SELECTION VERSUS RECOMBINATION - WHAT IS MAINTAINING IDENTITY IN THE 3' TERMINI OF BLUEBERRY LEAF MOTTLE NEPOVIRUS RNA1 AND RNA2

The 3' non-coding regions (NCR) of RNA1 and RNA2 of blueberry leaf mot tle nepovirus (BBLMV) are nearly identical with differences occurring at only four positions. The presence of this 1.4 kb duplication indica tes that recombination has occurred at least once in the evolutionary history of BBLMV. Since high mutation rates are common in RNA viruses, strong selection pressure and/or high frequency of recombination must be operating in order to maintain identity in this duplicated region. The possible involvement of high frequency RNA recombination in maint aining identity was investigated. The four conserved differences betwe en the 3' NCR of RNA1 and RNA2 were used as markers to detect recombin ants in a viral population. Nucleotide sequences of BBLMV cDNA clones were compared to the 3' consensus sequence and deviations were examine d to determine whether they were due to single base mutations or recom binational events. No evidence of recombination was found in any of th e cDNA clones sequenced and all differences were attributed to mutatio ns. If recombination occurred in the 3' NCR of BBLMV, the frequency wa s below 1.1 % between markers. The data indicate that identity in the 3' NCR of RNA1 and RNA2 of BBLMV was maintained without high levels of recombination. The high number of mutations observed in a BBLMV popul ation and lack of observable recombination indicate that other mechani sms, such as selection, play an important role in the conservation of identity in the 3' NCR.