PCR Technique Applied in the Ecological Study of Paulownia Witches’-Broom Disease in Taiwan

With the characteristics of insect-borne transmission and systemic infection, Paulownia witches’-broom (PaWB) disease has been considered a serious epidemic disease in Taiwan. PaWB phytoplasma (PaWBP) weakens paulownia plants seriously, and has an enormous influence on paulownia cultivation. To diagnose PaWB accurately, a rapid and reliable detection method, polymerase chain reaction (PCR) based analysis using primers derived from PaWBP 16S rDNA sequences, was established previously. We used PCR-assay to trace the incubation periods of PaWBP, symptom expression stages of infected paulownia, distribution and concentration of PaWBP in paulownia trees and insect vectors. The incubation period of the PaWBP-infected paulownia (10 cm height) was about 3 mo; distributions of PaWBP plants in mesophyll, petiole, vein and bark of paulownia were from high to low respectively by PCR-assay. We also found that it took about 3 mo for PaWBP to move from the top grafting site to the basal root in 30 cm height paulownia plants. In this study, it was proved that Halyomorpha mista could successfully transmit PaWBP from diseased paulownia to healthy paulownia seedlings, and detection of PaWBP in H. mista was confirmed by PCR as well. Field tracking showed 2 population peaks of H. mista during the year, March to April and August to October. These results may be helpful in insect vector control in the future. In resistance experiments, paulownia hybrids also showed higher resistance than purebreds.