Influence of mineral nutrients and freezing-thawing on peach susceptibility to bacterial canker caused byPseudomonas syringaepv.syringae

Abstract

Introduction. Bacterial canker, caused by Pseudomonas syringae pv. syringae ,i s 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 experi- mental 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 anddiscussion. 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 nitrogenandpotassiumconcentrationsaccordingly,buthadnocleareffectonlesionsizes.Inoculation during freezing-thawing cycles significantly increased lesion length. In another independent expe- riment, 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.