Interaction of witches’- broom disease of lime phytoplasma and lettuce phyllody phytoplasma in mixed infection of periwinkle plants

In this research the effect of mixed infection of witches’ broom disease of lime (WBDL) (16SrII-B) and lettuce phyllody (LP) (16SrIX-D) phytoplasmas on symptom expression and phytoplasma density in periwinkle plants (Catharanthus roseus (L.) G. Don) were investigated. Four healthy periwinkle plants of the same age were first inoculated with LP phytoplasma and after three weeks with WBDL phytoplasma using detached fragments of inoculative dodder (Cuscuta campestris Yank.). Disease symptoms and phytoplasma population in plants inoculated with both phytoplasmas were compared with those in plants inoculated with either WBDL or LP phytoplasma. In doubly inoculated periwinkle plants the disease symptoms mitigated to mild reduction of leaf size and internodes which strongly differed from those in periwinkle plants singly inoculated with either WBDL or LP phytoplasma. Plants with mixed infection lived longer than those inoculated singly with either phytoplasma. Both WBDL and LP phytoplasmas could be detected in singly and doubly infected plants by conventional and real time PCR assays using specific primer pairs. Analysis of the data obtained by real-time PCR showed that the population of both WBDL and LP phytoplasmas in the mixed infection was significantly lower than that in plants singly inoculated with WBDL or LP phytoplasma. It seems that interaction of WBDL and LP phytoplasmas in mixed infection of periwinkle is of the mutual suppression type.