- Volume 71, Issue 6, 1990

Three mutant brome mosaic virus (BMV) RNA-2 transcripts bearing two alterations in the pseudoknot region and one in arm C of the 3′ tRNA region, previously characterized as being deficient in tRNA-like functions, have been assayed for their ability to infect and replicate (in the presence of wild-type RNAs- 1 and -3) in Chenopodium hybridum plants. Although the introduced mutations have been shown to incapacitate the replication of RNA-2 in barley protoplasts, C. hybridum plants inoculated with these mutants developed local lesions indistinguishable in appearance and morphology from control inoculations containing wild-type RNA-2. Sequence analysis of progeny RNA-2 from two single lesion isolates for each mutant inoculum revealed that the input mutations were restored to functional sequences by homologous recombination within the 3′ tRNA-like region. These results, which reflect the ease with which progeny RNA can be characterized from single lesions, exemplify the value of C. hybridum for studying recombination among viral RNAs.

Agroinoculation of African cassava mosaic virus DNA A alone into Nicotiana benthamiana resulted in the occasional spread of viral DNA throughout the stem, leaves and root. The amount of DNA A reached 5 % of that associated with full infection following agroinoculation of both DNAs A and B, although the plants remained asymptomatic. Detection of virus particles in the upper leaves indicates that DNA B is not essential for virus assembly. The predominant form of the virus- specific DNA was single-stranded, which is possibly encapsidated within the virus particles. Double-stranded DNA forms could also be detected in the upper leaves.