Journal of Plant Pathology Archive

Abstract:

Epazote (Chenopodium ambrosioides L.), a plant native to South America, is a serious invasive weed in China. In May 2011, epazotes exhibiting small leaves and fasciation indicative of phyto- plasma infection were found in a pepper field in Qijiang County (China), with an incidence lower than 3%. Stem and leaf samples were collected from symptomatic and symptomless plants, total DNA was extracted and nested PCR performed using primers P1/P7 (Deng and Hiruki, 1991; Schneider et al., 1995) followed by primers R16F2n/R16R2 (Lee et al., 1998). Fragments of 1.2 kb corresponding to 16S rDNA were amplified exclusively from DNA extracts from symptomatic plants. Purified PCR products were cloned in pGEM-T Easy Vector (Promega, USA), sequenced (GenBank accession No. JN836942) and analyzed using iPhyClas- sifier online tool. The sequence shared 99.4% identity with the 16S rDNA sequence of the ‘Candidatus Phytoplasma asteris’ refer- ence strain (M30790) that belongs to 16SrI-B subgroup. The vir- tual RFLP pattern of the epazote phytoplasma 16S rDNA gene se- quence showed maximum similarity with the reference pattern of the 16SrI-B subgroup (NC005303), with a similarity coefficient of 0.98. A phylogenetic tree based on the 16S rDNA phytoplasma se- quences showed that the sequences clustered with members of the 16SrI-B subgroup. Taken together, the epazote phytoplasma was classified in subgroup 16SrI-B. Phytoplasmas identified as 16SrI-B strains have previously been identified in Morus alba, Amaranthus hypochondriacus and Sasa fortunei in China. To our knowledge, this is the first report of a subgroup 16SrI-B phytoplasma associat- ed with diseased epazote in our country. As a widely distributed weed in southwest China, phytoplasma-infected epazote may be a potential source of inoculum for crops.