Detection and Inoculation of Peanut Witches' Broom Phytoplasma (16SrII-A) and Periwinkle Leaf Yellowing Phytoplasma (16SrI-B) in Citrus Cultivars in Taiwan

摘要

To clarify the phytoplasma associated with Huanglongbing (HLB), a detection survey of phytoplasma in field citrus trees was performed using the standardized nested PCR assay with primer set P1/16S-Sr and R16F2n/R16R2. The HLB-diseased citrus trees with typical HLB symptoms showed a high detection of 89.7% (322/359) of HLB-Las, while a low detection of phytoplasma at 1.1% (4/359) was examined in an HLB-affected Wentan pummelo (Citrus grandis) tree (1/63) and Tahiti lime (C.latifolia) trees (3/53) that were co-infected with HLB-Las. The phytoplasma alone was also detected in a healthy Wentan pummelo tree (1/60) at a low incidence total of 0.3% (1/347). Healthy citrus plants were inoculated with the citrus phytoplasma (WP-DL) by graft inoculation with phytoplasma-infected pummelo scions. Positive detections of phytoplasma were monitored only in the Wentan pummelo plant 4months and 3.5years after inoculation, and no symptoms developed. The citrus phytoplasma infected and persistently survived in a low titre and at a very uneven distribution in citrus plants. Peanut witches' broom (PnWB) phytoplasma (16SrII-A) and periwinkle leaf yellowing (PLY) phytoplasma belonging to the aster yellows group (16SrI-B) maintained in periwinkle plants were inoculated into healthy citrus plants by dodder transmission. The PnWB phytoplasma showed infection through positive detection of the nested PCR assay in citrus plants and persistently survived without symptom expression up to 4years after inoculation. Positive detections of the phytoplasma were found in a low titre and several incidences in the other inoculated citrus plants including Ponkan mandarin, Liucheng sweet orange, Eureka lemon and Hirami lemon. None of the phytoplasma-infected citrus plants developed symptoms. Furthermore, artificial inoculation of PLY phytoplasma (16SrI-B) into the healthy citrus plants demonstrated no infection. The citrus symptomless phytoplasma was identified to belong to the PnWB phytoplasma group (16SrII-A).