Published online by Cambridge University Press: 05 June 2013
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 bacterialcanker susceptibility was evaluated in stone fruits. Materialsand methods. Field experiments were conducted to study theefficacy of foliar applications of calcium nitrate, and ground fertilizationwith CAN-17 plus low-biuret urea foliar spray on bacterial susceptibilityin ‘Riegel’ peach, ‘French’ prune and ‘Nonpareil’ almond growingin ring nematode-infested and nematicide-fumigated soils. Host susceptibilitywas evaluated by measuring the length of lesions developed followinginoculation with P. syringae pv. syringae. Results and discussion. Foliar applications of Ca(NO3)2significantly increased leaf nitrogen and bark calcium concentrationsin peach trees growing in both fumigated and nonfumigated areas.Peach trees growing in nonfumigated areas developed significantlylonger lesions than trees growing in fumigated areas. However, Ca(NO3)2foliar applications had no effect in decreasing peach susceptibility tobacterial infection in both nonfumigated and fumigated areas. Afterinoculation, diseased prune trees developed significantly longer lesionsthan healthy trees. Leaf and bark calcium concentrations of diseased prunewere significantly increased after Ca(NO3)2 foliar sprays, but againthe treatments did not significantly affect prune susceptibility tobacterial infection. However, nitrogen fertilization with CAN-17and urea significantly increased the bark nitrogen concentrationof almond trees, and these trees had significantly smaller lesionsthan those not receiving nitrogen fertilization. Foliar applicationof calcium (Nutri-Cal) did not affect almond susceptibility to bacterialcanker. Collectively, these data support the previous hypothesisthat increased susceptibility of stone fruits to P. syringae pv. syringae under nematode infestation conditionsis mediated by both nitrogen effects and nitrogen-independent effects,and application of ammonium nitrogen may have some beneficial effectsin reducing stone fruit susceptibility to bacterial canker wherering nematode infestation prevails.