Relationship Between Sorbitol and Solute Potential in Apple Shoots Relative to Fire Blight Symptom Development After Infection by<i>Erwinia amylovora</i>

Abstract

The soluble carbohydrate (SC) content and solute potential (Ψ s ) of individual leaves on apple shoots were determined to test the hypothesis that these parameters might be related to the progress of fire blight symptom development after infection by Erwinia amylovora. Experiments were based on the use of leaves and shoots of the same physiological age from 1-yr-old Jonathan and Delicious apple trees, which are susceptible and normally resistant to fire blight, respectively. After inoculation of the individual leaves with a bacterial suspension containing 10 8 cfu/ml, symptom severity declined with increasing leaf age. Inoculations of the first three apical leaves of Jonathan shoots and the first two leaves of Delicious shoots all led to the invasion and subsequent death of the supporting shoot