Jujube Witches' Broom ("Zaofeng") Disease: Bacteria that Drive the Plants Crazy

The jujube witches' broom (JWB) disease, called "Zaofeng" disease in Chinese, is associated with the JWB phytoplasma ('Candidatus Phytoplasma ziziphi') and causes heavy losses in the jujube industry. JWB disease has been recorded since the 1950s. Diseased trees have symptoms such as shoot proliferation, leaf-like flowers. The JWB phytoplasma is assigned to the 16SrV group, subgroup 16SrV-B, according to 16S rRNA gene sequence. The JWB phytoplasma is transmitted by leafhoppers and can infect a few plants other than jujube. Infection with phytoplasma affects biochemical and physiological process, altering the expression of genes encoding some transcription factors and functional genes, mainly involved in biotic stress response. The genome of JWB phytoplasma 'nky' strain has been sequenced and consists of 750,803 bp within one circular chromosome that encodes 694 protein-coding genes. The pathogenic mechanisms of a few JWB phytoplasma effectors have been investigated. The presence of JWB phytoplasma has been detected through symptoms observation, ELISA, DAPI staining and PCR, but new techniques, such as LAMP and CRISPR/Cas-12 based visual assay, have recently been developed. Some resistant jujube cultivars have been selected by infection screening. Although treatment with tetracycline antibiotics is effective, comprehensive control measures, including orchard management and sanitary measures, are needed for disease control. Further studies are needed in development of JWB phytoplasma culture method, expansion of genomic information, and phytoplasma effectors, resistance-related gene identification and resistant genotype developing.