Occurrence of Phytoplasma Belonging to 16SrII Group Associated with Witches’-Broom Symptoms in Emilia sonchifolia in Hainan Island of China

Abstract

Emilia sonchifolia is a medical plant belonging to the family of Asteraceae, mainly used as a traditional Chinese medicine with the function of anti-inflammatory, analgesic, antibacterial and so on. During October to November 2020, the plants showing abnormal symptoms including witches’-broom, internode shortening, leaf chlorosis and leaflet were found in Hainan province, a tropical island of China. The total DNA of the plant samples were extracted using 0.10 g fresh plant leaves using CTAB method. PCR reactions were performed using primers R16mF2/R16mR1 and secAfor1/secArev3 specific for phytoplasma 16S rRNA and secA gene fragments. The target productions of the two gene fragments of phytoplasma were detected in the DNA from three symptomatic plant samples whereas not in the DNA from the symptomless plant samples. The two gene fragments of the DNA extracted from the symptomatic plant samples were all identical, with the length of 1324 bp 16S rRNA and 760 bp secA gene sequence fragments, putatively encoding 253 (secA) amino acids sequence. The phytoplasma strain was named as Emilia sonchifolia witches’-broom (EsWB) phytoplasma, EsWB-hnda strain. To our knowledge, this was the first report that Emilia sonchifolia witches’-broom disease was caused by the phytoplasma belonging to16SrII-V subgroup in Hainan island of China, with close relationship to 16SrII peanut witches’-broom group phytoplasma strains infecting the plants like peanut, Desmodium ovalifolium and cleome from the same island of China and cassava from Viet Nam.

Molecular Identification and Characterization of Two Groups of Phytoplasma and Candidatus Liberibacter Asiaticus in Single or Mixed Infection of Citrus maxima on Hainan Island of China

“…The plants of chinaberry, lettuce and mulberry could be infected by the phytoplasma strains belonging to the 16SrI group [ 14 ]. The plants of Melochia corchorifolia , Tephrosia purpurea and Emilia sonchifolia could be infected by the phytoplasma strains belonging to the 16SrII group [ 27 , 28 , 42 ]. From this study, it could be seen that the plants of Citrus maxima and Trema tomentosa could be infected by the phytoplasma strains belonging to the 16SrXXXII-D subgroup [ 29 ].…”

“…Economic palm crops, such as areca palm, coconut and oil palm, were also planted on the farm. Moreover, there were many phytoplasma-infected plants reported previously, such as Melochia corchorifolia , Emilia sonchifolia , Trema tomentosa and Waltheria indica , which were also found on the farm [ 27 , 28 , 29 , 30 ]. Total DNA of the diseased plant samples was extracted based on the CTAB method, according to the rapid extraction kit for plant genomic DNA (Tiangen Biotech Co., Ltd., Beijing, China) [ 31 ].…”

“…The disease symptoms of Citrus maxima are similar to the symptoms caused by Citrus Huanglongbing disease. Furthermore, some phytoplasma diseases were reported previously in the regions associated with the disease symptoms of Citrus maxima [ 27 , 28 , 29 , 30 ]. Therefore, the plants with disease symptoms were suspected to be associated with the pathogens of phytoplasma and Candidatus Liberibacter asiaticus, based on a field investigation and a previous study [ 17 , 18 , 19 , 23 , 27 , 28 , 29 , 30 ].…”

“…Furthermore, some phytoplasma diseases were reported previously in the regions associated with the disease symptoms of Citrus maxima [ 27 , 28 , 29 , 30 ]. Therefore, the plants with disease symptoms were suspected to be associated with the pathogens of phytoplasma and Candidatus Liberibacter asiaticus, based on a field investigation and a previous study [ 17 , 18 , 19 , 23 , 27 , 28 , 29 , 30 ]. At present, there are no reports of mixed infection with phytoplasma and Candidatus Liberibacter asiaticus on the citrus plant hosts and even other plant hosts on Hainan Island in China.…”