Competitive multiplication of RNA3 species of different strains of alfalfa mosaic virus.

Competition between RNA3 from alfalfa mosaic virus (AlMV) strain S (RNA3-S), strain B (RNA3-B) and strain 425L (RNA3-L) was studied. The identification of the RNA3 species multiplying in infected leaves was possible since the RNA3 5' non-coding leader sequences in strains S, B and 425L differ in length. RNA3 present in total RNA from infected tobacco leaves was detected, and strains were identified from the length of the cDNA reverse-transcribed from RNA primed with a specific oligonucleotide. In competition experiments the inoculum, containing known amounts of RNA1, 2, 3 and 4 of one strain, was complemented with various amounts of heterologous RNA3 and inoculated to a systemic host. It is shown that RNA3-S was better replicated in vivo by the AlMV replicase of strain B than was RNA3-B itself, and to a lesser extent better replicated by the AlMV replicase of strain L than was RNA-L. Comparison of genetic information carried by the RNA3 species present in the inoculum suggests that the more efficient multiplication of RNA3-S is related to the structure of the leader sequence of RNA3-S.