Biological and molecular variation of Iranian Cauliflower mosaic virus (CaMV) isolates

Abstract

Seventeen provinces of Iran were surveyed during 2003-2012 to find Brassicaceae hosts of Cauliflower mosaic virus (CaMV). A total 397 samples were collected from plants with virus-like symptoms. Among those tested by ELISA, 255 samples (67.2%) were found to be infected with CaMV. Mechanical transmission tests showed that the Iranian isolates have similar biological properties on a number of Brassica and Raphanus plant species and cultivars tested. However, the isolates varied in the severity of symptoms they induced and in the capacity to infect B. oleracea var. capitata, on the basis of which they were grouped into two distinct biotypes L/MMo (latent/mild mottle) and severe (S) infection. The molecular diversity of natural population of CaMV were investigated based on the complete sequences of OFR 6 of 36 Iranian isolates collected from different geographically distant regions in Iran alongside the sequences of 14 previously reported isolates. Phylogenetic analyses indicated that the Iranian CaMV isolates belong to two groups (GI and GII). Most of the Iranian isolates fell into GI with other exotic isolates; however, the isolates from North-East Iran with Xinjiang from China fell into GII. The phylogenetic group GII (the North-East Iranian isolates) closely corresponded to the S biological group however other Iranian isolates corresponded to the L/MMo biological group. The within-population diversity was lower than the between population diversity suggesting the contribution of a founder effect on diversification of CaMV isolates. The Iranian isolates were differentiated from other exotic CaMV isolates and clustered into two RFLP groups using Hpy99I which closely corresponded to the biological and phylogenetic groups. This study showed the evolutionary process in CaMV isolates is shaped by a combination of host range differentiation and nucleotide substitution using the approach of population genetics.