3.7.58
BACTERIAL APICAL NECROSIS OF MANGO: A NEW DISEASE CAUSED BY PSEUDOMONAS SYRINGAE PV. SYRINGAE ON MANGO TREES IN SOUTHERN EUROPE

FM CAZORLA1, VE DURAN1, E ARREBOLA1, JM HERMOSO2, JA TORES 2 and A DE VICENTE1

1Departamento de Microbiologia, Facultad de Ciencias, Universidad de Malaga, 29071Malaga, Spain; 2Estacion Experimental "La Mayora', C.S.I.C., Algarrobo-Costa, 29750 Malaga, Spain

Background and objectives
Mango (Mangifera indica L.) is grown throughout the subtropics and tropics and is one of the world's most important tropical fruit crops. Some bacterial diseases of mango have been previously described A new necrotic bacterial disease of mango trees affecting buds, leaves, and stem was observed in Southern Europe plantings, with high incidence during winter dorfnancy, the most destructive phase. The main objective of this work was to identify and study the role of the causal agent of bacterial apical necrosis of mango , including the observance of Koch's postulates.

Material and methods
To isolate the causal agent related to apical necrosis, the affected tissues were processed and the isolated microorganisms were characterized as previously described [1]. Host tests were performed to confirm the diagnosis of bacterial strains. To test pathogenicity on mango of P. syringae pv. syringae isolates, two experiments were carried out, from March 1994 (open-air conditions) and from January 1996 (open-air and polyethylene greenhouse conditions) by inoculating bacterial suspensions on buds of young mango trees. Buds showing necrotic symptoms after 3 or 6 weeks were re and bacterial reisolation was carried out to confirm the presence of P. syringae. Experiments to estimate the infective dose of P. syringae pv. syringae isolates to incite the bacterial apical necrosis were perfomied and conducted under field conditions.

Results and conclusions
Fluorescent pseudomonads isolated from diseased and healthy mango tissues were conclusively identified as P. syringae pv. syringae, on the basis of their nutritional and biochemical pattern, the production of syringomycin and syringopeptin, and the ice-nucleation activity [2]. This bacterial plant pathogen was the most frequently recovered in samples from affected tissues of mango ums (91.6%). P. syringae strains isolated from mango induced typical necrotic symptoms in the host test on inoculated lemon and pear inmature fruits, lilac and tomato plants, but on bean pods induced hipersensitivity response.

The pathogenicity test on mango plants showed that this bacterium incites the apical necrosis, but the climatic conditions were determinant for the disease development. A higher incidence (81.3%) were observed in wet and cool conditions, likewise, when the environmental conditions were diier and warmer, this proportion was clearly lower (19.4% and 43.3%). Subsequently, P. syringae pv. syringae was generally reisolated from the affected buds. The minimal bacterial infective dose that develop symptoms of apical necrosis on inoculated mango buds is 100 cells/bud, however to produce a significant outbreak, a dose of about 104 cells/bud could be necessary.

Work is in progress in our laboratory about the molecular and biological characterization of P. syringae pv. syringae isolates, and evaluation of different substances (chemical and biological sources) for the disease control.

References
1. Cazorla FM, Olalla L, Tords JA, Codina JC, Pdrez-Garcfa A, De Vicente A. 1997. Pseudomonas syringae Pathovars and Related Pathogens. Rudolph K et al. Eds., pp.82-87.
2. Cazoria FM, Oialla L, Tords JA, P6rez-Garcfa A, Codina JC, De Vicente A. 1995. Journal of Applied Bacteriology 79, 341-46.