Propyl gallate, a free radical scavenger, counteracts the benefits of exogenously applied salicylic acid and aggravates the deleterious effects of the Southern bean mosaic virus in Rhizobium-nodulated Phaseolus vulgaris plants

Abstract

Infection of Rhizobium-nodulated Phaseolus vulgaris by the southern bean mosaic virus (SBMV) markedly decreased the growth and nodulation of plants. Exogenous applications of salicylic acid (SA) at concentrations 10 mM further decreased growth and nodulation of virus-infected (V) plants. Only SA concentration of 5 mM in the solution improved the growth, nodulation, chlorophyll concentration and the catabolism of ureide in leaves of V plants. The spray of leaves with 2 mM propyl gallate (þPg) decreased growth, nodulation as well as the chlorophyll and leaf ureide concentrations in V plants, regardless of the concentration of SA at which plants were grown. Ultrastructural damages in leaf cells caused by SBMV were also enhanced in VþPg plants. The massive proliferation of virus particles and the presence of virus crystalline arrays within symbiosomes of nodules in VþPg plants were attributed to proliferation of branched plasmodesmata in leaf vascular-parenchyma cell walls that facilitated virus movement. Virus particles were never observed in leaf and nodule tissues of V plants not sprayed with Pg. Exogenous applications of SA hindered while Pg increased the symbiotic performance of H plants, pointing out the complexity to be addressed in breeding for virus resistance in Rhizobium-nodulated beans.