Study on the Etiology and Insect Vectors oferiwinkle Leaf Yellowing Disease
Date Issued
2009
Date
2009
Author(s)
Huang, Yao-Jheng
Abstract
In 2005, periwinkle plants exhibiting symptoms of yellowing, witches’ broom, phyllody and virescence were observed in flower production fields in Dayuan, Taoyuan county. The sequences of 16S rDNA and 16S-23S rDNA intergenic spacer region of the causative agent of this newly discovered periwinkle leaf yellowing (PLY) disease were amplified with polymerase chain reaction (PCR) using the total DNA prepared from the diseased leaves as a template. Sequence analysis of 16S rDNA revealed that the causative agent of PLY was closely related to the phytoplasmas of the aster yellows group (16SrI group) those cause worldwide diseases in many horticultural and vegetable crops. The results of grafting experiment and TEM observation provided further evidences to support that the phytoplasma is the causative agent of PLY. The periwinkle leaf yellowing phytoplasma was thus named “Candidatus Phytoplasma asteris” strain PLY. According to the rDNA sequences of various 16SrI group phytoplasmas, the PCR primer pair AYTWf1/ AYTWr1 specific for 16SrI group phytoplasma was designed to detect the PLY phytoplasma in the plants and insect vectors. At present, four species of PLY phytoplasma-harbored leafhoppers were captured in Dayuan and identified as Macrosteles orientalis Vilbaste, Cicadulina bipunctella, Phlogotettix cyclops and Balclutha sp., respectively. Monthly PCR detection indicated that insect vectors harbored PLY phytoplasma from March to October in the year of 2008, and Macrosteles orientalis Vilbaste was the earliest PLY phytoplasma-carrier detected during the period of 2007 to 2009. Transmission experiments with field-collected Macrosteles orientalis Vilbaste and Cicadulina bipunctella showed that both leafhoppers can transmit the PLY phytoplasma to healthy periwinkle plants. The titer of PLY phytoplasma in diseased periwinkle plants and four species of PLY phytoplasma-harbored leafhoppers were quantified in relation to plant or insect DNA (genome units [GU] of phytoplasma DNA per nanogram of plant or insect DNA) using a quantitative real-time PCR. It was also proved that Macrosteles orientalis Vilbaste contains the highest titer of PLY phytoplasma than the other leafhoppers. Therefore, it is reasonable to conclude that Macrosteles orientalis Vilbaste plays a major role in the epidemiology of PLY disease, and the importance of the other leafhoppers call for further investigation.
Subjects
rRNA gene
polymerase chain reaction
periwinkle leaf yellowing phytoplasma
insect vectors
transmission experiments
real-time PCR
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