Correlation of Chemical Profiles of Xylem Fluid of Tomato to Resistance to Bacterial Wilt

Abstract

The relationship of tomato genotype- and soil fertility regime-induced changes in xylem fluid chemistry to the incidence of bacterial wilt (Ralstonia solanacearum) was investigated under greenhouse conditions in two separate experiments. In experiment 1, the incidence of bacterial wilt was evaluated on cv ‘Bonny Best’ (susceptible) in relation to 6 soil fertility regimes. All soil fertility regimes included standard and uniform N-P-K applications with or without additional applications of calcium or magnesium. The incidence of bacterial wilt was reduced with the application of calcium and magnesium, although the effect of the former was greater. Soil pH, calcium and magnesium as well as foliar calcium and magnesium levels were influenced by soil fertility regime. In an effort to understand the mechanism of calcium- and magnesium-induced reductions in bacterial wilt, changes in xylem fluid chemistry were investigated as a function of genotype [‘Bonny Best’ (no resistance), ‘Neptune’ (moderate resistance) andHawaii 7997 (high resistance)] and a calcium supplemented, a magnesium supplemented and a control soil fertility treatment (Experiment 2). The concentration of the primary organic compounds in xylem fluid (amino acids, organic acids and sugars) were statistically analyzed as a 3x3 factorial design. The effects of soil fertility treatment exceeded those of cultivar. Total amino acids and certain individual amino acids (glutamic acid, glutamine, aspartic acid, histidine, arginine, proline, tyrosine, valine, isoleucine, leucine and phenylalanine) were influenced by soil fertilization. Organic acids or sugars were not significantly influenced by treatment or cultivar. Further work is required to delineate the relationship of xylem chemistry and resistance to bacterial wilt.