Leaf and stem anatomical changes were studied in coffee plants infected with X. fastidiosa looking for the causes of the observed physiological disturbances. Samples of commercial cultivars of Coffea arabica L. were analysed - Catuaí Vermelho IAC H 2077-25-81 and Mundo Novo 515-20 grafted on the progenie IAC 2258 of C. canephora - and of Catuaí Vermelho IAC H 2077-25-81 without grafting. Samples were collected in the field, at the Centro Experimental de Campinas, Instituto Agronômico, State of São Paulo, Brazil, in a coffee plantation where the presence of the bacteria was detected. The leaf and stem structures of branches with and without visual symptoms of the bacteria were analysed. It was also estimated the percentage of obliterated stem xylem vessels. The infected branches presented internode shortening, and early foliar senescence in the base of the branches, in a more severe degree of the disease, resulting in a reduced number of leaves in the apex. The number and position of branches with symptoms varied among plants, but were more frequent in the lower parts of the plants. These branches also presented reduced petiole and leaf area, smaller and grouped fruits due to the pedicels and internodes shortening. A deposition of "gum" was observed in the xylem vessels of the stems, petioles and leaves, and an abnormal cellular division in the xylem, phloem and cortex of the stem, petiole and in the mesophyll. The leaf mesophyll cells also presented reduced chloroplast number, associated with a larger concentration of calcium oxalate crystals. It was suggested that the presence of the bacteria may induce leaf senescence which is related to one or more stress factors.
coffee plants; Coffea; Xylella fastidiosa; anatomy
