Detection and Inoculation of Peanut Witches' Broom Phytoplasma (16 S r II ‐ A ) and Periwinkle Leaf Yellowing Phytoplasma (16 S r I ‐ B ) in Citrus Cultivars in Taiwan

To clarify the phytoplasma associated with H uanglongbing ( HLB ), a detection survey of phytoplasma in field citrus trees was performed using the standardized nested PCR assay with primer set P 1/16 S ‐ S r and R 16 F 2n/ R 16 R 2. The HLB ‐diseased citrus trees with typical HLB symptoms showed a high detection of 89.7% (322/359) of HLB ‐ L as, while a low detection of phytoplasma at 1.1% (4/359) was examined in an HLB ‐affected W entan pummelo ( C itrus grandis ) tree (1/63) and T ahiti lime ( C . latifolia ) trees (3/53) that were co‐infected with HLB ‐ L as. The phytoplasma alone was also detected in a healthy W entan 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 4 months and 3.5 years 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 ( P n WB ) phytoplasma (16 S r II ‐ A ) and periwinkle leaf yellowing ( PLY ) phytoplasma belonging to the aster yellows group (16 S r I ‐ B ) maintained in periwinkle plants were inoculated into healthy citrus plants by dodder transmission. The P n WB phytoplasma showed infection through positive detection of the nested PCR assay in citrus plants and persistently survived without symptom expression up to 4 years after inoculation. Positive detections of the phytoplasma were found in a low titre and several incidences in the other inoculated citrus plants including P onkan mandarin, L iucheng sweet orange, E ureka lemon and H irami lemon. None of the phytoplasma‐infected citrus plants developed symptoms. Furthermore, artificial inoculation of PLY phytoplasma (16 S r I ‐ B ) into the healthy citrus plants demonstrated no infection. The citrus symptomless phytoplasma was identified to belong to the P n WB phytoplasma group (16 S r II ‐ A ).