BARLEY YELLOW DWARF LUTEOVIRUSES AND THEIR PREDOMINANT APHID VECTORS IN WINTER-WHEAT GROWN IN SOUTH-CAROLINA

Barley yellow dwarf is recognized as an important disease problem in w inter wheat production in the southeastern United States, but there is relatively little known about the ecology and epidemiology of barley yellow dwarf virus (BYDV) in this region. From 1991 to 1993, and in 19 96 and 1997, winter wheat was sampled for BYDV throughout the principa l wheat production areas in South Carolina. In addition, in 1997, a sm all number of samples were collected from fields in North Carolina and Kentucky. Plant samples were assayed to determine the BYDV serotype a nd, subsequently, coat protein sequences of isolates within the same s erotype were compared using restriction fragment length polymorphisms. Representative BYDV isolates from South Carolina and type isolates fr om New York were compared in aphid transmission experiments using aphi d species collected from South Carolina and laboratory colonies mainta ined in New York. The predominant BYDV serotype in South Carolina (in all years) was PAV, accounting for 94% of the total BYDV-infected samp les analyzed. The RPV serotypes were more abundant in samples collecte d from western North Carolina and Kentucky. PAV isolates from all regi ons were identical to the New York BYDV-PAV in terms of serology and r estriction fragment patterns. Furthermore, the aphid transmission phen otypes were similar for South Carolina and New York BYDV isolates. The predominant aphids colonizing winter wheat in South Carolina included Schizaphis graminum, Rhopalosiphum rufiabdominalis, R. padi, and Sito bion avenea. The South Carolina clones of R. padi and S. avenae were s imilar to the New York laboratory clones in their abilities to transmi t various BYDV isolates from New York and South Carolina. In contrast to the New York clone of Schizaphis graminum that can vector SGV, PAV, and RPV, the S. graminum clone from South Carolina was not a vector o f any BYDV serotype tested. R. rufiabdominalis was found to be an effi cient vector of PAV, RPV, and RMV isolates, but did not transmit MAV o r SGV.