Bacterial Canker of Peach: Effect of Tree Winter Water Content on the Spread of Infection Through Frost-related Water Soaking in Stems

Several experiments were conducted to study the influence of water content in trees on dye diffusion or controlled Pseudomonas syringae pv. persicae infection spread induced in winter by water soaking after freezing and thawing. These were carried out in a cold cabinet in excised dormant hardy 1-year-old slightly dehydrated or rehydrated peach shoots, and in whole variably hydrated peach trees cultivated outdoors in 3001 containers. In shoots, dye diffusion was more substantial and infection more widespread when water content was higher. In potted peach trees, the spread of individual bacterial cankers which was induced by inoculating different shoots over two successive winters, was more restricted when tree water content was lower. In both years, a high positive correlation coefficient was observed between individual tree water content and mean canker length. This study revealed that stem water content in peach trees during winter and frosts is a fundamental factor in infection because it can drastically affect bacteria diffusion in cortical tissues during frost- and thaw-related water soaking. The effect of water content may have important epidemiological consequences firstly due to the influence of several environmental and agronomic factors on tree water content, and then to the prevalence of frost-related water soaking in many perennial and herbaceous plants.