Influence of stem diameter, water content, and freezing-thawing on bacterial canker development in excised stems of dormant stone fruit

In excised dormant stems of peach (Prunus persica), prune (Prunus domestica), and almond (Prunus dulcis), stem diameter, stem hydration, and freezing-thawing influenced the extent of infection caused by Pseudomonas syringae pv. syringae. Bacterial lesion length increased with increasing stem diameter, demonstrating the need to account for the effects of stem diameter when lesion length data are analyzed. Lesion length increased or decreased with stem hydration or dehydration, respectively. However, tissue water content was not a good indicator of tissue susceptibility to infection by P. syringae pv. syringae, as larger diameter stems had larger lesions and lower water content than did smaller diameter stems. After freezing at -5 degrees C for 12 to 24 h, inoculations made during the thawing process produced significantly larger lesions than did inoculations performed before freezing or after thawing. These results support the hypothesis that the increased susceptibility to bacterial canker that is associated with noninjurious freezing is a result of the increased passive spread of bacteria through wafer redistribution when inoculation is performed during the thawing process. Plant tissue water relationship characteristics that can influence water movement during freezing and thawing may be an important component of bacterial canker development in stone fruit trees.