriophyid mites spread members of Rymovirus and Tritimovirus ( Abacarus Keifer , Aceria Keifer) [39,40,41] and whiteflies ( Bemicia Quaintance et Baker) spread members of Ipomovirus [42,43,44]. Only members of Bymovirus are transmitted by plasmodiophoroid fungus ( Polymyxa graminis Ledingham, Plasmodiophoridae ) [45,46,47,48]. It has been established that potyviruses are generally transmitted by non-circulative manner, which means that virus articles do not cross the vector cell membranes.…”