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.