‘Red Prince Delicious’/East Mailing (EM) VII trees were grown in sand culture and fertilized with a complete nutrient solution containing 0.5, 5.0 or 50.0 ppm Mn. 54Mn was supplied to provide the same specific activity in all treatments. Autoradiographs showed “islands” of radioactivity in bark patches from all treatments 2½ months after initiation of the experiment. These “islands” disappeared after 8 months in the 0.5 ppm treatment, and after 10 months in the 5.0 ppm treatment, but continued to exist in bark patches from the 50.0 ppm treatment through the last sampling at 15½ months. Typical, and some aberrant, symptoms of IBN first appeared after 5½ months in the 50.0 ppm treatment. Pimples occurred at sites where autoradiographs indicated Mn concentrations. As the pimple stage of IBN progressed to necrotic lesions, radioactivity was concentrated around the periphery of the lesions. Data is presented which suggests that, as Mn supply is increased, alteration of mechanisms for regulating uptake and distribution of Mn occurs.
Received for publication February 16, 1970. Contribution from the Departments of Soil Science and Horticultural Science. Published with the approval of the Director of Research as Paper No. 3080 of the Journal Series.
The authors gratefully acknowledge the considerable advice and assistance of W. A. Jackson, Dept. of Soil Science and of L. T. Caruthers, Radiation Safety Officer.
Asst. Profs. of Soil Science and Horticultural Science, resp., Mt. Hort. Crops Res. Sta., Fletcher, N. C. 28732.