| This dissertation encompasses several studies on Pseudomonas syringae pv. syringae (Pss) and stone fruit trees. Almond dormant bud drop, characterized by the premature abortion of flower buds in January, is new disease that appeared in 1996/1997 in the San Joaquin valley of California. Pss was the only pathogenic microbe found in the diseased buds, however, analysis of healthy and abscised buds revealed that Pss is not the cause of Winond bud drop.; Bacterial canker, caused by Pss, only occurs when one or more predisposing factors stress stone fruit trees. In one field study, the disease incidence of ‘French’ prune trees grafted on Lovell peach rootstock was significantly lower than in trees grafted on myrobalan 29C plum rootstocks regardless of grafting height. Plum rootstocks, grown one year in the field and grafted with prune scions at 90 cm above the soil, reduced disease slightly over the same rootstock grafted in the nursery at 15 cm above the soil. Copper sprays and fertilizer amendments containing nitrogen, phosphorus, potassium and micronutrients significantly reduced disease severity and tree mortality compared to untreated trees.; Soil composition factors, such as percent sand, silt, clay and organic matter as well as nematode species, were quantified for their potential to predispose ‘French’ prune and peach trees, to bacterial canker. The percentage of sand was the most critical factor for predicting tree mortality due to bacterial canker for both tree species.; Aqueous stem extracts from apricot and sweet cherry induced syrB, a gene involved in the synthesis of the toxin syringomycin, in Pss, to greater levels than extracts of ‘French’ prune. Extracts of stems harvested in May were more active than extracts collected at other time points. The Prunus species and the date of stem extract collection correlated with temporal expression and host sensitivity to bacterial canker in the field.; Pss cells, expressing green fluorescent protein (GFP), were observed both inside and outside of lesions that developed on inoculated, dormant cherry stems. Pss expressing GFP produced smaller lesions than the wild type strain as did strain B3AR-132, which is deficient in the production of syringomycin. |
