RESUMO
Rubus cochinchinensis, an important traditional Chinese medicine in China is used to treat rheumatic arthralgia, bruises and lumbocrural pain (He et al.2005). In January 2022, yellow leaves of R. cochinchinensis were found in Tunchang City, Hainan Province, a tropical island in China. Chlorosis spread along the direction of vascular tissue while the leaf veins remain green (Fig. 1). In addition, the leaves were slightly shrunken and the growth vigor is poor (Fig. 1). By survey, we found the incidence of this disease was about 30%. Three etiolated samples and three healthy samples (0.1g each) were used to extract total DNA (TIANGEN plant genomic DNA extraction kit). Using nested PCR method, phytoplasma universal primers P1 / P7 (Schneider et al., 1995) and R16F2n / R16R2 (Lee et al. 1993) were used to amplified phytoplasma 16S rDNA gene. Primers rp F1 / R1 (Lee et al. 1998) and rp F2 / R2 (Martini et al. 2007) were used to amplified rp gene. 16S rDNA gene and rp gene fragments were amplified from three leaf etiolated samples, but not from healthy samples. The amplified fragments were cloned and sequenced, and the sequences were assembled by DNASTAR11. By sequence alignment, we found the obtained 16S rDNA and rp gene sequences of three leaf etiolated samples were same. The length of 16S rDNA fragment was 1237 bp (accession number: ON944105) and the length of rp gene fragment was 1212 bp (accession number: ON960069). The phytoplasma strain was named as 'R. cochinchinensis' yellows leaf phytoplasma (RcT), RcT-HN1 strain. The 16S rDNA gene sequence of RcT-HN1is 99.8% consistent with 16SrI-B subgroup members such as the 'Brassica napus' dwarf phytoplasma strain WH3 (MG599470.1), Chinaberry yellows phytoplasma strain LJM-1(KX683297.1) and Arecanut yellow leaf disease phytoplasma strain B165 (FJ694685.1). The rp gene sequence of RcT-HN1 is 100% consistent with rpI-B subgroup members such as the 'Salix tetradenia' witches'-broom phytoplasma strain YM-1 (KC117314.1) and Chinaberry witches'-broom phytoplasma strain Hainan (EU348781.1). The phylogenetic tree analysis, based on concatenated 16S rDNA-rp gene sequence of same group phytoplasma by MEGA 7.0 employing neighbor-joining (NJ) method with 1000 bootstrap value, were performed (Kumar et al., 2016). The results showed that RcT-HN1 phytoplasma strain formed a subclade in aster yellows group B subgroup (Fig. 2). The virtual RFLP analysis based on the 16S rRNA gene fragment of RcT-HN1 phytoplasma strain was performed by the interactive online phytoplasma classification tool iPhyClassifier (Zhao et al., 2009). The results showed that the phytoplasma strain was same as the reference pattern of the onion yellows phytoplasma of 16SrI-B (GenBank accession: AP006628), and the similarity coefficient was 1.00. This is the first report that 16SrI-B subgroup related phytoplasma infected R. cochinchinensis and caused yellows symptoms in China. The discovery of the disease is helpful to the study of the spread of phytoplasma-related diseases and protect R. cochinchinensis resources.
RESUMO
Alocasia macrorrhiza, which belongs to the Araceae family, is an important landscape plant in China, and has of significant medicinal uses. In 2022, A. macrorrhiza displaying abnormal symptoms were found in Qionghai, Hainan Island of China (110°23'3.06â³ï¼19°7'56.29â³). The incidence of symptomatic plants was about 40% in the sampled areas. The abnormal symptoms included that the ovoid leaves color turned yellow from green gradually, with ovoid leaves chlorosis, mesophyll tissue yellowing, miniature leaves and systemic wilting. The diseased symptoms suspected to be associated with phytoplasma according to the protocols of phytoplasma identification. In order to identify the pathogen, eleven diseased samples and three asymptomatic samples were collected from an area of about 40 hectares. Total DNAs were extracted from 0.10 g fresh plant leaf tissues using a CTAB DNA extraction method. PCR amplifications were performed using primers R16mF2/R16mR1 and fTuf1/rTuf1 specific for the phytoplasma 16S rRNA and tuf genes. Target PCR amplicons were obtained from the DNA of 11 diseased samples, whereas not from the DNA of the asymptomatic samples. The PCR products were cloned and sequenced by Biotechnology (Shanghai) Co., Ltd. (Guangzhou, China), and the obtained sequences were assembled, edited and analyzed using the EditSeq program and DNAMAN version 6.0. The phytoplasma 16S rRNA and tuf gene amplicons were 1336 and 930 bp in length, respectively. The sequences of all 16S rRNA and tuf amplicons in this study were identical. The sequencing data were deposited in GenBank with accession numbers OR466206 (16S rDNA) and OR513090 (tuf). According to the methods and protocols of phytoplasma identified and classification, the phytoplasma strain was described as Alocasia macrorrhiza yellows (AmY) phytoplasma, AmY-hn strain. BLAST search were conducted based on 16Sr RNA and tuf genes. The results showed that the AmY-hn had 100 % 16Sr RNA sequence identity (1336 bp out of 1336 bp) with that of 16SrI-B subgroup phytoplasmas like onion yellows phytoplasma (OY-M, AP006628). The AmY-hn had 100 % tuf sequence identity (930 bp out of 930 bp) with that of 16SrI-B subgroup phytoplasmas like OY-M. RFLP profiles obtained with iPhyClassifier demonstrated that AmY-hn strain was a member of the 16SrI-B subgroup with a similarity coefficient 1.00 to the reference phytoplasma strain (AP006628). Separated phylogenetic analysis based on 16S rRNA and tuf genes obtained with MEGA 7.0 using the neighbor-joining (NJ) method with 1000 bootstrap value indicated that AmY-hn clustered into one clade with phytoplasma strains of OY-M and chinaberry witches'-broom (KP662119) with 100 % and 87 % bootstrap value respectively. To our knowledge, this is the first report that a 'Candidatus Phytoplasma asteris'-related strain belonging to 16SrI-B subgroup infects A. macrorrhiza in China. The 16SrI-B subgroup 'Candidatus Phytoplasma asteris'-related strains can spread outwards through the plant A. macrorrhiza. Thus, the findings in the study will be beneficial to the detection of phytoplasmas which parasitic in this plant and the epidemic monitoring of the related diseases.