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First Report of ‘Candidatus Phytoplasma solani’ Associated With Potato Stolbur Disease in Montenegro

    Authors and Affiliations
    • S. Radonjić
    • S. Hrnčić , University of Montenegro, Biotechnical Faculty, Centre for Plant Protection, 81000 Podgorica, Montenegro
    • A. Kosovac
    • O. Krstić
    • M. Mitrović
    • J. Jović , Institute for Plant Protection and Environment, Department of Plant Pests, 11080 Zemun, Serbia
    • I. Toševski , Institute for Plant Protection and Environment, Department of Plant Pests, 11080 Zemun, Serbia, and CABI, 2800 Delémont, Switzerland.

      Current data on the occurrence of plant diseases associated with ‘Candidatus Phytoplasma solani’ (16SrXII-A subgroup) in Montenegro apply only to grapevine (Kosovac et al. 2016; Radonjić et al. 2009). Potato (Solanum tuberosum), as an important food crop and export commodity of Montenegro, is being monitored regularly for plant diseases that can disrupt field production. Potato stolbur disease caused by ‘Ca. P. solani’ has already been reported throughout Europe and in neighboring Serbia (Jović et al. 2011; Mitrović et al. 2016). Field and molecular data were used to verify association of this pathogen with symptomatic potato plants in Montenegro. During July and August 2015, leaves with petioles from 14 symptomatic potato plants were collected at two locations in central Montenegro: Nikšić (42°50.29 N, 18°55.57′ E) and Danilovgrad (42°33.41′ N, 19°05.46′ E). All plants exhibited symptoms previously reported as typically associated with potato stolbur disease, such as leaf redness and yellowing, swollen stems, and aerial tuber formation (Mitrović et al. 2016). Approximately 10 to 15% of plants on both locations were symptomatic at the time of collection. In addition, 10 asymptomatic plants were sampled and analyzed as controls. Identification of ‘Ca. P. solani’ was conducted following the stol11 stolbur-specific protocol (Radonjić et al. 2009), while characterization of isolates was performed applying multilocus sequence typing of tuf, secY, stamp, and vmp1 marker genes (Cvrković et al. 2014). Sequences of the amplified genes were deposited in GenBank under accession numbers KU588188 to 93. The presence of ‘Ca. P. solani’ was detected in 10 of 14 symptomatic potatoes, all with symptoms of yellowing and areal tuber formation, while all control plants tested negative. The RFLP analysis of tuf gene nested PCR products using HpaII endonuclease (Fermentas) revealed uniform tuf-b type in all positive samples. Nucleotide sequence analyzes of secY and stamp amplicons identified single genotype on each of the genes, identical to the reference strain STOL for secY (AM992086) and Rqg50 for stamp (KC703019). However, amplification of the vmp1 gene was obtained in only seven samples and RsaI restriction generated two profiles: V14 (3 isolates) and V17 (4 isolates). Subsequent sequencing and comparison with reference vmp1 strains revealed closest relatedness with Mp46 isolate of the V14 profile (HM008606), and CrHo12_721 isolate of the V17 profile, i.e., Vm_At7 genotype (KJ469731). Multilocus tuf/stamp/vmp1 genotype of tuf-b/Rqg50/V17 was previously detected in Montenegro in association with Convolvulus arvensis, Vitex agnus-castus, and their corresponding Hyalesthes obsoletus population of vector (Kosovac et al. 2016), while tuf-b/Rqg50/V14 genotype is reported to infect symptomatic potato plants in Serbia (Mitrović et al. 2016). Presence of potato stolbur disease in Montenegro is an important finding with potential far-reaching consequences, requiring further research to determine the inoculum source plants and insect vector populations with the aim of devising and implementing effective vector control strategies.