Determination of distribution pattern of Candidatus Phytoplasma aurantifolia in tomato plants as revealed by real-time polymerase chain reaction

Tomato big bud is a phytoplasma disease which has been recently distributed in different areas of Iran. The aim of this study was to determine the concentration and distribution pattern of 'Candidatus Phytoplasma aurantifolia' within tomato plants for its rapid detection, especially during the incubation period of the disease.

Three tomato plants were graft-inoculated with 'Candidatus Phytoplasma aurantifolia' in a factorial experiment in a completely randomized design. At the time intervals of 10, 20, 40 and 70 days post-inoculation, samples of apical leaves, leaves above and below the grafting site and lateral roots were taken from the inoculated plants. The concentration of the phytoplasma and its distribution pattern were evaluated using real-time PCR. In addition, the direct and nested-PCR assays were used and compared for detection of 'Candidatus Phytoplasma aurantifolia'.

The current study found that after entrance into the tomato plants, 'Candidatus Phytoplasma aurantifolia' moved upward into the apical leaves as well as downward into the roots. The phytoplasma concentration in the apical leaves and roots was higher than the leaves of the middle and lower branches of the inoculated plants. The mean of disease incubation period was estimated to be about 40 days. The nested-PCR was more sensitive than direct-PCR in detecting the phytoplasma.

For the detection of tomato big bud disease associated with 'Candidatus Phytoplasma aurantifolia', especially during the incubation period of the disease, it is recommended to sample form apical leaves and roots as well as using nested-PCR.