Resistance of six varieties to witches-broom disease and difference in migration characteristics of phytoplasma in jujube

Abstract: 【Objective】Jujube is a unique fruit crop in China with a long cultivation history. However,jujube witches- broom disease caused by phytoplasma seriously threatens the yield of jujube trees.Therefore, in this study, six main jujube varieties in Beijing area including Gagazao, Dongzao, Fengmi-guan, Jixincuizao, Hongluocuizao and Houtouzao served as the test materials. This study aimed to ex-plore the differences in resistance to jujube witches-broom disease and the phytoplasma migrating char-acteristics in six varieties, which would provide reliable basic reference for the development and utiliza-tion of resistant varieties and the prevention and treatment of jujube witches-broom disease.【Methods】By collecting Jixincuizao with phytoplasma and grafting it onto the healthy jujube rootstock, the dis-ease incidence rate was investigated every 30 days from July to October 2016, and from 2017 to 2018.Phloem and leaves of 5 cm above the graft union, including the first, second and third branches, and 5 cm,10 cm, 15 cm and 20 cm below the graft union were collected after they were grafted 39 d, 60 d, 90 d,120 d and 300 d. In the summer of 2017 and spring of 2018, we collected leaves and phloem at 5  above the graft union and 20 cm below the graft union. The combination of field investigation and com-mon PCR technology were used to compare the resistance of 6 varieties to jujube witches-broom dis-ease and migration features of phytoplasma to different parts.【Results】The results showed that, 60 d after grafting, none of the 6 varieties of seedlings showed symptoms of jujube witches-broom disease; 90 d after grafting, Dongzao, Fengmiguanzao and Jixincuizao exhibited symptoms, and the incidence rates of the three varieties were: 13.8% (Jixincuizao), 11.6% (Dongzao), and 4.1% (Fengmiguanzao). Howev-er, 120 d after grafting except for Houtouzao, the other 5 varieties all showed symptoms, and the inci-dence rates were: 32.5% (Jixincuizao), 18.4% (Hongluocuizao), 29.0% (Dongzao), 8.4% (Gagazao) and 23.3% (Fengmiguanzao, respectively. After two years of grafting, all 6 varieties had symptoms of ju-jube witches- broom disease, and the incidence rates were: 79.3% (Jixincuizao), 69.6% (Hongluo-cuizao), 67.7% (Dongzao), 57.6% (Gagazao), 51.2% (Fengmiguanzao), and 49.0% (Houtouzao), respec-tively, indicating that none of the 6 jujube varieties was immune to phytoplasma, and different jujube va-rieties were differentially resistant to the disease and the difference was significant. According to the on-set time and incidence rate, cultivars such as Houtouzao, Fengmiguanzao and Gagazao belonged to dis-ease-resistant type, and Dongzao, Hongluocuizao and Jixincuizao belonged to susceptible type. After grafting with phytoplasma branches, the phytoplasma was first transferred to the trunk below the root-stock grafting interface, and then transferred to the trunk above the grafting interface, and finally spread to the whole plant branches. In addition, the migration speed of phytoplasma was different among differ-ent jujube varieties. Phytoplasma migrated fastest in Jixincuizao and Dongzao, followed by Fengmiguanzao, Hongluocuizao, and Gagazao, and the migration speed was the slowest in Houtouzao.【Conclusion】Among six varieties, Fengmiguanzao, Gagazao and Houtouzao showed a certain disease resis-tance, and the migration characteristics of phytoplasma in different jujube varieties were preliminarily confirmed, whose phytoplasma migrated fastest in Jixincuizao and Dongzao, followed by Fengmiguan-zao，Hongluocuizao, and Gagazao, and the migration speed was the slowest in Houtouzao. However, due to the limitation of the sample number of jujube varieties, whether the migration speed of phyto-plasma was positively correlated with the resistance of different jujube species needed deep research further.