MOLECULAR AND BIOLOGICAL CHARACTERIZATION OF A 16SrII PHYTOPLASMA ASSOCIATED WITH CARROT WITCHES' BROOM IN IRAN

During 2011-14 surveys, a witches' broom (CarWB) disease was observed in carrot fields of Chahgeer and Salim Abad in Abarkooh and Khatam regions (Yazd province, Iran). The main symptoms of CarWB disease were little leaf, yellowing, proliferation of shoots from taproot, stunting of taproot, virescence, phyllody, leaf reddening and witches' broom. The disease agent was transmitted by graft and dodder to periwinkle inducing phytoplasma-type symptoms. Orosius albicinctus leafhopper was identified as a natural vector of CarWB disease since it was able to transmit the agent from naturally witches' broom infected carrot to healthy alfalfa and carrot plants. Direct and nested polymerase chain reaction assays using phytoplasma-specific primer pairs amplified products of expected size from symptomatic carrot in the field and symptomatic grafted, dodder and vector inoculated plants. Restriction fragment length polymorphism and phylogenetic analyses of partial 16S rRNA gene sequence showed that phytoplasmas associated with CarWB disease in Yazd province belong to peanut witches' broom (16SrII) phytoplasma group, subgroup C. Considering the disease vector is found to be the same of alfalfa witches' broom infecting fields in the same areas, alfalfa seems to have an important role in the epidemiology of CarWB disease spreading in Yazd province. This is the first report of association of a 16SrII phytoplasma with carrot witches' broom disease.