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Effects of Pseudomonas putida S1Pf1Rif Against Chrysanthemum Yellows Phytoplasma Infection

First, third, fourth, fifth, sixth, and tenth authors: Università del Piemonte Orientale “Amedeo Avogadro”, Dipartimento di Scienze dell'Ambiente e della Vita, Viale Teresa Michel 11, Alessandria, 15121, Italy; second, fifth, and ninth authors: CNR, Istituto di Virologia Vegetale, Strada delle Cacce 73, Torino, 10135, Italy; seventh author: University of Waterloo, Department of Biology, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada; and second and eighth authors: Università di Torino, Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestali, Via Leonardo Da Vinci 44, Grugliasco (Torino) 10095, Italy.

Phytoplasmas cause damage on a number of plant species leading to relevant economical loss. Up to now, strategies to limit their spread led to only partial success. In this context, the use of plant-beneficial bacteria to control phytoplasmas has never been explored. The aim of this work was to assess the effect of Pseudomonas putida S1Pf1Rif against chrysanthemum yellows phytoplasma (CYP) infection of daisy. Plant biomass, root architecture, symptom severity, phytoplasma titer, and viability were evaluated in inoculated and control plants. CYP reduced plant growth and root development. Although the phytoplasma titer in young apical leaves was not affected by inoculation with S1Pf1Rif, the pseudomonad improved plant growth of CYP-infected plants. Whereas CYP titer increased over time in uninoculated plants, its viability decreased, regardless of the presence of P. putida S1Pf1Rif. Finally, phytoplasma cells in fully developed leaves of CYP-infected plants inoculated with S1Pf1Rif often appeared degenerated. Overall, our results indicate that P. putida S1Pf1Rif is able to alleviate the disease, although it does not affect the presence of viable phytoplasmas in young, developing leaves of the infected plants.