Phytoplasmas of two 16S rDNA groups are associated with pear decline in Taiwan

Polymerase chain reaction (PCR)-based detection strategies were adopted to examine the etiology and vectorship of pear decline in Taiwan (PDTW). 16S rDNA sequences were amplified from total DNAs prepared from PDTW-affected pear trees Pyrus serotina Rehd. cv. Hengshan and pear psyllid Cacopsylla chinensis using PCR. According to the sequence analyses, C. chinensis carried phytoplasmas of two 16S rDNA groups, PDTW (group 16SrX) and PDTWII (a newly discovered group 16SrII phytoplasma associated with pear decline in Taiwan), that were associated with PDTW-infected pear trees. The 16S rDNA sequences of PDTW and PDTWII phytoplasmas that were amplified from diseased pear trees were identical to those from C. chinensis. Transmission trials of phytoplasmas associated with PDTW to healthy pear plants were successfully performed with C. chinensis. One of the 17 tested plants was infected with both PDTW and PDTWII phytoplasmas while ten were infected with PDTWII phytoplasma. In grafting tests, both PDTW and PDTWII phytoplasmas were effectively and separately transmitted from diseased pear to periwinkle plants (Catharanthus roseus). For detection purposes, specific primers were developed and adopted to detect both PDTW and PDTWII phytoplasmas by nested or semi-nested PCR. Transmission electron microscopic examinations revealed phytoplasma bodies in the sieve tubes and phloem parenchyma cells of diseased pears and in the intestinal wall cells of C. chinensis and C. qianli.