BACTERIAL APICAL NECROSIS OF MANGO IN SOUTHERN SPAIN - A DISEASE CAUSED BY PSEUDOMONAS-SYRINGAE PV. SYRINGAE

A necrotic bacterial disease of mango trees (Mangifera indica) in Spai n affecting buds, leaves, and stems is described for the first time. N ecrosis of flower and vegetative buds on commercial trees during winte r dormancy was the most destructive symptom of the disease. The apical necrosis is caused by Pseudomonas syringae, which was always isolated from mango trees with disease symptoms. Of 95 bacterial strains isola ted from symptomatic tissues and characterized from 1992 to 1997, over 90% were identified as P. syringae pv, syringae. Additional strains w ere isolated from healthy mango trees, and they were identical to the isolates from diseased tissues. Pathogenicity tests on mango plants sh owed that P. syringae pv. syringae incited the apical necrosis, but th at climatic conditions determined the onset of disease development. Po pulations of total bacteria and of P. syringae and the number of activ e ice nuclei were monitored over a 3-year period. The largest populati ons of P. syringae were associated with cool, wet periods that coincid ed with the highest disease severity, whereas P. syringae was only occ asionally detected on healthy trees. The median effective dose was est imated from infectivity titration assays.