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Influence of water regime in the infection of young citrus plants by Xylella fastidiosa In Brazil, about 38% of the citric trees of the São Paulo State are affected by the Citrus Variegated Chlorosis CVC, causing annual losses of about 100 million dollars for the citrus industries. The causal agent of CVC is a gram-negative, fastidious bacterium inhabitant of the xylem vessels called Xylella fastidiosa. It is vectored by sharpshooter leafhoppers pertaining to family Cicadellidae and subfamily Cicadellinae. It was observed that young citrus plants, between 3 and 4 years of age, are more susceptible to CVC than adult plants. The disease is more severe in regions where additional stresses occur, such as high atmospheric demand (due to the increase of temperature and vapor pressure deficit) and water deficit in the soil. The physiological and chemical mechanisms that characterize the establishment of CVC within the host have not yet been totally understood, especially under conditions of stress. Therefore, studies that consider the interaction between seasons, water regime and the establishment of CVC in young plants are necessary in the elaboration of more efficient management programs. The survival of initial infections of X. fastidiosa in young citrus plants mechanically inoculated during the summer and winter, and kept in the field with and without irrigation, were evaluated 6, 12 and 18 months after mechanical inoculations. To analyze the influence of water regime separately, an experiment was carried through during the autumn (final of May and beginning of June) in a greenhouse. Young citrus plants kept in field capacity and water deficit were mechanically inoculated and inoculated with sharpshooter leafhoppers Bucephalogonia xanthophis and Dilobopterus costalimai. The mechanically inoculated plants were evaluated 5 months after the date of inoculation, whereas the plants inoculated with insect vectors were evaluated 10 months after the date of inoculation. In natural conditions, 6 months of the date of inoculation, higher survival rates of initial infections of X. fastidiosa were detected in inoculated young plants during winter in the absence of water deficit; however, 12 months after inoculation, the young citrus plants kept with and without irrigation presented statistically equal bacterial population averages. The mechanically inoculated plants kept in the greenhouse presented similar results to those kept in natural conditions and analyzed 6 months after mechanical inoculation. In the case of inoculation with sharpshooter leafhoppers, the presence of the bacterium was detected only in plants kept in field capacity. The results demonstrate that the water deficit is unfavorable for the establishment of primary infections of X. fastidiosa in young citrus plants. The results obtained 12 months after mechanical inoculation in natural conditions, right after the rainy season, indicate that, once the water deficit is removed, its negative influence ceases to exist and the bacterium reacquires its capacity of infection and colonization of the host.

Influência do regime hídrico na infecção de plantas cítricas jovens por Xylella fastidiosa