Beet curly top viruses in Iran: Diversity and incidence in plants and geographical regions

Beet severe curly top virus (BSCTV, recently named BCTV-Svr) and Beet curly top Iran virus (BCTIV) are the causal agents of curly top disease in sugar beet and several other dicotyledonous plants in Iran. In this investigation, genetic diversity and prevalence of curly top viruses in relation to host, geographical distribution and age of the main host plant (sugar beet) were studied. Polymerase chain reaction using specific primer pairs to amplify a part of the genome of BSCTV and BCTIV was applied to 734 plant samples collected from various hosts in five provinces in Iran. DNA fragments approximately 500 and 700 bp in size were amplified from 18 BSCTV and 10 BCTIV infected plants, respectively. Amplified fragments were subjected to sequencing and phylogenetic analysis. Effect of geographical location on genetic diversity of viruses was observed only for BCTIV isolates. Type of host plant had no correlation with genetic diversity of either BSCTV or BCTIV. The highest incidence of both viruses occurred in Fars province. Nonparametric analysis of PCR data showed that the prevalence of each virus varied in different fields and depended on the host, date of cultivation and geographical region. While the incidence of BCTIV in sugar beet plants was higher than BSCTV, BSCTV was more frequent in other plants such as tomato, pepper and bean.