Introduction. Bacterial canker, caused by Pseudomonas syringae
pv. syringae, is a devastating disease of stone fruit worldwide.
The effects of mineral nutrients and freezing-thawing on bacterial canker susceptibility
were evaluated using potted peach trees in an attempt to understand predisposing factors
in bacterial canker of stone fruit. Materials and methods. A split-plot
experimental design with randomized complete block main plots
(i.e., inoculations
associated with freezing-thawing or nonfrozen pretreatments) and subplots of trees with
the seven treatments
(i.e., solutions
deficient in N, P, K, Ca, Mg or Fe, respectively, and a full nutrient control) was adopted
to study the effect of mineral deficiency and freezing-thawing on peach susceptibility to
bacterial canker. Results and discussion. Phosphorus deficiency was the only
treatment to significantly decrease lesion length that developed after inoculation with
P. syringae pv. syringae, compared with the control
trees that received full nutrients. Nitrogen and potassium deficiency treatments
significantly decreased bark nitrogen and potassium concentrations accordingly, but had no
clear effect on lesion sizes. Inoculation during freezing-thawing cycles significantly
increased lesion length. In another independent experiment, nitrogen deficiency
significantly increased the number of P. syringae pv. syringae
leaf scar infections, but the subsequent infection was limited to a few
millimeters. Nitrogen-deficient trees, which had higher [carbon / nitrogen] ratios,
developed lesion sizes equivalent to trees provided with full nutrients. Collectively,
these data suggest that, in the absence of other major predisposing factors
(i.e., low soil pH or ring
nematodes), mineral nutrients may play a minor role in the susceptibility of peach to
bacterial canker.