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Introduction. Bacterial canker, caused by Pseudomonas syringae pv. syringae, is a destructive disease where stone fruit trees are cultivated. The efficacy of nitrogen and calcium fertilization on bacterial canker susceptibility was evaluated in stone fruits. Materials and methods. Field experiments were conducted to study the efficacy of foliar applications of calcium nitrate, and ground fertilization with CAN-17 plus low-biuret urea foliar spray on bacterial susceptibility in ‘Riegel’ peach, ‘French’ prune and ‘Nonpareil’ almond growing in ring nematode-infested and nematicide-fumigated soils. Host susceptibility was evaluated by measuring the length of lesions developed following inoculation with P. syringae pv. syringae. Results and discussion. Foliar applications of Ca(NO3)2 significantly increased leaf nitrogen and bark calcium concentrations in peach trees growing in both fumigated and nonfumigated areas. Peach trees growing in nonfumigated areas developed significantly longer lesions than trees growing in fumigated areas. However, Ca(NO3)2 foliar applications had no effect in decreasing peach susceptibility to bacterial infection in both nonfumigated and fumigated areas. After inoculation, diseased prune trees developed significantly longer lesions than healthy trees. Leaf and bark calcium concentrations of diseased prune were significantly increased after Ca(NO3)2 foliar sprays, but again the treatments did not significantly affect prune susceptibility to bacterial infection. However, nitrogen fertilization with CAN-17 and urea significantly increased the bark nitrogen concentration of almond trees, and these trees had significantly smaller lesions than those not receiving nitrogen fertilization. Foliar application of calcium (Nutri-Cal) did not affect almond susceptibility to bacterial canker. Collectively, these data support the previous hypothesis that increased susceptibility of stone fruits to P. syringae pv. syringae under nematode infestation conditions is mediated by both nitrogen effects and nitrogen-independent effects, and application of ammonium nitrogen may have some beneficial effects in reducing stone fruit susceptibility to bacterial canker where ring nematode infestation prevails. [ABSTRACT FROM AUTHOR]

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