Abstract:

A detailed investigation on jujube witches' broom disease associated with phytoplasmas was conducted at different ecological sites of jujube growing areas,including Shaanxi,Henan,Shanxi,Anhui,Zhejiang provinces and Beijing city.The historic and present circumstances of disease occurrence were surveyed,involving disease distribution,severity,transmission way,cultivation as well as geographic and environmental variation.It was found that the wide utilization of root-spouting seedling carrying phytoplasmas had been contributing the spread of disease in a diseased orchard and from diseased areas to disease-free ones.Several cultivars differed in resistance to the disease.Air pollution nearby the jujube orchard and improper cultivation,especially,the imbalance of fertilization,could reduce the cultivar's resistance to the phytoplasma.The phytoplasma detection by DAPI fluorescence microscopy and polymerase chain reaction (PCR) revealed that there were different proportion of symptomless infected plants (latent infection) in different infested orchards.It was assumed,therefore,that the wide use of latent infection seedlings as propagation materials and gradually deteriorating conditions for jujube growth and fruiting leaded to the prevalence of the disease in most regions.

Key words: Jujube witches' broom disease, Phytoplasma, Disease spread, Resistance, Latent infection