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First Report of Tomato “Big Bud” Disease in Syria Caused by ‘Candidatus Phytoplasma trifolii’-Related Strain

    Authors and Affiliations
    • H. Khalil1
    • R. N. Yousef1
    • N. V. Girsova2
    • D. Z. Bogoutdinov3
    • T. B. Kastalyeva2
    • S. Aldenkawe1
    1. 1Al-Baath University, Homs, Syria;
    2. 2All-Russian Research Institute of Phytopathology, Bolshie Vyasiomy, Moscow Region, 143050 Russia; and
    3. 3Samara State Agricultural Academy, Ust’-Kinel’sky, Samara Province, 446442 Russia

    Symptoms similar to the phytoplasma disease “big bud” have been observed on tomatoes (Solanum lycopersicum L.) grown in the field in the central and north-eastern part of Syria since 2013. Diseased plants were characterized by twisting, corrugated, yellowing, or reddening leaves. The sepals of the flowers acquired hypertrophied form, were fused, and created a bell-shaped sterile bud: phyllody of green or anthocyanin color. The stems of the plants were lignified, and necrosis of the phloem was observed on stem cuts. Incidence of the disease varied between 0.2 and 40%, depending on the region and weather conditions. An infected plant formed on average 70% less fruit than a healthy plant. In mid-September 2017, samples of 12 infected and two healthy (control) tomato plants (cv. Sheruk) collected in the Syrian province of Homs were transferred to the All-Russian Research Institute of Phytopathology (Russia), where an identification of phytoplasma was carried out. Total DNA was extracted from 0.3 g of leaf mid veins according to the method of Maixner et al. (1995). A nested polymerase chain reaction (PCR) was performed to detect phytoplasmas. Primers P1/16S-SR were used for the first amplification, followed by the second amplification with primers R16F2n/R16R2. The 20-fold diluted PCR product of the first amplification was used as the DNA template for the second amplification, resulting in the amplification of a 1.2-kb amplicon. The positive control included DNA isolated from the previously known phytoplasma-infected sample, and the negative control PCR reaction lacked a DNA template. Eleven of the 12 symptomatic plants amplified the expected 1.2-kb band in the nested PCR. All PCR products were subjected to the restriction fragment length polymorphism analysis (RFLP) and were digested by restriction enzymes AluI, HhaI, MseI (Tru1I), RsaI, Sau3AI, and TaqI. The electrophoretic profiles of the products digested were compared with published real and virtual profiles of phytoplasmas (Lee et al. 1998; Wei et al. 2007). All 11 profiles for each endonuclease were identical to each other and to RFLP profiles for clover proliferation phytoplasma group 16SrVI, subgroup 16SrVI-A. In 2011, there was the first report of phytoplasma isolated from grapevine in Syria and identified as belonging to 16SrXII group in mixture with phytoplasma of 16SrVI group (Contaldo et al. 2011). In 2013, phyllody disease of sesame with numerous different symptoms such as floral virescence, phyllody, witches’ broom, yellowing, short internodes, and twisted and reduced leaves was described in Syria (Khabbaz et al. 2013). It was shown that the causative agent was phytoplasma, but its group was not determined. To our knowledge, this is the first report of a 16SrVI group phytoplasma infecting tomatoes in Syria and ‘Candidatus Phytoplasma trifolii’ as the most probable pathogen species.


    Funding: Funding was provided by Russian Academy of Sciences (State Assignment #0598-2014-0007).