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Poster: Biology & Disease Mgmt: Cultural Control


Silicon Augments Xanthomonas gardneri symptoms in Tomato cv. Early Girl
W. ZELLNER (1), C. Krause (2), J. Locke (1), J. Boldt (1), S. Leisner (3) (1) USDA-ARS, U.S.A.; (2) USDA-ARS, U.S.A.; (3) The University of Toledo, U.S.A.

Silicon (Si) is a plant nutrient that enhances stress tolerance. Tomato accumulates a moderate amount of Si in foliar tissue, but its effect on Xanthomonas gardneri infection has not yet been determined. To test this, ‘Early Girl’ tomatoes were grown hydroponically in nutrient solution with (Si+) or without (Control) 2 mM potassium silicate. Plants were dip-inoculated with X. gardneri. Symptoms developed within 24 hrs post-inoculation. Total symptomatic leaf area was quantified 10 dpi, using the Assess 2.0 Program. Si-treated plants had significantly more lesions and higher symptomatic leaf area (11.7 %) compared to controls (6.5%). Symptoms present on Si+ plants were spread throughout the leaf, while lesions on control plants were concentrated around the leaf margins. This suggested entry by X. gardneri in Si+ plants was through both stomates and hydathodes, while control plants were infiltrated mainly via hydothodes. To determine if differences in symptom formation between Si+ and control plants was simply due to changes in stomatal opening, stomatal conductance was directly measured between Si+ and control plants that were removed from hydroponics solution for 2 min. At 570s, stomatal conductance in Si+ plants compared to control was slightly, but significantly lower. This suggests that differences in X. gardneri symptoms in ‘Early Girl’ are not due to changes in the stomatal conductance influenced by the dip-inoculation method.