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

Abstract

The influence of tomato cultivar, calcium nutrition, and cultivar/nutrition interaction on xylem fluid chemistry, bacterial colonization, and incidence of disease was investigated. Bacterial suspensions of Ralstonia solanacearum were added to the base of tomato cultivars grown in pasteurized field soil amended with various fertility treatments. Cultivars investigated included Bonny Best (no resistance), Neptune (moderate resistance), and Hawaii 7997 (high resistance). Fertility treatments included standard applications of N-P-K in combinations with various additional applications of calcium and magnesium. The progress of disease was followed up to seven weeks after inoculation. Thirteen days after inoculation, bacterial populations were estimated from 2 cm stem sections removed at several heights. Thirteen days after inoculation, xylem fluid was collected and analyzed for the content of amino acids and organic acids. Bacterial populations were highest in the stems of Bonny Best and lowest in Hawaii 7997. Disease incidence ranged from 100% in Bonny Best to 0% in Hawaii 7997. Calcium and magnesium amendments slightly suppressed bacterial counts in resistant cultivars, although these effects were minor compared to variation between cultivars. Amino acid concentrations in susceptible Bonny Best plants with standard N-P-K fertilization were 50% higher than the amino acid concentration in moderately resistant Neptune plants and over 100% higher than concentrations in highly resistant Hawaii 7997 plants. Addition of calcium (and to a lesser extent magnesium) lowered amino acid concentrations in xylem fluid in all three cultivars. The results indicate a relationship between organic compounds found in xylem fluid and resistance to bacterial wilt.