Some investigations on Cox's disease in Cox's Orange Pippin apple trees, grafted on dwarfing rootstock M IX.
AbstractIn 2-year sand and water studies with young Cox trees on M.9 and M.2 the effects were assessed of N deficiency, shading, impaired aeration of the growing medium and partial ringing. With trees grown in sand culture Cox disease occurred in the first year only, in the untreated control trees and in those grown under shade. With trees grown in water culture some roots suddenly stopped growing in July and the root tips died; by that time shoot growth had almost stopped and the shoots did not show any symptoms of the disease. Root die-back followed a period of good root growth, the no-N trees being the worst affected; however, some regrowth occurred, and by October recovery was best in the no-N trees. Studies with sand- and water-cultured trees of the distribution of 14C-labelled carbohydrates photosynthesized in the leaves showed that there was no accumulation of carbohydrates at the graft union and that carbohydrates were present in the root tips. Roots of the trees in water culture were longer and less branched than those in sand culture, suggesting a lower auxin content. Greater root length was associated with greater susceptibility to root mortality, indicating that Cox disease is associated with a low auxin level in the root system. (Abstract retrieved from CAB Abstracts by CABI’s permission)