Amaranthus spp. are cultivated worldwide as leafy vegetable, cereal, and ornamentals. In China, stems and leaves of Amaranthus hypochondriacus L. are used as a vegetable (2). In July 2010, sporadic amaranth plants exhibiting symptoms of cladodes and spica proliferation were observed in a vegetable garden near Foshan, Guangdong, China. Stem samples were collected from two symptomatic and two asymptomatic plants. Total DNA was extracted with a modified cetyltrimethylammonium bromide (CTAB) method (1). Nested PCR with a combination of phytoplasma-specific universal primer pairs (P1/P7 and R16F2n/R16R2) amplified 16S rDNA sequences with the expected size of 1.2 kb from all samples of symptomatic amaranth plants, but not from the asymptomatic plants (3). Nested PCR products yielded identical AluI, HhaI, HpaII, HaeIII, KpnI, MseI, RsaI, Sau3AI, and TaqI restriction fragment length polymorphism (RFLP) profiles with chinaberry witches'-broom phytoplasma (16SrI-B subgroup), but different from peanut witches'-broom phytoplasma (16SrII group), jujube witches'-broom phytoplasma (16SrV group), and paulownia witches'-broom phytoplasma (16SrI-D subgroup). Nested PCR products were purified, cloned in pMD18-T Simple Vector (TaKaRa, Dalian, China), and sequenced. The 16S rDNA sequences were identical and deposited in GenBank (Accession No. JF323034). GenBank BLASTn analysis indicated that the amaranth extracts showed as high as 99% sequence identity with the members of 16SrI group phytoplasmas, including those associated with arecanut yellow leaf disease (FJ998269) and aster yellow AY-27 (HM467127). A polygenetic tree was constructed using MEGA 4.0 based on the 16S rDNA sequences of amaranth cladode phytoplasma and other phytoplasmas belonging to 16SrI phytoplasma group. In phylogenetic analysis, the sequences clustered on a single branch with members of 16SrI-B subgroup in the tree. Therefore, the phytoplasma was classified in subgroup 16SrI-B. To our knowledge, this is the first report of a subgroup 16SrI-B phytoplasma associated with diseased A. hypochondriacus in China.
References: (1) E. Angelini et al. Vitis 40:79, 2001. (2) M. Costea et al. Econ. Bot. 57:646, 2003. (3) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998.