Abstract
Snake gourd (Trichosanthes cucumerina L.), an annual climbing plant belonging to the family of Cucurbitaceae, is native to Southeast Asia countries, e.g., India, Pakistan, Malaysia, China, and Indonesia. It is commonly consumed as a vegetable and also used as a traditional herbal medicine due to the antidiabetic, anti-inflammatory, antibacterial, hepatoprotective, and cytotoxic activities (Devi 2017). In September 2020, phytoplasma-induced disease symptoms such as little leaf, yellowing, phyllody, virescence, and witches' broom were observed on snake gourd in Yunlin County, Taiwan. The cross-sectional examination of the symptomatic plant by transmission electron microscopy showed typical phytoplasma-like pleomorphic bodies with spherical, oval and tubular shapes in sieve elements. Further examination by nested PCR revealed that a 1.2 kb DNA fragment for 16S rRNA gene was only amplified from symptomatic leaf of snake gourd using the phytoplasma universal primer pairs P1/P7 followed by R16F2n/R16R2. BLAST and iPhyClassifier (https://plantpathology.ba.ars.usda.gov/cgi-bin/resource/iphyclassifier.cgi) analyses on the amplified DNA fragment (accession no. MW309142) revealed that it shares 100% identity with that of GenBank accession NZ_AMWZ01000008 (complement [31109 to 32640]) of peanut witches' broom (PnWB) phytoplasma, a 'Candidatus phytoplasma aurantifolia'-related strain (Firrao et al. 2004), and could be classified into the 16SrII-V subgroup. Samples examined by nested PCR were further characterized by western blotting using the polyclonal antibody raised against the Imp of PnWB phytoplasma (Chien et al. 2020a, b). An expected signal of 19 kDa specific for Imp was only detected in the symptomatic snake gourd, but not in healthy snake gourd. Since the disease symptoms caused by phytoplasma infection are highly dependent on the secreted effectors (Namba 2019), phyllogen gene that is responsible for phyllody and virescence symptoms was amplified from symptomatic snake gourd by PCR. BLAST analysis revealed that phyllogen identified in snake gourd is identical with that of PnWB phytoplasma. In Taiwan, species of family Cucurbitaceae such as loofah, bitter gourd, and pumpkin are commonly infected by 16SrVIII phytoplasma (Davis 2017). In this study, we report for the first time that snake gourd, a species of family Cucurbitaceae, was infected by 16SrII-V PnWB phytoplasma in Taiwan.
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