Phylogeny and recombination analysis of Brazilian yellow passion fruit isolates of Cowpea aphid-borne mosaic virus: origin and relationship with hosts

The Cowpea aphid-borne mosaic virus (CABMV) causes the most important disease in passion fruit (Passiflora spp.) in Brazil. The genetic diversity of Brazilian CABMV isolates infecting yellow passion fruit was evaluated. Leaves presenting symptoms of mosaic and blister were collected in orchards in four Brazilian states. Samples were submitted to RNA extraction, RT-PCR, sequencing and phylogenetic analyses of two regions of the CABMV genome: complete coat protein (CP) and partial cytoplasmic cylindrical inclusion (CI), representing together about 20 % of the genome. Potential alternative hosts to CABMV in areas with intensive passion fruit farming in the state of So Paulo were analyzed. Isolates did not infect cowpea (Vigna unguiculata) and common bean (Phaseolus vulgaris). Only Macroptilium atropurpureum behaved as a differential host to an isolate from the southernmost region of the state of So Paulo. In spite of the little variation in biological properties, CABMV isolates from So Paulo presented moderate genetic diversity between one another, especially between isolates from the other states, with nucleotide identity between 88 and 99 % (84 to 100 % amino acid identity) for CP and 85 % and 99 % (93 to 100 % amino acid identity) for CI. Isolates did not group consistently by origin or hosts in the maximum likelihood tree. The parent strains of CABMV isolates in So Paulo occupied a more basal position in the phylogenetic tree, suggesting the possible origin of Brazilian isolates. Recombination events were observed only for CP. Isolates from So Paulo were the major parents of CABMV recombinant strains of cowpea, passion fruit and peanut from other Brazilian states. These results agree with the expansion pattern of passion fruit cultures in the country, and suggest that the So Paulo region is the origin of CABMV in Brazil, from which isolates spread to other regions and evolved.