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Influence of Powdery Mildew Infection on 35S and 45Ca Accumulations in Leaves of Apple Seedlings. J. Wieneke, Associate Research Horticulturist, Tree Fruit Research Center, Wenatchee, Washington 98801, Senior author is on leave from A. G. Institut fur Landwirtschaft in der Kerforschungslange Julich, 517 Julich, West Germany; R. P. Covey, Jr.(2), and N. Benson(3). (2)(3)Assistant Plant Pathologist, Horticulturist and Soil Scientist, respectively, Tree Fruit Research Center, Wenatchee, Washington 98801. Phytopathology 61:1099-1103. Accepted for publication 13 April 1971. DOI: 10.1094/Phyto-61-1099.

The influence of powdery mildew on translocation of root-absorbed 35S and 45Ca into leaves and areas of infection of young apple seedlings grown in nutrient solution was investigated by radioautography and counts of mildew-infected and adjacent tissues. On leaves with young colonies of mildew prior to labeling, sulfur accumulated at the infection site, but there was no accumulation in old colonies. Accumulation of 35S could not be detected 3 days after inoculation in young leaves labeled prior to inoculation. However, accumulation was demonstrated 10 days after inoculation. There was no detectable accumulation of 45Ca at the infection sites, although the spores became radioactive. The transport of 45Ca to diseased leaves was markedly less than that to healthy leaves of the same plant.

Additional keywords: Podosphaera leucotricha, obligate parasitism.