The viability of jujube witches' broom (JWB) phytoplasma in branches during winter and the necessity of roots in developing JWB symptom in Chinese jujube.

摘要

Jujube witches' broom disease (JWB) caused by phytoplasma is a destructive disease in Chinese jujube (Ziziphus jujuba Mill.). It has long been debated that whether JWB phytoplasma can survive in branches during winter and whether it is necessary for JWB phytoplasma to be transported to and propagated in roots before causing symptoms. Two methods, water culture and tissue culture of diseased branches/shoots, were firstly employed to clarify the questions. A great amount of phytoplasma fluorescent spots were found in the new shoots from water-cultured diseased branches during winter (December, January, and February). Moreover, explants from these new shoots produced plantlets showing typical JWB symptoms. These results sufficiently proved that JWB phytoplasma could well survive in branches throughout the winter. Tissue culture also showed that rootless plantlets from explants with JWB contained large amount of phytoplasma and showed typical symptom of JWB which continuously developed with the subculture of the rootless plantlets. In addition, obvious grads of JWB phytoplasma concentration were found in the branches just showing symptoms of tree newly infected with JWB, and usually no phytoplasma could be detected in the root of the tree. These results confirmed that roots were not necessary for the multiplication of phytoplasma and the development of phytoplasma symptom.