Molecular detection of ‘Candidatus Phytoplasma ziziphae’ in different jujube varieties.

Jujube witches'-broom phytoplasma disease is the most dangerous jujube disease in China. Samples from symptomatic and asymptomatic green shoots of Suanzao rootstock, and cv. Lang-zao, together with samples from hard shoots of cv. Langzao and leaves of cv. La-jiao-zao tested positive for jujube witches’ broom phytoplasma in direct or in nested PCR amplification with phytoplasma specific primers. Amplification of rp protein of the pathogen provided amplification only for those samples which resulted positive in direct PCR. RFLP analyses of PCR products confirmed that phytoplasmas infecting jujube belong to the 16SrRNA group V-B, rp subgroup C. Results indicate that the phytoplasma over-winters in aerial tree parts and is present also in asymptomatic parts of infected trees. Shoots from symptomatic and asymptomatic ‘Li-zao’ and ‘Hu-Lu-Zao’ plants were grafted on diverse rootstocks to propagate the Chinese gene pool in Italy and to test the infectivity of phytoplasma strains. The death of the plants obtained by cleft-grafting of symptomatic shoots as well as the difficulty to obtain patch grafting with phytoplasma-infected shoots didn’t allow an investigation on pathogen transmission.