First report of a 16SrXII‐A phytoplasma strain associated with Camelthorn witches’ broom disease in Iran

Abstract

Camelthorn (Alhagi maurorum, Fabaceae) is an important weed in Iran but in recent years it has also been planted as a crop to provide fodder. In 2021, camelthorn witches’ broom disease was observed in the Seneiee district in Abarkooh county (Yazd province, Iran). The main disease symptoms were little leaf, internode shortening, yellowing and witches’ broom (Fig. 1). The observed disease incidence was up to 10%. Total DNA was extracted from 0.2 g of fresh leaves from both 14 diseased and five asymptomatic plants. DNA samples were tested for phytoplasmas by direct PCR primed by P1/P7 (Lee et al., 1998) and nested PCR using primers P1/P7 and R16F2n/R16R2 (Gundersen & Lee, 1996). PCR amplicons of c. 1.8 and 1.25 Kb respectively were obtained from all 14 diseased Alhagi maurorum plants but not from the symptomless plants. Four R16F2n/R16R2 primed amplicons were sequenced directly. The sequences were identical and a consensus sequence of 1,245 bp was deposited in GenBank (Accession No. OP020342). Sequence comparison by BLAST analysis showed the highest sequence identity with phytoplasma members of the stolbur group (16SrXII). Phylogenetic analysis using the neighbour-joining method (MEGA 7.0) confirmed that the camelthorn phytoplasma clustered within the group 16SrXII phytoplasma clade, closer to strains affiliated to the 16SrXII-A subgroup than to other strains in the same group (Fig. 2). Computer-simulated analysis with 17 restriction endonucleases using iPhyClassifier (https://plantpathology.ba.ars.usda.gov/) showed that the RFLP pattern derived from the camelthorn phytoplasma 16S rRNA gene was identical to “Ca. Phytoplasma solani”, a 16SrXII-A strain (AF248959). This is the first report of a 16SrXII-A phytoplasma associated with camelthorn witches’ broom disease in Iran and to our knowledge, in the world. Previously a 16SrII subgroup C phytoplasma strain was reported to be associated with camelthorn witches’ broom disease in Iran (Esmaeilzadeh-Hosseini & Salehi, 2021). Since 16SrXII-A subgroup phytoplasmas have been detected previously in grapevine in Fars and Lorestan (Salehi et al., 2014) and Yazd (Salehi et al., 2016) provinces, it is suggested that camelthorn can serve as a reservoir for 16SrXII-A phytoplasmas.