A satellite RNA of arabis mosaic nepovirus and its pathological impact

Three RNA species were encapsidated in arabis mosaic nepovirus from lilac (ArMV‐L): the two genomic RNAs, RNA‐1 and ‐2, and an RNA‐3, Mr. 0.4 × 10⁶. The genomic RNAs from ArMV‐L separated by gel electrophoresis from RNA‐3 were infectious and, during ten passages of this isolate (ArMV‐SF) RNA‐3 was not produced; only RNA‐1 and RNA‐2. When inoculated with the genomic species of ArMV‐L, or with those of other ArMV isolates, RNA‐3 replicated but did not do so in the absence of RNA‐1 and RNA‐2. The RNA‐3 did not share extensive regions of nucleotide sequences with the genomic RNAs but, like them, was polyadenylated and was linked to a protein (VPg) which did not seem essential for replication. When the pathogenicity of ArMV‐L and ArMV‐SF was compared in 42 plant species/cultivars representing 36 genera and 14 families, the following differences were observed: in three species of legume, disease progressed more rapidly when RNA‐3 was present but in species from five families, the presence of RNA‐3 was correlated with symptom amelioration. When RNA‐3 was present, the amounts of ELISA detected antigen were not consistently different in tip leaves of Nicotiana megalosiphon, Chenopodium amaranticolor, C. quinoa or Pisum sativum from those in leaves where RNA‐3 was absent.