Detection of plant viruses by PCR using group or virus specific primers (potyviruses, bymoviruses) 1

A combined assay of reverse transcription and the polymerase chain reaction (RT‐PCR) utilizing degenerate primers derived from conserved regions in the genome of potyviruses was designed in order to amplify the 5’terminal part of the coat protein cistron, which can differ greatly in length between distinct potyviruses. Amplification on total RNA extracted from one sweet potato clone from China yielded three fragments of different lengths, and sequence analysis of these fragments indicated mixed infections by three distinct potyviruses in the sweet potato clone investigated. Two degenerate primers were also designed in order to amplify the 5’terminal part of the coat protein cistron of either potyviruses or bymoviruses. A third degenerate primer was selected from a region conserved in potyviruses and bymoviruses and used with primers specific for two different bymoviruses, barley yellow mosaic bymovirus (BaYMV) and barley mild mottle bymovirus (BaMMV). These primers allowed the identification of BaYMV and BaMMV barley plants from the field with single or mixed infection, and were used to clarify the etiology of a viral agent inducing mosaic symptoms on several barley cultivars considered so far as resistant to BaYMV and BaMMV. Amplification of fragments, including the variable 5’terminal region of the coat protein cistron, thus provides a convenient method for the detection and characterization of potyviruses and bymoviruses, without fastidious preliminary work of separation and purification of the components of viral complexes.