Crude Exopolysaccharides (EPS) from Xanthomonas campestris pv. manihotis, Xanthomonas campestris pv. Campestris and Commercial Xanthan Gum as Inducers of Protection in Coffee Plants against Hemileia vastatrix

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Abstract
Foliar‐applied exopolysaccharides, obtained from bacterial cells of either Xanthomonas campestris pv. manihotis (EPS‐Xcm) or Xanthomonas campestris 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 plants were treated with different concentrations of a commercially available preparation of xanthan gum (CXG).Systemic protection was induced by EPS‐Xcm, EPS‐Xcc and CXG even after the removal of the treated leaves immediately before the challenge. Local protection lasted at least 5 weeks, when EPS‐Xcm was applied at the concentration of 100 μg equivalents of glucose/ml. Fluorescent microscopic studies of pathogen development in protected and control leaves indicated that neither the germination, appressoria formation nor the number of infection sites were affected by treatment with EPS‐Xcm.