Multilocus Sequence Typing of Candidatus Phytoplasma Solani and Detection of RNA Viruses Infecting Cucurbits in the Marmara Region, Turkiye

The stolbur disease associated with Candidatus Phytoplasma solani (CaPsol) is very common in Europe and the Mediterranean regions and adversely affects perennial or annual plants but is rarely reported on cucurbits. We report the first multilocus genetic characterisation of CaPsol strains infecting cucurbit plants and the presence of some RNA viruses prevalent in cucurbits. Between 2019 and 2020, 156 symptomatic and nine asymptomatic plant samples were collected during surveys in cucurbit-growing areas. Symptomatic plants exhibited leaf deformation, growth retardation, yellowing, flower deformation and other virus-like symptoms. Molecular testing detected potyviruses, tobamoviruses and Cucumis melo endornavirus (CmEV) as single and double infections in 108 samples, but CaPsol was determined only in seven plants as a single infection. CaPsol strains infecting squash and watermelon in the Marmara region of T & uuml;rkiye were genetically characterised by describing their tuf, vmp1 and stamp gene sequences. All cucurbit-associated CaPsol strains were of the tuf-b1 genotype and five different stamp genotypes previously reported in other crops and wild plant reservoirs in Europe. Cucurbit CaPsol strains had vmp1 gene sequences corresponding to RFLP types V4 and V14, previously detected in the Mediterranean basin. These strains were not novel cucurbit-specific genotypes but shared similarities with genotypes from diverse plant hosts across Europe. This indicated that CaPsol is not restricted to cucurbits and may persist in alternative plant hosts. Thus, disease management should include monitoring alternative plant reservoirs, rather than focusing solely on cucurbit production areas. Viral infections showed significantly higher prevalence compared to phytoplasma infections in the region.