Interactions between lime witches' broom phytoplasma and phytoplasma strains from 16SrI, 16SrII, and 16SrIX groups in periwinkle.

The interactions of lime witches' broom phytoplasma (LWBP, 16SrII-B) with alfalfa witches' broom phytoplasma (AWBP, 16SrII-C), tomato witches' broom phytoplasma (TWBP, 16SrII-D), sesame phyllody phytoplasma (SPhP, 16SrIX-C) and rapeseed phyllody phytoplasma (RPhP, 16SrI-B) were studied in periwinkle plants graft-inoculated either with each phytoplasma alone or with LWBP and a second phytoplasma. The latter was inoculated below or above the site of LWBP inoculation, and was applied either simultaneously or non-simultaneously. In all treatments and all replications, the plants doubly inoculated with LWBP + SPhP or LWBP + AWBP showed milder symptoms and lived longer than those singly inoculated with LWBP, SPhP, or AWBP. In plants with mixed infection by LWBP + RPhP or LWBP + TWBP, characteristic symptoms were present regardless of the grafting order or inoculation site. Analysis of quantitative PCR data showed that the mean concentrations of LWBP in all doubly inoculated plants were less than in plants inoculated with LWBP alone. In the SPhP inoculated plants, a substantial decrease in LWBP concentration was measured, followed in order of decreasing concentration in the AWBP, TWBP, and RPhP inoculated plants. In the mixed infections, greater reduction in LWBP concentration was found in non-simultaneous inoculations and when the second phytoplasma was grafted below the site of LWBP inoculation. Based on symptoms and quantitative PCR results, the interactions of LWBP with SPhP and AWBP resulted in greater cross-protection than interactions of LWBP with RPhP and TWBP. [ABSTRACT FROM AUTHOR]