Abstract
The genetic diversity of Bean yellow mosaic virus (BYMV) was studied by comparing sequences of complete coat protein (CP) genes of 63 isolates. Phylogenetic analysis of CPs showed that isolates fell into eight distinct groups with an overall nucleotide diversity of 19%. The largest and most genetically diverse group was from natural infections in both wild and domesticated host plant species in both monocotyledonous and dicotyledonous plant families, indicating a generalized host strategy. The other seven groups had a narrower genetic base and in each case, isolates were from a single or limited number of domesticated species, indicating a specialized host strategy. We propose that the generalized group represents the ancestral type from which specialist groups evolved within domesticated plants after the advent of agriculture, since approximately ten millennia BP. The centre of origin of the ancestral group is unclear from its present distribution, but the specialized groups probably originated where their principal hosts were first domesticated, in most cases Eurasia. Specialist groups have adapted to domesticated hosts by often becoming seed-borne, facilitating their world-wide spread. Inter- and intra-specific recombination is a strategy used to increase genetic diversity in BYMV. Recombination was found in CPs and complete genomes and occurred between the generalized group and a specialized group, and between different specialized groups. Phylogenetic analysis of all genes within six complete BYMV genomes and 14VPg gene sequences showed that branch topologies were sometimes incongruous. This indicates that its different genes evolved independently.