ABSTRACT Two field experiments were conducted to study the effects of added
nitrogen,
calcium, and
indoleacetic acid, in the presence or absence of ring nematodes (Mesocriconema xenoplax), on susceptibility of peach to bacterial canker. When noninfested soil was inoculated with ring nematodes, peach tree susceptibility to bacterial canker
infection caused by Pseudomonas syringae pv. syringae was dramatically increased after a period of 2 years. However, no evidence was found that ring nematode infestation increased tree
water stress or, in turn, altered plant
calcium uptake. Soil fumigation with
methyl bromide prior to planting in a commercial orchard significantly reduced both nematode populations and peach tree susceptibility to bacterial canker
infection when compared with nonfumigated treatments. In both experiments, tree susceptibility, as measured by canker length following inoculation of stems with P. syringae pv. syringae, was negatively correlated with plant tissue
nitrogen content and positively correlated with tissue
calcium content. A principal components analysis showed that tissue
nitrogen and
calcium levels were negatively correlated, and that high-
nitrogen, low-
calcium tissues were less susceptible to bacterial canker than low-
nitrogen, high-
calcium tissues. These results indicate that the increased susceptibility of peach to P. syringae pv. syringae under nematode infestation conditions is mediated by both nutritional effects (primarily
nitrogen) and nutritional-independent effects, but do not support previous reports of beneficial effects of
calcium for reducing bacterial canker.