NITROGEN FORM AND SUSCEPTIBILITY OF PELARGONIUM X HORTORUM TO XANTHOMONAS

B. Digat, F. Lemaire
Numerous reviews have pointed out the effect of nitrogen nutrition of ornamental plants on the susceptibility to bacterial diseases. The purpose of this work was to study the effects of concentration and form of nitrogen nutrition on the speed of bacterial vascular migration and on the severity of wilt caused by the bacterium Xanthomonas campestris pv. pelargonii. Pelargonium x hortorum cv "Topcore" were grown individually in greenhouse during 151 days in Perlite substrate with four complete nutrient subirrigating solutions, differing in their mineral nitrogen concentration (7 and 14 meq./1) and their nitrogen form (NO3-N and NH4-N). After 110 days of growing, lots of 16 plants with four nutrition types were inoculated by infiltrating a suspension of Xanthomonas in the top leaf. Dynamic of bacterial population was followed in plant at 5, 10, 17 and 29 days after inoculation by using the indirect immunofluorescence technique. Notations of wilt symptoms were recorded 29 days after inoculation. Dry matter contents of leaves and stems fresh matter were determined in inoculated plants and controls at the end of experiment. The speed of bacterial vascular migration was promoted in plants fertilized with NH4-N : 17 days after inoculation, pathogenic bacteria were more numerous in the stems of these plants than in plants with NO3-N. The wilt symptoms were more severe in plants with NH4-N : 29 days after inoculation up to 67 % of these plants were wilted while only 7 % with NO3-N. The dry matter content of leaves and stems fresh matter in plants grown with NH4-N was higher in inoculated plants than in non-inoculated controls. Systemic infection of plants by bacteria increased the dehydration effect of NH4-N nutrition observed without bacteria.

Finally, the obtained results have improved our knowledge of pathogenesis mechanisms : the incidence of Xanthomonas on the water supply in plant and the promoting effect of NH4-N nutrition on the dynamic of bacterial population in vascular system and on the process of pathogenesis were proved. Pelargonium x hortorum susceptibility to bacterial disease was depending on the plant nutrition status : NO3-N had a tendency to mask the disease symptoms and too high NH4-N content in the nutrient solutions is not advisable. Biologically unstable substrates have to be avoided because their further degradation is able to produce briefly NH4-N that increases the plant susceptibility to bacterial diseases.

Digat, B. and Lemaire, F. (1993). NITROGEN FORM AND SUSCEPTIBILITY OF PELARGONIUM X HORTORUM TO XANTHOMONAS. Acta Hortic. 342, 25-36
DOI: 10.17660/ActaHortic.1993.342.3
https://doi.org/10.17660/ActaHortic.1993.342.3

Acta Horticulturae