PEACH TREE SHORT LIFE - EFFECTS OF PATHOGENS AND CULTURAL PRACTICES ON TREE PHYSIOLOGY

Peach tree short life in the southeastern United States is associated with old peach land, ring nematode (Criconemella xenoplax), rootstock, fall pruning, and fluctuating winter temperatures. The ultimate causes of tree death appear to be cold injury and bacterial canker (Pseudomonas syringae). Trees showing cold injury symptoms were found to have much lower levels of prunasin in the bark. Cyanide released as the result of prunasin breakdown has the potential to cause severe tissue damage and may be an underlying cause of tissue death. Trees on Lovell rootstock generally outlive those on Nemaguard on short-life sites, but little is known of the physiological basis for this superior survival. Efforts to develop long-lived rootstocks are hampered by lack of criteria on which to select superior lines. C. xenoplax infestation on Lovell and Nemaguard seedlings in the greenhouse caused reduced fresh and dry root weight and dry matter contents. Levels of ninhydrin-positive compounds were reduced in stem and roots. Root systems of infested plants had reduced total amino acids with molar percent of alanine, glycine, proline, and histidine increased, whereas arginine was decreased.