INFLUENCE OF INCREASED NITROGEN SUPPLY ON MINERAL COMPOSITION AND GROWTH OF SOUR CHERRY TREES IN THE ACUTE AND IN THE CHRONIC COURSE OF STECKLENBERG DISEASE
In bearing trees infected by pollen transmission of the virus the disease takes its acute course. The latter is characterized by a shock phase which is usually followed by recovery. In maiden trees raised from infected propagating material the disease takes its chronic course.
The main symptoms of both forms are described. Examination of the mineral content of leaves revealed the following results: In acute diseased trees content of N, P, Ca, and Mg is lower than in healthy ones and N content cannot be raised by increased N fertilization. Consequently, shoot growth and leaf development can hardly be improved by high N supply. Chronic diseased' trees have higher content of the minerals in question than non-infected sour cherry trees. Assimilation of the minerals, however, is obviously insufficient for normal development of growth. Therefore high fertilization is not likely to improve growth of infected trees. A moderate supply on the level of 60 kg/ha N to infected maiden trees and of 120 kg/ha N to diseased bearing sour cherry trees is recommended.