MOLECULAR DETECTION AND CHARACTERIZATION OF A PHYTOPLASMA FROM XIANLAJIAO CHILI PEPPER IN SHAANXI PROVINCE, CHINA

摘要

Surveys were performed in the main Xianlajiao chili pepper-producing areas of Shaanxi Province to determine whether a phytoplasma was associated with the incidence of Arbuscular Lobular Disease (ALD). During July 2012 and 2013, 92 and 86 chili pepper plants, respectively, showing ALD-like symptoms were collected from 12 counties and the cities of Baoji, Weinan, Xianyang, and Xian. Samples from paulownia trees and plantain with symptoms of paulownia witches’ broom and little leaf, respectively, located in pepper fields in Baoji city, Fengxiang county were also collected. Universal DNA primers for amplification of the phytoplasma 16S rRNA gene were used for nested PCR assays and DNA sequencing. Phytoplasma DNA was amplified from two chili pepper plants, the paulownia trees, and the plantain collected from Baoji city. The phylogenetic analysis of 16S rDNA sequences of the phytoplasmas detected in the chili pepper confirmed that these phytoplasmas are members of the 16SrI group “ Candidatus Phytoplasma asteris”. The results of virtual RFLP analysis and sequence homology comparison showed that the two Xianlajiao phytoplasmas have high homology with phytoplasmas 16SrI-B and 16SrI-M. Transmission electron microscopy assays revealed the presence of typical phytoplasma pleomorphic bodies in the phloem of phytoplasma-infected Xianlajiao chili pepper plants. Although our results did not establish a strong association between the presence of the phytoplasma and ALD, the simultaneous detection of a 16SrI phytoplasma in two symptomatic Xianlajiao chili peppers, the paulownia trees, and the plantain suggests a complex epidemiology related to the 16SrI phytoplasma pathogen in these new plant hosts.