Genotypic and phenotypic analysis of bromovirus adaptive mutants derived from a single plant

Eight adaptive mutant clones have been made from the total RNA extracted fr om uninoculated upper leaves of a single cowpea plant exhibiting systemic i nfection after inoculation with a hybrid cowpea chlorotic mottle bromovirus (CCMV) with the 3a movement protein gem of CCMV replaced by that of cowpea -nonadapted brome mosaic bromovirus (BMV). Sequence and mutational analyses of these clones showed genotypic and phenotypic diversity of the cloned vi rus population, but all examined clones had the adaptive mutation, A to C a t position 776 within the BMV 3a gene, required for the systemic infection of cowpea. The data support the quasispecies model for RNA virus population , and suggest that the maintenance of the adaptive mutation may be due to p owerful selection pressure in an infection process.