CRUDE EXOPOLYSACCHARIDES (EPS) FROM XANTHOMONAS-CAMPESTRIS PV MANIHOTIS, XANTHOMONAS-CAMPESTRIS PV CAMPESTRIS AND COMMERCIAL XANTHAN GUM ASINDUCERS OF PROTECTION IN COFFEE PLANTS AGAINST HEMILEIA VASTATRIX

Foliar-applied exopolysaccharides, obtained from bacterial cells of ei ther Xanthomonas campestris pv. manihotis (EPS-Xcm) or Xanthomonas cam pestris pv. campestris (EPS-Xcc), isolate NRRL B-1459, were tested for their ability to induce local and systemic protection against coffee leaf rust caused by Hemileia vastatrix. Both preparations of EPS were effective in inducing local and systemic protection when applied 72 h before challenge with the pathogen. Protection was also observed when planes were treated with different concentrations of a commercially av ailable preparation of xanthan gum (CXG). Systemic protection was indu ced by EPS-Xcm, EPS-Xcc and CXG even after the removal of the treated leaves immediately before the challenge. Local protection lasted at le ast 5 weeks, when EPS-Xcm was applied at the concentration of 100 mu g equivalents of glucose/ml. Fluorescent microscopic studies of pathoge n development in protected and control leaves indicated that neither t he germination, appressoria formation nor the number of infection sire s were affected by treatment with EPS-Xcm.