Watermelon (Citrullus lanatus, Cucurbitaceae) is a significant cultural plant cultivated in many regions of Turkey. According to FAO’s 2021 Türkiye is the country that produces the most watermelons after Senegal, Brazil, Russia, India and China. On October 2022, symptoms of virescence, leaf yellowing, multiple shoots and little leaf formation were observed on about 0.2% of watermelon planted a commercial orchard in the Şanlıurfa province (36°41′51"N, 38°55′08"E), Türkiye.

Eleven symptomatic samples were collected during the field studies and the total DNA isolation was performed using the CTAB method. Direct PCR was performed with universal P1/P7 primers, and two separate nested PCRs were performed with R16F2n/R16R2 and U3/U5 primers (Lorenz et al. 1995). From seven samples, amplification products of 1250 bp (for R16F2n/R16R2) and 882 bp (for U3/U5) were obtained. All PCR amplicons were bidirectionally sequenced. Since the obtained sequences were identical to each other, one of each was selected and recorded in GenBank (for R16F2n/R16R2 Acc.No:OP727727, for U3/U5 Acc.No: OQ719826). As a result of BLAST analysis, phytoplasmas obtained from watermelon plants were 99.92% similar to ‘Citrullus lanatus’ witches’-broom phytoplasma (16SrVI-A subgroup) in watermelon (OM991840). This phytoplasma strain was previously detected in watermelon plants by Salehi et al. (2022) for the first time in the world and in Iran. The association of 16SrVI-A phytoplasma strains with severe dwarfing, brooming, rosetting and small leaf in cucumber in Van province of Turkey has been previously reported (Usta et al. 2017).

16srDNA gene regions were used in MEGA software (version 11) to create a phylogenetic tree, and the UW isolate obtained in this study was in the same group with ‘Candidatus Phytoplasma trifolii’ strains. To our knowledge, this is the first report detecting ‘Candidatus Phytoplasma trifolii’ (16SrVI-A subgroup) in watermelon in Türkiye.