Investigations have been undertaken to determine which fungi species are responsible for occurrence of sooty blotch disease in Poland. It was found that disease complex is caused by Tripospermum myrti (Lind) Hughes, Phialophora sessilis de Hoog and Peltaster fructicola Jonhson. There was no evidence of the presence fun- gus described as Gloedes pomigena which was previosly considered as a casual agent of apple sooty blotch disease in Poland.

The fungi that cause sooty blotch grow only on the apple skin, so they use appropriate nutrients which are present on the fruit surface. It has been shown that when the first symptoms of sooty blotch occur a noticeable increase of glucose and fructose content both on the apple skin and in juice is observed. Such increase occurs at pH 4.4. An effect of surface glucose and fructose on the growth of patho- gens responsible for the disease was also confirmed by evaluating the germination of conidia of Phialophora sessilis de Hoog and Peltaster fructicola Jonhson in solution of above mentioned sugars, distilled water and standard d-glucose solutions.