Detection and distribution of Curtovirus species, the causal of beet curly top disease (BCTD) in Iran.

In this study a survey was conducted for determination of infection and distribution of Beet curly top virus-BCTV and related isolates in 10 important sugar beet cultivated provinces. A total of 1796 random and 177 symptomatic sugar beet leaf samples and 97 weed samples including Chenopodium amaranthicolor, Convolvulus arvensis, Solanum nigrum, Amaranthus spp., Malva neglecta, Datura stramonium and Datura metel were collected. BCTV infection was evaluated using Tissue Blot Immuno Assay-TBIA with specific antibody. Overall incidence of BCTV based on TBIA results in random samples was estimated 18.0%. Also, 48 out of 51 fields surveyed were infected by this virus. The highest virus incidence among the surveyed provinces was recorded in Fars, followed by Khorasan, Esfahan, Kermanshah, Semnan, Azarbayejan-e-gharbi, Qazvin, Zanjan, Khuzeatan and Hamedan. According to the TBIA results, viruses in decreasing order of incidence in sugar beet were (44.7%), followed by (26.3%), (19.8%), (15.6%), (15.4%), (12.1%), (11.8%), (9.7%), (7.8%) and (6.4%), respectively. All symptomatic beet samples and Chenopodium amaranthicolor, Solanum nigrum and Amaranthus spp. (3, 2 and 2 samples, respectively) showed positive reaction in TBIA. Our results showed that this virus is one of the most important and dominance air borne viruses in sugar beet fields. BCTV infection was confirmed by PCR results with a pair of primers designed (in this project) for coat protein amplification. Based on the ML and NJ phylogenetic tree, the 13 Iranian BCTV isolates, is clustered in a separate branch from the other isolates. The rate of identity between 13 Iranian isolates was 86.5-100%, but between foreign isolates was estimated 91.1-99%. Also, this estimation between Iranian and foreign isolates was 67.7-76.0%. This value is below the curtovirus species demarcation threshold of 80% that suggested by ICTV, therefore it seems that Iranian isolates of BCTV could to be a new species in Curtovirus genus. Based on the results of NJ and ML tree, Iranian BCTV cluster have three subcluster, that showed the variation between these isolates. Variation between Iranian isolates showed that the origin of BCTV could be in Middle East region. This result is so important for selection of resistance or tolerant cultivars against BCTV by breeders.